Using a generator in an isolated building.

Hi. I'm not a qualified electrician, and hope someone can provide me with some advice.
I've got a small log cabin that has no mains electrical supply going to it. I've got a small petrol generator (Honda EU20i) that I sometimes use to power a TV, little fm radio and other ad-hoc low power devices when I stay there overnight.
I've been trying to work out if I should be installing some sort of earth system. Most (if not all) of the appliances I use are double insulated, but I do sometimes use a class 1 mini fridge.
I'm pretty sure the generator has a floating earth (not that I really understand what that is). The manual talks about using a mcbo and an earth stake, but research on forums seem to indicate this shouldn't be done - so I'm confused. I also read talk about getting the generator modified so there is a connection between earth and neutral, but that seems to mean I can't use the generator out in the woods Etc... All the articles I've found talk about transfer switches where the generator is only being used as a backup. This isn't my use-case! Can anyone please give me a steer as to what (if anything) I should be doing ? I guess the answer might be to only ever use class 2 appliances - but would appreciate guidance from someone who really knows.... Tks, Damian

You shouldn't put (another) earth from a portable generator to the ground. You don't need to modify anything. It's designed to do exactly what you want. The principle behind earthing is to give a way for a large current to flow from a fault and thus trip the supply (blow a fuse). The supply from the generator will have an earth wire which does that job via a MCB. Many modern generators also have an RCD which limits the duration of a shock if you get yourself between the live wire and the earth wire (e.g. a faulty tool). This is not as likely to happen with the generator supply as with a house supply because there is no path for the current to flow through you back to the generator whereas, in the house, the ground itself is a return path. Few devices are not class 2 in your case (radios, TVs, etc). The mini frig may be class1 (needs earthing) but that is taken care of by the system described above so no problem. The manual's comments on earth stakes, etc are intended to cover the use with a building which has an electrical system which is itself earthed so doesn't apply to you.
The greatest danger from small generators is from carbon monoxide - hopefully you never use it indoors or where the exhaust can be sucked into the building.
Enjoy the cabin.

Looking at the Manual it would seem there is an earth connection you can use on this generator.

It is a complex 3 phase generator and the 3 phase supply is turned into a single phase supply using rather complex circuits and clearly one should not try altering anything in the generator. But the circuit does not show any existing RCD protection.

Using with a single item plugged in is the same as using a shaver socket and there is no need for an earth or RCD protection.

As you start to use multi items however there comes a point where some form of bonding or earthing may be appropriate and use of RCD would really be a good idea. It does not need to be a big thing the one shown fits in the lead and would be ample.

If using the generator in a metal shed of caravan then bonding may be a good idea. In a wood shed then going OTT and not really required.

Bonding is to connect metal parts together next stage to to earth those bonded parts. The answer as to bonding or earthing is complex as it could introduce danger where few items are used but remove danger where there are a lot used.

So from your description I would not bond or earth in your situation. However I would use a RCD like shown or built into plug.

There are a number of types 10ma and 30ma the 10ma offers more protection but 30ma more common and less likely to trip for no reason so I would go for 30ma.

Also Active and Passive the house type is passive and on a power failure stays on the active type is for when volt drop could stop the RCD from working and when volts drop these will drop out and need resetting. In your case either would do but with some generators you need a passive type as they have a load detector and when load is reduced the voltage drops so an active type will really be a pain. So in general for generators I would select a passive type.

So fit a passive 30ma RCD and your sorted. Cost around £16

viewer said:

You shouldn't put (another) earth from a portable generator to the ground. You don't need to modify anything. It's designed to do exactly what you want. The principle behind earthing is to give a way for a large current to flow from a fault and thus trip the supply (blow a fuse). The supply from the generator will have an earth wire which does that job via a MCB. Many modern generators also have an RCD which limits the duration of a shock if you get yourself between the live wire and the earth wire (e.g. a faulty tool). This is not as likely to happen with the generator supply as with a house supply because there is no path for the current to flow through you back to the generator whereas, in the house, the ground itself is a return path. Few devices are not class 2 in your case (radios, TVs, etc). The mini frig may be class1 (needs earthing) but that is taken care of by the system described above so no problem. The manual's comments on earth stakes, etc are intended to cover the use with a building which has an electrical system which is itself earthed so doesn't apply to you.
The greatest danger from small generators is from carbon monoxide - hopefully you never use it indoors or where the exhaust can be sucked into the building.
Enjoy the cabin.

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Your information is incorrect. An un-earthed generator may be used with one piece of current using equipment, but any more and the system needs tying down to earth and a N/E link. A small genny will usually not be able to provide enough current to operate protective devices under fault conditions hence the need for RCD protection. An RCD will not work without reference to earth.

Many thanks for all the replies. I seem to have three conflicting views being expressed here. My problem is, I'm not qualified to know which one is valid. The replies I've had seem to mirror the confusion I've seen in the past, which is why I decided to ask. Please don't take this as me being rude, but can anyone give me a clear answer?
Many thanks in advance,
Damian

DamianNewrick said:

Many thanks for all the replies. I seem to have three conflicting views being expressed here.

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FWIW, I'll change that situation slightly by aligning myself with the ricicle view (which was also partially reflected by what ericmark wrote). Some of what viewer wrote is essentially wrong.

Kind Regards, John

What exactly is wrong?

If you compare the portable generator to a mains supply from a power station to an imaginary single transformer providing SP to a house then, if the transformer was not earthed there would be no point in earthing the house and, as ricicle says, the rcd would need a link to a functional earth. So the RCD will not work, but, as I said, because there is no path back to the transformer via earth then the only way to get a person to receive a shock is if they touch both L&N - a situation in which an ungrounded person would not be protected by a RCD as the person would simply be a resistance in the circuit.
The Honda manual refers to grounding being required for two specific situations; where two generators are tied together and when the connected equipment is grounded. Honda do not suggest grounding the generator in any other situation. I don't and neither do these people:

https://www.osha.gov/OshDoc/data_Hurricane_Facts/grounding_port_generator.pdf
http://electrical.theiet.org/wiring-matters/39/portable-generators.cfm?type=pdf

Ricicle surely the earth for multiple devices refers to having an earthing system in the generator - device loop not earthing to ground. So for a 230-V system there will be 3 cores in the output L,N&E used as normal. Without this earth there would be no short circuit protection in the event of, say, wet / faulty devices where no earth connection would mean that one had a live exterior and another wet/faulty device might have a connection to neutral on the exterior.

If you want to check through, have a look at your views in
//www.diynot.com/forums/electrics/small-generator-earthing.381849/

Thanks again to all the contributing posters. Viewer, I find it somewhat interesting that you post links to two of the papers I did bother to read. I guess it's reading those that made me ask the question in the first place. As I sometimes use the fridge (A class 1), and all the rest of the stuff is class 2, I guess my use case fits nicely into their recommendations... so do nothing other than use what I've got ? Am I also correct in thinking that an RCD (as recommended previously) will not achieve anything because I've only got (what my ignorance dictates as being) a pretend earth - or does it help with a belt and braces approach? I don't particularly want to buy one as an ornament...

viewer said:

What exactly is wrong?

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I think there may be a misunderstanding here. I was not thinking/talking about adding a connection to true earth - which may well be as likely to create hazards as to reduce them. Rather, I was responding to the OP's comment that he believed that his generator had a floating output, and was asking whether it should have a N-'E' link installed. You wrote:

You don't need to modify anything. It's designed to do exactly what you want. The principle behind earthing is to give a way for a large current to flow from a fault and thus trip the supply (blow a fuse). The supply from the generator will have an earth wire which does that job via a MCB.

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As above, my understanding of the OP was that there is currently no N-'E' link in his generator, which seems to imply that the generator probably does not currently "have an earth wire which does that job via a MCB". I can but presume that the 'earth pins' of the generator output socket(s) are floating (maybe connected to generator frame - which would raise other issues), and therefore serve only to bond together the CPCs of cables plugged into them. Even if the generator/MCB combination were capable of clearing a live-CPC fault, in the absence of an N-'E' link, that obviously would not happen.

However, maybe I'm still misunderstanding you and/or the OP.

Kind Regards, John

Thank you JohnW2. So, in essence do I just do as Viewer suggests and use the generator as is, without adding any further protective devices?

DamianNewrick said:

Thank you JohnW2. So, in essence do I just do as Viewer suggests and use the generator as is, without adding any further protective devices?

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You could, but I would personally only advocate that if you can be absolutely certain that there will never be more than one Class I load supplied by it simultaneously. As ricicle said (although he didn't mention Class I explicitly), if you have more than one Class I load supplied by a generator with a floating output, that can potentially be hazardous.

You will probably be interested to read this article from the Summer 2011 edition of the IET magazine. As you will see, in relation to floating generators, on page 19 it says:

More than one item of Class I equipment should not be used simultaneously as faults can be presented as voltages and operatives can provide a path for current flowing between exposed-conductive parts of faulty electrical equipment.

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Kind Regards, John

My first thing was to read the data sheet OK there are a few so may have selected wrong one but would not expect much to change.

From the circuit diagram it is not plain as to if earth is floating or not as there are blocks which do not show what they contain.

This generator is a high quality device with some very hi-tech features such as ability to run in parallel with another unit. The connections for this include a earth connection and since the generator provides this I would not attempt to make any external connections between neutral and earth.

The noise filter or/and inverter unit may link the earth and neutral in some way it is impossible to tell without testing. This generator is a three phase brush less generator with an inverter with turns the output to single phase at 50Hz what ever speed the generator is running i.e. a complex unit.

The question originally related to earth rods and personally I feel with the use this generator is put to there is no need to fit earth rods as from description there is very little metal and a single room.

As far as I can tell the AC circuit protector is just a MCB likely thermal only so to fit a RCD to me is a sensible precision. As to if it will work will depend on the noise filter or/and inverter unit and only real way is either to ask Honda or to try using a RCD tester.

I would agree with more than one class I item earth bonding is required however since all items will have an earth pin any multi-socket output would bond the earth connection of all class I without there being a need to do anything other than plug them in. Unless the cabin in metal or have metal water or gas pipes these is nothing to bond within the cabin.

So doing a risk assessment of information given to my mind all that is required is a RCD.

Do remember bonding and earthing although similar are not the same. I personally see no advantage in sinking an earth rod. And to be frank to fit an earth rod would need equipment most electricians will not have. In a house with mains supply we compare our earth with boards earth but here there is not boards earth so it means using a very special tester and running wires out to two test probes the centre one which is moved to astatine the far one is far enough out. I have done this many times but all for a single job the other electricians joked I had got the job because I had zero potential. It is not a DIY job and likely any one that does it will need to hire the equipment even then such a rare job finding an electrician who has done it before is going to be hard. So I would forget the idea of any earth rod.

Only way to find if RCD works is to fit one and test it. If it does not work linking earth and neutral may damage the generator so since does not really matter if works or not you can't do anything then why bother testing it. Yes I would fit one but my personal risk assessment says no point in testing.

OK I know what I am saying is not following BS7671 to letter but trying to be sensible about it. So if it was me I would just fit a in-line RCD passive type and that would be it.

Many thanks Ericmark. I'll do just that!

Regards,
Damian

ericmark said:

So if it was me I would just fit a in-line RCD passive type and that would be it.

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I'm very confused. If the generator output is floating (although I agree that we are not sure), how on earth could an RCD serve any useful purpose? Under what circumstances could a L-N current imbalance arise to operate an RCD in that situation - what alternative return path could there be? What am I missing?

Kind Regards, John

I do not think it will be floating or I would not recommend a RCD but if I am wrong well he has wasted £15 if I am right and in the inverter there is a link then it will work A1 in the past Honda generators I have worked on have be bonded inside the generator in fact this caused me a problem where it was connected as 58 - 0 - 174 so when in 110 mode it gave 55 - 0 - 55 clearly not going to be a problem here as it's 230 volt only.

I would see little point in Honda linking the earth internal if it's fully floating why would the earth wire exist? As I said my first thing was to read the manual. As to overload that is a problem there is a warning lamp to show overload but you are unlikely to find a 7A MCB could fit a 7A fuse but if you then add a second generator this will not help so open to ideas but other than watching out for warning lamp little one can do.