Generator question





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  1. #1
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    Default Generator question

    I have one of those Mecer 2400va inverter boxes that are great for load shedding survival but I am considering a gennie backup.

    My problem is that I have 3 phase power to my house and the smallest 3 phase silent diesel gennie is 12 kva and quite expensive.

    Now that could be seen as an investment in a quality product that I could take with me one day or even sell as it should maintain its value reasonably.

    Question 1, what does it take and cost to change to single phase and why would I not want to do that?

    Question 2, is there a 6 or 7 kva diesel 3 phase gennie out there?

    I am not currently considering solar right now for a few reasons.
    4x4 less.

  2. #2
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    Default Re: Generator question

    Depends on your wiring set up. Although you have 3 phase into your property,99% of the stuff is single phase unless you have 3ph motors.

    What normally happens is that eg your plugs could be on a red phase, lights on white phase and stove and Geyser on blue phase.

    A stove can be connected into a 3phase or 1 phase supply.

    So if you go single phase, then perhaps rewire your system so that the generator powers a few lights and plugs meaning you only need a single phase generator.

    Why 3 ph and not 1 ph....
    Depending on your load. If you add up all your currents and it exceeds 60Amps,then single phase is not for you. With 3ph you basically balance your current over 3phases meaning instead of 1 phase carrying 60amps and tripping, now each phase is only carrying 20amps meaning you have a lot of currents left over.
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  3. #3
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    Default Re: Generator question

    Quote Originally Posted by hunter26 View Post
    Depends on your wiring set up. Although you have 3 phase into your property,99% of the stuff is single phase unless you have 3ph motors.

    What normally happens is that eg your plugs could be on a red phase, lights on white phase and stove and Geyser on blue phase.

    A stove can be connected into a 3phase or 1 phase supply.

    So if you go single phase, then perhaps rewire your system so that the generator powers a few lights and plugs meaning you only need a single phase generator.

    Why 3 ph and not 1 ph....
    Depending on your load. If you add up all your currents and it exceeds 60Amps,then single phase is not for you. With 3ph you basically balance your current over 3phases meaning instead of 1 phase carrying 60amps and tripping, now each phase is only carrying 20amps meaning you have a lot of currents left over.
    Thanks

  4. #4
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    Default Re: Generator question

    Dont you pay a levy for 3 phase? As per post above your wiring might need to be changed. The cost of having it chaged back to single phase might justify the cost of just getting 3 phase generator.
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  5. #5
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    Default Re: Generator question

    Thanks guys,

    Pretty much as I suspected, Hunter I have 100% single phase load and am sure my load is no higher than any other other single phase typical household.
    I don't know if I pay a levy for 3 phase, will check my bill.

    I guess I need to get an electrician out to quote and see if the re wire or the 3 phase generator is cheaper?
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  6. #6
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    Default Re: Generator question

    Hallo Brian

    I guess your setup is the same as what mine was, i.e. three phases split into different loads as already discussed above.

    I ran a single phase generator through a three phase change over switch (bridged the other two phases on the generator input). The problem with that is that your three phase earth leakage does not work which can be/is very dangerous (maybe as dangerous as the suicide lead). In the mean time I have changed over to single phase.

    If I had to do a single phase generator into 3 phase again (with your load setup) I would have an earth leakage for each phase. DB space might be a challenge, but can be overcome.

    I am no expert and would also like to hear the opinions about the earth leakage per phase.

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    Default Re: Generator question

    Connect the signal phase genset to the plug phase only and use a few plug in lamps for light. Shut down the main breaker until power comes back on. Install a single phase earth leakage between the plug breaker and the genset.

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  9. #8
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    Default Re: Generator question

    Quote Originally Posted by LdLL View Post

    I ran a single phase generator through a three phase change over switch (bridged the other two phases on the generator input). The problem with that is that your three phase earth leakage does not work which can be/is very dangerous (maybe as dangerous as the suicide lead). In the mean time I have changed over to single phase.

    Can you explain why the earth leakage won't work?
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  10. #9
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    Default Re: Generator question

    As I said. I am no expert.

    Mine didn't work.

    Maybe there is somebody much more qualified that can answer the above question.

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    Default Re: Generator question

    Quote Originally Posted by Brand2011 View Post
    Can you explain why the earth leakage won't work?
    The earth leakage should still work. The problem is probably the generators output voltage. It might have a V-0-V output and then the voltage to earth would not be high enough to generate the 30mA required when the test button is pressed to trip the earth leakage

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    Default Re: Generator question

    Quote Originally Posted by Brand2011 View Post
    Can you explain why the earth leakage won't work?
    Similar to a single phase Earth leakage. Each phase going in must be equal to any phase going out. If there is an imbalance between the phases the unit will trip
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    Default Re: Generator question

    Quote Originally Posted by hunter26 View Post
    Similar to a single phase Earth leakage. Each phase going in must be equal to any phase going out. If there is an imbalance between the phases the unit will trip
    Imbalance between phases won't trip a three phase earth leakage.

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  15. #13
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    Default Re: Generator question

    Quote Originally Posted by Bonesie86 View Post
    Imbalance between phases won't trip a three phase earth leakage.
    Current into a ELR must equal current out of an ELR. I'm not talking about a difference in load current ie Red phase draws slightly more than blue phase but rather currents going through the ELR must equal to currents returning back through ELR.
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  16. #14
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    Default Re: Generator question

    Sorry, I misunderstood what you meant.

    Agreed, the sum of the three-phases leaving must be equal to what is returning on the neutral.

    I think what was meant by the earth leakage not working is that it won’t trip.

    A V-0-V type generator (generally the type purchased from the local hardware) gives 110v to earth and 230V phase to phase (This is why in terms of SANS10142-1 they cannot be installed on in fixed installation), thus when you press the test button on the earth leakage as the test circuit is functioning at 110V and only 14mA is then generated and the earth leakage doesn’t trip.

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    Default Re: Generator question

    Quote Originally Posted by Bonesie86 View Post
    Sorry, I misunderstood what you meant.

    Agreed, the sum of the three-phases leaving must be equal to what is returning on the neutral.

    I think what was meant by the earth leakage not working is that it won’t trip.

    A V-0-V type generator (generally the type purchased from the local hardware) gives 110v to earth and 230V phase to phase (This is why in terms of SANS10142-1 they cannot be installed on in fixed installation), thus when you press the test button on the earth leakage as the test circuit is functioning at 110V and only 14mA is then generated and the earth leakage doesn’t trip.
    Haha, no harm done. Good to debate.

    I agree 100%.Unfortunately not all salesmen are clued up when it comes to selling generators to people. They should ask... For site use or home powering.
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  18. #16
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    Default Re: Generator question

    I think they just want to make a quick buck

  19. #17
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    Default Re: Generator question

    Thanks for all the comments,

    I had a look and I don't get charged any 3 phase levy that I can see, there is a network capacity charge of R5.73 per day?

    Also my phases are not plugs on one lights on one etc, there is a bit of everything on each one. The big consumers appear to be underfloor heating, electric towel rail and air con. These are switched off anyway.

    Each phase has an individual earth leakage.

    Will be getting an electrician to advise on how to proceed with single phase generator installation.
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  20. #18
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    Default Re: Generator question

    You could just ensure what you want to back up is all on the same phase and then back up that phase only with a single phase genny.
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