Need help for new circuit.

1 Oct 2009
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United Kingdom
Hello all,

Need to install a bulkhead light, switch for said light, single or double socket and an outside pir bulkhead light, this is on a farm.

This is for a viewing box for an indoor arena, will need to be waterproof, although it won't be getting wet as such. No outside cables.

The feed currently is a 4mm swa to a waterproof outside socket (mounted inside) this is run from a 32a mcb, rcd protected CU.

So I'm thinking...- from the org socket, run 4mm swa to water proof jun box inside viewing area.. And this is where my mind goes blank..

Or run 4mm swa to double waterproof socket, then from there to a FCU, then run the rest in 1mm or 1.5mm in trunking?

Do I need 2 fcus? One for the light and one for the outside light?

Does that make sense?

Thanks in advance.
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The rules in farms are slightly different to elsewhere because animals have a bigger distance between their legs.

SECTION 705 of BS7671:2008 has loads of special rules and one has to first decide is this part of the farm or part of the house? Fig 705 gives instructions about earth mats and the like. Clearly all power must be from a RCD device but as to how close you need to follow the rule book will depend on what the area is used for.

The general rules are lights limited to 16A supply and where ceiling roses are used then 5/6A supply so likely you will need to fuse down with a fused connection unit. But it's not the fusing which is a problem but the earthing.

To be honest I think the earth mats shown in the book are really OTT. The farmers I knew as a kid always wore caps to work light switches as they often became live. (May be as I would as a kid drop links onto electric fence?). But if your going to have people around then maybe better to get some one with public liability insurance to do the work so you can back heal if anything does go wrong.
holmslaw makes a good point. If it were my job I would start with risk assessment. It does not stop anyone getting injured but it does show to any court that you behaved in a responsible manor.

So if you assess that there is a greater risk from injury due to lack of light than due to electric shock so in the interests of safety you did not include a RCD then if some one is injured you can show you acted in interests of safety.

One could debate the pros and cons until the cows come home but at end of day it's up to the guy doing the job. No real black and white answer. Of course one could say how emergency lights are required but the expense of following rule book to letter would likely be prohibitive. So sorry the way forward has to be decided by guy doing the job. But if you do a risk assessment and the risk changes then you can show how you acted in good faith.
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