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  1. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    Hello, I've got a question that I thought I throw out to the crowd and see what comes back... I am a little stuck with a recent EICR that followed a change of occupier.

    The home is 30 ish years old and has been extended several times. It is a fairly large home with swimming pool, multiple outbuildings and annexes.

    The main DB is where I am struggling a little.

    The supply is single phase fed from two meters. It enters the DB via 25mm2 tails two from one meter. One from the other meter. At a glance it looks like a 3 phase supply... there is a 125A main switch to the DB and there is a single neutral. It is a three phase DC with colours marking out where you would normally expect to find L1, L2 and L3.

    The issue I am having is that the single neutral is carrying the entire current from both supplies and so too is the meter it is connected to. One meter has no neutral connection to the DB.

    The meter (I think) is rated to 80 amps... but the full load is passing through it.

    The tails (meter to DB) are short so I am less concerned about the neutral being overloaded.
    The main switch on the DB is rated 125A so should be fine but I imagine the rating is for a reasonably well balanced 3 load across all 3 phases. It isn't. No current is flowing between phases so everything must be going down neutral.

    For clarity the main DB is the only source of distribution to the whole building. There are a further 5 sub DB's fed off this one board. The board is near full to capacity at 0.4 diversity.

    So my question is this.... any harm in the neutral from one meter handling this load? What about the main switch? Are there any regs transgressions in this? I've never encountered this particular set-up before.

    Here is the full horror:
    IMG_3164.JPG
     
  2. SparkyChick
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    SparkyChick Making a banana smoothy for my fave gorilla Electrician's Arms

    Location:
    South Wales
    Business Name:
    SparkyChick
    I think you'll find that the neutral connections on the meter are simply a big terminal block with a small connection for use by the voltage coil. The current coil which is connected in series with the two line terminals are what the rating applies to.
     
  3. Rob
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    Rob Trusted Advisor

    Location:
    North west
    Are you sure there isn't 2 phases there? Cause that's what it looks like.

    Also the main switch is rated at 125A per pole, it doesn't care if it's balanced load.
     
  4. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    Yep - just a big terminal block for the neutral... but I assume the rating is still relevant. The insulation and terminal block are more than capable we can assume but it won't have been tested for this... therefore is it compliant?

    @Rob@Rob - definitely not 2 phases. 240V across phase to neutral. 0V across "phases".

    The 125A switch isn't a question of balance.... it is a question of how much is going through that neutral contact. If there is 65 Amps per "phase" then there is 130 Amps going via that single neutral pole.

    In most 3 phase installations (for which this switch is intended) some current would be phase to phase and not 100% of the current via the neutral pole.

    This installation is littered with C1's regardless of this little problem! Any other thoughts are most welcome... I really don't like the look of it. Most of the install is OK but I am not sure the use of the three phase CU was the best move. It would have been better if two CUs were installed each taking a supply from the meter. I'm sure that single neutral conductor taking the load of the three single phase conductors is less than optimal and I'm sure that neutral pole of the switch is over loaded.
     
  5. Pete999
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    Pete999 Trusted Advisor

    Top Poster Of Month

    Location:
    Northampton
    3 phase DC?? Those meters are rated at 240 Volts
     
  6. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    @Pete999@Pete999 typo.... not sure if I was supposed to type 3 phase DB or CU... it just came out DC instead!

    Here is what I meant...
    It is a CU marked up for 3 phases with 4 pole isolation and feed arranged inside in the usual pattern of 3.

    Someone has wired it up with 3 25mm2 tails all from the same phase.

    That results in the neutral potentially being overloaded as it is carrying all the current and the phase conductors / main switch carry just a third each.

    Since in an application where there is only a single phase all current flow phase to neutral. There is no phase to phase path (obviously).
     
  7. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    From what I can see both meters are single phase, the right one appears to have two outgoing line conductors into one terminal. One neutral goes to the right meter which from where the board neutral is connected. The neutral for the left side meter goes direct to the service head, correct?
     
  8. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    If it's two phases then the neutral current will not add, it will cancel in the same way as if it was three phase.
     
  9. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    Could this be a two phase supply rather than two phases of a three phase supply?
     
  10. Richard Burns
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    Richard Burns Trusted Advisor

    Location:
    Cambridgeshire
    Business Name:
    Richard Burns
    If both line conductors are coming from the same fuse then you are limited to 100A max and so it would be fine.
     
    • Agree Agree x 1
  11. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Bad picture but they appear to come from the middle and right side fuses.
     
  12. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    Thanks all...

    The supply is not multi-phase. It is single phase. Proven via meter measuring 0 volts across line conductors. and 240V to neutral / earth.

    One meter has two line conductor tails from it and a single neutral
    The other meter has a single line conductor and no neutral

    The sum of all breakers in the DB is 543A
    At 0.4 diversity we have 217.2A

    So there is possibly 217.2A on that neutral conductor which is broken by a 125A main switch.

    The BS1361 DNO fuse will offer some protection since there are two meters and thus just two fuses in play... so we could say that we are limited to 200A in theory... but the reality is that a BS 1361 100A fuse is going to take an eternity to disconnect a 110A load.

    Sorry for the poor photo!

    What do you think? The whole DB is a C1 due to it failing to meet IP2X I might as well C1 it for having an undersized switch.
     
  13. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    C1 one for what!
     
  14. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    You do realise a C1 is immediate danger present?
    And why have you added all the mcbs up?
    It's the potential loading you need to apply diversity to not adding all the breakers
     
  15. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    C1 for having a penetration that a whole hand can fit in. DB is in a cupboard used by the family including children for school bags, coats and shoes.

    If you look closely at the photo the tails are not nicely dressed and bare copper is visible in the line conductors on the DB side of the meters. The cover that should be over that is broken and again that wouldn't meet IP2X... although I'm not sure it has to but in this instance is absolutely must given it is a very real possibility that a metal zipper, bag buckle or wet coat could quite likely come into contact with it.

    The install is not very nice in general. There are 4 circuits that are a mess. It fails to meet Zs to a DB. There is evidence of rodent damage to some cables, the swimming pool lights are full of water, there is thermal damage to a FCU, there is cable trucking missing for swimming pool plant room... I have something like 4 C1 and 12 C2/C3 out of 27 circuits.
     
  16. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    Get your hole hand in where. What type of devices are in that Square D board.
     
  17. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    @Ian1981@Ian1981 swimming pool pumps, sauna, spa air pump are high demand (for a residential install) and they are normally in use simultaneously. Then add in an electric hob, and oven and we are starting to pull close to 80amps.
    The home has a second kitchen, external workshop with a large inverter. I'm being lazy... with my methodology... sum the breakers, multiply by 30% perhaps... here I thought 40%... but there is easily a 100 amp demand on this place. Peak it will exceed it and there is a very real chance that it is well north of 125A.
     
  18. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    @Ian1981@Ian1981 swimming pool pumps, sauna, spa air pump are high demand (for a residential install) and they are normally in use simultaneously. Then add in an electric hob, and oven and we are starting to pull close to 80amps.
    The home has a second kitchen, external workshop with a large inverter. I'm being lazy... with my methodology... sum the breakers, multiply by 30% perhaps... here I thought 40%... but there is easily a 100 amp demand on this place. Peak it will exceed it and there is a very real chance that it is well north of 125A.
     
  19. westward10
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    westward10 In echoed steps I walk across an empty dream. Electrician's Arms

    Location:
    Northamptonshire
    What do you mean it fails to meet Zs at a DB.
     
  20. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    @westward10@westward10 whole of hand can fit inside the Square D board. It is clearly a C1.

    Board has 125A 4 pole switch.
    4293 RCBOs
    60898 MCBs

    I think it was 27 or 28 circuits altogether.
     
  21. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    @westward10@westward10 Zs measures outside minimum Zs values at a sub-board supplied from this DB.
     
  22. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Why not put a clamp meter on the tails (each one at different times) and see what load it's pulling?
     
    Last edited: Aug 2, 2017
  23. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    @Ian1981@Ian1981 swimming pool pumps, sauna, spa air pump are high demand (for a residential install) and they are normally in use simultaneously. Then add in an electric hob, and oven and we are starting to pull close to 80amps.
    I'm lazy with my demand calculations... but I suspect that the demand is higher than 125Amps. I can see 40 Amps in the swimming pool plant room. There are 2 kitchens and 3 american fridges. Air conditioning and a 16Amp inverter for motor drive in a workshop.
     
  24. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    I here what you are saying and you maybe right.
    Is there evidence of thermal damage anywhere, particularly the protective fuses supplying the installation, are they hot to touch ,including the main switch at the dist board?
     
  25. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    @Ian1981@Ian1981 I have...

    If I sum L1,L2 and L3 (which is actually all L1 because it is not 3 phase) then I arrive at around 28 Amps and that is a "quiescent" current... there was no one home. That is all just fridges and pool filtration.

    I obviously can then see that 28Amps (all of it) on the neutral. Because the current is all flowing through that conductor.

    So I can see the building demand being in excess of 125A and that is fine when you consider the line conductors and the 125A x 3 switching of the line conductors.... but there is a 125A switch in the neutral and it all goes through that one pole.
     
  26. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    Fair enough you are the inspector.
    Looks like they will require 2 or 3 phase
     
  27. itsonly3wires
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    itsonly3wires EF Member

    Location:
    Newcastle
    @Ian1981@Ian1981 No evidence of thermal damage. Main switch makes and breaks. No heat anywhere in and around the DB.

    It has been installed like this for 20+ years.... but I don't want to be the one to EICR it as OK and then the smoke comes....
     
  28. Ian1981
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    Ian1981 Electrician's Arms

    Location:
    North east
    I would honestly do a load check with a clamp meter.
    You could always advise that the installation may need upgrading in terms of loading but if it's been functioning for years as it is then it maybe adequate.
    No heat damage anywhere especially the main switch and cut out fuse plus terminals may indicate that it's not being overloaded. just a thought pal
     
  29. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
    Business Name:
    F.H. Electrical
    Thanks for a most interesting thread.
     
    • Like Like x 1
  30. davesparks
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    davesparks Trusted Advisor

    Location:
    guildford
    That will only give an instantaneous snapshot, it won't help with the point in question.
    Measuring the maximum and average demand can only be done with a data logging meter over a period of time.
     
    • Agree Agree x 1
  31. static zap
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    static zap Regular EF Member

    Location:
    west midlands
    At a glance things look normal ! Thanks ...
    (Neutral for a different reason)
     
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