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Thread: 2 x 10mm in Isolator.

  1. #1
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    2 x 10mm in Isolator.

    Morning
    I did a job for a client and, as usual, did it to the best of my ability/knowledge. The client told me the AIA inspector would be going to have a look which I was more than happy for them to do. It was a big project and the client has been screwed by a few other electrcians and it was also a fair sum of money (block of flats).

    So bet the client a 4 pack of Leffe blond beer that the inspector would find nothing more than labels and cosmetic things (client wanted cheap but compliant)

    Other than labeling all was good on the AIA inspectors report (usual really picky things - but they really had to dig for them)

    Only thing I had a issue with was:- '

    I have an 80amp 3 phase breaker supplying boards via 25mm GP with 16mm c.p.c. run in existing metal conduit in risers to individual boards on each floor of the block. In the riser board I have a 100 amp 4 pole isolator. The boards (there are 5 floors - 1 x 80 amp 3 phase circuit for each) feed 5 flats (one floor has 6) per floor. Each flat has its own 50 amp single phase breaker covering the flat DB. I spread the flats over the 3 phases alternating over the floors. So on 1st floor - red has 2 flats, yellow had 2 and blue had 1 then the next floor, red had 1, yellow had 2, blue had 2 etc...).

    1 have a 2 x 10mm Gp cable coming from the bottom of the isolator feeding 2 breakers (or 1 if its the phase for that floor to only have one flat).

    I also have 2 x 10mm neutrals coming out of the 4th pole of the isolator to feed to neutral bars (1st 2nd and 3rd flat on one bar 4th and 5th on the second bar.

    The AIA picked up on just the neutral coming out of the isolator. No mention/problem with 2 x 10mm GP's to supply individual breakers - just the neutrals

    My line of thought was you will never get more than 50 amps through either neutral (3 x 50 amps = 50 amps in neutral).

    It was picked up because :- 'Neutral connections inadequate - conductor of cross sectional area exceeding 4 mm not to be install to allow conductor to be disconnected without disturbing the disconnection of any other neutral conductor.'

    I know that applies to neutral bars in DB boards - up to 3 cable less than 4mm in a neutral bar etc (if someone could find that reg number because I have been looking for about half hour now)

    If its the same circuit - the supply to the board - why would you try remove a neutral?

    I don't like putting 2 or 3 cables in a terminal in a neutral bar but does this regulation apply to the isolator. I pretty sure its ok to have 2 neutral going into an isolator/breaker (parallel supply) so why not out?

    I could understand if i had jammed all the neutrals from the flat suply in there. But the isolator can easily take a 25mm cable.

    Sorry for the bad pic. but it was snipped of the report.

    Any one see a problem with what I have done?

    Click image for larger version. 

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    P.S. would have like to have put bus bar system in but space was limited. Thats the biggest board I could get in teh cupboard

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    Diamond Member AndyD's Avatar
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    I agree with you, at that point the two neutral wires form part of the same circuit.

    Looks like a nice neat board by the way, especially given the space constraints.
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    Hi

    Have pasted the reg with regards to the neutral

    6.6.1.11 If a conductor of cross-sectional area exceeding 4 mm2 is used, it
    shall be so installed to allow any one neutral conductor to be disconnected
    without disturbing the connection of any other neutral conductor

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    Take a short piece of bussbar fit it into the bottom of the breaker with 2 legs and connect each neutral to a leg ...either by drilling and taping a hole or use the find and old CBI breaker and remove the terminal ... neutral bars are generally exposed .. .so i dont see a problem ... or slide a piece of heat shrink or sleeving over it.
    Comments are based on opinion...not always facts....that's why people use an alias.

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    Quote Originally Posted by GCE View Post
    Hi

    Have pasted the reg with regards to the neutral

    6.6.1.11 If a conductor of cross-sectional area exceeding 4 mm2 is used, it
    shall be so installed to allow any one neutral conductor to be disconnected
    without disturbing the connection of any other neutral conductor
    Thats the one. Thanks

    But does it apply to my situation in that its the same circuit. I wouldn't want either neutral to be disconnnected. I mean if you were going to remove a neutral from a circuit then you isolate the circuit and remove. This is the same circuit both neutrals connected to the same 4 pole isolator. I understand if its different circuits and even then its not a good idea to remove a neutral from a shared terminal without isolating all circuits relying on that neutral (crackle crackle).

    If you have a parallel supply/feed is it ever going to be the case you will remove one cable. I would be more inclined to crimp them together so that can't be removed individually to be honest.

    What I have done is better way as the neutral bars are carrying less current than if I had put in 25mm and bridged the 2 neutral bars.

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    Hi

    I would say the regulations applies - It is one regulation that is not grey and no matter which way it gets read , it still does not go grey.

    Practically what you did, would work fine and as you say not create a neutral fault but unfortunately there are to many so called contractors doing dodgy work and a lack of common sense and so the regulations are starting to become more specific

    I once had a contractor say that it is grey due to 6.1.5 - I say no , as the regulation 6.6.1.11 is very specific to the neutral.

    6.1.5 A maximum of three conductors may be connected to any one
    terminal provided that the terminal has the correct rating

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    So then the same would apply if you have a bunch of dp breakers in a db ? You are then not allowed to jump from one to the other to the next using 16mm or 10mm depending on supply ?

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    Quote Originally Posted by JustJohann View Post
    So then the same would apply if you have a bunch of dp breakers in a db ? You are then not allowed to jump from one to the other to the next using 16mm or 10mm depending on supply ?
    Correct - The neutral's would need to come from the neutral bar

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    Quote Originally Posted by JustJohann View Post
    So then the same would apply if you have a bunch of dp breakers in a db ? You are then not allowed to jump from one to the other to the next using 16mm or 10mm depending on supply ?
    No, not really, as this the sub main switch. You wouldn't have multiple circuits coming out of a double pole. This is a submain switch. If its off, the board is off. Completely isolating all phases and neutral.

    The netral bar idea would have been ideal but the supply cable 25mm to the top of the isolator and the space is tight as is (existing cupboard resticted DB size - we had to cut a slither of wood out of the frame to fit as is). Getting a 25mm into the existing neutral bar won't go and 16 is 1 amp to small (yes they will pick up on this).

    Just feels like what ever else I put in is going to be not as good as whats there now in terms of cable rating (2 x 10mm has better currrent capacy that 1 x 16 and 25mm just won't fit). And like I said - space.

    Might be able to squeeze in a distribution block which will have a 25mm going to it and 2 x 10mm coming out - exactly what I have now just that its coming from an isolators not a distribution block. That would take up the last couple of spaces in the board I was able to leave free. Besides, to safely remove a neutral from that distribution block, as both neutrals relate to the same circuit, you would be switching off the same main switch to safely remove them.

    The point fo teh reg they state is so you can remove neutrals from other circuits from a terminal in a neutral bar. Thsi is the same circuit and I don't want them to remove either from the terminal in the isolator - same circuit.

    Might just crimp them together?

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    The other way is maybe use a piece of 16mm RVK "welding cable" which will have a higher rating and be able to carry the current -

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