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Thread: Generator connection

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    Generator connection

    I am getting lots of generator inquiries again, people are getting nervous and want to prepare themselves for what they think is going to happen.

    I have a simple solution and would like to hear your thoughts.

    For my own house i am using a 2.2 kva generator.

    I have a changeover switch mounted directly above my meter box, fed from the 60 amp circuit breaker using a 16 mm wire into one side of the changeover switch.

    I have a 16 amp plug top with a 2.5 mm x 3 core feed from the generator to the other side of the changeover switch ( the generator has built in overload protection)

    from the other side of the changeover switch i have run a 16 mm wire which is connected to wire feeding the house in the meter box using a ferrule and heat shrink.

    For my application as an electrician i know what to switch on and off as i have a current clamp and have replaced my element in my geyser for example to a 1kw element.

    I would recommend a 5.5 kva generator or bigger to customers, but with this comes a few challenges.

    My question to you all fellas...

    1/ Would you recommend this setup to your customers, considering they dont have a current clamp?

    2/ How do you overcome the problem of supplying 20- 25 amps (5.5 kva generator) via a 16 amp sockets outlet?

    3/ Would you use a circuit breaker next to the generator to protect the cable or rely on the generator overload protection?

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    Diamond Member Justloadit's Avatar
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    I think that the generator may not supply the current you think it can. Note that a grid has a low impedance and is able to supply the current demand, as per a generator, which has a high impedance, and would overload the motor any way to the point that it would probably choke and stop. All the generators that I have seen have a circuit breaker.

    With respect to the 16A plug, the generator will probably struggle to supply that , with the CEE plugs are under rated anyway, so the few extra amps wont do any heating of the plug. Bear in mind, that the generator would probably never run at full power for long periods of time anyway. Maybe include a moving iron amp meter which is relative inexpensive as a gauge for the customer.
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    Diamond Member AndyD's Avatar
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    I would personally never recommend a generator for a domestic customer, by the time you work out the capital outlay, the installation, the fuel cost, the fuel storage, the servicing etc the real cost per kWh is absolutely extortionate and the smaller generators are often completely not suitable for connection to a DB plus unless it's a high-end unit the frequency and the voltage instabilities cause havoc with electronics etc.
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    Diamond Member Justloadit's Avatar
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    Hi Andy,

    I agree with you on your statement as far as a large generator is concerned however, what we are doing here in Jhb, is installing a 5.5KVA genny, with a manual change over switch, connected to the DB board, BUT, we isolate a number of circuits only which are connected to the generator. Usually lights, fridge circuit and entertainment circuit.

    Basically during a black out, the user starts the genny via a key switch on the genny, as most 5.5Kva have an electric start, once running, they change the switch manually to genny, have power during the black out, and when the power returns, they simply change over back to mains, switch the genny off and wait for the next one.

    This makes it safe for any one to use, and due to the simplicity can even be done by the home manager if required during the day.
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    Diamond Member wynn's Avatar
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    When the power goes off I know to switch the 'Genny' on because there is no power, but how do I know the power is back on if my 'Genny' is running?
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    Bronze Member ACEsterhuizen's Avatar
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    You can wire the change over switch with a pilot light and a pulse once (or more) alarm or a manual alarm cancel switch so you will know when eskom power is back on, or, as described above, if you only wire certain circuits through the change over switch, the other circuit will obviously become "live" once eskom is back on, eg you leave the some light on which is NOT wired to the Gennie and that light will remain off as long as eskom is off and will come on once eskom is on.

    Just remember to have the install done by a registered electrician (ask for proof and follow up and get a coc for the job) The Neutral Bar must be split according to the regs i have seen many installs where the neutral bar was not split. (except if it a 3 phase install at the mains)

    7.12.3.1.4 Where only part of an installation is switched to the alternative
    supply in the same distribution board, the neutral bar shall be split (see
    figures S.2 and S.3 in annex S).
    Last edited by ACEsterhuizen; 22-Jan-15 at 12:36 PM. Reason: more info

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    Diamond Member AndyD's Avatar
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    The problem with a lot of the small generators is the the neutral is at an equal voltage as the live with respect to earth so they're configured 115(L)-0(Earth)-115(Neutral) L-N is 230v. You cannot connect this type of genny to a DB, it's designed for use with trailing leads only. Also genny's are notoriously poor at producing sufficient current in the case of a fault and don't achieve required disconnection times of circuit breakers or other OCPD's.
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    Gold Member Houses4Rent's Avatar
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    I am thinking of a far simpler set up. I really only need power during load shedding and other outages for my PC, printer, router, screen etc. so I can continue working. Is it feasible if I buy a small genny (what size would I need?) and when the power went I just start up the genny and use an extension to plug my PC gear straight into the genny.

    What are the pros and cons/risks?
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    Diamond Member wynn's Avatar
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    On 'The Other' Forum it was discussed that you would set up a series of batteries (Deep Cell) in a cage outside your office (say under the roof eaves) and run an inverter through them to your necessary equipment (PC, screen, printer, router, remote phone and emergency lights) so they would all work during a 'Load Shit' and as soon as power came back on it would recharge the batteries for the next 'Dump', like a giant UPS.
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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by ians View Post
    2/ How do you overcome the problem of supplying 20- 25 amps (5.5 kva generator) via a 16 amp sockets outlet?
    Typically those generators have two socket outlets. If you expect to push past 15A, perhaps use both outlets in parallel?

    Quote Originally Posted by Justloadit View Post
    I think that the generator may not supply the current you think it can. Note that a grid has a low impedance and is able to supply the current demand, as per a generator, which has a high impedance, and would overload the motor any way to the point that it would probably choke and stop. All the generators that I have seen have a circuit breaker.
    Definitely go with voltage regulated generators. This solves lots of problems.

    Quote Originally Posted by AndyD View Post
    The problem with a lot of the small generators is the neutral is at an equal voltage as the live with respect to earth so they're configured 115(L)-0(Earth)-115(Neutral) L-N is 230v.
    Is the earth tapped in the middle like that, or is it just that without an anchor the live and neutral float off the "ambient" earth voltage in equal measure?

    My experience so far is if you bridge the earth and neutral at the generator, the neutral stays at 0V and live goes to 220V relative to earth, which solves the problem. Of course, make sure your earthing system is appropriate (have an earth spike).
    The trouble with opportunity is it normally comes dressed up as work.

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