Electrical Safety

Electricity on a show carries three risks at once: electric shock to people, fire from overheating, and damage to equipment. The defences against them are layered, each covering a different failure. Overcurrent protection, provided by circuit breakers and fuses, is sized to protect the cable: it disconnects the circuit before the conductor can overheat, a principle IEC 60364-4-43 expresses as Ib ≤ In ≤ Iz. Nuisance tripping is therefore never solved by fitting a larger breaker, which would remove the protection the cable depends on. Earthing, or grounding, gives fault current a path back to the source. In TN systems, common in the United Kingdom and on many industrial networks, the fault current is high enough to trip the breaker; in TT systems, the standard for low-voltage public supply in France, it is the residual current device that disconnects the supply. Residual current protection detects current leaking to earth and cuts the supply within a few tens of milliseconds at typical shock currents. Its thresholds differ by region. IEC practice, where the device is called an RCD (DDR in France), uses devices of 30 mA or less under IEC 61008 and IEC 61009, while the North American GFCI (UL 943, Class A) trips at around 4 to 6 mA. This protection is essential near water, outdoors and wherever performers are in direct contact with equipment. Temporary installations for shows are covered by IEC 60364-7-711 (part 7-711 of NF C 15-100 in France, BS 7909 in the United Kingdom) and, in the United States, by NEC Articles 520, 525 and 590.