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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

Parents
  • 0

    On a TN system, certainly on the DNO side, there is no need to break the neutral to isolate for work such as changing a meter- indeed on 3 phase it is strongly discouraged. The DNO will not be breaking any of their rules.The customers need to meet BS7671 is met by the switch in the CU, much as it would be if no such isolator was present and you were working with the (single pole!!) DNO fuse pulled to swap the CU.

    I suggest no action required. The DNO is likely to respond that they are not obliged to provide means of switched isolation at all, unless you offer to pay for it, and then they  will charge accordingly.

    Mike.

Reply
  • 0

    On a TN system, certainly on the DNO side, there is no need to break the neutral to isolate for work such as changing a meter- indeed on 3 phase it is strongly discouraged. The DNO will not be breaking any of their rules.The customers need to meet BS7671 is met by the switch in the CU, much as it would be if no such isolator was present and you were working with the (single pole!!) DNO fuse pulled to swap the CU.

    I suggest no action required. The DNO is likely to respond that they are not obliged to provide means of switched isolation at all, unless you offer to pay for it, and then they  will charge accordingly.

    Mike.

Children
  • 0 in reply to mapj1

    Generally DNO responsibility will only be upto the head now. The meter and possibly the isolator will be down to whoever they buying the electric from. The single pole isolator could well be classed as the consumers if after the meter. Best practice is to get a double pole isolator fitted before replacing the consumer unit where possible. 

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