Supports
Unless specifically designed for use at a low level, put lighting rigs out of reach of performers and the audience. If cables to lights are run overhead, support them along their length (preferably by an earthed strain wire) unless the cable is of the special type which incorporates its own strain wire. Take the strain off the flexible cable of suspended light fittings by supporting them with chains or other suitable devices.
Circuit separation
If possible you should take the electrical supply for lighting from sockets which are separate from those used for audio equipment. This avoids problems that may occur with RCDs on lighting circuits. The audio equipment needs reliable RCD protection.
Residual current devices
RCDs may not always be appropriate for lighting circuits. Some types of dimmer control have a relatively high electrical leakage which may cause nuisance tripping when a number of units are fed from one RCD. Other dimmers produce a direct current which can prevent some types of RCD operating correctly.
It might be tempting to put an RCD on the secondary (output) side of a dimmer to give additional protection to a lighting rig, particularly where it is positioned at low level. However, some RCDs which contain electronic components do not
operate satisfactorily at voltages much lower than 230 so the additional protection may not work. Check with the manufacturer of the RCD.
Remember: RCDs are recommended for circuits supplying outdoor lighting.
Three-phase supplies
If lighting is connected to two or three phases of the electrical supply, use separate dimmer cubicles on different phases to avoid confusion. Only supply a single phase to any one boom.
Connections
If you have lighting on a bar or boom, connect the individual lights to the boom by plug and socket. For indoor lighting these can be the 'old type' 15 amp or 5 amp three (round) pin types which are often used and quite satisfactory for lighting.
High power lights, eg 5 kW 'follow' spots, need correspondingly high power sockets, usually a 32 amp industrial type or the sort used for theatre or location lighting.
The metalwork of individual lights and the bar or boom should be adequately connected to the protective earth conductor.
Always disconnect the supply locally before changing any lamps. The use of plugs and sockets makes this easier as well as providing flexibility for different lighting arrangements.
Plugs and sockets to BS EN 60309 (previously BS 4343) provide better protection against damp and rain, and are ideal for use at outdoor locations. Since they are a tougher design, and are usually cheaper than the specialist 15 amp designs, they
are also recommended for all new installations.
Cables
Power cables from the lighting booms to the dimmer cabinet or control cubicle are often multi-core. You should ensure that such cables are suitable as regards flexibility and protection against abrasion or other mechanical damage. If
there is any risk of the cables getting hot from the lights, they should be of a type which is sheathed in, or protected by, heat resisting material.
• Make sure flexible cables are properly secured in a cable grip at the plug or other termination.
• Multi-core power cables should not be used to feed more than one phase to a boom.
• All plugs and sockets should be adequate in terms of voltage and current ratings and they should be in good condition; the protective earth connection is particularly important.
• Every circuit should have its own line and neutral conductors. If earth connections are looped, you must take care that the wire size is adequate along its whole length.
Earthing
Dimmer control cubicles also provide the marshalling points for cables to the lighting booms. All the exterior metalwork of the cubicles should be adequately earthed. There is sometimes separate provision for the connection of outgoing earth wires for lights. Alternatively, you can rely on the earth connection
of the outgoing plugs and sockets. There should be no provision in control cubicles for 'lifting' (ie disconnecting) earths.
Special effects
Lasers, strobes and other high-intensity lighting may require special arrangements or approval from the local authority etc before use. Some of these items use high voltages internally so it is particularly important to ensure they are in good condition and properly earthed if necessary. There may be non-electrical
risks such as radiation or epilepsy-induction from such equipment as well. HSE publication HS(G)95 The radiation safety of lasers used for display purposes [ref. 3] contains useful advice.
