rcd's

[soontobe]

can anyone solve a problem for me please?
checked a ring main the other day which had 6 rcd sockets on it. its fed in 2.5 singles from the db on a 32a mcb. when nothing is plugged in the test buttons will not stay in,so i assume its a prob with the circuit. some of the test buttons stay in but when you try to press the others in the other ones trip out. i changed a socket front which looked damaged and now more of the sockets stay on.
however there is no rhyme or reason to which ones stay on.
could the sensitivity of certain sockets nuisance trip the other ones?
any advice would be welcome.

 

[securespark]

Is the supply to them OK? They could be failsafe - meaning they trip on loss of supply...

 

[soontobe]

supply is sound,240 at the back of every socket. the only socket that doesnt trip is the new one. could all of the rcd sockets have become damaged by some type of surge or something similar?

 

[tim west]

Strange they trip with nothing plugged in as the RCD's are on the output side of the circuit so internal wiring shouldn't in theory affect the current flow through the L+N coils in the RCD, maybe the pick up coil is seeing some form of noise enough to trip already weakened trips?

 

[soontobe]

can trips weaken with time and become more/less sensitive?

 

[JohnD]

they more often go sticky and fail to trip

 

[Spark123]

I suppose if you have a sound supply including a low earth fault impedance then the socket outlets could be shot at. IIRC the RCD socket outlets use electronic RCDs which are a more prone to problems from overvoltages than the old wire wound variety.
I once saw a trailer which visits the school go through about 4 of the plug in electronic variety for no apparent reason, they had 2 extension leads run inside the building, one to run the air con and the other to run tv screens/computer. As it happened the school sockets were on an RCBO anyway so didn't really need them.

 

[soontobe]

thought about replacing all the socket fronts with normal ones and fitting a rcbo,but instead backheeled the job until next week!