to the 16th Edition IEE Regulations
   
   
   
 
 

chapter 5
Earthing

chapter 6
Circuits

Special Installations
  --1. - Introduction --2. - Bath tubs and shower basins
  --3. - Swimming pools --4. - Sauna rooms
  --5. - Installations on construction sites --6. - Agricultural & horticultural
--7. - Restrictive conductive locations --8. - Earthing for function & protection
--9. - Caravan, motor homes, caravan parks 10. - Highway power & street furniture
11. - Heating appliances & installations 12. - Discharge lighting
13. - Underground & overhead wiring 14. - Outdoor installations & garden buildings
15. - Installations of machines & transformers 16. - Reduced voltage systems
17. - Marinas 18. - Medical locations
19. - Exhibitions, shows and stands


7.19.2 - Recommendations for exhibitions, shows and stands

Shock protection
Protection against direct contact (see {3.4.5}) by means of obstacles and placing out of reach must not be used, and neither must non-conducting location and earth-free equipotential bonding be used as protection against indirect contact (see {3.4.6}). Automatic disconnection of the supply is the preferred method, but because of the difficulty of bonding all accessible extraneous conductive parts, PME supplies (TN-C-S system) must not be used for temporary or outdoor installations. A TN-S system (where the supply company provides an earth) could be used, but a TT system (earthed using an electrode) is preferable. The maximum disconnection times are reduced to 0.2 s for 240 V and to 0.05 5 for 415 V systems, which means that the earth fault loop impedance values are reduced to those shown in {Table 7.4} for agricultural applications. Livestock are often present at agricultural shows. In this case, supplementary bonding must connect all exposed conductive parts and extraneous conductive parts which can be touched by them.

Distribution circuits which are at an increased risk of damage must be protected by an RCD with a 300 to 500 mA rating; to provide discrimination with other RCDs protecting final circuits, they should be time delayed. All final circuits for socket outlets must be protected by RCDs rated at 30 mA. Final circuits for lighting which are accessible to the public must also be protected by 30 mA RCDs. However, loss of light in a crowded space is likely to cause a serious hazard, and such areas should be fed from at least two separate circuits with separate RCD protection. Extraneous conductive parts on vehicles, wagons, caravans etc. must be bonded to the protective system using conductors of not less than 4 mm˛.

Fire protection
Because of the increased risk of fire and burns in these locations, it is very important to follow the advice given in {3.5}. Where SELV or PELV Systems are used (see{3.4.4}) they must be insulated and tested as if they were 240 V circuits. Stored material, such as cardboard boxes and fodder, are a special fire hazard. Remotely or automatically controlled motors must be fitted with manual reset controls against excess temperature and must be accessible only to skilled persons. Lighting equipment, such as incandescent lamps, spotlights, projectors, etc., must be suitably positioned and guarded to prevent overheating to themselves or of. adjacent surfaces. Sufficient ventilation must he provided to prevent the build-up of heat.

Isolation
Every separate temporary structure and each distribution circuit supplying outdoor installations must he provided with its own easily accessible and clearly identified means of isolation.

Equipment
Equipment must he mounted away from positions which may not be weather-proof. Tent poles are the most obvious place to mount equipment, but are often the weak point in the weather tightness of temporary structures. Switchgear should be mounted in closed cabinets which can only be opened by a key or a tool, but isolators must be always accessible.

Wiring Systems
The types and protection of cables is of particular importance, as is the current carrying capacity. Wherever there is a risk of damage, mechanical protection or armoured cables should be used - trailing flexibles should never exceed 2 m in length to reduce the risk of tripping and of damage to the equipment and terminations. Underground cables should be clearly marked, hearing in mind that structure support pins may be 1 m long. Where a fire alarm is not installed, cables must be of the flame retardant, low smoke type or enclosed in conduit or trunking to prevent the spread of fire. There must be no joints in cables except as a connection into a circuit. Where lurninaires are mounted below 2.5 m (within arm's reach) they must be firmly fixed and carefully sited to reduce danger to people and the possibility of fire. Electric motors must have isolation equipment breaking all poles, and must be provided with adjacent emergency stop systems. Socket outlets are subject to particular abuse by users in these situations. They should:

1. - be adequate in number,

2. - preferably not he floor mounted, but if so, must be mechanically protected and waterproof,

3. - have no more than one flexible cable or cord connected to each plug,

4. - never have multiway plug-in adapters connected, and

5. - have no more than one portable trailing block multiway socket connected by means of a
----- flexible cord not exceeding 2 m in length.

Safety systems
Where a generator is used to supply the temporary installation, there must be full earthing using separate earth electrodes. For TN systems, all exposed conductive parts must be bonded back to the generator. Where the exhibition is held in a building, care must be taken to ensure that temporary structures do not impede escape routes. Where an exhibition is constructed out-of-doors, a fire alarm system must be installed to enclosed areas, and emergency lighting must be provided for escape routes.

Inspection and testing
The electrical installations of all stands must be re-tested on site after each assembly. Exhibitors and stall holders must be encouraged to visually check electrical equipment for damage on a daily basis.

 

 

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Extracted from The Electricians Guide Fifth Edition
by John Whitfield
Published by EPA Press Click Here to order your Copy

Click here for list of abbreviations