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Topic Title: Earthing a generator
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Created On: 16 July 2017 10:01 PM
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 16 July 2017 10:01 PM
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Lillpete

Posts: 129
Joined: 04 August 2011

I am in the process of wiring out a barn which in the future will be connected to the mains however for the next few months/maybe a year it will be run from a 3ph generator.

I've never worked with generators before so am not aware of how they should be treated. should I be earthing to the body of the generator or the mass of earth?

Is there anything else I should be wary of?

It is a grain store with no livestock on site.

Thanks

Peter
 16 July 2017 11:27 PM
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broadgage

Posts: 2437
Joined: 07 August 2007

Presuming that this is a fair size generator, not portable, then I would proceed as follows.

At the generator, connect together all of the following.
The frame of the machine, a local earth rod, any nearby building steel or other services, the star point of the alternator windings, the outgoing neutral, and the outgoing CPC.

A four core plus earth cable is then required from the generator to the origin of the installation.(future location of DNO cut out)
At the origin bond in line with normal practice to any gas, water or oil pipes or structural steelwork.
Protect subcircuits against over current and earth leakage in line with normal practice.

If possible, try to obtain a mains supply as well, even if of very limited capacity indeed.
A few dozen 5 watt LED lamps fed from a 6 amp circuit could be most useful when the generator is shut down or stops unexpectedly.
 17 July 2017 11:28 AM
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AJJewsbury

Posts: 16017
Joined: 13 August 2003

And if the generator doesn't have enough oomph to take out any overcurrent devices used for protection against electric shock within the required times, then an RCD as close as you can after the N-PE link.
- Andy.
 17 July 2017 03:06 PM
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mapj1

Posts: 9581
Joined: 22 July 2004

It is in effect to be regarded as a TN-S source, with an NE bond at the star point, normally inside or maybe a removable link in the output terminal box, but usually inside, and all wiring from your board back to it is 5 core, or 3 core for single phase, ending either red 5 pin plug or ring lugs and reach for the 19mm socket set depending where you are on the KVA scale.. . you will need a sensible electrode or two to terra-fima, and I'd say have an RCD anyway, unless you can prove with total confidence you really do not ever need one. On larger rigs (100kVA to MW ) this protection is more often built into the genset as discrete pick up coils and contactor in the form of an earth fault relay.
Even set to be the humble 100mA with 0.1 sec delay will stop many things that might otherwise sizzle and smoulder, if you don't want 30mA instant, so you get some discrimination between load side and distribution side faults.
Non maintained light fittings without the stickers fitted are a handy thing to refuel by ..
Note that larger rigs can have external fuel tanks, not commonly done for anything towable or smaller, but certainly can be done.

-------------------------
regards Mike
 17 July 2017 07:06 PM
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Zs

Posts: 3829
Joined: 20 July 2006

Lillpete, I drew one of these out for someone on here a while back. Took ages and he never said thank you but that's by the bye. It is an Island system.

Would you like a copy of it? You will need to check that it is the right configuration. I got it from CIBSE and put it in to plain English.

Text me your email address and I can do the scanning soon because I am a lady of leisure for a couple of weeks whilst between jobs and working on the house.

Actually, pop by for tea and I'll do you a copy....floorboards are up here but the welcome is warm and the kettle still works.

Zs
 18 July 2017 06:50 AM
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Lillpete

Posts: 129
Joined: 04 August 2011

A lot of information there, thanks very much for the help.

And I think everyone agrees which makes life simpler

Thanks Zs I'll text you my address x
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