Thursday, April 30, 2009

Electrical Safety - Grounding continuity

When you think that your lighting batten is inherently grounded, you may want to check that it really is grounded. Modern rigging systems use Nylatron (plastic) pulleys and the counterweight carraige arbor shoes may be Nylon, leaving the only electrical path back to the safety ground as the ground wire in the SO power cable or flexible conduit that feeds your plugstrip or plugbox. If the fixed conduit or flex conduit body is the only ground path you have, then the ground is broked (open circuit) if the conduit becomes separated.

The same is true if your ground lead on a lighting instrument becomes disconnected. This can happen several ways:
  • A two wire connector (an old style two-pin 2P&G stage plug or a two-bladed Edison plug) is installed on a three-wire cable
  • A ground-lift adapter is installed on the end of a normally grounded NEMA 5-15P connector
  • The wire breaks internally
  • The wire gets yanked-out of the connector body
  • The wire gets yanked out of the lighting instrument body

In any case, you are in a situation that would let the fault current of an internal problem in a lighting instrument look for another path back to the source, and that path may be you!

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