Discuss How to test/certify a small 230V generator installation? in the Electrical Forum area at ElectriciansForums.net

a-z electrics

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Hi all,
Got a client with a small barn workshop and caravan powered by a portable 230V 6kW petrol generator. (Loncin 8000D-A) . The original 32A commando lead had a domestic double skt on the end, and theres another lead with a commando socket for the caravan. Theres only one 230v o/p.

He asked me to fit 2 double skts and 2 lights so he can work in the barn, via a modern fusebox. There's also a water borehole pump.
Its not a commercial venture but temporary whilst he wants to eventually build a permanent dwelling on the site, also powered by a larger generator. Give him credit, he wants it all done proper with test certificate..
Wired that up for him with an rcd main switch db, 20A mcb for the 2 d/skts and a 6A for lights but then realised it doesnt use terra firma as an earth so cant do Zs and rcd tests, altho the rcd test button works.. Looked up the on site guide and realised it must be a floating earth type of jenny.
All dead testing is ok ..
So whats the situation with the live testing and certificate then for this temp set up?
Thanks in advance..
 

bill01803

Regular EF Member
Messages
145
Location
Devon
You need to install an earth stake and at a point before the dis board you need to link n and e together and label it so. You also need to make sure the client knows this and that they must consult an electrician in the event of a change of generator.
 
OP
a-z electrics

a-z electrics

Regular EF Member
Messages
387
Location
Exeter area
Oh ok, So make it into a TNS system then.. that should be no trouble but can I do the link in the DB? After all, thats the MET.
Everything will be labelled.
 
OP
a-z electrics

a-z electrics

Regular EF Member
Messages
387
Location
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The other thing I should mention is that there was no blue wire on the output lead, it had 2 browns. Is that ok? should i tag one Blue?
 

Rob

Control System Engineer
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How do you know it's a floating earth type of genny?
 
OP
a-z electrics

a-z electrics

Regular EF Member
Messages
387
Location
Exeter area
Yes, the one connected to the neutral pin.
You can link it in the dis board and label it, presumably you will have to install a socket for the caravan off your db.
ok.. well I could but the caravan lead can be substituted for the DB lead when required.
 

Rob

Control System Engineer
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Well I've not seen it, so I couldn't tell you if it is or isnt.

I can tell you you shouldn't be linking N and E together without knowing for sure.
 
OP
a-z electrics

a-z electrics

Regular EF Member
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Location
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Well I've not seen it, so I couldn't tell you if it is or isnt.

I can tell you you shouldn't be linking N and E together without knowing for sure.
i see.. well the potential between the earth pin and each of the two brown wires measured about 90V, but an earth stake was also connected to the earth met at the db.. has this complicated things?
Whats the best test to make sure what type it is then? As you can see, I've not had any dealings with this type of scenario b4, hence my post. Thanks for yr help..
 
OP
a-z electrics

a-z electrics

Regular EF Member
Messages
387
Location
Exeter area
Caravan should not be used with floating earth generator, that is why you need to install a socket for it
Oh ok, thats what was happening before. Unfortunately I havent access to the gen manual but Im trying to get one online..
So it seems I may have assumed too much, see my previous reply to Rob.. so i need to establish exactly the type of earthing first then, what test to do?
 

Lucien Nunes

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As you are getting a significant voltage between each live conductor and earth, it is evidently floating at the moment, i.e. it is an IT supply. Whether it was supposed to be, by design, is another matter.

When you earth one side, making it the neutral, it becomes a TN system. Provided that there are no combined neutral-earth conductors downstream of the N-E link (there shouldn't be) it will be TN-S. It would only be TN-C if you earthed the neutral at one point e.g. on the genny, then ran a single CNE conductor to another point, where you split the earth and neutrals to the installation.
 
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OP
a-z electrics

a-z electrics

Regular EF Member
Messages
387
Location
Exeter area
Well that is very helpful Lucien, thank you.. so it IS a TNS then if I make the link in the DB before the main switch, as suggested.

I've managed to find the manual online.. its a bit pidgin english but
it suggests (not instructs!) that the machine is grounded to an earth stake at the terminal provided, which I must admit I didn't see when I was there but I now know where to look.
 

Lucien Nunes

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You might find that the terminal is connected only to the casing, and not to either live conductor, in which case it will want to be connected to your earthing system but you will still have to make the N-E link elsewhere. Check the circuit diagram and inspect the machine to discover whether provision has been made for linking one pole or the other to earth, and that the centre-tap, if there is one, is not linked in any way.
 
OP
a-z electrics

a-z electrics

Regular EF Member
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Location
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Yes those were my thoughts too Lucien.
Beginning to get my head around this.. there doesn't appear to be any other instruction or facility on the genny to make any other link, just the connection to earth stake.
Many thanks for your help..
 

Lucien Nunes

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FWIW, many people incorrectly assume that connecting an earth rod to a generator-powered installation makes it a TT setup. For anyone who is confused, the rod of a TT installation completes a circuit from the MET back to the earth electrode at the source of supply (substation) via the general mass of earth rather than via a cable. When connecting a generator to a rod, it IS the earth electrode at the source of supply. You would not then generally bang in a second, independent rod to earth the installation, you would run a cable to the generator, making it TN-S.
 

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