equipotential bonding

[Matt]

when setting up trussing attached to a woodne stage that is obviously insulated, what are the rules about earthing such a structure, becuase the school I have working in have done it before, and I have recieved one or two static shocks from them.

 

would be most grateful if youcould help as this would help me a great deal because I and planning to use some trilite very soon...

 

Matt.

[PaulDF]

Equipotentional bonding refers to making all metallic objects within a given space of the same potential (faraday cage). This usually refers to any metallic pipework etc which is connected to external influences which could give rise to danger i.e. if two pipeworks potentials are different, hence earthing these at source and cross bonding in bathrooms and kitchens where the risk is greatly increased by moisture.

In your case, when a lamp is connected to the trussing and plugged into the mains the trussing should incidentally be earthed through the metallic body of the lamp (earth bonded) providing the lamp is class 1 earthed equipment and there is a clear metallic path from the lamp to the trussing through the fixtures and the paint. All flexible cables connecting the lamps to your control gear must be double insulated and visually checked for any damage before use. Special care must be taken whilst installing your gear not to damage the cables or lamps. All your gear should be (arghh) PAT tested prior to use (this checks the earth bonds, insulation etc).

It will be worth consulting a qualified sparky to check if supplementary bonding is required and if so, to install a point from which you can attach an earth bond.

Hope this helps,

[robloxley]

Going to 'first principles' & considering what supplementary bonding is for, you could measure the truss's resistance to the main earthing terminal; if this value is 50 kOhms or greater and the environment isn't wet (e.g. bathrooms etc.) then bonding probably isn't necessary to prevent a dangerous shock.