Category 2
– Any data, telecommunication, intruder alarm systems and circuits operating at extra low voltage. (not exceeding 50 volts AC and 120 volts DC)Category 3
– Any fire detection system, emergency lighting or alarm system.Category 1 Circuits
Circuits operating at low voltages (50 to 600 volts AC) and supplied from the electrical mains.
Lighting circuits
All lighting circuits and their control wiring are included in category 1. One way; two way; intermediate; contactor controlled, timer controlled, automatically controlled are all examples of Category 1 circuits. Lighting that operates at less than 50 volts from a direct supply is NOT included.
Power circuits
All power circuits and their control wiring are included in category 1. Ring main and radial socket circuits; cooking appliances; fixed equipment; motors are all examples of Category 1 circuits. Control circuits that operate at voltages less than 50 volts are not included.
Heating circuits
All heating circuits and their control wiring are included in category 1. Dual-element immersion heaters; cistern-type water heaters; non-pressure water heaters;
Instantaneous water heater; controllers; timers; thermostats; pumps; boilers are all examples of Category 1 circuits.
Environmental control circuits
All circuits that provide cooled/heated air to a building are included in category 1. Air conditioning units; controlled; pumps; electronic shutters; valves; heating elements are all examples of Category 1 circuits.
Standby power supplies
All circuits that provide back up supplies to an electrical installation are included in category 1. Generators; temporary power leads; fixed back up battery units are all examples of Category 1 circuits.
The electrical supply in this country is very reliable and secure. However, as with all systems there are occasional interruptions that for some installations would be dangerous as well as inconvenient. Hospitals, air-traffic control and the petrochemical industry are just a few installations that could not tolerate an interruption to the mains supply, so a standby system needs to be
available.
Large installations need a standby generating system, whereby a large combustion engine cuts in automatically and drives a generator capable of supplying the load needed to continue working safely
Smaller establishments such as small offices cannot afford complex standby generation systems, but nevertheless they may have computer systems that cannot afford to be off or, worse still, risk losing data. In this situation
standby power systems known as Uninterruptible Power Supplies (UPS) are used, which consist of a battery supply that is charged up via the mains when not in use. When the mains supply is lost the UPS automatically cuts in and, via the electronics contained in it, converts the D.C battery supply to a mains supply capable of powering several computers.
Category 2 Circuits
Any data, telecommunication, intruder alarm systems and circuits operating at extra low voltage. (Not exceeding 50 volts AC and 120 volts DC)
Data Transmission
Fibre-optic cables
This cable is used for digital transmissions used by equipment such as telephones and computers. They are made from optical-quality plastic (the same as spectacles) where digital pulses of laser light are passed along the cable from one end to another with no loss or interference from mains cables (assuming the insulation is sufficiently rated). They look like SWA cables but of course they are much lighter and contain either one core or many dozens of cores.
Tight radius bends in this type of cable should be avoided, as should ‘kinks’, as the cable will break. Jointing of these cables requires specialist tools and equipment.
Never look into the ends of the cable as the laser light could damage your eyes.
The applications of optical fibre
communications have increased at a rapid rate since the first commercial installation of a fibre-optic system in 1977. Telephone companies began early on replacing their old copper-wire systems with optical-fibre lines. Today’s telephone companies use optical fibre throughout their system as the backbone architecture and as the long-distance connection between city phone systems.
Fibre-optic cables are also used in Local Area Networks (LAN). These collective groups of computers, or computer systems, connected to each other, allow for shared program software or databases. Colleges, universities, office buildings and industrial plants, just to name a few, all make use of fibre-optic cables within their LAN systems. Power companies are emerging as big users of fibre optics in their communication systems. Most power utilities already have fibre-optic
communication systems in use for monitoring their power grid systems.
If you wanted to see down a dark corridor, you might shine a torch down it. But what if the corridor had a bend in it? You could probably put a mirror in just the right place at just the right angle and shine the light round the corner. But what if the corner had lots of bends? Well, what if I made the entire corridor walls out of mirrors, then I wouldn’t need to put them in just the right place or angle. The light would be able to bounce around all the mirrors along the walls.
Believe it or not, that’s the theory behind fibre-optics, as the glass core is essentially a mirror wound into a thin tube. Some 10 billion digital bits can be transmitted per second along an optical fibre link in a commercial network, enough to carry tens of thousands of telephone calls. The hair-thin fibres consist of two concentric layers of high-purity silica glass, the core and the cladding, which are enclosed by a protective sheath.
Co-axial cable
UTP (CAT5) cable
Cat (Category) 5 cable
This cable is used extensively for data transfer in computer networks and telephone systems. It has four pairs of wires that transmit and receive data along them at very high frequencies; typically 350 MHz. Special termination ends are required for these cables.
There are three basic types of cabling used in data systems: coaxial, fibre-optic and Unshielded Twisted Pair (UTP). Coaxial is widely installed in older networks but is not recommended for new network installations.
Fibre is used for high-speed networks and to connect networking devices separated by large distances. But UTP is currently the most common and recommended cabling type. UTP is inexpensive, flexible and can transmit data at high speeds. Most new installations are currently installed with Cat-5 UTP cabling and
components.
Intruder / Security Alarms
Alarm systems are classified as Category 2. All cabling that connects to keypads, remote sensors, sounders, beacons or door contacts all need to be kept separate.
Closed Circuit Television (CCTV)
Camera equipment uses a co-axial cable that transmits (and sometimes powers) cameras on an installation.
MICC Cable
Category 3 Circuits
Any fire detection system, emergency lighting or alarm system Fire Alarms
A correctly installed fire-alarm system installation is of paramount importance and can be compared to any other electrical undertaking, as life could be lost and property damaged as a result of carelessly or incorrectly connected fire-detection and alarm equipment.
Fire alarms typically use red FP200 (or equivalent) or MICC cable.
Emergency Lighting
Emergency lighting is not required in private homes because the occupants are familiar with their surroundings. However, in public buildings, people are in unfamiliar surroundings and in an emergency they will require a well-illuminated and easily identified exit route. Emergency lighting should be planned, installed and maintained to the highest standards of reliability and integrity, so that it will operate satisfactorily when called into action.
Emergency lighting typically use white FP200 (or equivalent) or MICC cable. When they are installed as an integral part of a lighting circuit they use the general circuit wiring (i.e. PVC cable).
Also included in category 3 are any circuits that are used as an evacuation system. This could be a system that is a person-operated loudspeaker system or a computer or panel operated one.
Check your learning by answering the questions below
1. State the voltage range of a category 1 circuit
2. What type of lighting circuits are not included in category 1?
3. Give two examples of a power circuit.
4. What is a UPS and how does it function?
5. What type of circuits are included in category 2?
6. Explain the basic theory behind fibre optics.
7. Explain why you think category 3 circuits have their own classification.
Standard Circuit Ratings
The table below shows most of the standard circuits found in domestic premises and the ratings of the overcurrent devices that may be used to protect them.
TYPE OF CIRCUIT RATING (A) TYPICAL CONDUCTOR SIZES (mm²)
Lighting 5, 6, 10 1.0, 1.5
Socket outlets (BS1363) 20, 30, 32 2.5, 4
Socket outlets (BSEN60309) 20 2.5
Immersion Heater (3-4kW) 15, 16, 20 2.5, 4
Cooker, electric shower (6-10kW) 30, 32, 40,45 4, 6, 10
There may seem little difference between a 5A and 6A protective device and indeed, in terms of performance, there is little difference. This reflects the changes in
standards over time. Rewirable fuses to BS3036 and cartridge fuses to BS1361 are made in ratings 5, 15 20, 30 A. Miniature circuit breakers and (mcb’s) to BS EN60898 are made in sizes 6, 10, 16, 20 and 32A.
The third column on the table shows the cable sizes that are typically used in these circuits. The list is not an inclusive list as unique installation conditions may require a larger cable. The list is for thermoplastic (p.v.c) cable. If m.i.c.c were being used then it would be found that a cable one size smaller would usually suffice. This is because the mineral insulation can withstand higher temperatures than p.v.c and so the current ratings of m.i.c.c are higher as a result.
RCDs are required to protect users of appliances and equipment where sockets rated up to 20 amps are used. The highest risk is outside of the equipotential zone. This is due to the fault return path not being sufficient
Class discussion
Dave, an electrical apprentice needs to isolate a lighting circuit so he can fit a dimmer switch to an upstairs bed room for his parents. Explain the step by step process he will go through to ensure he does the isolation correctly.
Lighting Circuits
Lighting is a vast and varied subject and beyond the scope of these notes. However we will see some of the basic requirements, the different lighting circuits used and the types of lamps associated with standard installations.
BS7671 makes the following reference to lighting circuits:
• All electrical equipment must be accessible for operation, inspection & testing, maintenance and repair. (Reg: 132.12)
• Where an installation has only one lighting circuit, the circuit may need to be divided into two circuits to minimize the danger that may arise in the event of a fault.(Reg: 314.1 (iii) )
• Light fittings must be installed so that any radiated heat does not cause any damage. (Reg: 559.5.1)
• The fixing supporting a light fitting must be able to support a weight of at least 5kg. (Reg: 559.6.1.5)
• Domestic lighting circuits should not be rated at more than 16A. (Reg: 559.6.1.6)
• Edison screw lampholders (excluding types E14, E27) should have the outer contact connected to the neutral conductor. (Reg: 559.6.1.8)
• Lighting circuits must be controlled by the appropriate number of switches. (Reg: 559.6.1.9)
• Through wiring is only permitted in a light fitting where the light fitting is designed for such wiring. (Reg: 559.6.2.1)
• Through wiring in a light fitting must be suitable for the temperature generated inside the fitting. (Reg: 559.6.2.2)
• The lamp inside an outdoor light fitting mounted less than 2.8m above the ground must only be accessible after removing an enclosure or barrier with the use of a tool.
(Reg: 559.10.3.1)
• Electrical equipment outdoors must be rated at least IP33.
(Reg: 559.10.5.2)
• Switchlines must be marked brown at their terminations.
(Reg: 514.3.1 and App.7 chapter 3
Lighting points
For each fixed lighting point one of the following must be used.
1. Ceiling rose 2. Device for connecting a
luminaire (DCL)
3. Batten lamp holder 4. Luminaire designed to be connected directly to the circuit wiring
BS7671 states that the maximum rating of overcurrent protective devices of circuits must not exceed the lamp holder rating. These are:
Small Bayonet Cap B15 Max Rating 6 Amps
Bayonet Cap B22 Max. Rating 16 Amps
Small Edison Screw E14 Max. Rating 6 Amps
Edison Screw E22 Max. Rating 16 Amps
Giant Edison Screw E40 Max. Rating 16 Amps
Lamp types
Incandescent filament lamps (GLS and reflector)
Filament lamps are used mainly for domestic and display lighting. There are many types of filament lamp, the most common being general lighting service (gls) and decorative.
Their finish – clear, diffuse/pearl or coloured – is a significant factor in their application. Reflector lamps are similar but have an
envelope with an internal reflective coating.
Advantages of filament lamps include low initial cost, simple operation (no control gear required) and good colour rendering.
Disadvantages of filament lamps are low efficacy (measure of the energy efficiency of a light source, ie lumens per watt) and a relatively short life. Certain extended life filament lamps have only about half the efficacy of standard lamps. The light output of filament lamps is particularly sensitive to voltage variations.
Halogen filled filament lamps (tungsten halogen) The main reason for filling a tungsten filament lamp with a halogen gas is to prevent evaporated tungsten
from blackening the envelope. Tungsten halogen lamps also have an increased light output and/or an extended life compared with standard filament lamps. The envelope is of small dimensions and made of quartz or hard glass. Some mains voltage lamps have an outer protective envelope.
Lamps that are suitable for use in luminaries without a safety screen should be so marked. Otherwise, tungsten halogen lamps should only be used in suitably enclosed luminaries.
Extra low voltage (elv) lamps are, in general, more compact than their mains voltage counterparts and the small filament size can improve the optical efficiency of integral or external reflectors (generally dichroic). Elv reflector lamps make it possible to use compact luminaires for display lighting.
Low pressure mercury fluorescent tubes The light output from a tubular fluorescent lamp comes from phosphors that convert energy from a low pressure gas discharge into visible light. The colour temperature and colour rendering are determined by the phosphor mix coated on the inside of the tube.
The argon-filled t12 (38mm diameter) tubes are
being discontinued. The modern range of krypton-filled triphosphor t8 (26mm) diameter tubes should be the first choice for switchstart, quick start and high
frequency luminaries. Such lamps have a higher efficacy, longer life, improved lumen maintenance and better colour rendering than earlier types of tube.
Triphosphor (or multi-phosphor) tubes offer a wide range of colour temperatures from very warm (2700k), warm (3000k) and intermediate (3500k) through to cold white (4000k), daylight (5000-5500k) and northlight (6000-6500k).
Compact fluorescent lamps
A compact fluorescent lamp (cfl) has the characteristics and advantages of linear fluorescent lamps but its compact size is achieved by folding the discharge path, retaining high efficacy. The two main groups of cfls are those with external control gear and those with internal control gear.
High frequency control gear is now available
integrated into the cfl lampholder, making lamp conversion from gls to cfl very simple.
Many modern fluorescent lamps are operated at high frequency (typically at or above 30 khz) which results in a reduction of energy losses both in the lamp and the control gear. The control gear size and weight are often less, the efficacy higher, dimming where required is easier, and operation is silent.
Incandescent
The main tube lengths and their respective power ratings are:
600mm = 18w 1200mm = 36w 1500mm = 58w 1800mm = 70w
High pressure sodium lamps
Light is generated by an electrical discharge in a gas containing sodium and mercury (sodium amalgam) contained in a sintered alumina arc-tube.
High pressure sodium lamps are used for road lighting, floodlighting and industrial interior lighting.
Low pressure sodium lamps
Low pressure sodium lamps consist of a u tube containing the discharge, and an outer heat reflecting glass jacket.
The monochromatic light is concentrated in the yellow part of the visible spectrum which is close to the maximum sensitivity of the human eye at normal lighting levels.
The efficacy is the highest of all lamp types, but with very poor colour rendering. Low pressure sodium lamps are used mainly for exterior applications such as road and security lighting (but are not suitable for repeated on/off (operation).
Metal halide discharge lamps
Metal halide lamps have quartz or sintered alumina (ceramic) arc tubes, generally with an outer glass envelope. Light output is from mercury and other metallic elements introduced in the form of halides.
Metal halide lamps of the ‘protected’ type are now available for operation in luminaries without safety
screens. According to the mix of elements, there is a wide range of efficacy and/or colour appearance, but colour rendering is generally good.
Metal halide lamps are generally used in commercial interiors, industry and floodlighting, and (in smaller ratings) for retail lighting.
High pressure mercury discharge lamps
The high pressure mercury discharge operates in a quartz envelope. Mercury lamps were used for illuminating road signs and industrial lighting but have largely been replaced by the more efficient lamps now available. Such lamps offer low cost
discharge lighting where high efficacy is not important. They often incorporate a third electrode for starting and in such cases the control gear required generally consists only of a ballast and a power-factor corrected capacitor.
Induction lamps
Induction is a process whereby electrical power is passed from one circuit to another without the use of physical electrical conductors. It enables lamps to be constructed without the need for wire connections to pass through the glass or quartz envelope. Induction lamps are available as low pressure mercury lamps, using the same triphosphor coating of the inner envelope surface as the familiar fluorescent tubes. The commercially available range of induction lamps is limited.
Light emitting diodes (leds)
Light emitting diodes have been used for indicating purposes for several decades and recent developments have created larger diodes and extended the range of colours including white.
A dramatic increase in efficacy is predicted in the near future.
Leds have an extremely long life and are likely to be built into the luminaire and will not be a consumable item as far as the end user is concerned.
V
Lighting design current calculations
Example 1
A house with ten rooms requires a light in each room. Calculate the design current.
i) Select the correct formula (basic resistive lighting)
ii) Input the data into the formula and work it out to two decimal places and be sure to add the unit (A)
Example 2
A warehouse office has two rooms with two, four tube light fittings rated at 36 watts per tube. Calculate the assumed design current for the 230v circuit.
i) Select the correct formula (discharge lighting). Three line circuits use a similar formula but the V (230v) is replaced by √3 x 400
ii) Input the data into the formula and work it out to two decimal places and be sure to add the unit (A)
Assumptions
1. A lighting outlet shall be considered to have a connected load of minimum 100 W. (Standard lighting points with lamps)
2. Discharge lighting calculations needs to take into to account harmonic currents and control gear losses. Where the exact manufacturer’s information for gear losses is not available the maximum demand shall be assumed to be 1.8 x the lamp rating
Note: If the manufacturer’s discharge lamp information is obtainable from a catalogue this would be used to gain a more accurate value of design current.
Standard lamp ratings are approximately increased by 10%.
1. A 230v lighting circuit supplying twelve rooms with one standard light point in each.
2. A 230v lighting circuit feeding twelve rooms has one centre light in each room and two wall lights in two rooms.
The wall lights are twin 40w maximum
The wall lights are twin 40w maximum