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Thread: Connecting backup generators to existing electrical installation

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    Connecting backup generators to existing electrical installation

    When connecting a generator to the electrical board of my house ,do I have to install cross over switches on the neutral and earth as well

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by Kevin Stubbs View Post
    When connecting a generator to the electrical board of my house ,do I have to install cross over switches on the neutral and earth as well
    Certainly not on the earth. It would be a bastard to seperate anyway unless you were crossing over the entire installation.

    I don't see much need to isolate the neutral* - the allowed potential between earth and neutral is so low anyway, but then some electrical appliances need to have isolators (live and neutral disconnect)

    Hopefully a more definitive answer will be forthcoming shortly.

    *I'm just a director of an electrical contracting company - but not an electrician.
    Last edited by Dave A; 20-Jan-08 at 06:45 PM.
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    Hmm. I've been looking at our wiring diagram (we're using an interlocked contactor rig) and thinking about this. You certainly want the neutral between the generator and the crossover switch isolated when you're on mains power. Which means yes, run the neutral through the cross-over switch.

    Whilst I'm about it, I read an article this morning where the ECA had commented on generators. A few points from that:
    • A COC has to be issued when wiring a generator into an existing installation that also has mains supply.
    • There has been one death by electrocution by a generator in Durban already. (I see the main problem being they don't have earth leakage units.)
    • The "plug generator into a plug point to power your house" is very dangerous.

    I think I'm going to get my guys to point out to me anything in the SANS electrical installations code to do with generators. Murdock mentioned there was very little in a previous post. This could be interesting.
    The trouble with opportunity is it normally comes dressed up as work.

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    Site Caretaker Dave A's Avatar
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    I've just run through this neutral issue with my guys. In brief:

    On a single phase installation, just like the live line has to be seperated from the main supply whilst under generator power, exactly the same with the neutral.

    On a 3 phase installation being powered by a 3 phase generator, the neutral does not need to be isolated from the main supply.

    If you are energising just one phase with a generator on a three phase installation, you need to treat that part of the installation as a single phase supply. Thus you'll also need a mechanical isolator to that part of the installation as well as the cross-over switch.
    Last edited by Dave A; 21-Jan-08 at 07:48 AM.
    The trouble with opportunity is it normally comes dressed up as work.

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    electrical installation

    gee..i want to learn more about Martinez Electric installation
    Last edited by Dave A; 14-Jun-08 at 07:39 AM. Reason: removed link

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    Site Caretaker Dave A's Avatar
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    Los Angeles is a whole different world away from South Africa, Topak.

    Aren't you guys on 110V in those parts.
    The trouble with opportunity is it normally comes dressed up as work.

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    a single phase and three phase supply must isolate the neutral... the changeover contact must be a 2 pole for single phase and a 3 phase must be a 4 pole.

    the installation must be done by a qualified electrician...who knows and understands generator supplies...lots of electricians i have come acroos recently dont have enough experience to advise or install generators

    beware south africa and america have different volatages earthing systems ie TT...TNC...TNC-S etc and the voltages are diffferent... we have phase to neutral 240 whereas they have phases to phase 240 volts...and 120 volts...60 hz not 50 hz...our electricity supply must not be compared in any way...if you do want to compare it must be with uk and australia.

    most generator installation which i have come across are illegal but they work so the customer is not prepared to spend the money to make it right...they say why fix something that works.

    i found a changeover other day where they using a contactor as a changeover switch the n/c contact is the generator supply...the n/o...n/c contacts of a contactor are not rated to 30 amps

    but unfortunately until they start impossing heavy fines for illegal work the public will be the ones who suffer...and in saying that the public are half the problem because they the ones who are using the unregistered companies...because they are.............yes that is correct.... CHEAPER...in these difficult times who blames them.

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    Quote Originally Posted by Kevin Stubbs View Post
    When connecting a generator to the electrical board of my house ,do I have to install cross over switches on the neutral and earth as well
    by the question i can only assume you are not qualified to do the installation but if you plan on doing anyway....do you have a 3 phase supply or single phase supply...are you installing a automatic changeover system or manual?
    are you feeding the entire electrical installation with the generator or only part....have you made provision for only partial if using a small generator...have you installed an earth spike...are plugs being fed from the generator on earth leakage...have you fitted barriers in the DB if only feeding part of the DB...have you clearly labelled the DB indicating which part of the DB will be fed by the generator...do you have a main switch in the DB if only part of the DB is supplied by the generator to isolate that part of the installation in case of accident leakage...have you done a loop impedance test and earth leakage test to verify if the earth leakage will trip in case of a fault while running on generator power...etc etc etc.

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by murdock View Post
    i found a changeover other day where they using a contactor as a changeover switch...
    Murdock, given that the changeover must be mechanically and electrically interlocked, how can this be achieved without contactors?
    The trouble with opportunity is it normally comes dressed up as work.

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    it is a single phase installation using the main contacts for the supply and the n/c contact for the generator...so there is no way the mains and generator can be on at the same time...the problem is the n/c contact while the generator is running the 30 amps are being drawn through the aux n/c contact which is not rated for 30 amps...but i say it again it doesnt help making a whole lot of rules and not policing them...i need that banging my head on the wall smilie...please add it dave.

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