The higher than normal distortion in the generator's output is the
least of your worries (it's much better than the quasi sinewave or
modified squarewave of the cheaper inverters commonly used in sub
500VA UPSes and 12v inverter supplies).
The real problem with such gensets is their susceptability to
overvolting when driving a load with a relatively small amount of
leading current (capacitive loading). Such excess capacitive loading
can cause a 230v generator head to output in excess of 270v which the
AVR module can no longer control. Resistive and inductive loads are
free of this effect (incandescent lamps, electric toasters or motors
of almost any type).
Unfortunately, most electronic kit tends to demand some amount of
leading current with older UPS designs being the worst offenders by
placing a considerable capacitive load across their incoming mains
The more expensive inverter gensets are free of this overvolting
effect on both leading and lagging current loads so are the only
viable emergency backup to UPS protected IT kit in the 2 to 5KVA
The larger 10KVA and up gensets aren't free of this unfortunate side
effect, they only perform acceptably when the IT kit loading is only a
tiny fraction of the genset's VA rating. This is the basis of the myth
that only oversized gensets are of good enough quality to power IT
kit. In all honesty, the purity of their waveforms is little better
than the cheap 2 to 3 KVA home emergency gensets commonly sold in
hadware retail outlets Like Home Depot in the US of A and B&Q (and
Aldi) here in the UK.
That is because the neutral is not tied to ground.
You may already have an earth rod for your house electrics. if so then there
is no need for another earth rod rod for the genny.
Sometimes I link the neural and earth in the lead from the genny - it is
sometimes needed to do this to fire up boilers.
On Saturday, March 21, 2015 at 12:09:26 PM UTC, Paul Carmichael wrote:
Portable gens have a neutral, its whichever of the 2 power output terminas
you connect to ground.
They don't have an earth, a house needs that. If you have a local earth rod
, that's already covered, though its best to also connect earth to (genny)
neutral. If no local earth rod, its easy to fit one as a supplementary eart
h. You can't rely on a supplier earth when power's off.
I'm not sure I understand any of that.
The genny has two "normal" socket outlets including earth connectors.
There is an earth terminal connector on the chassis (see photo in other
Both lines light up the neon screwdriver.
I don't know what a "supplier earth" is. The house has 6 earth spikes under
the extension which are also connected to all the steel reinforcing in the
There is no PME here. Touch the neutral to earth and the RCD trips
I'm going to inspect the genny wiring to see if the earth terminal is
internally connected to one of the lines.
One wire from the earth terminal goes to the earth connectors in the
sockets. Another goes off to the generator.
Coming from the generator we have black and brown at 12v and blue and red at
I still don't know how to get a live and a neutral from what appears to be
true AC at 115-115 but without a 0.
I was too... by your use of three different usenet identities (Paul,
Paulus and Paul Carmichael).
However, leaving that aside, once I managed to find the posting with
a dropbox link to your photo of the generator panel, it would seem to
be the sort of small portable emergency generator sold by the likes of
Aldi from time to time back in blighty.
These are designed to power incandescent lighting and fridges and
freezers. Unfortunately, when it comes to supplying electrical loads
with anything more than a microfarad's worth of excess leading
current, the generator itself reacts by overvolting despite any AVR
controller circuit's best efforts to maintain the correct voltage
level. IOW, you might find problems if you have much in the way of
computer kit in your office, especially if you have a UPS or two in
What appears to be the model number (GG2500C) suggests that it's a
2.5KVA rated generator (the Aldi one was 115v / 230v 2.8KVA rated, for
all the use it was for _my_ needs).
From your description, it appears that the two 110v windings have
been permanently linked in series in the generator head itself rather
than brought out to a voltage selector switch on the panel to cover
both mains voltage options as in the case of the Aldi 115/230v 2.8KVA
It's standard practice to leave the stator windings floating on
single phase gensets. The splittedness of the stator windings makes
for a very balanced floating supply, hence being able to detect
voltage using a neon tester on either outlet socket pin (live and
neutral as you referred to them. Are they actually 13A sockets hidden
under the flaps?).
If you're going to use it to provide emergency power to fridge /
freezer and incandescent table lamps, you're safest method is simply
to run an extension cable or two to where your appliances are and
transfer their plugs from the house sockets to the genset extension
However, the floating output could still represent a hidden danger in
the event that items like fridges or freezers with their earthed metal
casings were to develop a live to casing fault which on its own
represents no immediate danger of electric shock (other than a mild
sensation of 100Hz tickle when lightly touched due to leakage paths to
earth , largely capacitive leakage when everything is nice and dry).
A worst case fault scenario is when a fridge adjacent to a freezer
develops respectively a live to case and a neutral to case fault. The
lack of a path to earth in the former case (because the neutral is
isolated from a good safety earth) means that the usual fuse
protection against such faults is rendered ineffective (the neutral to
case contact isn't normally a shock hazard).
An obvious way to get around this problem is to use an rcd breaker
between the genset and the extension socket but you need to strap
what's marked as the neutral pin on the genset sockets across to the
earth and make sure to connect to a reasonably good earth connection.
With domestic electrical supplies, there are already enough ways to
create dangerous/lethal shock hazards. Adding an emergency genset into
the mix multiplies this risk management considerably. It can be done
with properly installed equipment and wiring practice by an
electrician who specialises in such installations.
For more casual use of such emergency gensets, limit your hook ups to
simply transferring the appliance plugs from the house sockets to the
genset sockets and stay mindful of the potential danger in using a
floating 220v supply.
 Neutral already being connected to earth at the sub-station anyway
on a single phase supply - I don't know about your Spanish supply. You
say the rcd breaker trips to an earth contact from any of the two
supply pins in the house sockets which implies the possibility of the
more expensive bi-phase cabling distribution system (two lives at 110v
each, summing up to 220v between the two power pins).
 If this was a UK installation with a good old fashioned
sub-station earth provided over the incoming cable's armouring, I'd
suggest the obvious solution of providing a special 2 or 3 way 13A
socket by which to physically plug appliances into the genset supply
where the genset connections for the 'neutral and the frame earth can
be strapped across to the house neutral and earth leaving the genset's
live only connected to the special 13A socket's Live and nothing else.
You could make up a connecting lead to go from the genset, normally
kept outside, with a suitable inline socket (a 10A IEC female socket
as used by the detachable mains leads used by PCs would be fine for
this where you plan to trail the lead into the house. The associated
permanent panel mounted shrouded plug will only give finger access to
the house neutral and earth connections and a dead "live pin"
A technically better (and marginally safer) option would be to use an
external weatherproof 16A IEC connector designed for such usgae on the
outside wall of the house handy to where you plan to run the emergency
Whichever method you use to connect to the special genset 13A
sockets, you gurantee that one of the generator terminals is connected
to neutral leaving the other connection to act as a live phase and the
genset framework earthed to the house earth which is generally an
order or three magnitude better than an earth spike alone.
However, it won't do any harm to provide the genset's frame an
additional connection to an independant earth spike connection. It
will keep it safe if you're using it to power external electrical
tools or just running it up for testing (or simply if someone pulls
the plug whilst the genset is still running).
Which is in fact the case. The main reason for wanting the emergency supply
was to be able to carry on working in my office (with it's 3 UPSs) in case
of power cut (we have many such things here as all the lines are above
Anyhoo, thank you for a well thought out and comprehensive reply. The thread
has been interesting for me and educative.
However, the conclusion I have to come to is that this genny is fit for what
I bought it for (site) but not for an emergency house supply.
Thanks to all for your input.
I shall now consider either a proper genny (now that I've forked out the 90
euros for a changeover switch) or a solar solution (we see a lot of sunshine
That is probably the best reply to this thread.
Now after reading the rest of the posts we can conclude that the OP has a TT
supply (or a Spanish equivalent) and that the house CU will have RCD
protection (a quick Google search suggests that Spanish electrical
installations require DP switched RCDs/RCBOs on all circuits).
So the OP now needs to suck it and see. Your point about the genny being a
110-0-110 V centre tapped earth supply does not preclude it from operating
most of the house electrical supply.
It will not matter if the genny is supplying 110-0-110V or 220V to most
equipment - the waveform of the gennys output is more relevant and might
cause some items not to work.
On Sun, 22 Mar 2015 12:53:03 -0000, "ARW"
Thank you very much for that praise. :-)
I think there is some confusion here. When Paul mentioned he could
trip the rcd by earthing either pin in his house sockets I
concluded that he may have been on a bi-phase supply.
My reference to the generator head having a pair of 110v stator
windings wasn't intended to imply a centre tapped bi-phase option,
just to indicate why a neon lamp test would indicate such a bi-phase
supply due to the fairly balanced nature of the capacitive leakage to
the frame and surrounding ground he was stood upon. Once you've
strapped either end of the series connected windings to the frame and
earth, any resulting leakage current would merely be microampres in
magnitude and of no consequence.
In this case, it seems that the two windings have been linked
together in the generator head with only the 220v connections brought
out to the panel. IME, it seems to be standard practice to leave the
generator windings floating so that the end user remains free to deal
with this problem as they deem appropriate.
Whilst it's true that the waveshape can noticablly depart from a pure
sinewave when under load, that's not really the issue. The real issue
is such generators' reaction to, well, reactive loads (leading
current, capacitive loads to be more specific) whereby they go into an
uncontrollable overvolt condition which the AVR cannot compensate for.
Lagging current (inductive) loads aren't a problem in this regard
other than the more prosaic issue of low PF loadings reducing the
usable real power output (wattage) in the face of a large reactive
current demand on the total VA available from the genset.
 I may have misinterpreted exactly what Paul was trying to describe
so the question of a bi-phase supply on his property is most probably
a red herring.
Some 110V sources are split either side of earth. I have no idea of this
is the case for your genny, on either/both the 230 and 115V settings.
Personally, I would earth the earth lead to your house earth. Depending
on how you use it, that might happen anyway.
I was going to connect a plug to the house side and plug that into the
genny, which would include an earth connection. But I don't know how to wire
the plug if I don't know which wire will be "neutral". I suppose I could
connect the genny earth terminal to a nearby earth spike, fire it up and see
That's called a Jesus Cord.
Because when you pick up the wrong end, you either yell "Jesus" or you
Seriously - stop it now. You're dangerous.
One other factor you may need to consider is that it is unwise to rely
on the supplier's earth during supply failure - indeed, if the supplier
has a nuetral fault and you're on a TN-C-S (also referred to as PME)
your supply earth may drift quite some volts (10s, 100s if you were
really unlucky) above nominal earth outside your house.
The usual route here is to put an earth spike or two in and bond that to
the MET - but as this connection may become a route for current in the
event of certain faults, it needs special consideration to do it correctly.
And no, you cannot switch the house earth between the supply earth and
your local rod when you are using a generator.
At the risk of repeating myself, I don't know what a supply earth is.
I'm amazed that I have a 220v generator with no way of connecting it to my
house (with it's magnificent earth).
Oh, and I've already said about 3 times that we don't have PME here.
You've been told 3 times not to use a cable with a plug at each end. Is
there some significance of being 3 times?
Indeed have no idea why you have felt the need to mention you don't have
PME. Do you know what earthing arrangement you have? I can assure you
that in the UK, even without PME, neutral should only be a few volts
different from earth potential. Do you know the normal potential on each
Additionally, if you don't understand the concept of earth bonding,
protective conductors, PME supplies, earth spikes and centre tapped
supplies, I would give up now and get help from someone who does.
On Sun, 22 Mar 2015 10:27:47 +0000, Tim Watts wrote:
Aye, in theory it is trivial to make the connections and be fine
under no fault conditions. It's handling the many "what if" fault
conditions and still meeting the regulations for supply and
installation when on grid power and when on generator power.
Which is why I use extension cables to the appliances I wish to power
from the generator during power cuts. But having more than one
appliance connected to a "live" and "neutral" floating generator
isn't strictly legal either.
I have thought about replacing the isolator switch on the genset with
a 16 A DP RCBO but if both "live" or "neutral" are floating there is
no fault circuit via "earth" to unbalance the the "live" and
"neutral" currents and trigger a trip.
One possibilty is to connect the earth pin of the genset output
socket to the "neutral" pre the RCD. But that doesn't produce a trip
if the still floating "neutral" has an earth fault condition, only if
the "live" does, I think!...
I don't think there is 1/2" of regs just for generator/grid power
It gets trickier when one of the appliances is a boiler that has an
implicit reference to earth too.
I suppose on one hand, even if the supplier earth failed as part of the
outage, the inside of the house would be an equipotential zone, no
The problems get more interesting when you have extraneous conductive
parts like an outside water tap or gas feed pipe that are now doing
random stuff with respect to the actual ground nearby, especially in the
I have it on reasonable authority from someone who specialises in
generators that the correct thing to do is to add sufficient local
grounding to the MET - and further reading suggests this is the only
practical way to be bomb proof - but there remains a danger that under
certain local area faults you could be providing a path to earth for
your neighbours so it needs doing properly.
I do not have chapter and verse on what "properly" entails - but it is
something I've been considering in case I wanted to have an independent
radial circuit supplied from a generator with sockets in key locations
(fridge, internet stuff, boiler).
Because I have bonded copper pipes running in touchable positions
outside of my house, I'd personally be inclined to take (insured,
indemnified, written) engineers advice before doing anything permanent.
But the real sticking point is the boiler. If it were just a few
internal appliances, then it's probably all fine on an extension lead.
True - I was making a general conclusion that nothing is actually as
simple as they might appear.
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