RCD trip at socket but not origin

Hi All

Not come across this before but general nuisance tripping on RCD trip investigation ( TT with 30mA main switch). Normal results at origin with no loads but  tripping at x 1/2 current at sockets with variation depending on circuit. New kitchen ring causing x 1/2 trip but no evidence of wiring fault. Any ideas ?. Thanks.

Break the ring circuit in half into two radials and see which leg is faulty.

Then keep on breaking it down.

Have you done dead tests? An IR test might help you here.

mattski said:

Hi All

Not come across this before but general nuisance tripping on RCD trip investigation ( TT with 30mA main switch). Normal results at origin with no loads but  tripping at x 1/2 current at sockets with variation depending on circuit. New kitchen ring causing x 1/2 trip but no evidence of wiring fault. Any ideas ?. Thanks.

Click to expand...

Your work or others?

Best start by testing the RCD and new ring .... then the other circuits

Do you have an earth leakage clamp meter?

Does sound odd - why were you testing at the rng?

So are you saying a 30ma RCD covering the whole installation is tripping when you test at the load of a circuit whilst other circuits are still connected? The guidance for testing RCD's is as near to source as possible with load(s) disconnected. So if the RCD itself is working OK when tested at source with no loads, that could suggest some cumulative natural leakage on any combination of the circuits connected via that RCD. How many circuits are connected via this RCD? It may be just a poor installation design not allowing for natural leakage on multiple circuits. 

Doc H.

Thanks for replies.

As per regs, RCD tested at cu with loads disconnected.

Curiosity( after finding shorts in garden lights connected to 1 of the final rings in house) led me to test RCD from a remote location and this is when I found rcd tripping at x 1/2 regardless of where (or how near) to cu the test was performed and was the same from any circuit or location.

IR's satisfactory and none of wiring in house is my work and only recent alterations were new kitchen sockets by B and Q in refit

Have noted that there is some debate whether to test at origin and/or  at receptacles for Rcd

Some guidance would be welcome as this is the first time a tripping RCD has caused me this much trouble.

Thanks

Matt 

Ramp test? 

My Fluke has no ramp tester but tripping 30mA x1/2 assumes 15mA is causing trip but at sockets only

Have you dropped the socket fronts in new ring by the Bodgit Quickly guys? You may find your problems. 

The sockets are all fine but the house is of an age when JB's used and hidden in voids. Repaired one such issue following lighting circuit failure a few years ago.

The issue I have is that this tripping at 1/2 can be prompted by either of 2 final ring circuits but only one seems to stop tripping when isolated.

mattski said:

...

Have noted that there is some debate whether to test at origin and/or  at receptacles for Rcd

...

Thanks

Matt 

Click to expand...

Welcome to the forum Matt.

The debate wrt testing at the RCD or @ a remote socket is only one of safety.

You still must have all loads disconnected.

So, all other mcb's off & everything unplugged/disconnected from the circuit used for testing.

This however still leaves a capacitive load on the RCD, in the way of the circuit used for testing.