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I. GENERAL RULES
1.1 PURPOSE OF RULES
1.2 APPLICABITY OF RULES
1.2.1 CONSTRUCTION AND RECOSNTRUCTION
A. SERVICE DROP
B. SUBORDINATE ELEMENT
C. REPLACEMENT
1.2.2 MAINTENANCE OF PLANT
1.2.3 CONSTRUCTION PRIOR TO THIS CODE
1.2.4 RECONSTRUCTION OR ALTERATION
1.3 SCOPE OF RULES
1.4 EQUIVALENTS
1.5 LIMITING CONDITIONS REQUIRED
1.6 EXEMPTIONS OR MODIFICATIONS
1.7 SAVINGS
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SECTION I
GENERAL RULES
1.1 PURPOSE OF RULESThe primary purpose of these rules is to establish, for the Republic of Philippines, uniform standards, regulations and requirements for Electronics and Communications Design, planning manufacture, production, fabrication, construction, installation, operation, and maintenance, the application of which will insure adequate protection and safety to persons therein engaged and as well as in the provision, operation and use of electronics and or communications components, devices, equipment, systems, plants, stations, services, and or facilities. Application of the rules will also establish an acceptable level of protection for electronics and communication devices, equipment, and plant from damages due to electrical and/or physical hazards.
1.2 APPLICABILITY OF RULES
These rules apply to all electronics and/or communications design, planning, construction, installation, manufacture, production, fabrication, operation, and maintenance, which comes within the jurisdiction of this Code, located indoor or outdoor, terrestrially or extra terrestrially.
1.2.1 Construction and Reconstruction
The requirements apply to all devices, equipment, and plant constructed hereafter and shall become applicable also to such components, equipment, devices, stations, plants, facilities, system and/or services now existing, or any portion thereof whenever they are reconstructed.
The reconstruction of an element of a plant, station, system, or service requires that all elements subordinate to the reconstructed element meet the requirements of these rules.
For the purpose of this Code, reconstruction will be constructed to mean that work which in any way changes the identity of the station or plant or which it is performed excepting:
A. Service Drop
Service drops may be added to existing plant without necessitating changes in the circuit for which they are originated.
B. Subordinate Element
An element added to an existing plant shall meet all requirements of these rules but does not require any change in like elements already existing except where the added element is related to existing like element. The plant or structure to which any subordinate element is added shall meet the strength/safety factor.
3 C. Replacements
Replacement of poles, towers, structure, or supports is considered to be reconstruction and requires adherence to all strength and protection of this Code.
1.2.2 Maintenance of Plant
The plant or station shall be maintained in such condition to provide safety levels not less than the minimum specified in rule 4.3.3. The plant or station, or portions thereof, constructed on or after the effective date of this Code shall be kept in conformity with the requirements thereof.
The restoration of clearance and protection levels originally establish prior to the effective date of this Code, where the original clearance or protection has been reduce by additional sagging or other causes, is not considered reconstruction and the reestablish clearance or protection shall not be less than the original clearance or protection at the time the plant or station was established. The changing of clearance or protection for any other purpose is reconstruction and clearances or protection so changed shall comply with the rules of this Code applicable to reconstruction.
1.2.3 Construction prior to the Code
The requirement of this Code, other than the requirement specified in Rules 1.2.2 and 1.2.4 do not apply to plant or station constructed or reconstructed prior to the effective date of this Code. In all other particulars, such plant or station or portions thereof shall conform to the requirements of the rules in effect at the time of their construction or re-construction.
1.2.4 Reconstruction or Alternation
The Commission thru the appropriate government instrumentalities may order reconstruction or alteration of existing plant or station or portions thereof whenever strength and electrical protection requirement of this Code are not met and when public interest so requires.
1.3 SCOPE OF RULES
These rules are not intended as complete construction specifications, but embody only the requirements which are most important from the standpoint of safety and protection. Construction shall be according to accepted or established good practices for the given local conditions in all particulars not specified in the rules.
1.4 EQUIVALENTS
Wires sizes specified in this Code may be substituted with its nearest metric equivalent. Copper wire may be substituted with aluminum, copper clad steel, or other make/materials provided the current-carrying capacity is identical.
Flat or braided copper may be substituted for round or stranded copper wire provided the current-carrying capacity is not less than that of the latter.
4 1.5 LIMITING CONDITIONS SPECIFIED
The requirement specified in these rules as to clearance, strength and protection are limiting conditions expressed as minimum or maximumvalues, as indicated. In cases where two or more requirements establish limiting conditions, the more or most stringent condition shall apply, thus providing compliance with other applicable conditions. Greater strength of construction, more ample clearances and higher protection level may be desirable or practical in some cases, and may be provided accordingly if other requirements are not violated in so doing.
1.6 EXEMPTIONS MODIFICATIONS
If in a particular temporary and emergency case wherein a special type of construction, exemption from or modification of any of the requirements herein is desired, the Commission shall consider an application for such exemption or modification only when accompanied by a full statement of conditions existing and the reason why such exemption or modification is asked and is believed to be justifiable. It is to be understood that unless otherwise ordered, any exemption or modification so granted shall be limited to the particular case or the special type of construction specifically covered by the application.
1.7 SAVING CLAUSE
The Commission reserves the right to change any of the provisions of this Code in specific cases when, in the Commission‟s opinion, public interest shall be served by so doing.
Compliance with these rules and regulations shall not relieve a utility firm, entity, person or group of persons from compliance with any statutory requirement.
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SECTION II
DEFINITIONS OF TERMS AS USED IN THE RULES
OF THIS CODE
This section defines technical terms as used in the rules of this Code. The meanings of some terms differ with the field in which they are used, thus requiring more than one definition. Definitions contained in this section have been restrictively worded to emphasize the special purpose they are used in this Code. ACCESS ACCESIBLE ACCESSIBLE PART ACCESSORIES ACOUSTICS ACOUSTIC SHOCK AGING AIR GAP ALARM ALIVE ALPETH
A point of entry or a means of entry into a circuit.
Admitting close approach because not guarded by locked doors, elevation or other effective means.
A part so located that it can be contacted by a person, either directly or by means of a probe or tool, or that is not recessed the required distance behind an opening.
Devices that performs a secondary or minor duty as an adjunct or refinement to the primary or major duty of unit of equipment.
The science of sound.
The physical pain, dizziness, and sometimes nausea caused by hearing a sudden very loud sound. The threshold of pain is about 120 dBm.
The changes in properties of a material in time.
A separating space between two magnetic materials or conductors.
A visual or audible signal which alerts personnel to the existence of an abnormal condition.
To have an electrical potential or charge different from that to earth.
A type of telephone cable sheath featuring a corrugated aluminum tape applied longitudinally and a polyethylene jacket overall.
6 AMERICAN WIRE GAUGE
(AWG) AMPERE-HOUR ANCHOR ANHYDROUS ANTENNA APPLIANCE ARRESTER ARRESTER GAS-FILLED ASSEMBLY ATMOSPHERE, EXPLOSIVE ATTACHMENTS AUDIO AUTOMATIC
A scale of cross sectional measurement for non-ferrous (copper, bronze, aluminum, etc.) wires.
The quantity of electricity represented by a current of one ampere that flows for one hour.
Any device which holds something secure; a device buried in the ground to which anchor rods and guys are fastened. Dry; containing no water.
A means for radiating or receiving radio waves.
Any device that uses or needs electrical or usually an electric current supply to perform a certain function or operation; any equipment, usually complete in itself, that transforms electric energy into another form usually aural, visual, heat, or motion at the point of utilization.
Device which diverts high transient voltage to ground and away from the equipment thus protected; the voltage limiting portion of a protector.
Protector consisting of opposing spaced metal electrodes within a sealed tube or enclosure filled with gas such as neon or argon.
A grouping of components to accomplish a particular function.
Air holding in suspension dust, metal particles of flammable gas in such proportions that may ignite explosively.
All of the plant elements (cables, cross-arms, brackets, etc.) which are fastened to a supporting structure such as a pole. Pertaining to frequencies which can be heard by the human
ear.
Describing the actions of a device or equipment which are taken without human supervision in response to certain to pre-determined conditions.
7 BACKBONE BANDWIDTH BASEBAND BATTERY BOND BUS CABLE CIRCUIT CLIMBING SPACE CONDUCTOR COMMUNICATION
The main system route, usually the route carrying the majority of the traffic, ad often the longest series of cascaded hops.
Range of frequencies of a device, within which its performance, in respect to some characteristics conform to some specified limits; the difference between the upper and lower limits of the operating frequency of the device. Band of frequencies occupied by aggregate of all the
information signals use to modulate a carrier.
A group of two or more cells connected together to furnish current by conversion of chemical, thermal, solar or nuclear energy into electrical energy. Common usage permits this designation to be applied also to a single cell.
A low resistance electrical connection between two cable sheets, between two ground connections or between similar parts of two circuits.
A conductor or group of conductors, that serves as a common connection for two or more circuits.
Assembly of insulated conductors into a compact form which is covered by a flexible, waterproof, protective covering.
(1) The complete electrical path between terminals over which telecommunications are provided; (2) A network of circuit elements: resistances, reactances, semiconductors etc. to perform a specific function.
The vertical space reserved along the side of a pole or tower to permit ready access for linemen to equipment and conductors located thereon.
Anything such as a wire or cable which is suitable for the carrying of an electric current.
(1) Transmitting and/or receiving of information signals, or messages between two or more points; (2) the information thus received.
8 dB DROPWIRE ELECTRONICS ELECTRONIC SWITCHING EXPLOSION ROOF EXPOSED PART FACILITY FACILITIES FAULT FAULT CURRENT FLAME ROOF
Abbreviation for “decibel”, which is one-tenth of a bel. A unit expressing the ratio of two voltages, currents or powers. It is equal to 20 times the common logarithm of the ratio of the two voltages or two currents and 10 times the common logarithm of the ratio of the two powers.
Insulated wires, used to run a subscriber‟s line from the terminal on the pole to the protector at the house of the building.
The branch of science and technology which deals with the control and utilization of electron flow.
The selective interconnection of channels of communication by means consisting essentially if not entirely of electronic circuitry and circuit elements.
One that is designed and constructed to withstand an explosion of a gas or vapor that may occur within it or in its immediate vicinity and to prevent the ignition of the gas or vapor surrounding or within its enclosure.
A part which can be inadvertently touched or approached nearer than a safe distance.
Anything used or available for use in the furnishing of communication service.
The elements used or available for use in the furnishing of communication service, such as radio facilities, outside plant facilities, indoor plant facilities etc. The term does not normally include the customer‟s equipment.
A physical condition that causes a device, a component or an element to fail to perform in a required manner.
A current that flows from one conductor to ground or to another conductor owing to any abnormal connection (including an arc) between the two.
Apparatus so treated such that it will not maintain a flame or will not be injured readily when subjected to flame.
9 FLAME RETARDING FLASHOVER FUSE GROUND GROUND BUS GROUND RING GUY GUY, OVERHEAD GUY, ANCHOR GUY EXPOSED
Property of materials or structures such that they will not convey flame or continue to burn for longer times than specified in the appropriate flame test.
A discharge through air, around or over the surface of solid, liquid or other insulation, between parts of different potential of polarity, produced by the application of voltage such that the breakdown path becomes sufficiently ionized to maintain an electric arc.
A device used for protection against excessive currents. Consisting of a short length of fusible metal strip which melts when the current through it exceeds the rated amount for a definite time.
A conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the earth, or to some conducting body of relatively large extent that serves in place of the earth.
A bus to which the grounds from individual pieces of equipment are connected, and that, in turn, is connected to ground at one or more points.
A configuration of grounding conductors arranged around a structure such as building, tower footing, tower guy, anchor etc. normally connected to an earth ground at one or more points.
A tension member (of solid or stranded wires) used to withstand an otherwise unbalance force on a pole or other overhead lines structures.
A guy extending from a pole or structure to a pole structure or tree and is sometimes called a span guy.
A guy which has its lower anchorage in the earth.
A guy which has any part less than 2.5 meters from the vertical plane of any electric power conductor of more than 250 volts.
10 GUY IN PROXIMITY GUARDED HANDHOLE HAZARD INSULATED JOINT USE LIGHTNING ARRESTER LINES, COMMUNICATION LINE, POWER
A guy which has any part within a vertical distance of less than 2.5 meters from the level of power conductors and a radial distance of less than 1.8 meters from the surface of a wooden pole or structures.
Covered, shielded, fenced, enclosed, or otherwise protected by means of suitable covers, or casings, barriers, rails or screens, or platforms to remove the likelihood of dangerous contact with or approach by persons or objects to a point of danger.
An opening in an underground run or system into which workers reach, but do not enter. A sub-surface box having a cover flush with the ground.
Any condition which imperils life, limb and property. Separated from other conducting surfaces by a dielectric
substances or air space permanently offering a high resistance to the passage of current and to disruptive discharge through the substance or space. When any object is said to be insulated, it is understood to be insulated in suitable manner for the conditions to which it is subjected. Otherwise, it is, within the purpose of this Code, uninsulated.
Occupancy of poles or structures by two or more different entities by mutual agreement.
A device designed to protect apparatus from high transient voltage, by diverting surge current to ground and capable o repeating this function as specified.
The channels or conductors and their supporting or containing components or structures usually located outdoors which are used for transmission/reception of information/intelligence in communication service (telephone, telegraph, data telemetering, video, etc.). The conductors and their supporting or containing
structures which are located outdoors used for transmitting a supply of electrical energy.
11 MAINTENANCE MANHOLE MANUAL MESSENGER NOISE OPERATING CONTROL PLANT PLANT, INSIDE PLANT, OUTSIDE PRACTICABLE PROTECTOR PROTECTOR, CARBON BLOCK
All of the work required to keep the plant, circuits, lines, facilities, systems and services up to standards. This includes testing, trouble clearing, repairing, and replacing defective elements.
A subsurface chamber, large enough for a person to enter, in the route of one or more conduit runs, and affording facilities for placing and maintaining in the runs, conductors, cables, and any associated apparatus.
Operated by mechanical force, applied directly by personal intervention.
Stranded steel wires in a group which generally is not a part of the conducting system, its primary function being to support wires or cables of the system.
Any unwanted disturbance in a communication system which tends to obscure the clarity and validity of a signal in relation to its intended end use.
A control, usually a knob, pushbutton or lever, provided to enable the user to cause the appliance to perform its intended function, without the use of tools, when the appliance is in normal operating condition.
A general term applied to the whole or portion of the physical property of a communication company which contributes to the furnishing of communication service. All plant which is inside of building.
All plant which is “out of doors” not in building, such as poles, conduits cables, etc. installed overhead or underground.
Capable of being accomplished by reasonably available and economic means.
A device which provides protection from over-voltage and/or over-current.
A protector whose voltage limiting element utilizes carbon blocks.
12 PROTECTOR, GAS TUBE
QUALIFIED RADIANT ENERGY RADIATE ROD, GROUND ROD, LIGHTNING RECONSTRUCTION SERVICE DROP SAG SPAN SUPPLY CIRCUIT SYSTEM, ELECTRONIC TELECOMMUNICATION
A protector whose voltage limiting element employs electrodes in a gas filled (neon, argon, etc.) envelope. Persons trained and authorized for the construction,
maintenance and operation of the apparatus, circuit or system and responsible for the safety precautions involved. Any energy which radiates in the form of radio waves,
infrared (heat) waves, light waves, X-rays, etc. The spreading out of radiant energy.
A metallic rod, driven into the ground to provide an electrical connection to the earth.
A metallic rod carried above the highest point of a pole or structure and connected to earth by a heavy copper conductor intended to carry lightning currents directly to earth.
That work which in any way changes the identity of the plant or stations or portions thereof.
The installation from the terminal on the pole to the protector at the customer premises.
The maximum departure, measured vertically, of a wire or cable in a given span from a straight line between the two points of support of the span at 60° C and no wind loading. The horizontal distance between two adjacent supporting
points of a cable or wire.
The branch circuit supplying electrical energy to the equipment or appliance.
A configuration or arrangement of one or more electronic equipment producing the desired performance.
Any transmission, emission or reception of signs, signals, writings, images, sounds or intelligence of any nature by wire, radio, visual, or other system that may in the future become known or developed.
13 TENSILE STRENGTH TENSION TENSION, MAXIMUM ALLOWABLE TENSION, MAXIMUM WORKING TOWER DISPLACEMENT TOWER SWAY TOWER TWIST UNDERGROUND WORKING SPACE
The pulling stress required to break a material, such as a wire, express in kilograms of stress per cross-sectional area. Mechanical stress caused by forces which tends to stretch
or severe the material stressed.
One half of the tensile strength for the messengers guys, etc. and one fourth of the tensile strength for communication cables and wire.
The tension resulting under theconstruction arrangement with the maximum loading conditions specified in section 4.
The horizontal displacement of a point on the tower axis from its no-wind load position at that elevation.
Tower sway at any specified elevation shall be defined as the angular displacement of a tangent to the tower axis at the elevation from its no-wind load position at that elevation.
Tower twist at any specified elevation shall be defined as the horizontal angular displacement of the tower from its no-wind position at that elevation.
Describing communication facilities installed below the surface of the earth.
The space extending laterally from the climbing space, reserved for working below, above between conductor levels; the space surrounding a device or equipment.
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III. GENERAL ELECTRICAL PROTECTION AND
GROUNDING REQUIREMENTS
3.1 GENERAL
3.1.1 Objective
3.1.2 Lightning
3.1.3 Power Contact / Induction
3.1.4 Acoustic Shock
3.1.5 Electric Shock
3.2 PROTECTION METHODS
3.2.1 Shielding
3.2.2 Voltage Limiting
3.2.3 Current Limiting and Interrupting
3.2.4 Grounding
A. Purpose
B. Ground Resistance
C. Made Ground3.3 METHODS AND MATERIALS
3.3.1 Lightning Rods
3.3.2 Fuses
3.3.3 Surge Arrester
3.3.4 Grounding and Bonding
3.4 MEASUREMENTS
3.4.1 Ground Resistance Test Methods
3.4.2 Earth Resistivity
3.4.3 Determining Good Electrode Location
3.4.4 How to Improve Grounds
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SECTION III
GENERAL ELECTRICAL PROTECTION AND
GROUNDING REQUIREMENTS
3.1 GENERAL
Electrical protection measures covered in this Code are directed against the effects of lightning, accidental contact with power lines, voltages/electromagnetically/electrostatically induced into communication circuits by normal or fault currents in parallel runs of power lines and, also, local earth potential rises due to the flow of lightning or power fault currents.
3.1.1 Objective
Communication systems are subject to electrical hazards from exposure to lightning and power systems and unless adequate protection measures are employed, such exposures may result in loss of life, service interruptions and excessive maintenance expense.
A. The primary considerations of electrical protection are:
a) to minimize, as far as practicable, electrical hazards to persons engaged in construction, operation, maintenance or use of communication systems;
b) to reduce, as far as practicable damage to equipment and plant;
c) to eliminate, as far as practicable, any fire hazard resulting from the operation of communication systems; and,
d) to minimize, as far as practicable, acoustic shock hazards to anyone using communication services.
B. The amount of protection to be adopted and employed is determined by a proper balance between:
a) the cost of protection measures employed plus the amount required to maintain the protection level and adopted; and,
b) the value of damage to or loss of life and property and/or that of service interruptions caused by electrical hazards.
C.Protection measures may be more costly or impractical to add on or to an operating plant, so, it is desirable to consider protection requirements in the initial setting-up of the plant.
D.The standards specified in the Code evolves around optimum protection, explain in 3.1.1.B, but sometimes the state of the art progresses and new techniques evolve that meet the intent of the Code
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much more effectively that its own specific requirements, and in such cases, additional protection may be use provided no provision in this code is violated.
E. When the safeguarding od human life is involved, even if not actually required by this Code, communication entities should update its practice voluntarily and as soon as possible rather than wait for the revision.
3.1.2Lightning
Lightning is an electrical discharge which occurs between clouds and also from cloud to earth. It is latter type of discharge that is of concern in this Code.
A. Lightning surges can appear in various parts of a communication system and produce explosive effects, dielectric failure and fusing of conductors.
B. The path lightning takes depends upon the impedance presented to its wave front. With a wave that rises from zero to crest value in from 1 and to 10 micro-seconds, the wave front appears to be a signal whose frequency is from 25 to 250 KHZ.
C. Lightning behaves very much like radio frequency voltages and as much as such its behavior can be predicted fairly accurately and protection measures can be selected, considering this characteristic.
D. Lightning surges may reach indoor equipment and circuits thru exposed portions of the communication system such as antenna towers, transmission lines, telephone cables, etc. Lightning may reach buried plants by a direct stroke on portions of the plant exposed above ground and by arcing to the plant from ground thru plant, trees, man-made structures or the ground itself.
3.1.3. Power Contact/Induction
The necessity for constructing power and communications facilities near each other and the advantages to both interest of joint occupancy of poles and support structures present power contact/induction problems that must be carefully considered.
A. Good construction and adequate spacing between power and communication facilities are the first line of defense against power contact and power induction hazards. This essentially keeps foreign potential out of the communication plant.
B. The second measure is to provide paths to ground on the communication facilities sufficient to prevent excessive voltage rise in the communication plant and utilization of current limiting devices.
C. Insulation on communication conductors may in many instances withstand secondary power potentials but dependence on insulation alone introduces a considerable hazed.
D. Where the possibility of a power line contact is eminent, equipment connected to such lines shall be provided with protectors capable of discharging sufficient current to fuse the line conductor, or they shall be provided with lines fuses and surge arresters. Such protectors shall be adequately grounded to prevent excessive rise in potential at the equipment locations.
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E. Communication control circuits to electric power stations are always required to function more so during periods when there are faults on the power systems, so adequate protection is required.
F. A disturbance affecting communication circuits serving electric power stations is ground potential rise at the power stations. This potential is developed between the power station ground and the remote ground during periods when large ground currents, such as phase to ground fault currents are flowing in the station ground. The magnitude of this potential is the product of the ground current and the ground impedance.
G. Isolating transformers and/or neutralizing transformers and or other appropriate devices should be utilized to prevent disturbance in communication circuits exposed to a rise in ground potential. 3.1.4Acoustic Shock
Acoustic shock results from an abnormally high sound level, the physical effects of which may vary from minor discomfort to serious injury.
A. Voltage surges on the communication plant initiated by foreign potential, principally lightning, constitute the major hazard, although switching transients may also be the cause.
B. To reduce the effect of acoustic shocks, a device consisting of two rectifiers, or other semi-conductor elements in parallel with opposite polarities, shall be connected across the telephone receiver or headset.
C. The device shall meet the following:
a) It should occupy a small space, so that it can be placed, for example, in the case of the telephone receiver capsule.
b) Its electrical characteristics should not show significant changes under the temperature and humidity conditions to which it is subjected in service.
c) It should not degrade the performance of the circuit it is connected to.
d) It should operate such that the amplitude of the sound pressure caused by the diaphragm of the telephone receiver does not exceed 120 dB above 2 × 10-4microbar at 1000 Hz.
3.1.5 Electric shock
Current through the body rather than voltage of the circuit determines electric shock intensity. Voltage is significantly only in so far as it is one of the factors determining the magnitude current.
A. Shock current is also dependent on the impedance of the circuit contacted plus the body impedance of the victim.
B. Studies have shown that the average resistance of a dry adult human body is approximately 1,000,000 ohms. Wet or damage skin reduces this figure and 1,500 ohms is a conservative figure representing the body resistance for safety calculations.
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C. Ventricular fibrillation is likely to occur when a 60 Hz rms. Current of 0.030 amperes and above passes through one‟s chest cavity. Because of this, ANY CIRCUIT FROM WHICH IN EXCESS OF 30 MA RMS AC OR 90 MA DC CAN BE DRAWN THROUGH A 1500 OHM RESISTOR (45V RMS AC OR 135VDC) SHALL BE CLASSIFIED AS HAZARDOUS.
D. THE POTENTIAL DIFFERENCE AT ANY TIME BETWEEN ANY EXPOSED STRUCTURE (EQUIPMENT CABINETS, HOUSINGS, SUPPORTS, ETC.) TO GROUND (FLOOR, EARTH, ETC.) OR BETWEEN ANY EXPOSED STRUCTURE WITHIN THE REACH OF AN ADULT PERSON (AOOROX. 1.5 METERS) SHALL BE NO GREATER THAN 45 VOLTS RMS AC OR 135 VOLTS DC.
E. THE POTENTIAL DIFFERENCE AT ANY TIME BETWEEN TWO POINTS ON THE FLOOR OR EARTH SURFACE SEPERATED BY A DISTANCE OF ONE PACE, OR ABOUT ONE METER, IN THE DIRECTION OF MAXIMUM POTENTIAL GRADIENT SHALL BE NO FREATER THA 45 VOLTS RMS AC OR 135 VOLTS DC.
F. The limits specified in 3.1.5 D, and 3.1.5 E concern only the safety of personnel and should not proper equipment performance.
3.2 PROTECTION METHODS
Rarely will it be economically feasible to meet protection requirements for all situations by means of basic insulation incorporated in the design of equipment and plant. Additional protection measures are usually required and may use one or combination of the following basic protection measures.
3.2.1 Shielding
Shielding is the provision of a grounded electrical conducting material located such that foreign potential will be intercepted and surge currents diverted to ground with the least damage to plant equipment possible. Parallel or conductivity is essentially similar to shielding since a parallel conducting path is provided to absorb surge current which otherwise can flow and cause damage to communication plant/equipment.
3.2.2 Voltage Limiting
Voltage limiting prevents development of hazardous potential difference in communication plant by direct bonding, when permissible or by use of surge current, discharges gaps, diodes, etc. which operate under abnormal voltage condition.
3.2.3 Current Limiting and Interrupting
Current in a circuit can be kept from rising above a predetermined value by the use of a fuse in series with the circuit. When current flows through a fuse for a specified time with a magnitude greater that its rating, the fuse will interrupt the current.
19 3.2.4Grounding and Bonding
The foreign potential has entered the communication plant, the extent of possible damage will be reduce if some means are available for its rapid removal such as low impedance paths to ground at. Or close to. the point of entry.
A. Purpose
Grounds or connections thereto are used to divert undesired currents before they reach the equipment being protected and often are installed both at and some distance away from the protected equipment. When the difference of potential between the “grounded plant” and remote earth does not exceed the breakdown potential of the plant and does not present a shock hazard, the plant is adequately grounded.
B. Grounded Resistance
Ground resistance is the is the resistance path of a ground connection which includes the ground wire and its connection to ground electrode. the ground electrode, the contact between the electrode and the earth and surrounding soil. This value should be kept as low as feasible and should NEVER EXCEED 5.0 OHMS FOR EQUIPMENT LOCATIONS, ANTENNA TOWERS,AND ALL ALLIED INSTALLATIONS, AND 25 OHMS FOR OUTSIDE PLANT TELEPHONE POLES AND MANHOLES AS WELL AS CUSTOMER PREMISES.
C. Made Ground
A made ground is an electrode buried in the ground for the purpose for establishing a low resistance electrical contact with the earth. Types of made grounds include driven rods, driven pipes, buried plates, buried cones, or other similar devices placed in the ground.
3.3 METHODS AND MATERIALS
Electrical protection usually employs one or a combination of two or more methods to attain a sufficiently reliable level or safety. The basic idea is to keep foreign potential out of the communication facility or plant or when it manifest itself in the communication facility, it should be diverted to ground as near the point of entry and at the shortest time possible.
3.3.1 Lightning Rod
Structures do not influence the mechanism or path of a thunder-storm. Tall structures, such as antenna towers, only provide a favorable discharge point for lightning that would otherwise strike the earth in the vicinity of the structures if they were no present.
A. The area within which strokes are likely to be diverted to a structure varies with the structure‟s effective height. This area for the purpose of this Code shall be a cone having a radius of three times the effective height is measured from the top of the structure to the level of the point being considered.
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B. The material for the lightning rod shall be of galvanized iron/steel, copper weld or other corrosion-resistant material. The material selected shall be resistant to any corrosive condition existing at the installation or shall be suitably protected against corrosion.
C. Lightning rods shall be mounted atop structures not less than 30 cm. above the highest point of the structure or not less than 30 cm. above the point which creates an effective electrical height for the structure and to encompass all other elements, mounted and protruding horizontally from the structure, within the area explained in 3.3.1 A.
D. A No. 2 AWG grounding conductor connected to the lightning rod shall be run in the shortest route directly to the master ground bus or direct to earth without intervening splices or connection, free from sharp bends. Each lightning rod shall require a separate of # 2 AWG grounding conductor.
E.Structures not requiring lightning rod installations are:
a) Structures within the area described in 3.3.1.A. due to nearby taller buildings or structures. b)Passive reflectors and other similar fully metallic structures. Provided that its footing or a connection to a separate made ground provides sufficient grounding for the structure and that provision 3.1.5 D. is not violated.
c) Metallic antenna towers or poles where the antennas and their supports mounted on the metallic tower or pole have electrical continuity all the way from all elements to the structure and its footings and where a connection to a separate made ground provides sufficient grounding for the structures and provided further that provision 3.1.5. D. is not violated.
F. All other structures not covered by provision 3.3.1.E. shall be provided with lightning rod or rods as required considering provision 3.3.1.C.
G. The grounding system of lightning rods shall not be used as grounding conductors for any part of a plant.
3.3.2 Fuses and Current Interrupting
Current interrupting may be accomplished by employing one or any combination of the following: a)Fuse Link (fuses)
b) Heat coils c) Fuse cable
d) Automatic circuit breaker
A. Fuses are effective only when its time and current operating characteristics are matched to that of the circuit it is intended to protect.
B. After the fuse has opened, an arc may persist under the influence of excessive voltage. Failure of the arc to clear rapidly constitutes hazard and defeats the purpose of the fuse.
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C. Fuses are not effective for limiting short duration surges so it becomes necessary to provide some means of diverting surge currents through other paths having adequate current carrying capacity.
D. Heat coils that guard against “sneak current” fire hazard and will carry 0.35 ampere for about three hours and will operate within 210 seconds and 0.54 ampere.
E. Fuse cables are telephone cable sections installed in series and prior to the plant being protected and are one size smaller than the section to which they are connected.
F. An automatic circuit breaker is a device which opens the circuit when the current exceeds a predetermined rating a specified time without causing injury to itself and capable of being reset when a default condition no longer exist.
G. The choice of current interrupting device or method shall consider the cost of the protection measure/s against the value of service continuity and cost of system damage but personnel safety shall never be jeopardized.
3.3.3 Surge Arresters
Surge Arresters are normally open circuited devices and pass no significant current at normal operating potentials and shall meet the following fundamental requirements:
A. Striking voltage must be as constant as possible even after several successive discharge. B. The transition from glow to arc discharge must occur at less than one ampere. Are discharge, once established, must be very stable, and spontaneous transition from an arc to glow discharge must never occur.
C. The arcing voltage must be as small as possible.
D. It must be capable of carrying several tens of amperes for periods of the order of one second. It must be able to repeat such operation several times at very short intervals without its characteristics being affected.
E. If the above are exceeded, the surge arrester must “fail safe”, this shall be achieved through final short-circuiting of the electrodes. The surge arrester must never be destroyed by shattering of the enveloped in such a way as to leave the electrodes exposed, or by breakage of an internal connection, since in such cases the circuit is no longer protected and no warning of the fact is given.
F. The choice of breakdown voltage rating of surge arrester shall be as low as may possible be allowed by the facility to which it is to be connected.
22 3.3.4 Grounding and Bonding
A. A properly designed grounding system shall result in the following:
a) Limiting to definite value the potential to earth of the entire communication system by maintaining some point in the system at earth potential. Limiting the voltage to which the system to ground insulation is subjected results in fixing the insulation rating of system components.
b) Keeping the voltage to ground of metallic enclosures and other structures that may be contacted by personnel to values safe for personnel.
c) Protecting against static electricity with its attendant shock and fire hazards.
d) Providing a low impedance path for currents, induced due to direct contact of the communication plant with lightning and/or electrical power systems.
B. No cutout switch or fuse shall be placed in the ground lead.
C. The copper grounding conductors should be insulated to allow continuity testing at the time of installation and periodically thereafter.
D. Ground conductors should be run only in NON-METALLIC conduit or not in conduit. When the use of metallic conduit cannot be avoided, the grounding conductor shall be bonded to both ends of the conduit.
E. For radio stations, telephone/telegraph offices, Computer/DATA centers & the like except telephone/telegraph/telex subscriber stations, data terminals and residential installations, WATER PIPE GROUND SHALL BE AN ADDITION TO THE PRIMARY (MADE GROUND) GROUNDING ELECTRODE SYSTEM AND SHALL NOT BE A SUBSTITUTE FOR IT, OR VICE VERSA.
F. Ground wiring shall be as short as possible without sharp bends and kinks.
G. All elements of the communication plant designed to be at ground potential shall be bonded together.
3.4 MEASUREMENTS
Because formulas for ground resistance are complicated and earth resistivity is neither uniform nor constant, direct measurement of ground resistance is needed.
Ground Resistance Test Methods
3.4.1 Ground resistance measurement procedures are simple and straightforward and instruments are mostly direct reading. Two basic test methods for ground resistance measurement are:
(a)Direct method or two terminal test.
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A.The direct method is the simplest way to make an earth resistance test. With this method, resistance of two electrodes in series is measured the electrode under test and the reference ground or water system.
There are three important considerations with this test method:
1) The reference ground or water systems must be extensive enough to have negligible resistance.
2) The water pipe must be metallic throughout without any insulating couplings or flanges. 3) The earth electrode under test must be far enough away from the water-pipe system to be
outside its sphere of influence.
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B. The Fall of Potential method uses two reference rods. Placing of the two reference rods is critical and the instruction of the instrument manufacturer must be followed.
Fig. 3-2 Connections for a Fall of Potential or Three Terminal Ground Resistance Test.
Fig. 3-3Fall of potential method of testing.
C. Other methods for ground resistance measurements may be used such as Voltmeter-ammeter Method and Triangular method, provide the limitations of each method are considered and due safeguards taken.
25 3.4.2 Earth Resistivity
Earth Resistivity expressed in ohm-centimeter is the resistance of parallel faces of a one cubic centimeter of soil. Actually the earth is a poor conductor of electricity compared to copper, but, if the area of a path for current is made large enough, resistance can be quite low and the earth can be a good conductor.
A. Different types of soil exhibits different resistivities. This is shown is the following table.
Table 3-1 RESISTIVITIES OF DIFFERENT SOILS
Resistivity, Ohm-Cm
Type of Soil Average Min Max
Fill; ashes, cinders, brine, wastes 2,370 590 7,000
Clay, shale, gumba, loam 4,060 340 16,300
Same with varying proportions
of sand and gravel 15,800 1,020 135,000 Gravel, sand, stones, with little
clay or loam 94,000 59,000 458,000
From: US Bureau of Standards Technical Report 108
- RESISTIVITIES OF DIFFERENT SOILS
Type of Soil Resistivity, Range, Ohm-Cm.
Surface soil, loam 100 5,000
Clay 200 0,000
Sand and Gravel 5,000 100,000 Surface limestone 10,000 1,000,000
Limestone 500 00,000
Shales 500 10,000
Sandstone 2,000 00,000
Granites, basalts, etc. 100,000
Slates, etc. 1,000 0,000
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B. In soil, conduction of current is largely electrolytic so the amount of moisture and salt content of the soil radically affects its resistivity. Amount of water in the soil varies with the weather, time of the year, nature of sub-soil and depth of the permanent water table.
-
Moisture Content Resistivity, Ohm-Cm.
% by weight Top Soil Sandy Loam
0 1000 × 106 1000 × 106 2.5 250,000 150,000 5 165,000 43,000 10 53,000 18,500 15 19,000 10,500 20 12,000 6,300 30 6,400 4,200
From: “An Investigation of Earthing Resistance” by P.J. Higgs I.E.E.E. Jour., vol. 68, p. 736, Feb. 1930.
Pure water has a high resistivity; naturally-occurring salts in the earth, dissolve in water, lower its resistivity.
- Added Salt % by Weight
of Moisture Resistivity, Ohm-Cm.
0 10,700 0.1 1,800 1.0 460 5 190 10 130 20 100
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C. An increase in temperature will decrease resistivity because water in soil mostly determines the resistivity and an increase in temperature decreases the relativity of water. This is shown in the following table.
- EFFECT OF TEMPERATURE ON EARTH RESISTIVITY
Temperature Resistivity, Ohm-Cm.
C F 20 68 7,200 10 50 9,900 0 32 (water) 13,800 0 32 (ice) 30,000 -5 23 79,000 -15 14 330,000
D. Earth resistivity is a very variable quantity and to determine the value at a given location at a given time, the only sure way is to measure it.
E. The deeper ground electrode gives a more stable and lower value of resistance. Electrodes must reach deep enough level to provide permanent moisture content and stable temperature.
Determining Good Electrode Location
3.4.3 A good low-resistance ground electrode depends upon a low-resistivity soil in a location where the electrodes can be driven. There are two approaches to picking this location:
a) Drive rods in various locations to such depths as may be required and measure the resistances while the rods are being driven.
b)Measure the earth resistivity before driving ground rods then calculate the number and length of rods required.
28 How to improve grounds
3.4.4When the ground-electrode resistance is not low enough, undertake the following: A. Lengthen the ground-electrode in the earth
Fig. 3-4 Earth resistance decreases with depth of electrode in earth.
B. Use multiple Rods.
Fig. 3-5 Comparative resistance of multiple rod earth electrodes. Single rod equal 100%
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Fig. 3-6 Effect of variation in earth resistivity with depth on the resistance of a horizontal ground 150 meters long and 0.4 cm, diameter buried at the surface.
Fig. 3-7 Variation of resistance of vertical ground rod with length for various diameters as indicated on curves, for an earth resistivity of 100 meter-ohms.
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Fig. 3-8 Variation of resistance of horizontal ground with length ground at the surface and at a depth of 30 cm, for an earth resistivity of 100 meter-ohms and for a wire diameter of 0.2E cm (# 10 wire).
Fig. 3-9 Variation in combine resistance of rods connected in multiple when arrange on a straight line or a circle with spacing between rods equal to length of rods. Dashed line indicates combined resistance without mutual effects. Rod length 240 times rod radius as for 5 ft. rods of ½ inches diameter.
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D. Treat the soil when 3.4.4 A or 3.4.4 B is not feasible. This is not a permanent way to improve the ground resistance.
Fig. 3-10 Trench method of soil treatment
3.5 MAINTENANCE
It is not enough to check the ground resistance only at the time of installation. A continuous, periodic ground resistance testing should be adopted.
3.5.1 Grounding system requirements from year to year can change depending on the following factors: A.A plant or facility can expand in size or change its operation and such changes create different needs in the grounding system.
B. As more non-metallic pipes and conduits are installed underground, such installation becomes less and less dependable as effective low ground connections.
C. In many locations, the water table is gradually failing, and grounds formerly effective may end up ineffective.
3.5.2 Ground resistance shall be tested when installed and periodically afterwards, at least once a year during the dry or non-rainy months and ALL VALUES OBTAINED SHALL BE NO GREATER THAN REQUIRED IN RULE 3.2.4. B.
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3.5.3 All grounds connections, be it solderless or soldered, shall be checked at least once each year to be sure they are tight. Physical damage to ground wires shall be checked at the same time and damages rectified or damaged conductors replaced.
3.5.4 DO NOT TEST GROUNDS DURING THUNDERSTORM DAYS.
3.5.5 Never take hold of two wires or a wire or rod or probe in such a way that should complete a circuit through yourself.
3.5.6 Stray earth currents, accidental contacts or ground faults in the power system may produce an undeterminable difference of potential between two points, so use rubber gloves and handle ground wires under test as if they are energized.
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IV. GENERAL STRENGTH REQUIREMENTS
4.1 GENERAL
4.2 LOADING ZONES
4.2.1 Heavy Loading Zone
4.2.2 Medium Loading Zone
4.2.3 Light Loading Zone
4.3 SAFETY FACTORS
4.4 TRANSVERSE STRENGTH
4.5 VERTICAL STRENGTH
4.6 LONGITTUDINAL STRENGTH REQUIREMENTS
4.6.1 Reduction in Stress
4.6.2 Use of Guys and Braces
4.6.3 Unbalance Loads
4.7 ULTIMATE STRENGTH OF MATERIALS
4.7.1 Wood
4.7.2 Structural Steel
4.7.3 Reinforce Concrete
4.7.4 Conductors, Span Wires, Guys, Messengers
4.7.5 Tower or Pole Foundations and Footings
4.8 DETAILED STRENGTH REQUIREMENTS
4.8.1 Poles, Towers and Other Structures
4.8.2 Crossarms
4.8.3 Pins and Conductors
4.8.4 Conductors
4.8.5 Insulators
4.8.6 Guys and Anchors
4.8.7 Messenger and Span Wires
4.8.8 Hardware.
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SECTION IV
GENERAL STRENGTH REQUIREMENTS
4.1 GENERALThe Section established provisions covering mechanical strength requirements used in conjunction with electronic equipment or systems either alone or when involved with electrical power systems. The provisions of this Section are supplemented in many instances by provisions in other sections.
The rules in this Code complement applicable provisions in the Building Code of the Philippines and the Philippine Electrical Code. The more restrictive or stringent rules shall prevail.
4.2 LOADING ZONE
The following conditions of the temperature and loading shall be used for the purpose of this Code in determining the strength required by poles, towers, structures, and all parts thereof as well as in determining the strength and clearances of conductors. More stringent conditions may be used if desired. 4.2.1. Heavy Loading Zone
A. Heavy loading shall apply to those parts of the Republic of the Philippines as shown in Fig. 4-1. This loading shall be taken as the resultant stress due to wind and dead weight for 240 kilometer per hour (kph) wind velocity.
a) Wind pressure on protect area on cylindrical surfaces shall be computed as being 60% of that for flat surface.
Where lattice structures are used, the actual exposed area of one lateral face shall be increased by 50% to allow for pressure on the opposite face, provided by this computation does not indicate a greater pressure than would occur on a solid structure of the same outside dimensions, under which conditions, the latter shall be taken.
b) Temperature shall be considered to be 27°C at the time of maximum loading. The maximum temperature shall be assumed as 65°C in computing sag under this condition.
B. Medium loading shall apply to those parts of the Republic of the Philippines as shown in Fig. 4-1. This loading shall be takes as the resultant stress due to wind for 200 KMP wind velocity and dead weight under the following conditions:
a)Wind pressure on project area on cylindrical surface shall be computed as being 60% of that for flat surface.
When latticed structures are used, the actual exposed area of one lateral surface shall be increased 50% to allow for pressure
35
36
on the opposite face, provided this computation does not indicate a greater pressure than would occur on a solid structure of the same outside dimensions, under which conditions, the latter shall be taken.
b) Temperature shall be considered to be 27°C at the time of maximum loading. The maximum temperature shall be assumed as 65°C in computing sag under this condition.
C. Light loading shall apply to those parts of the Republic of the Philippines as shown in Fig. 4-1. This loading shall be taken as the resultant stress due to wind for 160 KHP wind velocity and dead weight under the following conditions:
a) Wind pressure on protected area on cylindrical surface shall be computed as being 60% of that for flat surface.
When latticed structures are used, the actual exposed area of one lateral surface shall be increased 50% to allow for pressure on the opposite face, provided this computation does not indicate a greater pressure than would occur on a solid structure of the same outside dimensions, under which condition, the latter shall be taken.
b) Temperature shall be considered to be 27°C at the time of maximum loading. The maximum temperature shall be assumed as 65°C in computing sag under this condition.
4.3 SAFETY FACTORS
4.3.1 The safety factors specified in these rules are the maximum allowable ratios of ultimate strengths of materials to the maximum working stress, except that:
A. The safety factors for structural steel (towers, poles, cross-arms, supports) shall be applied as specified in Rule 4.7.2 and
B. The safety factors for wood members in bending shall be applied to longitudinal tension and compression as ratios of the module of rupture to the maximum working stress. The maximum working stresses used with these safety factors shall be the maximum stresses which would be developed in the materials under the construction arrangement with temperature and loadings as specified in Rule 4.2. 4.3.2 Lines and elements of lines, upon installation or reconstruction shall provide, as a minimum, the safety factors specified in Table 4-1 for vertical loads and load transverse to lines and for loads longitudinal to lines except where longitudinal loads as balanced.
37 Table 4-1
MINIMUM SAFETY FACTOR
Elements of Construction Safety Factors
1. Conductors, splices and conductor
Fastenings (other than tie wires) 2
2. Pins 2
3. Pole line hardware 2
4. Line insulators (mechanical) 3
5. Guy Insulators (mechanical)
Interlocking 2
Non-interlocking 3
6. Guys except in lights loading zone 3
7. Guys in light loading zone 2
8. Messengers and span wires 2
9. Wooden poles 4
10. Structural or tabular steel poles, towers,
cross-arms and steel members of foundation 2
11. Foundations against uplift 2
12. Foundations against depression 3
13. Reinforced concrete poles 4
14. Cross-arm Wood 2
4.3.3. Replacement
Lines or parts thereof shall be replaced or reinforced before safety factors have been reduce (due to deterioration or changes on construction arrangement or other conditions subsequent to installation) to less than 2/3 of the construction safety factors specified in Rule 4.3.2. In no case shall be application of this be held to permit the use of structures or any member of any structure with a safety factor less than unity.
4.4 TRANSVERSE STRENGTH REQUIREMENT
In computing the transverse strength requirements of all parts of structures and in calculating allowable stresses and allowable minimum sags for conductors under the temperature and loading conditions specified in Rule 4.2, safety factors at least equal to those of Table 4-1 shall be used. In heavy loading areas for supporting structures carrying more than 10 wires (not including cables and supporting messenger wires) when the pin spacing does not exceed 40 cm the transverse wind load shall be calculated on two-thirds of the total number of such wires with a minimum ten. In cases where, due to change of direction in conductors, an unbalance side stress is imposed on the supporting structure, a transverse load shall be assumed equal to the resultant of all conductor tensions under the assumed loading conditions.
38 4.4.1 Special Provisions
Where it is impossible to obtain the required transverse strength except by the use of side guys or special structures and it is physically impossible to install them at the location of the transversely weak support, the strength may be supplied by side guying the line at each side of, and as near as practicable to, such weak support with a distance not in excess of 245 m. between the supports guyed; provided that the section of the line between the transversely weak structures is weak in regard, to transverse loads only, that it is in a straight line and that the strength of the side guyed supports is calculated on the transverse loading of the entire section of line between them.
4.5 VERTICAL STRENGTH REQUIREMENTS
In computing vertical strength requirements, the loads upon poles, towers, foundations, cross-arms, pins, insulators, and conductor fastenings shall be their own weight plus the superimposed weight which they support, including that of wires and cables under the loading conditions of Rule 4.2 plus that which may be added by difference in elevation of supports. The resultant of vertical and transverse loadings on conductor shall be used in determining the allowable and working tensions or sags in accordance with Rule 4.2. In addition, a vertical load of 90 kg. at the outer pin shall be included in computing the vertical loads on all cross-arms. All members of structures shall be constructed to withstand vertical loads as specified above the safety factors at least equal to those specified in Rule 4.3.2.
4.6 LONGITUDINAL STRENGTH REQUIREMENTS
In computing the longitudinal strength requirements of structures, or any parts thereof, the pull of the conductors shall be considered as that due to the maximum working tension in them under the loading conditions specified in Rule 4.2.
4.6.1 Reduction in Stress
Stresses in supporting structures due to longitudinal load may be reduced by increasing the conductor sags, provided that prescribed conductor clearances in Section VII are maintained.
4.6.2 Use of Guys and Braces
The longitudinal strength requirements for poles, towers, and other supporting structures shall be met either by the structure alone with the aid guys or braces. Deflection shall be limited by guys or braces where such structures alone, although providing the strength and safety factors required, would deflect sufficiently under the prescribed loadings to reduce clearances below the required values.
4.6.3 Unbalance Loads
Poles, towers, or structures with longitudinal loads not normally balanced (as the dead ends or angles greater that can be treated as in Rule 4.4) shall be sufficient strength or shall be guyed or braced, to withstand the total unbalanced load with the safety factors at least equal to those specified in Rule 4.3.
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4.6.4 Longitudinal load on each end support of crossings, conflicts or joint use, shall be taken as the unbalanced load equal to the tension of one-third of the total number of conductors that produces the maximum stress in the supports. If the application of the above results in the fractional part of a conductor, the nearest whole number of conductors shall be used. The construction of the supports (including poles, structures, towers, cross-arms, pins, insulators, conducting, fastenings, and guys) shall be such as to withstand at all times the load specified with a safety factor at least equal to 2/3 of the safety factors in Rule 4.3.2.
4.7 ULTIMATE STRENGTH OF MATERIALS
Values used for the ultimate strength of materials in connection with the safety factors specified in Rule 4.3 shall not be more than as follow:
4.7.1. Wood
Values used for moduli of rupture, for wood in bending in conjunction with the safety factors given in Rule 4.3 shall not exceed those shown in Table 4-2.
Table- 4-2 WOOD STRENGTHS
Species Modulus of Rupture in Bending
1. Apitong 6.4 Kg/mm2 2. Bagtikan do 3. Maungachapui do 4. Almon 5.2 Kg/mm2 5. Benguet pine do 6. Lanipan do 7. Pahutan do 8. Palosapis do 9. Red Lauan do 10. Tanguili do
Figures are for selected structure grade of material under short time loading with the neutral plane parallel to a side. Multiply the values by 1.4 where the neutral plane is on the diagonal of a square. Multiply the given values by 0.55 when the loading being considered is a long time loading (continuous load for a year or more). Poles shall be given suitable preservation treatment.
4.7.2 Structural Steel
Steel structures, steel structural members and their connections, shall be designed and constructed so that the structures and parts thereof shall not fail or be seriously distorted at any load less than the maximum working loads (developed under the construction arrangement with loadings specified in Rule 4.2) ; multiplied by the safety factors specified in Rule 4.3. The safety factors specified in Rule 4.3 shall be applied as follows to structural steel:
40
Tension and Bending: The yield point, 23.2 Kg/mm2 shall be divided by the safety factor to determine the maximum allowable working stress.
Compression: The Maximum allowable working stress shall be calculated by the following formula:
Where Smax = maximum allowable working stress in Kg/mm 2
fs = safety factor specified in Rule 4.3
YP = Yield point of the steel. 23.2 Kg/mm2 1 = unsupported length of a member r = radius of gyration of a member.
Shear: The ultimate tensile strength, 3.876 Kg/cm2 shall be multiplied by 2/3 and divided by the safety factors specified in Rule 4.3 to determine the maximum allowable working stress.
Where the figures given are used, structural steel shall conform to ASTM A7-39 for carbon steel of structural quality. Other values may be used for steel of other strength provided the yield point and ultimate tensile are determined by test.
4.7.3 Reinforced Concrete
Values used for ultimate strengths of reinforced concrete in conjunction with safety factors given in Rule 4.3 shall not exceed the following:
Reinforcing steel, tensile or compression strength in Kg/cm2 3867
Concrete, 1:2:3 Age Compression Strength
7 days 63.5 Kg/cm2 30 days 169.00 Kg/cm2 90 days 218.00 Kg/cm2
6 months 310.00 Kg/cm2
If reinforced concrete is designed for higher strength values which are proven by test, such values may be used in lieu of the figure given.
4.7.4 Conductors, Span Wires, Guys, Messengers
Values used for ultimate strength of wires and cables shall not exceed those given in Tables 10 to 14 in the Appendix. For use of types of wires and cables of other materials or composition not included in the Appendix, values for ultimate strength similarly derived from specifications of the ASTM shall be used except that, if such specifications are non-existent, manufacturer‟s specifications may be used provided that test have been made which shall justify the manufacturer‟s rating for ultimate strength.