Paging ARW - generators bla bla



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 connections.
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 genset range.
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.
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J B Good

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That is correct - but see below

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.
--
Adam


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On Saturday, March 21, 2015 at 12:09:26 PM UTC, Paul Carmichael wrote:

he

re

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.
NT
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snipped-for-privacy@care2.com wrote:

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 post).
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 concrete base.
There is no PME here. Touch the neutral to earth and the RCD trips immediately.
I'm going to inspect the genny wiring to see if the earth terminal is internally connected to one of the lines.
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Paul
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Paul Carmichael wrote:

Right. Inspected.
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 220v.
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.
Confused.
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wrote:

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 the mix.
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 genset.
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 sockets.
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[1]).
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[2].
[1] 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).
[2] 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" connection.
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 genset.
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).
--
J B Good

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Johny B Good wrote:

Heh. Fixed that now I think.

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 ground).
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 here).
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Paul.
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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.
--
Adam


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On Sun, 22 Mar 2015 12:53:03 -0000, "ARW"
====snipped===

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[1] 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.
[1] 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.
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On 21/03/2015 15:46, Paul Carmichael wrote:

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.
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Fredxxx wrote:

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 what happens.
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Paul wrote:

That is lethal and known as a widow-maker. You clearly have no idea what you are doing. Stop right now and get local knowledgeable help.
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On 21/03/2015 16:55, Paul wrote:

Have you measure between lines and earth? And checked the earth pin is connected to the genny frame?
I thought those connectors did specify neutral and live?
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On 21/03/15 16:55, Paul wrote:

That's called a Jesus Cord.
Because when you pick up the wrong end, you either yell "Jesus" or you meet him.
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.
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Tim Watts wrote:

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.
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On 21/03/2015 19:57, Paul wrote:

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 conductor?
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.
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Fredxxx wrote:

Missed that 3 times, as I've not even mentioned such a possibility.

Yup. As mentioned "several times". Six 1.5m earth spikes.

One has to know all that stuff to connect a simple generator to a house? Blimey.
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On 22/03/15 10:19, Paul wrote:

The generator might be simple - but being safe in a variety of corner cases is not trivial. That's why the IET Wiring regs are half an inch thick.
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On Sun, 22 Mar 2015 10:27:47 +0000, Tim Watts wrote:

bonding,

tapped

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 installations/switching.
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On 22/03/15 11:49, Dave Liquorice wrote:

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 matter what.
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 rain.
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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