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HMO conversion

Discussion in 'Electrical Forum' started by SJA79, Mar 20, 2017.

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  1. SJA79

    SJA79 EF Member

    Hi Guys,

    After a bit of help in regards to sub main runs for some flats which are on dual tariff for storage heaters.

    Ive been asked to take this job over by the client and first fix has been done already. I admit I have limited experience when it comes to dual tariff supplies installed from new.

    It was an HMO which has been recently converted into 3 seperate flats. At CU end from what I can see there have been 2 slots cut into the stud walls, one above the other where the CU position/s will be situated and the final circuits are fed from. (Top slot for peak circuits and lower slot NSH) These have been fed by two seperate 16mm T&E's for each flat and they have all been run starting from under the communal stairs. DNO has installed 3 seperate meter boxes with 3 100A supplies remotely outside the building for each flat. Dual tariff meters will be going in the meter boxes. Assuming this was a normal non dual tariff setup I would have just run in the 16mm swa from a sw/f unit in the meter box direct to the CU as normal but the dual tariff is throwing me a bit along with the 2 x 16mm's for each flat that have already been installed only to under the stairs. Personally think its been a miscommunication between the supply company and the previous spark as to where the supplies were to go in the first place.

    1.) It is my understanding that the new dual tariff meters are 2 wire and it is just a single meter with L+N IN and L+N out, same as an ordinary supply meter. Is this right? In addition how would I be able to get everything connected up correctly under the stairs with the current setup above. Is it just a SPN SW/F unit out in SWA and connect into the 16mm's?

    2.) I also cannot see how the 16mm t&e has been run in as everything has now been boarded :(. I am thinking that 30mA additional protection is also going to be needed to the flats.

    All advice appreciated
    • Like Like x 1
  2. streamer

    streamer Regular EF Member

    Scottish Borders
    I'm always wary when being asked to take over from someone else on a job. Do you know why the other electrician isn't finishing it?
    I think you are right, the sub mains should have gone all the way to the meters. The dual tariff meters will usually have a 24 hour live, an off peak live and a neutral coming from them into a DNO isolator. So you would have to come from this isolator into two separate switch fuses. Depending how the twin and earth cables have been run, like you say, they may need 30mA rcd protection which isn't really acceptable in an external meter box. Also, they may not support main bonding if required in the flats.
    Last edited: Mar 20, 2017
  3. SJA79

    SJA79 EF Member

    Hi, Thanks for the reply. Yep I would normally avoid it like the plague but this is a friend of a family member so I ignorantly said I'd try and help out but beginning to regret what I've let myself in for now.

    I am not entirely sure, all I know is that the previous electrician has parted ways possibly if the error was due to not confirming where the incoming supplies were to be sited. No sign of any bonding for water services and at this stage I am assuming plastic and no gas to speak of.

    So if the meters are 24hr live and offpeak lives out could I use a 63a Tpn sw/f if space permits in each meter cupboard and use 2 of the fuses and a 4c swa to under the stairs into trunking and somehow split the neutral in the trunking to meet with 2 rcd units to then supply each flats 2 CU's in 16 t&E.? Sounds wrong to me to put a neutral block in trunking. Or another unconventional idea would be 4c again and use 2L +2N and armour as cpc?

  4. Wilko

    Wilko Electrician's Arms

    Business Name:
    Wilko Electrics
    Hi SJA, just a reminder that SWA armour likely won't be ok for bonding, if you need it. Cheers.
    Last edited: Mar 21, 2017
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