downstairs socket RCD keeps tripping

[Zehroni]

Dear All,
After successful installation of Volex, 10ways dual RCD C/U, I have problem with downstairs socket. They are four in total and fed by 32A MCB which is the only one connected to 80A RCCB in the consumer unit. The rest of the house is connected to the other RCD which is working fine. It worked for a day then the RCD kept tripping despite the fact the all socket are switched off. I open all the socket and the connection inside every and each of them very good, no lose wire nothing. Three of the sockets are connected in a ring and the fourth one is connected to the third radial. Can some one help please?

 

[sparkyspike]

When you installed the CU, did you do/someone else do, a continuity test and insulation resistance test on the ring before turning on? And an earth loop impedance test? And a 15mA RCD test? And a 30mA RCD test?

You will have a wiring fault or an RCD fault. Both will be picked up by the above tests which MUST be done when changing a CU.

 

[Spark123]

Sounds like there is a fault on the cabling which may have been there a long time but as there didn't used to be an RCD on it the fault wansn't aparrent. To fault find needs an insulation resistance tester and the knowledge to use it. Volex - urghhh!

 

[Zehroni]

guys,
Many thanks for the advice, can you tell me how much roughly it cost to call an electrician out to carry out those. Do you recommend a decent one in Swindon, I rang two so far and both let me down.

 

[bongos]

guys,
Many thanks for the advice, can you tell me how much roughly it cost to call an electrician out to carry out those. Do you recommend a decent one in Swindon, I rang two so far and both let me down.

Unfortunately faults like this are not always easy to find. If you're lucky then it might only be an hours work but if your not...how long is a piece of string.

This is why it is so important to do a PIR on your existing installation before changing a CU - so you know what state your wiring is actually in. TBH it's probably a good idea to have a spark come out anyway so they can cast an eye over your new CU and make sure nothing is amiss there either.

 

[AndyPRK]

insulation resistance test on the ring before turning on?

And an earth loop impedance test?

Out of interest.

what voltage do you use to test for insulation, and what ohm reading are you trying to exceed ?

What is the max impedance allowed ?

 

[ban-all-sheds]

what voltage do you use to test for insulation, and what ohm reading are you trying to exceed ?

LV circuits are tested at 500v - resistance should be at least 1MΩ, but anything less than 2MΩ should be investigated. In reality new circuits should be returning several '00MΩ, or even GΩ...

What is the max impedance allowed ?

That depends on the type and rating of the protective device, and possibly the type of circuit: //www.diynot.com/forums/viewtopic.php?p=76467#76467

http://www.amazon.co.uk/exec/obidos/ASIN/0863418449 or http://www.theiet.org/publishing/books/wir-reg/17th-edition.cfm

http://www.amazon.co.uk/exec/obidos/ASIN/0863418570 or http://www.theiet.org/publishing/books/wir-reg/inspection-testing-5th-edition.cfm

 

[AndyPRK]

thanks very much for the reply