Generator volts on neutral ?
John
makers plate but judging its physical size against others I've seen , it's
probably about 4-5 Kva.
It has been converted to belt drive off a replacement engine ,it's seems to
be working ok.
But today I thought I'd put a meter across the output, to see if it was
running at the correct speed. I got 240V between live and neutral ok , but
also to my surprise 140V between live and earth and the same 140V between
neutral and earth. ( earth terminal on chassis )
Is this normal for generators ? Or has previous owner been playing with the
wiring ?
"Electrickery" is not my strong point , I'm a bit out of my depth on this.
John
--
<From> address has tinmeat added,
<Reply to> address is correct.
Peter Parry
<jo...@tanygraig.forcetinmeat9.co.uk> wrote:
>But today I thought I'd put a meter across the output, to see if it was
>running at the correct speed. I got 240V between live and neutral ok , but
>also to my surprise 140V between live and earth and the same 140V between
>neutral and earth. ( earth terminal on chassis )
>Is this normal for generators ?
I've two that do this - I assume it's to give added protection
against fault conditions. No leg is more than about half mains
voltage above earth.
--
Peter Parry.
http://www.wpp.ltd.uk/
Dave Liquorice
> But today I thought I'd put a meter across the output, to see if it
> was running at the correct speed.
Not quite sure how measuring the voltage is going to tell you if it's
at the correct speed.
> I got 240V between live and neutral ok , but also to my surprise
> 140V between live and earth and the same 140V between neutral and
> earth. ( earth terminal on chassis ) Is this normal for generators ?
You haven't got the same 140v they differ in phase by 180 deg, one is
going positive as the other is going negative.
Are your sure it wasn't 120v or less. I'm not quite sure why the sum
of the two voltages is greater than the L-N voltage. I'd actually
expect the measured voltage to earth to be less than half the full.
How ever if the "neutral" isn't bonded to earth then yes it's what I
would expect. When using a generator the "neutral" should be bonded to
the chassis and a local (to the genny) earth spike put in also bonded
to the chassis/neutral. At least when feeding into a house supply that
expects such an arrange ment for safety reasons.
But if you using it for power tools on a building site then it can be
argues that having both live and neutral floating with respect to
earth is safer than bonding the neutral.
--
Cheers new...@howhill.com
Dave. Remove "spam" for valid email.
Mike Ring
news:vnPD9.7998$dz2.1107777@stones:
> I have an old generator
I thought I'd put a meter across the output, to see if it
> was running at the correct speed. I got 240V between live and neutral
> ok , but also to my surprise 140V between live and earth and the same
> 140V between neutral and earth. ( earth terminal on chassis )
> Is this normal for generators ? Or has previous owner been playing
> with the wiring ?
>
Sounds OK, on a building site you have to use an isolating transformer
which gives the same effect.
I think for safety you should connect the generator/chassis earth to a
local earth, so the supply isn't floating, one leg could get earthed and
force the other up to 240 with no obvious effect till someone gets zapped.
I should point out that my knowledge of grotty old sites is thankfully
theoretical, in other words I might be talking c**p
Mike R
Mike R
Frank Erskine
> "John" <jo...@tanygraig.forcetinmeat9.co.uk> wrote in
> news:vnPD9.7998$dz2.1107777@stones:
>
>> I have an old generator
> I thought I'd put a meter across the output, to see if it
>> was running at the correct speed. I got 240V between live and neutral
>> ok , but also to my surprise 140V between live and earth and the same
>> 140V between neutral and earth. ( earth terminal on chassis )
>> Is this normal for generators ? Or has previous owner been playing
>> with the wiring ?
>>
> Sounds OK, on a building site you have to use an isolating transformer
> which gives the same effect.
>
> I think for safety you should connect the generator/chassis earth to a
> local earth, so the supply isn't floating, one leg could get earthed
> and force the other up to 240 with no obvious effect till someone
> gets zapped.
Be careful here! It could be that the "centre-tap" is actually earthed.
Earthing one leg would then short out half of the supply and cause a bit of
a burn-out.
I wonder if there's a transformer built in to the genny, or if it could be a
two-phase machine. Best to open it up to see what the wiring arrangement is.
140+140 = 240? Hmmm! That does somewhat suggest a two-phase system with some
strange waveform.
--
Frank Erskine
Tony Williams
Frank Erskine <frank....@btinternet.com> wrote:
> 140+140 = 240? Hmmm! That does somewhat suggest a two-phase
> system with some strange waveform.
The voltage discrepancy could also be a stator
winding with 240V across its ends, running totally
floating, so that the 140+140 is the result of
capacitance between stator and frame, as measured
with a high impedance voltmeter.
The "totally floating" could be deliberate or
accidental... ie, a poor connection, so does need
to be thoroughly checked.
--
Tony Williams.
tony sayer
Dave Liquorice <new...@howhill.com> writes
I wonder if the gennie windings are floating and aren't connected to
earth, well the *earth* frame of the gennie.
Suppose with a high Z meter this would show almost anything due to
capacitance and leakage...
--
Tony Sayer
John
"Dave Liquorice" <new...@howhill.com> wrote in message
news:nyyfbegfubjuvyypb...@snail.howhill.network...
> On Sat, 23 Nov 2002 18:02:39 -0000, John wrote:
>
> Not quite sure how measuring the voltage is going to tell you if it's
> at the correct speed.
The output voltage seems to be very sensitive to spring tension in the
engine governor and engine revs.
> Are your sure it wasn't 120v or less. I'm not quite sure why the sum
> of the two voltages is greater than the L-N voltage. I'd actually
> expect the measured voltage to earth to be less than half the full.
I went back to the shed this morning with a better meter, this one shows
110v on each leg, and 220v total. So it seems one should never trust a multi
meter that cost a fiver on the local market.
I did put a few hundred watts load on it this time too. that stabilized the
fluctuations a bit.
> How ever if the "neutral" isn't bonded to earth then yes it's what I
> would expect. When using a generator the "neutral" should be bonded to
> the chassis and a local (to the genny) earth spike put in also bonded
> to the chassis/neutral. At least when feeding into a house supply that
> expects such an arrange ment for safety reasons.
>
> But if you using it for power tools on a building site then it can be
> argues that having both live and neutral floating with respect to
> earth is safer than bonding the neutral.
>
I've only been using it for power tools so far , But if I wish to bring a
cable into the house ( to give the freezer a boost during a power cut for
instance ) then I will bond neutral and earth, and ensure that the genny is
earthed too.
Thanks to all who responded