3 phase generator earthing problem

[Iainmc123]

I have been asked to rigged up a temporary generator for a hotel who have been cut off by the supply autorites for an unpaid bill the generator may have to run for a couple of weeks. Its a 150kva 3 phase generator I connected everything up put an earth rod in the ground and connected to generator frame. when i connect the earth from the generator to the hotels main switch it trips the generators 3 phase rcd switch. I think it could this be a neutral-earth fault within the hotel. when i have the earth from the generator disconnected at the hotels main switch i still get a reasonable EFLI probably through parrell paths as the supply authorities earth and neutral are both disconnected. Is there any danger if i put another seperate earth rod in for the hotels side and leave the generators earth disconnected(the frame still connected to its own earth rod). I dont install generators very often so is there any other reason apart from neutral-earth fault within the hotel that the generator main switch would trip when the earth is connected? any advice would be appreciated

Iain

 

[davelerave]

i'm on the wrong track

 

[Iainmc123]

the dno was tn s and the genny is tns or might be tncs its 150kva

 

[davelerave]

sorry it's a bit late for me- i thought for a minute the rcd was an incomer on hotel

not too familiar -assume the genny is tn-s also

not quite sure why there's rcd on it- is it 300ma?

 

[Dunc]

Where abouts in the country are you? Had an issue before where the supply was TNCS in to the building so the neutral to earth connection at the PME took the trip out. Disconnected main neutral at DB and problem solved. Hope the hotel can afford your bill even if they can't afford the electricity bill!

 

[davelerave]

yes

i'd think of an excuse to avoid this job

 

[Knobhead]

Is the neutral connected to the frame of the generator? If not you need to earth it making it TN-S and stop any “floating” neutral problems. Take the earth direct to the neutral and then the frame. Make sure the DNO earth is disconnected.
I would have driven more than one earth spike and linked them.

 

[davelerave]

hardly seems surprising if the dno was tn-s with no rcd incomer on hotel

and now the supply is front-loaded with an rcd via genny

 

[Iainmc123]

Is the neutral connected to the frame of the generator? If not you need to earth it making it TN-S and stop any “floating” neutral problems. Take the earth direct to the neutral and then the frame. Make sure the DNO earth is disconnected.
I would have driven more than one earth spike and linked them.

So if the neutral is not connected to the frame i take the earth from the earth spike to the neutral then the frame. Do you think this would be causing the generator main switch to trip when the generators earth is connected to the hotels main switch. The dno earth is disconnected.

 

[Knobhead]

I having horrible thoughts here, do you have the connection diagram for the generator? It should show where to link neutral/earth. Does the generator shut down when the RCD trips? Depending where the neutral/earth link is the RCD can protect either the load or the generator. If it’s to protect the generator it’s what’s call “restricted earth fault protection” and it shuts the engine down.

You’ve got to get the information!

 

[harvey26]

i have encountered the same same problem today with a 3 phase geny. The 200amp 100mA trip keeps on trippin under load conditions. The geny has connections of L1 L2 L3 N E. No other earths in the premises are connected and all cables which are used from geny were tested and are clear of fault. Any help would be appreciated

 

[johnboy6083]

Are you switching everything on at once? Try turning everything off. Start genny, and switch one circuit at a time.

 

[harvey26]

the geny is being used in a unused factory which has had all power swithched off due to vandals breakin in and stealing copper. I am tryin to use the geny to run a security hut and also feed an external lighting board for car park lights etc. i dont no if the problem may be 2 different earthin systems bein combined somehow, The external lightin board is enclosed in one of the large switch room panels and im confused as to why it is tripping as all is on the circut is this lightin board and nothin else. Could it be a different earthin arrangement from the panel bein earthed from a different system from the geny although no other power is on in the factory only that bein supplied by the genertator

 

[Knobhead]

i have encountered the same same problem today with a 3 phase geny. The 200amp 100mA trip keeps on trippin under load conditions. The geny has connections of L1 L2 L3 N E. No other earths in the premises are connected and all cables which are used from geny were tested and are clear of fault. Any help would be appreciated

How is the generator earthed?