TT tripping issues

[itchy]

System has had a new 16mm earth upgrade whilst the existing box was relocated. Ze (or Ra) has a new reading of 35ohms. (well within the parameters).

The issue the system is now having is, despite not having any circuits connected except one radial to one double socket to provide power whilst works are carried out on the home, as soon as power is drawn, the system trips out.

We've had the mcbs tested but the 63a rcds trip either at 35ms and 45ms (split board).

Didn't have time to have any more tests provided, but it stumped me...

Any ideas before we return to this on monday?!!

 

[telectrix]

faulty RCD. faulty wiring, faulty tools, one thing to note is if 110v transformers are being used on a 16A type MCB< that MCB will trip through surge. you need c or even a d type MCB.

 

[itchy]

The RCD's were fine prior to moving. No transformers were plugged in. The tail to the socket was initially on a 16a mcb, but the 63a rcd for that side of the board tripped. So the radio was replaced with a DIY'ers socket and see to check for polarity, all fine. Plugged in a battery charger, again tripped.
Removed from the 16a, and temporarily attached to a 32 mcb. Tripped again.
Started running tests, checked earth rod connection, re-tested Ra, still around 35.

fluke tester on 1xIdeltaN @ - & + = 35/45ms on either side of the split board. from my recollection tt's are allowed up to 200ms disconnection time?

Literally had the cable stripped that was used for the supply to the double socket, no damage anywhere, still, had it replaced and still had tripping on all circuits!

 

[telectrix]

sounds like a N/E reversal.

 

[itchy]

there were only 3 wires coming out of the board to one socket. All were correctly positioned.

if the socket was connected (to any mcb) it would only trip once it was under load.

Would the type of rcd on the system have any relevance? I don't think that was checked, but the main issue is that the board worked fine prior to the move. (same supply cable used as it was moved closer to the inlet), but new 16mm earth cable as the old 10mm was not long enough.

 

[Sav]

Hi,
Is it a dual board (2 x RCD'S) ? If yes, then could it be possible that the neutrals in the board are mixed up on the neutral bar in the consumer unit ?

Sav

 

[itchy]

hi thanks for the replies so far by the way.

It's a hager split board. 2x 63a rcd with an abundance of 16/20/32 mcbs on either side... but none connected to any other circuit.

The board was powering a couple of sockets prior to the move. and all the board connections were left in place as before.

All cables in the box were checked numerous times.... I can only think it's a fault to do with the new earth as hypothetically, it's the only part of the system that has changed!... but it seems to test fine!

 

[Iddy]

Hi mate

I am no expert in the field but if i remember correctly i once read some power tools do have a small amount of earth leakage on start up...

has anyone else heard of this>? or have i got my wires wrong Lol

 

[Richard Burns]

From what you describe of the fault I would say that somewhere there is a link between the neutral bar for the RCD that is tripping and another neutral bar.
If you have both RCDs tripping on use of power then there is a link across all neutral bars or between the RCD neutral bars; if there is only one RCD tripping then there is a link from that RCDs neutral bar to the main neutral.

This link could be either directly in the CU or via circuits with line in one side and neutral in the other.

Is this CU wired up in any way apart from the described sockets, i.e. are there any other circuits or are there just the unconnected breakers?

 

[itchy]

The rcds trip individually depending on which side of the board the feed is taken from.
The mcbs are empty, apart from the one feeding the one socket.
No other cables are present. Literally moved the box 8' and all lines were left as they were previously installed when working!
Wish I'd taken a photo of it before we left yesterday!

 

[itchy]

When I say other lines, I mean the links to the bars from the rcds etc.

 

[telectrix]

if all other things are as was and the only difference is the repositioning of the rod, then it's got to be something to do with the rod, though how eludes me. try moving the rod.

 

[Des 56]

The way I see it.
Concentrating on what changes to the earth or rod will sidetrack you with the problem

Back to basics,the Rcd will trip with an imbalance of Live-neutral,that is if the Rcd is operating correctly

I was going to list all the tests I would do, but you seem to have covered everything
I haven't, however, seen mention of the actual accessories being tested
I cant see anything about the earth cable or electrode being part the problem

 

[rich.250]

Sounds like a N/E fault somehow.
Ramp test Rcd, and insulation test all cables connected.

 

[RogertheBodger]

Is it a metal panel, could it be that in re-fixing it, you have drilled a neutral buried in the wall?