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Tris Zanker

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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?
 
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telectrix

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Mentor
Arms
Esteemed
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.
 
T

Tris Zanker

  • Thread Starter Thread Starter
  • #3
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.
 
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 ?
 
K

Knobhead

  • Thread Starter Thread Starter
  • #5
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.
 
T

Tris Zanker

  • Thread Starter Thread Starter
  • #6
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.
 
S

sedgy34

  • Thread Starter Thread Starter
  • #7
Check mains connections and at the meter you know what tails are like!! They can pop out has it recently had a new meter?
 
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?
 
T

Tris Zanker

  • Thread Starter Thread Starter
  • #9
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

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

Tris Zanker

  • Thread Starter Thread Starter
  • #11
i havn't a clue i wasn't there when he came.
 
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
 
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sedgy34

  • Thread Starter Thread Starter
  • #13
I would probably go through the neutrals again on the circuits if DNO are saying nowt to do with them
 
T

Tris Zanker

  • Thread Starter Thread Starter
  • #14
i'll try that, it just did me the fact that every appliance was making the RCD trip.
 

rich.250

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Arms
Whats your Ze reading?
I wouldn't personally believe the DNO.
They told me a install was fine when the whole estate had a very high resistance neutral lol
 
S

sedgy34

  • Thread Starter Thread Starter
  • #20
The op needs to issue a danger notice until the problem is rectified as I'm assuming there is no main earth on the installation.
 

telectrix

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be a better solution to bang a rod in . ( a proper one, before eng54 reads the thread.). probably got a decent Ze on the gas and water anyway.
 
G

Guest55

  • Thread Starter Thread Starter
  • #24
My moneys on a N-E fault on the installation
agreed.
the DNO arent gonna do jack until
A. youve catagorically proved the fault is on their side of the supply or
B. other nearby properties are reporting the same problem.
and intermittant dno neutral faults will show other symptoms than rcd tripping.
 
Last edited by a moderator:
P

Philpot

  • Thread Starter Thread Starter
  • #25
I have been reading this thread and i have been trying to remember a similar fault . It just came to me.

The rcd looks at the difference between the L and N. If you loose the neutral from the supply you then provide a false N from any bonding or earth spike or water pipe but it may not go through the RCD ....so no unbalance in the RCD. After all the earth and the neutral are really the same thing.
This is much the same as has already been stated but I am sure that I had a similar fault myself, a long time ago. This would explain why the RCD fails to trip on the button and everything else.

Isolate the CU
Disconnect the PME earth wire from the Earth block. ( stop and earth going back to the supply)
Test the voltage at the the meter or on the In connection of the CU isolator.
You need to be sure that there really in a neutral coming into the house.

I hope this helps and doesn't just confuse the situation even more

Phil
 

rich.250

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Arms
Incoming voltage??
Had a couple strange ones like this.
Reversed polarity, resulting in exposed parts being live!! Due to PME n-e connection.
And lost neutral, this would stop the Rcd operating as the Rcd does not have the correct voltage to operate.
Although I don't think this is the whole story for this one.
If you have done all your insulation tests this should rule out it being a internal fault, unless it's an appliance.
 
P

Philpot

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  • #28
As long as the wager isn't tooooo large.
Phil
 

telectrix

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i'll put a tenner on it being a fault outside the customer's installation.
 

hasel5

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Arms
Crumbs cant afford that sort of money thats 2 hrs worth of labour in the present climate according to agencies
 
S

sedgy34

  • Thread Starter Thread Starter
  • #33
Well the op said he was called out to a fault
so it has been working
hes changed the main switch
DNO saying nowt to do with them
no new meter
hes done ir on circuits and all >20Meg
Im thinking it's an appliance that's started to Cause this problem it's the freezer with the lead pipe in the kitchen lol
 

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