RCD trip help

[sirocco]

Just been called out investigate RCD tripping on downstairs ring at my parents it just went in the early hours with no history. Have unplugged all appliances from the 10 sockets on this ring and switched all sockets off. There are no other appliances fed from this ring other than those plugged in via sockets. There are 3 other circuits protected by the same RCD in the CU ie Shower, Cooker and upstairs ring, these are all functioning normally and don't trip the RCD. I have substituted the downstairs ring MCB but the circuit still trips the RCD immediately when the MCB is switched on with nothing plugged into the sockets. My next step is to disconnect the ring, split the dead ring at the midpoint and test each half, but before doing this I removed the 2 CPCs for the ring at the CU from the earth bar and the circuit now stays on and doesn't trip. Before I plough on , disconnect the phase and neutrals and do dead circuit testing is there anyway that I can identify why the disconnection of the CPCs allows the ring to operate? Graham

 

[monkeyelectric]

Ir test

 

[babylonsBurning]

It indicates that you have a live to earth fault. Insulation resistance test would show this. Then split the ring half way, test again and continue this procedure.

 

[ALD]

Double check that there isnt a faulty imersion wired on the ring. Ive had this before.

 

[guest119]

Looks like an all insulated ring with no parallel paths and earth from the cpcs only.
Then leakage through maybe dampness. Underfloor joint box, painters been using a steam stripper and water running into the sockets, dampness by other route to sockets on external wall etc etc.
As already stated, IR wins.

Boydy

 

[GLENNSPARK]

Just been called out investigate RCD tripping on downstairs ring at my parents it just went in the early hours with no history. Have unplugged all appliances from the 10 sockets on this ring and switched all sockets off. There are no other appliances fed from this ring other than those plugged in via sockets. There are 3 other circuits protected by the same RCD in the CU ie Shower, Cooker and upstairs ring, these are all functioning normally and don't trip the RCD. I have substituted the downstairs ring MCB but the circuit still trips the RCD immediately when the MCB is switched on with nothing plugged into the sockets. My next step is to disconnect the ring, split the dead ring at the midpoint and test each half, but before doing this I removed the 2 CPCs for the ring at the CU from the earth bar and the circuit now stays on and doesn't trip. Before I plough on , disconnect the phase and neutrals and do dead circuit testing is there anyway that I can identify why the disconnection of the CPCs allows the ring to operate? Graham

so Graham....after removing the 2 CPCs then energising the circuit (a no no for a start)...did you expect the device to still let go?

 

[Jabbajaws]

This could be something as small a hole in a conductor sheath, with the bare wire touching a metallic backbox. Ive had this happen before. Check for recently hung pictures and nails which may have been inserted, into a wall perhaps, somewhere on the cable run.

If you have an RCD activating and there is no load, there has to be an earth fault in a place where you would least expect to find it...

And like GLENNSPARK says. If you disconnect the CPCs on the ring. The RCD that protects it, will not operate as it wont detect the earth fault...

 

[sirocco]

The RCD is protecting the other three circuits and is operating under load. I was trying to understand why Babylons Burning suggests that it points to EL fault rather than say EN fault. At 8am tomorrow I will be back on the case with my trusty Fluke, split the ring and crack on. I have a feeling it will turn out to be in the kitchen, where steam abounds! There is also some evidence of mice in the kitchen and I wonder if they have been chewing on a wire. As always any other helpful suggestions welcome.

 

[Cnobby]

It could be either a LE fault or NE fault. I would definitely do an IR test and then identify which cable is giving you the problem. If it is a cable and difficult to replace, i would split the ring and have two radials if you have the room in the CU.

 

[spark 68]

It could be either a LE fault or NE fault. I would definitely do an IR test and then identify which cable is giving you the problem. If it is a cable and difficult to replace, i would split the ring and have two radials if you have the room in the CU.

It will be a L-E fault, as the RCD trips only when the MCB (single pole) is on.

Glenn is correct, the CPC's should never be removed to fault find live, as this is a hazard.

 

[Sintra]

If it was a N-E fault the RCD would not hold at all. What the OP has described would appear to be a L-E problem.

 

[Ducksy]

Awwwww man this would be a perfect opportunity to use my new earth leakage clamp meter........some people get all the fun

 

[GLENNSPARK]

Awwwww man this would be a perfect opportunity to use my new earth leakage clamp meter........some people get all the fun

there`l be plenty of time for that....
knowing some of the DIY crap & dodgy appliances going about now...

 

[tony mc]

Awwwww man this would be a perfect opportunity to use my new earth leakage clamp meter........some people get all the fun

I can't see a clamp meter being any good if the RCD will not hold !

Disconnect the circuit split the ring if it is a ring and start your IR testing.

 

[telectrix]

could bypass the RCD, strictly for clamping the leakage, of course.