Petrol Generators and Earthing

That's what I meant.  Maybe I didn't word it clearly enough.

gkenyon said:

All of this is covered in BS 7430, quite adequately. Other guidance also covers it.

Unfortunately I don't have access to a copy and at £289 don't think I will be buying one any time soon.

sparkiemike said:

1. I can't see what function any earthing would provide as the N and E are not connected, if they were connected it would result in catastrophic failure of the machine. Is this correct?

If N and E are connected, ...

N and E are not connected on this genset. My preference would be to have a NE link and install an earth electrode making it a TNS system. Then connect the generator by CEE plug and socket with change-over switch.

... then imagine an accident in which the line conductor is accidentally "spiked" to the ground. What happens then, is "exposed-conductive-parts" are immediately at full line voltage, which is obviously very dangerous. It's imperative if you intend to operate this as a floating system, for the generator to have an RCD immediately at its output terminals, just in case this happens - at least the poor person touching the "exposed-conductive-parts" stands a chance. This is illustrated in A722 of BS 7671.

sparkiemike said:

2. Secondly I am correct in thinking that this generator is not suitable for connecting to a house, and he would be better off getting a new machine with correct type earthing arrangement, or are there alternative ways of connecting this generator safely?

This kind of generator is definitely suitable for connecting to a house, either stand-alone, or as a switched-alternative of supply.

BUT

(a) If stand-alone (no grid supply), a consumer's earth electrode is required to make it a proper TN-S system - either connected to MET, or directly to the generator frame and neutral; or

(b) If a switched-alternative to the grid supply, the installation must comply with Regulation 21 of ESQCR. All live conductors must be disconnected from the Grid when the generator is in operation, and in accordance with Regulation 551.4.3.2.1, a consumer's earth electrode is required. The switching arrangement should also consider that both BS 7671 and ESQCR prohibit two N-E connections at the same time, so this generator must only be connected by a change-over switch.

But you would still need a NE link on the generator for option (b)?

All of this is covered in BS 7430, quite adequately. Other guidance also covers it.

sparkiemike said:

1. I can't see what function any earthing would provide as the N and E are not connected, if they were connected it would result in catastrophic failure of the machine. Is this correct?

If N and E are connected, then imagine an accident in which the line conductor is accidentally "spiked" to the ground. What happens then, is "exposed-conductive-parts" are immediately at full line voltage, which is obviously very dangerous. It's imperative if you intend to operate this as a floating system, for the generator to have an RCD immediately at its output terminals, just in case this happens - at least the poor person touching the "exposed-conductive-parts" stands a chance. This is illustrated in A722 of BS 7671.

sparkiemike said:

2. Secondly I am correct in thinking that this generator is not suitable for connecting to a house, and he would be better off getting a new machine with correct type earthing arrangement, or are there alternative ways of connecting this generator safely?

This kind of generator is definitely suitable for connecting to a house, either stand-alone, or as a switched-alternative of supply.

BUT

(a) If stand-alone (no grid supply), a consumer's earth electrode is required to make it a proper TN-S system - either connected to MET, or directly to the generator frame and neutral; or

(b) If a switched-alternative to the grid supply, the installation must comply with Regulation 21 of ESQCR. All live conductors must be disconnected from the Grid when the generator is in operation, and in accordance with Regulation 551.4.3.2.1, a consumer's earth electrode is required. The switching arrangement should also consider that both BS 7671 and ESQCR prohibit two N-E connections at the same time, so this generator must only be connected by a change-over switch.

David Stone said:

It is currently a floating supply that will not operate RCDs or MCBs with Earth faults. It is an IT supply without Earth fault monitoring.

Well, that's not quite true. A floating system will deal with "faults to the cpc of the system" but unless there's fortuitous earthing, not faults to Earth, and additional protection as we know it for earthed systems won't be guaranteed to operate.

I know that it doesn't help, but customer seems to have bought something which is totally unsuitable for it's intended purpose.

"Fuel should be emptied before storage for 30 days or longer." As I said!

96 dB - you wouldn't want that under your kitchen window for very long.

Perhaps in this situation the best response is to walk away?

Hmm not the most useful documentation is it. I'd try grounding the neutral via a modest resistance - in the old days I;d have said a light bulb, now in the world of the LED  it probably has to be a small appliance like a fan or a heater, to see if the neutral shifts to 0V and the live goes up as you'd expect.

M

It might be worth having a careful look at the way the changeover between 115 & 230 is done on the Gen. I've seen these windings tapped in such a way that its not possible to modify the set such the NE bond is at one end of the winding in 230V mode but yet correctly at the 55-0-55 tap when in 110V mode - I've had to completely disable the 110V option to make this work.

As others have said, without connecting the 'earth' to one end of the winding, there will be no path for an earth fault current to take & hence an RCD or MCB will not operate in the event of such a fault. Indeed with such a small genset, its doubtful it will be able to deliver enough current to operate anything bigger than about a 10A MCB in the instantaneous region - more likely that either the prime mover will stall or the voltage will collapse.

mapj1 said:

Do you have a web link to the genset datasheet?

Data sheet 

User Manual 

mapj1 said:

Normally you can earth the neutral of such a genset (and should if you want to use it to run an installation where the ADS relies on an NE bond) , but you should perhaps try to do so via a limiting resistance first to check that nothing untoward happens.

OK

Do you have a web link to the genset datasheet?

This is a link to the Hyundai HY10000LEK-2 and there are links to the datasheet and user manual on the page

Note that without an interconnection between windings and CPC, then RCDs will not work, and single pole MCBs and fuses will not be in the right pole, or more correctly without a clear neutral, there is no clear live either.

Agreed

Be aware that you will need to provide an NE bond and an electrode, as during an external mains fault you cannot rely on the mains for earthing - the cable be be disconnected in the street for example, and then be aware that in areas cvered by the ecsqr, that NE bond has to be on the other side of a double pole switch to the one from the DNO.

Agreed, the cables are overhead and it is a TNCS supply, if the cables are brought down by tree then no mains earthing. Thanks for the reminder about the position of the NE link

broadgage said:

I agree that petrol seems an unlikely and maybe unwise choice of fuel for an 8 kw generator. Only 30 litres of petrol may lawfully be stored, and 30 litres wont last very long in an 8 kw generator.

Not my choice of generator, already purchased and currently connected via widow maker cable .

Returning to earthing, I would proceed as follows. Provide at the changeover switch a fixed 32 amp ceeform plug via which the generator may be connected. Bond together all the following, the blue and the green/yellow wires from the generator, the blue and the green/yellow wires into the changeover switch, a green/yellow wire to a local earth rod, and a green/yellow wire to the MET of the existing electrical installation.

Provide a standard 32 amp ceeform extension lead, with a plug for the generator end and a trailing socket for the connection to the changeover switch.

Presuming that the stated capacity of the generator is 8 kw short term or intermittent, with the long term capacity being 7 kw or less, then  32 amp connectors will be fine. If however 8 kw can be supplied CONTINUALLY then 63 amp connectors should be used.

This will ensure that neutral of the generator supply is connected to the general mass of earth and to the CPC. This then resemble a public supply with an earthed neutral.

I would advise against modifying the internal connections of the generator as that renders it non standard and will void the warranty.

Thank you, all of the above makes sense and is my design intent, I just don't want to bond N and PE if it will damage the genset