30ma RCD tripping on TT circuit

[bluetof]

Shoot me now but.

Went to a house today with a TT system. RCD tripping but not identifiable to a particular circuit. Spent all day trying to identify which circuit was the problem. Each circuit would stay on independently but when other circuits where added, the RCD would trip - tried all combinations. Ended up changing the 30ma RCD to 100ma trip, all sorted.

Absolute nightmare to IT all circuits, clip on current leak tester was useless.

Tell me what I have done wrong ?

:good night:

 

[M107]

I had a similar fault last year (post is here somewhere.......patch is sure to find it), individual circuits on all was fine, all circuits on & turn on any appliance you wanted & 30milly tripped.

Traced the fault to a knackered pool pump/heater (from costco i seem to remember) up the garden, unplugged said pump/heater & problem was solved.

 

[green-hornet]

It is very possible that if all circuits have passed all tests, then the RCD is faulty.

I have had a similar experiance and posted my findings on the forum.

Others have had similar experiances.

Changing a 30mA for a 100mA, would not be a good idea if 30mA protection is required, even as a temporary measure.

Try another RCD unit in there and see if that resolves the problem.

 

[bluetof]

Good stuff, but should i have upgraded the 30ma RCD to 100ma RCD. I think this is ok as is is a TT circuit. There is obviously a fault ?????????

 

[bluetof]

It is very possible that if all circuits have passed all tests, then the RCD is faulty.I have had a similar experiance and posted my findings on the forum.

Others have had similar experiances.

Changing a 30mA for a 100mA, would not be a good idea if 30mA protection is required, even as a temporary measure.

Try another RCD unit in there and see if that resolves the problem.

Tried new 30ma RCD after ramp testing existing (25ma). It is a very old board - would 30ma protection be required on a TT system ??

Thanks for the quick reply.

 

[tom1]

Good stuff, but should i have upgraded the 30ma RCD to 100ma RCD. I think this is ok as is is a TT circuit. There is obviously a fault ?????????

your special location circuits, most socket, will need 30ma

and there is prob cable conceled at <50 mm

 

[green-hornet]

Was going to reply but Tom said what I would have

 

[Lillpete]

Good stuff, but should i have upgraded the 30ma RCD to 100ma RCD. I think this is ok as is is a TT circuit. There is obviously a fault ?????????

I wouldn't exactly call that an upgrade TBH

 

[bluetof]

I wouldn't exactly call that an upgrade TBH

No you are quite right but should the system not be 100ma protected anyhow?

 

[bluetof]

your special location circuits, most socket, will need 30maand there is prob cable conceled at <50 mm

This is a 35 YO installation, still need 30ma protection ?

 

[Lillpete]

Old regs used 100ma for TT supplies but even then sockets for use outside needed RCDing but to current regs pretty much everything domestic needs 30ma and 100ma does not meet with requirements

 

[green-hornet]

TT installations use 100mA RCD's because to meet disconnection times RCD,s had to be fitted.

The 100mA was fitted to help discriminate with 30mA, so if a circuit tripped out, you did not loose the whole installation.

So the main switch was 100mA, the circuits requiring additional protection would have 30mA RCD's fitted.

 

[tom1]

This is a 35 YO installation, still need 30ma protection ?

yes, and if you was working there then the new work is likely too.

so it was on a 30ma rcd and you changed it for a 100ma because it was tripping?

 

[Andy™]

the RCD will be tripping for a reason. removing the RCD does not fix the fault, and its there for a reason.

and changing 30mA to 100mA is like changing a 6A to 50A because it keeps tripping

 

[bluetof]

yes, and if you was working there then the new work is likely too.so it was on a 30ma rcd and you changed it for a 100ma because it was tripping?

Yes Tom, there are 2 boards. 1 is supplied by a 100ma RCD and the other is supplied by a 30ma RCD. This is a really old installation. I am starting to think that a prev sparky had been before and replaced a 100ma with a 30ma RCD.

 

[bluetof]

[quote name='Andy

 

[spinlondon]

So, do the circuits that require 30mA RCD protection in this board have that protection, or are they now protected by the 100mA RCD?

 

[Andy™]

Totally agree Andy:But

Lets say a ring main circuit wired in 2.5mm twin and earth (ring circuit verified) was on a 16A Type B MCB and was constantly tripping - would you change the MCB to 32A ?

only if it was designed to have a 32A MCB, which being a ring it probably was.

but in your case, its designed to have a 30mA. your little scenario has no relation. if you had said 'if you had a 2.5 radial wired on 20A MCB and it kept tripping, would you change to 32A'. answer obviously being no, because its not designed to be protected by 32A

 

[Lillpete]

So, do the circuits that require 30mA RCD protection in this board have that protection, or are they now protected by the 100mA RCD?

The problem is that most likely all the circuits need 30ma protection.

if the instalation had a faulty 100ma rcd I would say you are ok to replace that like for like as it would have been ok when it was designed to previous regs, but unfortunatly despite the installation being old you cannot change it now to meet previous editions of BS7671

 

[ianmacd]

This is a 35 YO installation, still need 30ma protection ?

If its 35 YO then did you do an IR test on all the circuits on that RCD?