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?

 

[rich.250]

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

 

[hasel5]

My moneys on a N-E fault on the installation

 

[telectrix]

mine's on the supply.

 

[hasel5]

could be interesting if we get a reply

 

[sedgy34]

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]

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.

 

[bob22]

Hi, is it a new board, if so, are the neutrals in the correct order in the cu?

 

[hasel5]

Good point bob LOl

 

[Guest55]

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.

 

[Philpot]

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

 

[hasel5]

Think we need to set up a wager on this lol

 

[rich.250]

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.

 

[Philpot]

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

 

[rich.250]

Sorry not correct voltage, Neutral lol

 

[hasel5]

In the present climate i wont be half a shandy an a bowl of nuts is about my limit