RCD not tripping on test

[rustynails]

Had a strange one today, hager 100a 30ma rcd failed to trip with the tester. TT earthing arrangement, also very strange readings. ze 197.4 ok normal for around that area the zs around 0.53. Went and got a replacement 80a 30ma rcd, the 100a was on the large side. Failed the test again. Went home pulled out the cupboard an older hager 80a 30ma rcd the ones that took up 4 module slots and it tested fine, all other circuits were disconnected. Can't see how it would be a neutral to earth fault unless I put the circuits back one at a time to see if one causes a problem...just not sure.

 

[SPARTYKUS]

Zs prob caused by parallel path via main bond conn'd to neighbours who happen to be TN.

If it failed with the tester, them its duff or the tester is. Imho

 

[rustynails]

Don't think it's me tester. Calibrated the other week and works on other rated rcds

a good point you make about the zs tho. I was unable to explain this to myself. I did try this older rcd and that tested fine. I sometimes wonder about wholesales do they think it'll be funny to take one from the faulty shelf...

 

[NickD]

Failed which RCD test(s)? Both x1 and x5? Does the test button work?

 

[Engineer54]

Don't ever be surprised that a replacement RCD device is as faulty as the unit it's replacing, seen that happen far too many times, as well as a complete package box of them being faulty!!

When you come across units that won't trip under test, operate the units test button a few times to free up the the internal mechanism, wait a few minutes and try testing them again. Sometimes the contacts and.or internals stick.

Having said that, i have an inherent distrust of anything that fails testing straight off the bat so to speak. If it can happen once when testing, it can happen again in service when it's actually needed to operate!!

 

[NickD]

When you come across units that won't trip under test, operate the units test button a few times to free up the the internal mechanism, wait a few minutes and try testing them again. Sometimes the contacts and.or internals stick.

Having said that, i have an inherent distrust of anything that fails testing straight off the bat so to speak. If it can happen once when testing, it can happen again in service when it's actually needed to operate!!

Agree with your second paragraph. Anything as safety critical as an RCD or MCB that doesn't work right first time straight out of the box without cajoling is suspect and unfit for purpose and should be returned for replacement or refund. This ties in with the RCD testing best practice of checking whether the RCD tester trips it correctly BEFORE going anywhere near the test button, and failing it if it doesn't.

 

[SPARTYKUS]

The fastest testing 30mA RCDs I have had to pleasure to test are the relly old Wylex ones that are the size of a house brick.

they don't make stuff like in the old days

 

[telectrix]

could these RCDs be ones that require a couple of short tails fitted for testing?

 

[Engineer54]

could these RCDs be ones that require a couple of short tails fitted for testing?

Think that's the older MEM RCBO's, i'm not aware of RCD's requireing short bit's of tails to be fitted for testing... I could be wrong mind!! lol!!

 

[Jay Sparks]

could these RCDs be ones that require a couple of short tails fitted for testing?

Wylex rcbo's have this problem. You insert your probe into the neutral terminal and you think its made contact with the screw but it hasnt. You need to fit an adaptor that I believe you can buy, or make one as I have done. But then again, if the OPs probe wasnt touching the neutral, it wouldnt even carry out the test.

 

[shanky887614]

Wylex rcbo's have this problem. You insert your probe into the neutral terminal and you think its made contact with the screw but it hasnt. You need to fit an adaptor that I believe you can buy, or make one as I have done. But then again, if the OPs probe wasnt touching the neutral, it wouldnt even carry out the test.

?

Take the end off probe?

If that doesnt work push it in with cable

 

[Jay Sparks]

?

Take the end off probe?

If that doesnt work push it in with cable

My probes don't have the ends on any more.lol they have mysteriously vanished. You can buy an adaptor for them but I made one using some 6mm cable in a connector block. This then attached to my probe and fit perfeclty in the hole.