RCD Problem - HELP NEEDED!

[davesparks]

With the Quals you have + your test equipment. You should figure this out in no time.

This, plus his opening line, speaks volumes and does rather invite a certain assumption to be made about him.

 

[luke]

First off I dont claim to be great with electrics!

I have installed a new consumer unit today, from the meter it has some 16mm T&E tails at considerable length - maybe 10 meters where I have put a KMF switch with an 80amp fuse.

The board is a 2 way split, when i open the main RCD switch at 100amp to the CU that sits open, when I open the 2 x 63amp RCD's one snaps back in a fault condition whilst under no load at all. The other sits comfortable operating some lights.

Assumed it must be a faulty RCD i thought i would swap them, same problem.

I cant work out what is going on here and would appreciate some help, has anyone seen this before please?

Many thanks in advance.

Harry

Can you take a picture of the set up and post it on here?

 

[Paul.M]

This, plus his opening line, speaks volumes and does rather invite a certain assumption to be made about him.

Erm.... Let him figure it out on here first before going too far into the electrical abyss.

We have given him a chance. Lets see if he takes it?

 

[arry01]

Hi Paul
I will give it another check through tomorrow and update you but to my knowledge there is no borrowed neutral, the CU only has one lighting circuit and one ring main. The fault occurs with the final circuits disconnected.

Luke I will take a photograph!

Thanks

Harry

 

[Marvo]

Hi Paul
.....The fault occurs with the final circuits disconnected.

The RCD is sensitive to faults on both the live and neutral legs of the circuits. When you say disconnected were the neutrals also removed?

 

[davesparks]

Hi Paul
I will give it another check through tomorrow and update you but to my knowledge there is no borrowed neutral, the CU only has one lighting circuit and one ring main. The fault occurs with the final circuits disconnected.

Luke I will take a photograph!

Thanks

Harry

What earthing system?

 

[arry01]

Hi Marvo
Yes neutrals removed and the earth's. Earthing arrangement is TNCS.

Cheers

Harry

 

[davesparks]

So you have disconnected all circuits from the board and the RCD still trips?

 

[arry01]

Yes only one side though, and i swapped the rcd's and the other one did the same. The only common theme is its always the first RCD position. Im going to rip the unit down tomorrow and have a proper look at it.

Harry

 

[davesparks]

So not all of the circuits in the board then? Only the ones on one side?

The problem is not in the CU, there is a fault in the installation. This is a very common fault, so much so we get a topic started on here every month or so about it which a quick search might reveal (hint hint)

You should be able to find the fault pretty quickly with a megger and following the basic fault finding procedure of eliminating halves of the circuit.

 

[Paul.M]

Harry, sorry I'm closing this thread.

#1 Look at the terminations and the Polarity of your main incoming tails.

#2 Internal wiring of the CU's Neutral tails. Make sure they are correct.

#3 Use test equipment to find any faults before energizing a fuse board!

#4 Thread closed. Start a new thread when you can describe the items of electrical protection you are connecting to.


Sorry but this Q&A thread is at a finish until more information is provided. We are Part P-ing in the wind.