New RCD required, but what goes wrong in them?

[OnOff]

Testing my kitchen ring today and looks like I need a new RCD!

A TT system installed in 1987. Stand alone "Keyswitch Varley" 80A, 30mA RCD in it's own enclosure fitted between the meter and DP switch in the CU. CU is a metal clad Crabtree with a line of C50 Type 2 breakers so yes, all circuits on the one RCD. Excuse the photo angles the CU is mounted against the ceiling in the porch with 2'6" between walls.

View attachment 2867

View attachment 2866

Anyway, I did the 3 step dead tests all ok then moved onto the IR tests again no problems. Polarity OK. Moving on and earth loop tests at the sockets just show up the need for a working RCD with circa 50A only for L-PE.

Then doing the RCD test and 1/2x no trip. On 1x it just read >299ms and on 5x >40ms. It tripped "eventually" but was noticeably slow. I appreciate a new RCD is needed ASAP but what was odd was that even pressing the test button it took a good while for it to trip? Out of interest before I bin it does that suggest a mechanical fault within the RCD. Don't worry, not thinking I can repair it but what makes them go wrong? Appreciate it is nearly 30 years old! I know the theory from college as to how they work but again what makes them "go slow"?

(By the way the meters used were a Megger BM221 Insulation Tester and a Megger RCD & Loop Tester LCB2500/2).

Straight down to TLC tomorrow! Any best make to get? MK, Hager?

Thanks

 

[SPECIAL LOCATION]

Has the RCD been tested quarterly (every 3 months), each year since it was installed?

Were you testing it with all loads disconnected?

(as per 11.1 top of page 106 Green On Site guide)...

:|

 

[batty]

If it has not been tested in the past it probably won't work to well when was the last time it was tested with the test button?

 

[OnOff]

If it has not been tested in the past it probably won't work to well when was the last time it was tested with the test button?

Don't know. Not regularly I'll admit. Just dug out some old rough notes, seems its been going downhill slowly:

25/5/2009 - x1 0 deg /68ms, 180 deg / 64.2ms.

post 25/5/2009 (no date) - x1 0 deg /108ms, 180 deg / 114ms.

 

[NozSpark]

First off what were your IR results and dis you isolate the circuits at the main switch?,,, high resistance N-E faults can incapacitate RCDs in TT installations.

If you do find that you need a new RCD then it would probably be worth while changing the whole CU,,, a new RCD is going to cost you say

 

[OnOff]

Has the RCD been tested quarterly (every 3 months), each year since it was installed?Were you testing it with all loads disconnected?

(as per 11.1 top of page 106 Green On Site guide)...

:|

No, not tested regularly - no excuses there. But will be on the calendar from now on when the new one is fitted. As for loads, no......off to read the OSG now though I only have the red one.

 

[batty]

It will be the same testing hasn't changed only the certificates.

 

[sprocketflup]

Has the RCD been tested quarterly (every 3 months), each year since it was installed?Were you testing it with all loads disconnected?

(as per 11.1 top of page 106 Green On Site guide)...

:|

just been sat here thinking "that wouldnt work....." but then ran it through my head again.................

 

[SPECIAL LOCATION]

No, not tested regularly - no excuses there. But will be on the calendar from now on when the new one is fitted. As for loads, no......off to read the OSG now though I only have the red one.

Red book (OSG)...

Page 91 onward is Ch 11 Operation of RCD's...

11.1 mid way down pg 91 is test procedure.