Fault

[Tris Zanker]

Been called to a fault today customer saying RCD tripping when under load.

I go rcd holds in till he plugs something in that say uses more that 50w, I try and ramp test rcd - no trip, 5x no trip, 1x no trip, rcd test bottom - no trip. so I think it’s a faulty rcd, i put a new rcd in and test again 5x no trip, 1x no trip, rcd test bottom - no trip same thing again as soon as he plugs something with some load in it trips the new rcd out.

I look in to it a bit deeper IR on all circuits >20M.

I then disconnect the main earth from the PME, everything is then fine, RCD trips correctly and stays on under load, I've now decide it's done to the DNO so out comes western power they that one look and say nope it’s on your side it must be a faulty appliance.

In the mean time I’ve replaced the consumer units Main switch with an RCD due to the property having unstable earth.

Any ideas as to where i can go from here as it’s something I’ve never came across before?

 

[telectrix]

i suspect a fault on the DNO supply or a fault in a neighbours installation. will await other input as this is something i've not seen before.

 

[Tris Zanker]

The DNO have been to the propety and have passed it back to me, I forgot to mention that yesterday we had heavy thunder and lightning storms all day and scene then it’s been doing that.

 

[malcolmsanford]

Did you try the ramp test via the BS 1363 lead? If so try doing it at the CU.

Did you do a normal RCD test to see if it trips?

Why did you disconnect the main earth ? What happens if you disconnect the earth to just the socket circuit?

How many RCDs have you on this board now? You have said you replaced the main DP switch with an RCD ............is this holding? Is it a 30mA ?

 

[Knobhead]

Sounds like a bad neutral on the DNO side.
Try shorting the RCD and disconect the PME earth. Test for voltage rise between neutral and earth with some load applied.

 

[Tris Zanker]

i did a ramp test at the cu with all circuits isolated, i did a full range of rcd test and none tripped, i disconnected the main earth to do an earth loop test, it is a 16th ed board but i have put a temp rcd in place of the main switch, its a 30mA rcd its holding in fine and test fine until the supplys earth is reconnected once thats reconnected as soon as load is pulled throught it, its trips out again.

 

[sedgy34]

Check mains connections and at the meter you know what tails are like!! They can pop out has it recently had a new meter?

 

[malcolmsanford]

Then as Tel and Tony have just suggested it looks like a fault on Neutral be it outside on the DNO joint or internal of the installation. All connections at the meter, CU are good I assume?

 

[Tris Zanker]

no the meter and fuse all looked rather old and there both sealed, western power have now been to the propety and just said its somthing wrong with the consumer unit or maybe a faulty washer or fridge.

 

[telectrix]

but did western power send out an engineer or a pillock? i.e. did he have T shirt and snickers keks, or a suit?

 

[Tris Zanker]

i havn't a clue i wasn't there when he came.

 

[malcolmsanford]

If your feeling competent then Tony as given you the test to do. You will have to as he said disconnect the main earth as you could be exporting your fault to another installation, bypass the RCD and unplug and disconnect everything, and that is everything, and then start to plug things back in one at a time...........

But for goodness sake make sure you don't let anyone get to use the installation. Test as you go along and if you get that voltage on E-N you will have found the appliance........................start with the fridge

 

[sedgy34]

I would probably go through the neutrals again on the circuits if DNO are saying nowt to do with them

 

[Tris Zanker]

i'll try that, it just did me the fact that every appliance was making the RCD trip.

 

[sedgy34]

i'll try that, it just did me the fact that every appliance was making the RCD trip.

Dont forget to come back and update What the problem was!