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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

    By my hob and oven in my kitchen there is a double pole switch to isolate both the live and neutral in the supply to them, but when they are isolated the metal cases of the appliances are earthed to the DNO PEN conductor so are hardwired to the neutral.

    Similarly in my garage there’s a double pole main switch in the consumer unit that isolates the whole installation, but all the earthing system within the house along with the exposed-conductive-parts and extraneous-conductive-parts are hardwired to the DNO PEN conductor.

    There is a double pole switch to isolate the central heating system, but the water and gas pipework is hardwired to the DNO PEN conductor as as the enclosures of the boiler, pump, three port valve, etc.

    There is a lot of emphasis on installing double pole switches as over the place, but they only really serve the purpose of achieving isolation from the DNO network in TT earthed installations.

    The main purpose of double pole switches is isolating faulty hardwired appliances which are tripping a RCD, other than that they aren’t particularly useful are they?

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  • 0

    By my hob and oven in my kitchen there is a double pole switch to isolate both the live and neutral in the supply to them, but when they are isolated the metal cases of the appliances are earthed to the DNO PEN conductor so are hardwired to the neutral.

    Similarly in my garage there’s a double pole main switch in the consumer unit that isolates the whole installation, but all the earthing system within the house along with the exposed-conductive-parts and extraneous-conductive-parts are hardwired to the DNO PEN conductor.

    There is a double pole switch to isolate the central heating system, but the water and gas pipework is hardwired to the DNO PEN conductor as as the enclosures of the boiler, pump, three port valve, etc.

    There is a lot of emphasis on installing double pole switches as over the place, but they only really serve the purpose of achieving isolation from the DNO network in TT earthed installations.

    The main purpose of double pole switches is isolating faulty hardwired appliances which are tripping a RCD, other than that they aren’t particularly useful are they?

Children
  • 0 in reply to Sparkingchip

    Thinking again, perhaps 2-pole isolation has its uses.

    Testing of appliances. Can't do ccp to PE insulation resistance test if the Neutral is still connected.

    Also, you'll trip RCDs when testing, fault-finding or repairing if you don't disconnect L and N on single-phase.

    Finally, Neutral is considered a live conductor according to BS 7671.

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