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Thread: Power trunking with tap offs

  1. #1
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    Power trunking with tap offs

    I have been asked to rewire an office which was once 4 shops. Each shop was fed of an overhead trunking with a tap off. The tap off is basically a small DB with a breaker in fixed to the trunking. The trunking has 4 x 50mm GP cables running through it. The trunking itself has stagered terminated (R,Y,B and Neutral. The 50mm cables are clamped in a fixed insulated Allen key head terminals and a 16mm goes from that to the tap off box which houses a breaker which then went on to feed the shop DB. The Earth for the tap off is a fixed point on the trunking - a purpose made terminal fixed to the trunking. Now I know you can't use wireways as earth (c.p.c.'s) according to the new regs. This trunking is designed to be used as the earth. I wouldn't use metal conduit, tray or normal trunking in a new install as the earth but would it be considered acceptable seeing as this is specifically designed as such? The trunking metal is thicker than usual. Can I consider it as a bus bar trunking? The Earth fault loop test results are text book perfect at the tap off I want to use. What do you think?
    Again I know wire ways can't be used as earth but if the product was specifically designed as such would it be considered ok.

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    Hi

    The system you described often has a copper busbar strip on the inside that ran the length .
    You are signing off the COC under reasonable safe and as long as it complies to fundamentals then it would be fine. The system was installed at a time when using the earth as part of the trunking was an acceptable practice.Same way that metal conduit used to be used as an earth .

    In my opinion it is acceptable

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    You have been asked to rewire, that means you will be putting in a whole new installation which must meet all requirements to certify. The terminal on the trunking is not to be used as an earth, it is there because all metal building components must be bonded to each other and connected to the earth. You still need to install an earth of equal dimensions to your supply cable.

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    I have to agree and disagree with Sparks statement .

    I agree if the complete installation from point of supply is being rewired but disagree if only 4 shops are being amalgamated out of say 20 shops.

    If it is 4 out of 20 then I would say that the existing reticulation would need to be reasonable safe and the new piece would need to adhere to the latest SANS 10142

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    I have only been asked the rewire from one of the existing tap offs so I am using an existing supply and as it is purpose built that the trunking be used as the earth and the reading are good then I think its OK. If it was normal, standard trunking I would run a separate earth. The trunking is a lot more heavy duty than standard trunking. Picture bus bar trunking but with cable.

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