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Do I need to do anything about single pole Isolator owned by DNO

Alan B

I was changing a consumer unit today on a property where there was an isolator supplied by the DNO (owned by _______ molded in to it) but it was only single pole. The supply was TNCS and the consumer unit has a double pole isolator. The property is about to be put on to the rental market.

My initial thought is that the double pole isolator switch in the CU provides the isolation function and its a TNCS supply with limited risk of dangerous voltages on the Neutral. Therefore the single pole isolator upstream of the CU isn't ideal but not immediately dangerous and I should just note it on the installation certificate.

Or should I be highlighting the problem to the owner and suggesting they contact their DNO to request a change and what is the likely response from the DNO?

Looking forward to your views and advice.

Thanks

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  • 0

    It's not that uncommon to see SP supplier's isolators - I've even seen pictures of dual tariff supplies with the 24h supply on one pole and the off-peak on the other pole of a DP isolator.

    BS 7671 wise there's no need to isolate the N on a TN system (421.6) unless it's the main switch intended to be operated by ordinary persons (household etc.) when the N does need to be switched as well (462.1.201). So it's all down to whether the supplier's switch is being used as the 'main switch' - which is possible, e.g. if there are multiple CUs connected by Henley blocks directly after the supplier's switch, otherwise the CU incomer is likely to be deemed to be the main switch and so it wouldn't appear to be an issue.

       - Andy.

  • 0 in reply to AJJewsbury

    I agree with what Andy says ... but with the further thought that the supplier's equipment is outside the scope of BS 7671. So, provided there's BS 7671-compliant means of isolation within the consumer's installation, I guess that's all that can be done.

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  • 0 in reply to AJJewsbury

    I agree with what Andy says ... but with the further thought that the supplier's equipment is outside the scope of BS 7671. So, provided there's BS 7671-compliant means of isolation within the consumer's installation, I guess that's all that can be done.

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