Below procedure will help you to establish a safe standard for the installation of temporary and permanent electrical fixtures/appliances on project sites.
Overhead Cables: Overhead supply from the supply point or metering point to the distribution boards on the site should be of a robust pattern and preferably pliable and wire armoured with a further outer sheath of insulating material. Braided screened cable may be used but the more usual types will be PVC insulated wire armoured and PVC sheathed cable.
All these cables must be properly terminated and have suitable and efficient protective devices such as H.C. fuses or moulded circuit breakers. The cables should be so sited as to present the minimum of obstruction on the site. The cable stands to be used to suspend cables from ground level.
Underground Cables: The cables must be suitable for the duty and loading expected, e.g armoured PVC cables. The cables (both temporary and permanent should be buried at a safe depth and their routes clearly marked both on the site and on the site plans. The cables should be properly terminated and be provided with efficient circuit protection. Cable routes should be so arranged that the minimum of obstruction be caused.
Distribution Cabling: These cables will normally be multi-strand multi-core armoured or flexible PVC cables but, in certain cases, may take the form of mineral insulated copper clad (m.i.c.c.) cables. The latter type should be sheathed with PVC.
The installation must be so arranged as to prevent the need for long trailing cables. Socket outlets should be located as near the working point as possible.
Power and lighting circuits should be kept separate. Adequate records should be made of all parts of the installation and should be kept up to date when alteration or extensions are made.
Distribution Boards
- These should be accommodated in weatherproof positions or cabinets. They should be proofed against interference or unauthorized operation and they should be large enough to accommodate all the necessary apparatus required.
- Each electrical circuit should be clearly labelled and a circuit diagram should be located at each board. Boards should be positioned such that extension leads to power tools are no more than 30m in length.
- All Boards will have cover plates so as not to expose circuit breakers and display a legend.
- Certificate of Compliance (COC) issued by competent person regarding DB and its components to be displayed on the outside box. All DB Boards must be mounted on Metal Frames not combustible material.
- The supply from DB Board to portable electrical tools must be 110 vol DB Boards must be locked at all times so as to prevent unauthorized entry. In addition, all DB Boards must have pull wire from Main Circuit Breakers to isolate. A Pull wire must run from Main Circuit Breaker down through a hole or open cable gland position.
Earthing and Grounding
The entire distribution system, and all connected apparatus, must be efficiently earthed. The earth lead and the earth continuity conductors must be connected to an efficient ‘earth’.
The electrical conductivity or impedance of the earth continuity conductor, including metal conduits, metal cable sheaths or armouring must be sufficiently low to provide adequate and efficient protection when earth faults occurs. This impedance must be related to the fuse or overload ratings of the protective devices but should never exceed 1 ohm.
Each installation must be provided with an efficient earthing electrode, of low impedance, together with adequate earth leads and earth leads and earth continuity conductors.
Earth continuity of all circuits and of all apparatus should be tested by means of a ‘loop tester’ with an appreciable current of the order of 20 amperes.
All temporary distribution boards should be externally grounded regardless of their status as being „internally grounded‟.
Fire Extinguisher in near vicinity should be provided.
Residual Current Device (RCD)
An RCD or ELCB is to be installed to all final distribution boards and tested before use on each shift. To allow only the use of 110 volt for portable electric tools.
Earth Leads
Earth leads must be colored yellow and green, and yellow should be of stranded copper or copper alloy with a cross section of at least 6 sq.mm. The maximum size need not exceed 70 sq mm.
Every earthing connection and joint must be properly made by means of efficient clamps or couplings. Non-ferrous materials should be used.
Wiring and Cables
All interval wiring should conform to the relevant International Best Practices. For general site work additional precautions are necessary.
Other than supplies for welding purposes, cables carrying a voltage to earth in excess of 65V should have continuous metal armour or sheath which has been effectively earthed. Where trailing cables are concerned, this earthing should be in addition to the normal cable earth conductor. All cables should be sheathed overall.
Where cables need to be buried, they should be set at least 18 ins. (0.5m for permanent & 0.2m for temporary) below final ground level and be protected by tiles or enclosed in G.I. pipe.
When the trench is filled in, surface markers should indicate the cable route.
Low and medium voltage cables suspended should have bold marking erected to indicate their presence. Where these cables need to cross open areas, or where spans of 10 ft. (3m) or more are involved, a centenary wire on poles or other supports will provide a convenient means of suspension. Minimum height should be 19 ft. (5.8m) above ground.
If cables are required to be laid on the ground on a temporary basis, additional protection must be provide.
Joints in cables should be avoided wherever possible. Where unavoidable, they should only be made in purpose-built housing.
Cables on site are almost inevitably subjected to rough treatment. Special care should therefore be taken to ensure that earth – continuity conductor remains intact because, if it gets broken, the supply will not be interrupted, but the whole system will no longer be safe. Cables to be suspend as cable racks to keep them off ground level.
Extension Cables/Cords
All extension cables / cords should have a current inspection tag affixed and should be checked for damage prior to use. Extension cables / cords in one office should not be used to supply power to another office, building or adjacent offices. Cables / Cords may not run through doors, windows or ceilings unless for the purposes of temporary construction which require the cable to be physically protected from damage.
Extension cables / cords should not be overloaded and care should be taken to ensure that the cable / cord have sufficient capacity to carry the electrical load.
Extension cables / cords that are frayed or have insulation tears, cracks (exposed wires) or abrasions or with bent, broken or “spread” prongs should not be used.
Welding Transformer
The welding transformers must be connected to the supply by heavy duty cables, and an efficient isolating switch, together with protective fuses or circuit-breaker, should be located in an accessible position – usually on the transformer tank. Fixed transformers should be permanently wired in conduit or armoured cable but movable or transportable items require heavy duty flexible cables, preferably armoured.
Insulated flexible cables must be provided for the welding cable to the electrode holder and care should be taken to provide an effective return lead from the work piece to the transformer. The welding transformer should be efficiently earthed; this will automatically provide an earth connection for the welding return lead.
A properly constructed and insulated electrode holder should be used. It should have the insulated handle so arranged that accidental contact with live parts cannot be made. The holder should be well balanced and easy to handle. Although the welder should be equipped with suitable clothing and gloves the latter cannot, and should not, be relied upon as insulation.
Provision should be made for accommodating the holder from the supply. Although electric arcs for welding do not normally exceed 100 volts AC or DC, all electrical equipment, auxiliary cables and connections should be checked frequently. Special low voltage devices are available and should be used in hazardous conditions e.g. where the welder is standing on or surrounded by earthed metal.
Fire Exit in near vicinity should be indicated..
Temporary Lighting Arrangement
Temporary lighting must conform to the following points:
Lamps and fittings must be of weatherproofed construction. Secure runs for all cables.
Cables should be of the armoured or screened pattern, including an earthing core to which the metal work of the lamps and supporting structures should be bonded.
Lamp holders fitted with pin-contacts intended to be pressed through the cable sheath should NOT be used.
Lamps should be of sufficient output to provide even and adequate illumination with no ‘black spots’ in between pools of light.
All lamps must be fitted higher than should height so as not to create a burn hazard.
Hazard or obstruction lighting
It is a requirement that all obstructions, excavations, and any other impedance to pedestrians or vehicle traffic should be provided with warning lamps. The warning lamps can be run at either 110 volts or 24 volts but must never be supplied at the full mains voltage. Installation should conform to the following:
110-volt or 24-volt supply.
The supply must be properly earthed at the transform.
If metal barriers are used these must be bonded together and earthed.
Fittings must be of weatherproof construction.
Plant Used on Construction Work
Heavy plant and motors of 5hp and above. The supply to these should be as follows:
- 400 volts, 3 phase, 50 Hz.
- Cables should be of a robust, pliable wire, armoured type, properly routed.
- Local mains switches and circuit breakers should be installed in a semi permanent, weatherproofed, tamper-proofed, cubicle or cabinet.
- The equipment should be provided with a monitored-earth protection.
- Plugs and socket outlets must be of a specialized non-interchangeable pattern completely different from those on 240 volt, 110 volt, or 24 volt supplies.
- Other plant, etc, and motors of up to 5 hp.
It is usual for these to operate at a mains voltage of 240 volts. All plant, motors, equipment, lights, heaters, cookers, and any other appliances used at this voltage must be safe before being taken into use and must comply with the following:
Cabling should be as in Section Wiring and Cables.
Local switches for the mains supply, circuit breakers, fuses, etc., should be installed correctly in semi-permanent weatherproofed, tamper-proofed cubicles or cabinets.
Plugs and socket outlets should be of robust construction and must be non- interchangeable with those used for other voltages.
- Gray and Yellow = 110V
- Gray and Blue = 220V
- Gray and Red = 440V
Auxiliary Fittings
Lamp holders
Brass lamp holders should not be used anywhere on site, except in well constructed fixed fittings. All lamp holders should be fitted with a protective skirt forming part of, or securely attached to the lamp holder so that the brass cap (either screw or bayonet) of the lamp cannot be touched during the fitting or removal of the lamp.
Screw cap electric lamps and fittings
The screw cap of this type of lamp is part of the electrical circuit; therefore the wiring must be arranged so that the live side of the circuit is connected to the center contact of the lamp holder and the neutral side to the screw part of the lamp holder. The lamp holder must be fitted with a protective skirt. Great care must be taken to ensure that the polarity of individual circuits containing such lamp holders remains constant, i.e, live side to center contact, even during and especially after alterations, repairs, additions, etc.
Screw cap festoon lighting fittings having two pins, which penetrate the insulation of flat twin cable, should NOT be used because:
- it cannot be guaranteed that the centre contact the lamp holder is in contact with the live side of the circuit, and
- two small, almost invisible holes are left in the sheath and insulation and these affect the integrity of the insulation rendering it liable to breakdown, leakage and shock.
- This is the correct method of wiring a screw cap lamp holder. If a fuse is fitted into a circuit it must be on the live side not the negative side.
Plugs and socket outlets
It is not expected that anything larger than 16-ampere size will be needed for general application, apart from those instances where distribution cables may be connected to sub-distribution boards via heavy-duty plugs and socket outlets.
On heavy equipment running off 400 volts the supply should be provided with some form of monitored-earth protection, and therefore plugs and sockets of a specialized non- interchangeable pattern will be required. These must be of adequate size and strength for the voltages and current involved.
Plugs and socket outlets in all offices, stores, etc., may be of the 13 ampere fused type, made of tough insulating material. These provide an excellent method of ensuring closely rated fuse protection for individual items of equipment.
The use of fully waterproofed plugs and sockets (or cable connectors where applicable) should be restricted for the use of extension leads to tools, equipment, lights, , which are liable to be used in the early stages of construction work where it can be expected that the cables and connectors will be on damp or muddy ground or even completely under water. The reason for this restriction is that certain types of waterproof connections are hard to make – this leads to the waterproofing skirt being deliberately cut away. If waterproof plugs, etc., were in general use this would eventually lead to the situation where an accident would occur, possibly with fatal results.
Plugs and socket outlets and cable connectors used for different voltages must be non- interchangeable with those of other voltages. It is also advisable to label the sockets, e.g., a 110-volt socket should have label saying, “Use only 110v equipment‟.
Flammable and Explosive Conditions
When in the presence of flammable liquids and vapors (petroleum, oil, liquefied petroleum, oil, chemicals, liquefied petroleum gases, hydrogen, etc.), special precautions are necessary to ensure that, should a flammable atmosphere arise, no electrical source of ignition will be present. (Flame Proof Equipment intrinsically safe)
Inspection and Testing
The temporary power supply at all sites should be tested and inspected at three monthly intervals by competent personnel.
Portable electrical tools, tools and extension cables / cords should be inspected and tagged at three monthly intervals by competent personnel.
Tools and equipment should be inspected frequently using form Electrical Equipment/Tools Inspection Report as the record of inspection.
Electrical Equipment and Tools Inspection Report
|
NO. |
CHECK ITEMS |
RESULT |
REMARKS |
|
1 |
EQUIPMENT/TOOLS | ||
|
a |
Is equipment/tool free from damage or defects? | ||
|
b |
No vibration or abnormal sound at operation? | ||
|
c |
Are safety guards provided for moving/rotating parts? | ||
|
d |
Is the power supplied via ELCB? (See note below) | ||
|
e |
ELCB activates correctly? (Sensitivity/effectiveness) | ||
|
f |
Is Portable / Moveable equip. / tool externally grounded? | ||
|
g |
Earthing? | ||
|
h |
Is equipment securely installed? | ||
|
2 |
CABLES AND CONNECTORS | ||
|
a |
Is correct cable used? | ||
|
b |
Are all terminals secured, insulated and not exposed? | ||
|
c |
Is the cable insulation free of damage? | ||
|
d |
Are correct cable connectors used / damage free? | ||
|
e |
Are correct receptacle used / damage free? | ||
|
f |
Are correct switches used / damage free? | ||
|
g |
Are all cables laid correctly and in safe location? | ||
| Note: ELCB: Earth Leakage Circuit Breaker | |||
| Articles: Power drill, cutter saw, bender, concrete blower, submersible pump etc. | |||