Initial inspection checklist
18. Erection methods
Remember, if any of the initial verification checks require you to remove covers then you will need to carry out safe isolation, otherwise you will contravene the Electricity at Work Act 1989. The key point with all electrical work is that you maintain yours and everyone’s safety when carrying out such work.
Initial Inspection at a glance:
1. Connection of conductors 2. Identification of conductors
3. Routing of cables within mechanical protection
4. Selection of conductors for current carrying capacity and volt drop.
5. Connection of single – pole devices in the line conductor only
6. Correct connection of equipment 7. Presence of fire barriers and suitable
seals
8. Methods of protection against electric shock (earthing)
9. Prevention of detrimental influences 10. Presence of appropriate devices for
isolation and switching
11. Presence of under – voltage protective devices
12. Choice of setting of protective devices
13. Labeling of protective devices, switches and terminals
14. Selection of equipment
appropriate to external influences 15. Adequacy of access to switchgear
and equipment
16. Presence of warning signs and danger notices
17. Presence of diagrams, charts, instructions and similar information
18. Erection methods
Pick two different inspection checks from above and try to describe what is required
Inspection and Testing REV4.1 22 1. Connection of conductors
Every connection between conductors or between conductors and equipment must be electrically continuous and mechanically sound. We must also make sure that all connections are adequately enclosed but accessible as required by the regulations.
Loose connections can lead to many dangerous events from electric shock to fire.
Note: Before attempting to re-secure any electrical accessory you must ensure that the supply has been isolated.
Questions to ask ourselves:
• Are terminations electrically and mechanically sound?
• Is insulation and sheathing removed only to a minimum to allow satisfactory termination?
Dangers:
Movement of the socket outlet may dislodge circuit connections and contact exposed conductors.
Work to this standard generally means connections are also loose. Can lead to arcing;
overheating; electric shock; fire.
Remedy:
Dangers:
Constant use of this main isolator with a loose supply connection can catch fire through arcing and overheating.
Remedy:
Inspection and Testing REV4.1 23 2. Identification of conductors
A check should be made that each conductor is identified in accordance with the requirements of BS7671 Table 51A and Table 51B. Although numbered sleeves or discs may be used in special circumstances, the most common form of identification is by means of coloured insulation or sleeving. It should be noted in particular that only protective conductors should be identified by a combination of the colours green and yellow.
Questions to ask ourselves:
• Are conductors correctly identified in accordance with BS7671?
• Are switch wires identified as live at both terminations?
Harmonised colours of conductors to BS7671:2008
Dangers:
Old switch wire colours not
identified as live at two way switch so could present a danger when switch is replaced.
Remedy:
Inspection and Testing REV4.1 24 3. Routing of cables within mechanical protection
Cables should be routed out of harms way and protected against mechanical damage where necessary. Permitted cable routes are clearly defined in the 'on site guide' or alternatively cables should be installed in earthed metal conduit or trunking.
Questions to ask ourselves:
• Are cables installed so that external influences from mechanical damage, corrosion or heat etc have been considered?
• Are covers and lids in place to prevent unauthorised access?
Danger:
Remedy:
Install cables away from
terminations and ensure they are protected from mechanical damage
Dangers:
Unprotected single insulated conductors may get snagged or damaged by persons or
equipment.
Remedy:
Single core insulated cables should only be installed where they are afforded mechanical protection. Name five types different types of installation where they are properly protected.
Inspection and Testing REV4.1 25 4. Selection of conductors for current carrying capacity and volt drop
Where practicable the size of cable used at the consumer unit should be checked for current carrying capacity and voltage drop based upon information provided by the installation designer. Incorrect ratings can lead to equipment failure and overheating of conductors.
The maximum permitted voltage drop allowable from the nominal voltage is 3% for lighting and 5% for power. This value is from the origin of the installation to the furthest point of utilisation. At 230V that is 6.9V for lighting and 11.5V for power.
If we know the conductor size the procedure to measure voltage drop is simple.
1. For each circuit - when isolated – the L and N conductors are joined at the furthest point and the resistance of the loop measured at the distribution board.
2. We then calculate the approximate length of the circuit.
Circuit length in metres = 29.4 x R x S
Where R = loop resistance value and S = cable cross sectional area in mm² Example: the loop resistance of a lighting circuit, shorted out at the furthest point is found to be 0.7Ω. If the c.s.a of the cable is 1.0 mm², what is the circuit length?
L = 29.4 x 0.7 x 1 = 20.6 metres.
The voltage drop may then be determined by reference to appendix 4 of BS 7671.
1.0 mm² is listed as dropping 44mV/a/m
Therefore if the above circuit is carrying a current when fully loaded of 5A, the voltage drop will be:
Vd = Ib x L x mV/a/m = 5 x 20.6 x 44 = 4.53 Volts 1 000 1 000
Questions to ask ourselves:
• Are conductors selected for current carrying capacity and voltage drop in accordance with the design requirements?
How can we determine that the size of the conductor is correct for the intended use of the circuit?
Inspection and Testing REV4.1 26 5. Connection of single pole devices in the line conductor only
This is verification of polarity. A check must be made that all single pole devices are connected in the line conductor only. Where neutrals are used to switch devices the equipment or circuit remains live when the circuit is seemingly isolated.
Note: Before attempting to re-secure any electrical accessory you must ensure that the supply has been isolated.
Questions to ask ourselves:
• Are single pole devices and switching devices connected in the live conductor only?
• Are there only live conductors terminated into switches and circuit protection?
Dangers:
A fault or an overload will cause the fuse to operate but the
equipment will still remain live but not operational. Electric shock risk Remedy:
L
N
E
Load
Danger:
Remedy:
Disconnect the neutrals from the switch and connect the live conductors into the switch terminals
L N
E
Load
Inspection and Testing REV4.1 27 6. Correct connection of equipment
Accessories and equipment should be checked to ensure they have been connected correctly including correct polarity. Incorrect connection of equipment can lead to damage to the equipment or fire.
Questions to ask ourselves:
• Are all accessories and items of equipment correctly connected?
• Do all terminals have the correct conductors connected into them?
Danger:
Remedy:
Isolate circuit and re-wire strappers with a three core and earth and re-connect the switch
Danger:
Remedy:
Disconnect and re-connect socket conductors into the correct
terminals
Inspection and Testing REV4.1 28 7. Presence of fire barriers and suitable seals
A check must be made (preferably during construction) that fire barriers, suitable seals and/or other means of protection against thermal effects have been provided as necessary to meet the requirements of the regulations.
Suitable fire barriers need to be installed where cables pass through floors and walls.
Due to there being an entry to pass the cable through it would provide a path for fire to travel through. Expanding foam or transient blocks are the main form of seal used.
Where conduit, trunking or ducting does not exceed an internal csa of 710mm² it need not be sealed internally as it passes through walls and floors. Where this dimension is exceeded it needs to be sealed against the spread of fire.
Questions to ask ourselves:
• Are fire barriers present where required and protection against thermal effects provided?
• Where cables pass through walls and floors are the access holes sealed?
• Are correct termination methods used for cable entries?
• Where there is a danger of overheating conductors have they been protected by heat resistance sleeving or barriers?
Dangers:
An electrical fire within this
trunking would escape through the open cable entries. Also carries an electric shock risk.
Remedy:
Danger:
Remedy:
Disconnect and circuit conductors.
Remove conduit and re-terminate using a 25 to 20mm reducer.
Reconnect the conductors.
Inspection and Testing REV4.1 29 8. Methods of protection against electric shock
A check must be made that the requirements of the regulations have been met for the method of protection used. Failure to comply with BS7671 could result in an electric shock.
Basic Protection
Basic protection is protecting from touching parts that are live under normal use. This generally corresponds to contact of persons or livestock with live parts. The
unfortunate being receives maximum shock voltage. We are granted basic protection by:
Insulation
Although protection by insulation is the usual method of protection against direct contact other methods can be used. However, where insulation should be present it should be checked to ensure that no live conductors have been left exposed.
Barriers / Enclosures
Where live parts are protected by barriers or enclosures (e.g. bare bus-bars enclosed in a metal bus-bar chamber) they should be checked to ensure that all covers have been fitted and all fixing devices are secure.
Obstacles
Protection by obstacles provides protection only against unintentional contact with live conductors. If this method is used the area should be accessible only to skilled persons or persons under supervision.
Out of reach
Placing live parts out of reach can also provide protection against direct contact although increased distances may be necessary where long or bulky conducting objects are likely to be handled in the vicinity.
Questions to ask ourselves:
• What methods have been used to provide basic and fault protection?
• Are all live parts correctly protected from contact of persons or livestock?
• Are all barriers in place so contact with live parts is not possible?
• Are all points of earth termination on accessories and equipment connected to earth?
• Have all exposed conductive parts been connected to earth?
• Have all extraneous conductive parts been connected to earth?
BS7671 defines it as:
“Protection from electric shock under fault free conditions.”
Inspection and Testing REV4.1 30 Fault protection
Methods of fault protection are given in BS7671 as:
Automatic disconnection of supply.
Use of class II equipment.
Non-conducting location.
Earth-free local equipotential bonding Electrical separation.
Where persons or livestock come into contact with an exposed conductive part that has become live under fault conditions they should be protected by the part being earthed. Examples of exposed conductive parts include metal trunking, metal conduit or exposed metal parts of an appliance such as an electric kettle. Should the
insulation of any of the live parts within the kettle become defective then the metal casing may become live and anyone touching the kettle would be at risk of receiving a dangerous electric shock.
BS7671 defines it as:
“Protection against electric shock under single fault conditions”
Danger:
Remedy:
Isolate CU. Remove supply busbar. Replace with correct model and ensure it is shrouded
Dangers:
Access to live parts via poorly fitting terminal shroud. Electric shock
Remedy:
Inspection and Testing REV4.1 31 The most commonly used method of fault protection is automatic disconnection of the supply (ADS) and it these requirements that should be checked at the initial inspection stage.
Earthing arrangements; earthing conductors; main protective bonding conductors;
circuit protective conductors and supplementary bonding conductors should all be checked to ensure that they have been correctly installed and are of the correct size and are correctly labelled.
Protection against both basic and fault protection
Separated extra low voltage (SELV) is the most common method of providing protection against both. Requirements for this type of system include:
An isolated source of supply - e.g. a safety-isolating transformer to BS3535.
Also numbered BS EN 60742.
Electrical separation, which means no electrical connection between the SELV circuit and higher voltage systems.
No connection with earth or the exposed conductive parts
There must be no connection to earth and precautions must he taken to ensure, as far as possible, that earth faults will not occur. Such precautions would include the use of flexible cords without metallic sheaths, using double insulation, making sure that flexible cords are visible throughout their length of run, and so on. Perhaps the most common example of a separated circuit is the bathroom transformer unit feeding an electric shaver. By breaking the link to the earthed supply system using the double wound transformer, there is no path to earth for shock current.
Danger:
Remedy:
Remove brass light switch and replace with a plastic one or use the earth terminal point on the switch cover
Inspection and Testing REV4.1 32 9. Prevention of detrimental influences
Account must be taken of the proximity of other electrical services of a different voltage band and of non-electrical services and influences. E.g. fire alarm and
emergency lighting circuits must be separated from other cables and from each other and category 1 and category 2 circuits must not be present in the same enclosure or wiring system unless they are either segregated or wired with cable insulation suitable for the highest voltage present. This is due to the magnetic influence low voltage circuits can have on extra low voltage circuits. This can appear as false signals or “noise” on telephone lines for example.
Voltage Bands / Circuit Categories Category 1
Circuits operating at low voltages (50 to 600 volts AC) and supplied from the electrical mains.
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 Questions to ask ourselves:
• Are wiring systems installed such that they can have no harmful effect on non-electrical systems?
• Are systems of different voltages are segregated where necessary?
Dangers:
Circuit with different categories are in close proximity which can lead to interference or false signals
Remedy:
Dangers:
Circuits with different categories are in close proximity which can lead to interference or false signals
Remedy:
Inspection and Testing REV4.1 33 10. Presence of appropriate devices for isolation and switching
BS7671 requires, that effective means suitably positioned and ready to operate shall be provided so that all voltage may be cut off from every installation, every circuit within the installation and from all equipment, as may be necessary to prevent or remove danger.
This means that switches and/or isolating devices of the correct rating must be installed as
appropriate to meet the above requirements. It may be advisable, where feasible, to carry out an isolation exercise to check that effective isolation can be achieved. This should include switching off, locking-off and testing to verify that the circuit is dead and no other source of supply is present.