Electrians thoughts

[normspanners]

Hi Guys
Went out to look at a job today, a 3ph generator 15-20 kva, running some submersible pumps and the two rcds I think one was 100ma and the other was 30ma on the genny were tripping, the genny is 3ph +1ph and earth and is earth grounded by an earthing rod, the output is 5pin but only 4 core cable is used which is connected to a panel with three 3ph mcb breakers then off to three seperate pump control panels, I isolated it to one pump, well the control panel actually, I disconnected the pumps and float switches but the panel was still tripping the rcd, when I looked closer the incoming earth was connected to the neutral connection on the 4p isolator!!, but not the boxes earth lug, in the control panel there is some 240 single phase control gear, timers etc, the guy that designed the panels said it did not matter as earth and neutral is bonded. I said yes but not after the rcd surely.
The thing is this has worked for months like this. I tried to explain as the 240 1ph unit operated it was 'liveing' up the boxes earth by using the earth as a neutral return to the genny.
The thing is they have just put a new main supply for the job to save having the genny, but only 3ph +earth, no neutral. I said to the boss I was disconnecting the genny for safety reasons. I said that the panels would need at least a 415 -240 tranny but then the neutral would be 'floating', could this cause problems with rcd's etc or would it be better to have a 415 to 240 but centre tap it and ground the centre ?? to give a more reliable neutral?

 

[madkayaker]

the earth being connected to your neutral is what is tripping RCD. if there is single phase kit it either needs a neutral or a transformer. PEN conductors are specifically outlawed in all but special occasions

 

[normspanners]

Thanks yes thats exactly my thoughts, but it has been working for months like that how i am not sure do you think a floating neutral would cause problems with the rcds when the new mains are commisioned?. Or would it be better with a centre tapped tranny?

 

[madkayaker]

it wants a 400V to 230V transformer fitting when its on proper mains. TBH i don't know how its not tripping all the time off the generator. only think i can think of is the earth rod is earthing the case of generator and not the floating Neutral. there might be enough difference between earth and the PEN

 

[Spark plug]

I don't understand why the RCD's haven't been tripping. But as MK says it must have either a new supply with a neutral or probably the simpler solution a 400-230v transformer fitting.

The PEN conductor must not be retained, it's just not allowed.

 

[normspanners]

Thanks Guys the problem I have is, now in my mind I have a total lack of confidence in the panel designer / modifier as originally these panels were just basically switches to switch on the 3ph pumps but have been modded with timers etc to cut down on hysteresis switching of the pumps, but to say it does not matter where the earth is connected because neutral and earth are 'bonded' baffles me.
I need to advise the boss man that his panel man is full of----.

 

[Spark plug]

I would tell him the way it is because you don't want to put your name on somebody els's substandard or dangerous work.

 

[wheresmejumper]

Hi Guys
Went out to look at a job today, a 3ph generator 15-20 kva, running some submersible pumps and the two rcds I think one was 100ma and the other was 30ma on the genny were tripping, the genny is 3ph +1ph and earth and is earth grounded by an earthing rod, the output is 5pin but only 4 core cable is used which is connected to a panel with three 3ph mcb breakers then off to three seperate pump control panels, I isolated it to one pump, well the control panel actually, I disconnected the pumps and float switches but the panel was still tripping the rcd, when I looked closer the incoming earth was connected to the neutral connection on the 4p isolator!!, but not the boxes earth lug, in the control panel there is some 240 single phase control gear, timers etc, the guy that designed the panels said it did not matter as earth and neutral is bonded. I said yes but not after the rcd surely.
The thing is this has worked for months like this. I tried to explain as the 240 1ph unit operated it was 'liveing' up the boxes earth by using the earth as a neutral return to the genny.
The thing is they have just put a new main supply for the job to save having the genny, but only 3ph +earth, no neutral. I said to the boss I was disconnecting the genny for safety reasons. I said that the panels would need at least a 415 -240 tranny but then the neutral would be 'floating', could this cause problems with rcd's etc or would it be better to have a 415 to 240 but centre tap it and ground the centre ?? to give a more reliable neutral?

you know more about electrics than a fair percentage of sparkies ive come across

change that username to normpliers

 

[normspanners]

Went today to look at the new supply that has been put in by electricians, they have now changed it to 25mm 3ph-N-E, with about 3 radials, great no probs for single phase gear now but they have used 63 amp 3pole switch fused breaker CLANG type with 63 A fuses with what looks like 2.5 maybe 4 mm sy (didnt strip socket) into a 32A 5 pin socket!! on each box and no rcd's, the cable to be plugged in is a 1.5 sy.

 

[Robotstar5]

Have you pulled the carriers and checked the fuse rating?, they should be considerable lower rating than 63A to protect 2.5 or 4mm² cable.

 

[Wallace]

Any chance one of the submersible pumps has water in the windings causing the trips to go?

 

[normspanners]

Thanks Guys

Have you pulled the carriers and checked the fuse rating?, they should be considerable lower rating than 63A to protect 2.5 or 4mm² cable.

Exactly my thoughts but yes i did they are 63A's but there is no need to go to 63A in the first place
I understand the incoming 25mm coz its along run to the first box then 3 other radials off it but there is no need for 63A.

Any chance one of the submersible pumps has water in the windings causing the trips to go?

Dont think so coz---
From first post

I disconnected the pumps and float switches but the panel was still tripping the rcd, when I looked closer the incoming earth was connected to the neutral connection on the 4p isolator!!, but not the boxes earth lug,

 

[Wallace]

Can I borrow your glasses Norm?

 

[normspanners]

yes i just need to find them first been lookin but cant see em