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Converting 3 phase to single phase

Discussion in 'Electrics UK' started by Talay, 10 Jul 2019.

  1. sparkwright

    sparkwright

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    I remember some excitement (possibly on this forum, I really can't remember) about modular lights on different phases being fitted one the same metal ceiling grid - but not sure how likely this could be a problem.
     
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  3. ban-all-sheds

    ban-all-sheds

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    One can postulate fairly unlikely scenarios.

    How about changes which resulted in several sockets being removed/moved/added, and cables re-routed and an "Ah - I could use that cable to go to here, and then run a new cable to meet up with that one over there"?
     
  4. JohnW2

    JohnW2

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    Hmmm.

    It is obviously in the nature of 3-phase installations and 3-phase equipment/appliances that all three phases very commonly exist in close proximity to one another within the installation, enclosures and connected equipment, so some people must spend a lot of time 'getting excited'.

    Kind Regards, John
     
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  5. SUNRAY

    SUNRAY

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    Well the atoms in the wires certainly get very excited:whistle:
     
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  6. ban-all-sheds

    ban-all-sheds

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    And some motors.
     
  7. Talay

    Talay

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    We're not on about a DIY option but trying to estimate the work involved when it sure isn't a day's work, which is what we first got quoted.

    Of course we already have single phase on site but at present the cabling in question runs from 7 x 3 phase breakers to 7 machines. The replacement machines are single phase and thus, though we won't need the 2nd and 3rd phase wiring, we will need to do work at the consumer unit.

    In my layman's eyes, changing 7 breakers to single phase is a couple of hours work, not a day's labour.

    Testing post installation is a given.
     
  8. wgt52

    wgt52

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    OK, understood...

    So some questions; how old are the installations?
    Are 3P wiring colours 'Harmonised' (Brown/Black/Grey) or UK (Red/Blue/Yellow)?
    In an outer sheath (grey cable) or separate wires in conduit?
    If cabled - 3 or 4 wires plus earth inside the sheath?

    With that info we can offer better guidance...
     
  9. bernardgreen

    bernardgreen

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    If you want to convert 3 phase to single phase instead of simply using a phase and the neutral per machine then this

    upload_2019-7-14_9-58-14.png

    maybe the answer. A 3 phase motor driving a single phase generator.
     
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  11. JohnW2

    JohnW2

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    As has been implied, there are issues which have not been discussed.

    It sounds as if you are thinking of just having the breakers changed, and using one phase of the existing (3-phase) wiring - whereas the 'proper' approach would be to install new single-phase wiring.

    As has also been implied, the 3-phase wiring may not have a neutral, in which case one would have to use a (wrong colour) phase conductor for that purpose, which is far from ideal.

    Furthermore, if the replacement (single phase) machines are of a similar power to the old ones, one of the phase conductors in the wiring might not be adequate for the much higher current needed by the new machines. One might therefore have to contemplate using two of the phase conductors in parallel (or all three if there is a neutral), which is even less 'nice'/ideal.

    In other words, we don't yet really know how long this piece of string is!

    Kind Regard, John
     
  12. scousespark

    scousespark

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    The electrician who quoted a day has seen your installation. Nobody in here has that luxury, so this is pure guesswork. I would say a day is reasonable for what you are asking.
     
  13. Talay

    Talay

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    Some useful comments, thanks. For the jokes, thanks also :)

    To round it off, we asked and the original quote (though not detailed) had him disconnecting the existing machinery and connecting the new machinery (which won't be there on the day) and it was then padded out to a day's charge.

    Clearing that up has pulled it down to 2/3 hours which is where we thought it might be. This is not a one off job as we've done jobs together on 5 figure budgets.

    For interest, loads are 6A to 10A so existing wiring is good enough. The whole lot might be ripped out in 12 month to make way for a refit so no point going overkill right now.
     
  14. SimonH2

    SimonH2

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    Just a thought ...
    IF the existing supplies are 3P, AND they have a neutral, AND the cables & breakers are OK for the new loads, then: it should be possible to connect the single phase machine to the 3P isolator on the wall - just using 1 phase and neutral. No need for any changes or even swapping out the 3P breakers for 1P ones. So if the supplies are already suitable, the only cost involved is disconnecting one machine and connecting the new one :whistle:
    Such an arrangement is quite common where there's an existing 3P connection and something only needs 1P.
     
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  15. SUNRAY

    SUNRAY

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    Now I'm annoyed...
    This thread popped up at the bottom of the page and I speed read, got to the end and tried to 'like' #27. Sadly I couldn't as it looks like I did it a year ago.

    I reckon that means I think its been correct all the way along.
     
  16. sxturbo

    sxturbo

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  17. plugwash

    plugwash

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    Is there anything in BS7671 that would prohibit what the americans call a "multi-wire branch circuit" where a 3 phase or split phase circuit feeds single phase sockets?
     
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