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Thread: Single phase generator feeding 1 phase of 3 phase db - discuss.

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    Single phase generator feeding 1 phase of 3 phase db - discuss.

    I have a client who we are doing a commercial insatall for. They said they were buying a generator from a "proper generator supplier". I had already started to wire a sub DB (which covers a bar area in a restaurant, main board covers large commercial kitchen). Now they say they are only getting a single phase generator. I try and explain you can't just use any generator (centre tapped earths. V-O-V etc etc) . I wire the DB so the essential loads are in one phase (loads are minimal - led lights and a socket for the DJ) which is to be backed up.
    Now the nice people at Ryobi have managed to convince them that the thing they bought (haven't seen it yet but I'm pretty sure its going to come in on wheels and have 2 x 16 amp sockets on it) will work fine. I have already told them I will refuse to connect that kind of generator. They say that's fine, someone else will.
    Now I believe I have wired my change over as per the regs (4 pole change over and indicator lamps and everything). I have told them my C.o.c. will not include the generator unless it is the right type (neutral and earth connected at generator and earth spike installed).

    What position does that leave me in. As long as I detail what's covered and what's not. I have no control what generator they connect after I'm gone.

    Opinion?

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    HI

    I would state on my COC the "installation was commissioned without a generator - Owner may purchase a generator at a later stage. Supplementary COC will be added when generator is connected and commissioned ."
    That way you have covered yourself and who ever installs the generator will need to add the supplementary COC.
    If the supplementary COC is not added it becomes the owners responsibility as the OHSA holds him responsible for the electrical installation.Nothing to stop you from getting him to sign next to that statement as well for your records.

    We often complete commercial installations with change over switches etc built into the DB's to allow the owner to purchase at a later date if he decides to -

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    As per GCE, complete instalation and testing of SubDB and changeover, issue CoC for work you've done specifically excluding actual generator installation and including sketch on cert. Take plenty of datestamped photos. If customer persists in buying camping generator decline to connect (and find new customer).
    _______________________________________________

    _______________________________________________

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    The tricky thing is that I have a 4 pole manual change over and a generator connected to one phase but there is still a common neutral going back so if they use their Vov generator they put a potential on the common neutral meaning all the neutrals of the circuits on the other 2 phases would have potential on them. All 3 phases and neutral have to go through the change over as I don't want mains and the Genny to possibly run at the same time. If they had the right kind of generator there would be pretty much zero potential on the earthed neutral with the vov generator they are going to have between 90 and 120 volts there. So in theory all the neutrals points at socket and isolators would be sitting with a potential to earth.
    Alternatively when the mains goes back on it will continue to feed normal circuits and the generator will continue to feed essential circuits until the change over operated. The neutrals would off course be separate but I don't see how I can have a section running on generator and a section running on mains at the same time (despite having separate neutrals)

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    There again I don't suppose its unusual to have part of an installation on generator whilst part is still on mains. Like when a sub DB is fed from a generator and mains goes back on the sub Db would be on generator for the change over period? But in the same sub db, even with separate neutrals sounds sketchy. And besides if the did get the right kind generator, with the earthed neutral, then you would have 2 points where neutral and earth are connected.
    I mean you can have normal and essential circuits in the main db? Why not in a sub db?

    At least if I did it this way it would prevent there being potential on the other phases neutral bars. The down side is normal circuits would run on mains when the power comes back on and the essential circuits would be on generator until change over occurs.....
    None of this would be an issue had they not blow there budget of R60000 worth of tiles rather than getting a proper generator.

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    Crap....

    7.12.2.5 Where an alternative supply is provided to an installation or part of an installation as a switched alternative to the main supply, the change-over switching device shall disconnect the main supply before the alternative supply is switched in. The change-over switching device shall be interlocked in such a way that the main supply and the alternative supply cannot be connected to the installation or part of the installation at the same time.

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    Hi

    Either I am confused or you confusing yourself - There cannot be a common neutral to the supply on a 4 pole change over when in generator mode.
    I understand the concern with the VOV when only one phase is connected , but you have warned the owner , and he will put his equipment at risk if he has any chance of an earth fault on a phase.

    If the supply comes back on , your neutrals and phases will be separate -

    Depending on the clients request - It may be better to install a double pole change over just for the single phase circuits that you are going to feed -

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