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Thread: 230 volt generator with a V-O-V earth connection

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    Diamond Member AndyD's Avatar
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    To be honest I have limited experience of generator wiring schemes so I'm going to do some more homework when time permits.

    From my understanding a V-O-V type generator is basically a 2-phase supply with 220v between the phases so I would say it should have a 2-pole breaker. If the generator is SABS approved then the overload protection supplied ought to be compliant.
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    AndyD

    I am an electrical contractor. This whole generator thing is one big disaster. I would go as far as to say that 99% of electrical contractors don't know generators inside out.

    I have spoken to countless contractors and let me tell you the one is as confused as the next. Even the council inspectors are confused. You ask them a question and they simply reply with a word for word quote from S.A.N.S 10142.

    The regulations should be written in plain english. If they say V-O-V gen sets may not be connected then tell me why?

    Most of the big diesel gen sets are installed at the boundary boxes and the main supply cable run via the auto change over switch.


    If V-O-V is one method of wiring the alternator then what are the other methods and what do they mean? How does one tell if it is V-O-V? Is the only way to actually check if the centre tap on winding is earthed? Is this actually possible short of taking the whole alternator to pieces. Is there a more simple method?

    I contacted Honda SA regarding my unit and they do not know what type it is. (Honda EP6500CXS 220 Volt)

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    Gold Member Martinco's Avatar
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    Quote Originally Posted by AndyD View Post

    If the generator is SABS approved then the overload protection supplied ought to be compliant.
    Andy,
    I am sure non of these "keep in a cool and dry place " 5,5 or 6,5 Kva gensets are SABS approved. These also tend to be about 95% of the sets you find installed in homes.
    So, my thinking on this is, that if you do have a V-0-V set then there is no way around the ELC and proper earth for both the set and the home UNLESS the center tap is removed from earth and the N is then earthed in its place.

    This turns out to be quite a relevant thread that is affecting many people without them/us realizing the dangers !
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    Site Caretaker Dave A's Avatar
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    My suggestion:

    (While the genset is not running) Do a resistance test between earth to neutral and earth to live using a multimeter. If there is no connectivity between earth and both live and neutral, you've got a genset like we use at the office. The "earth" isn't tapped into the generator circuit at all.
    (BTW - resistance between neutral and live came in at 0.84 ohms on our genset.)

    If you are getting continuity between earth, live and neutral:
    Put a load on the genset and then bridge earth and neutral via a lightbulb (or other handy resistor).
    With the generator running - check the voltage for earth to neutral and earth to live.

    A low earth to neutral reading together with a high earth to live reading probably means the genset is not V-O-V.
    If the earth to neutral and earth to live readings are about the same, you've got a V-O-V genset.

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    Dave A

    Now this starts making sense.

    On my Honda EP6500CXS I get the following readings when running and nothing plugged into the generator. Honda themselves can't tell me if the unit is V-O-V or not.

    N to E 67 Volts
    L to E 147 Volts

    From the alternator I get a brown and white which run through to the two sockets on the genset. There is also a 2.5mm earth which runs with them to the sockets. This earth is connected onto an earth stud in the alternator. There are no other earth wires connected with it.

    When the generator runs if one puts a plug tester into the sockets the earth light does not come on and indicates an earth fault. Like wise when connected to the house circuits none of the sockets in the house show an earth on the tester and one can also not get the earth leakage to trip when testing either with the test button or the tester.

    I also have a 6mm earth running from the council earth to the generator earth stud. From the generator earth stud there is another 6mm earth which goes to an earth spike next to the generator.

    Now when I bridge out the Neutral to earth on the alternator I get the following readings.

    N to E 0 Volts
    L to E 224 Volts

    When the house load is connected all the sockets work correctly with the plug tester and the earth leakage trips when tested.

    Regarding V-O-V sets. If the voltage between N and E and L and E is the same one is surely going to battle to tell which one is Live and which is Neutral. At the moment I use a wibre line tester. If one puts the one end on the one terminal and the other end on your finger or earth terminal the indicator light lights up. (without pushing the test button on the tester.)

    If my thinking is correct this could be another way to know what unit one has.

    I want to get my hands on a V-O-V genset so I can put my theories to test.

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by Greg View Post
    If the voltage between N and E and L and E is the same one is surely going to battle to tell which one is Live and which is Neutral.
    Effectively in this situation both neutral and live are "live"

    Perhaps I should also point out that in our office genset (the one with no earth connected to the generator circuit) we get a earth to live and earth to neutral reading of approximately 110V each when we don't bridge the earth and neutral.

    I feel like I'm rehashing some of this stuff, though. Wasn't there another thread on generators where this floating neutral came up before?

    Anyway, two parting thoughts:

    If you've got no continuity between earth and neutral you can't have a V-O-V genset.

    And

    Just how much safer is 110v than 220v AC anyway?

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    Diamond Member AndyD's Avatar
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    Thanks Dave, I'm guessing one of your electricians shed some light on this for you. I've bumped my generator research to the top of the things to do pile for this coming weekend so I might have some more concrete answers by Monday.

    Quote Originally Posted by Dave A View Post
    Just how much safer is 110v than 220v AC anyway?
    I would think it's considerably safer if you drop the voltage with respect to earth. Last time I was contracted to a project in the UK, all the site power there is via a 110v transformer or generator and this is legislation. All the power tools are 110v although the normal national grid voltage there is 230 (used to be 240) so contractors need a separate set of power tools for site work and normal domestic work. The site transformer is a similar system where the L&N are 110v with respect to each other and 55v wrt earth. I don't have figures on the statistical likelyhood of surviving a shock as the voltage is halved but I assume it was high enough to prompt their legislation.
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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by AndyD View Post
    I'm guessing one of your electricians shed some light on this for you.
    Not in this case. I may not be an electrician, but many, many years ago I was nearly an electrical engineer and some basic principles seem to have stuck... long story.

    Anyway, a little applied theory, some practical testing to make sure I hadn't missed something, and hey presto.

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    a v-o-v generators works the same as the american system and simmilar to the circuit for isolocks in hospital theatres..which use double pole isolators...

    i dont know of a small generators (5,5kw) which is not v-0-v

    i am trying to remember the proceedure told to me when i started this thread...will check it again...but if i can remember corrrectly it goes something like this...


    if you test from v-o you should get 110 volts if you test from o-v you should get 110 volt then if you test from v-v you should get 220 or there about...

    some people just take the v from one side and join it to earth with the earth spike...without removing the earth point in the middle...which must be isolated from the body and the earth stud on the generator removed...otherwise you will burn out one of the v-0 windings

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    Quote Originally Posted by Greg View Post
    AndyD

    I am an electrical contractor. This whole generator thing is one big disaster. I would go as far as to say that 99% of electrical contractors don't know generators inside out.

    I have spoken to countless contractors and let me tell you the one is as confused as the next. Even the council inspectors are confused. You ask them a question and they simply reply with a word for word quote from S.A.N.S 10142.

    The regulations should be written in plain english. If they say V-O-V gen sets may not be connected then tell me why?

    Most of the big diesel gen sets are installed at the boundary boxes and the main supply cable run via the auto change over switch.


    If V-O-V is one method of wiring the alternator then what are the other methods and what do they mean? How does one tell if it is V-O-V? Is the only way to actually check if the centre tap on winding is earthed? Is this actually possible short of taking the whole alternator to pieces. Is there a more simple method?

    I contacted Honda SA regarding my unit and they do not know what type it is. (Honda EP6500CXS 220 Volt)
    The EG is V-O-V, as al all Honda gensets brought into SA by Honda.
    Honda does make a V-0-O EU65 but for some reason Honda SA does not bring it into the country.

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