Rcbo test buttons not working - but works ok when tested

[johnduffell]

My bets is a neutral-earth fault, possibly on one of the two TPN circuits

I'm intrigued how a fault purely between any upstream conductors could affect the operation of an RCD, assuming the L-N potential is still 230V. What are your thoughts on the mechanism?

 

[Leesparkykent]

I'm intrigued how a fault purely between any upstream conductors could affect the operation of an RCD, assuming the L-N potential is still 230V. What are your thoughts on the mechanism?

Read Richard burns post 10 from this link RCD test button not working - https://www.electriciansforums.co.uk/threads/rcd-test-button-not-working.92618/

 

[johnduffell]

Read Richard burns post 10 from this link RCD test button not working - https://www.electriciansforums.co.uk/threads/rcd-test-button-not-working.92618/

Thanks for the link:

If there is a neutral earth fault in a circuit then when the RCD test button is pressed the current that should flow from the test button, to out going neutral,

As you can see he is talking about the outgoing neutral itself, in a case where the polarity is reversed. post 12 explains the same thing now clearly

If the test button circuit goes from supply L to load N, a downstream N-E fault can stop it working by reducing the test current returning to the supply N through the sensing transformer. But if the test was from load L to supply N, the fraction of test current going to earth at the fault would pass through the transformer twice in the same direction, possibly making it test OK even if it had reduced sensitivity. This makes me think that all RCDs have the test circuit the first way round, but I can't say I've spent enough time looking at the schematic on the side to notice.

This is confirmed by the original post

with 2 30mA rcd, left side wont trip when test button is pushed but the right side seems fine

 

[johnduffell]

Also just to add, every installation in the country has an upstream N-E fault, it's called the earth link in the cutout or at the transformer. So it definitely can't cause an issue

 

[Toneyz]

I'll have to go back with my leakage clamp meter and check it out .. customer would be a tad unhappy to buy 6 new ones ....that also didn't work.

Has the customer been periodically testing them? I find a lot of the time they stick as never tested.

 

[richy3333]

Hi all
Odd one today .. all 6 Hager rcbo's in a tn+n db have the test buttons not working..
But when tested with a multifunctiontester they react fine..
Now..I guess I'm going to have to fail them..even though they work fine.
Hager technical say they have never heard of this.
Db is in a plant room with a raised ambient temperature but not hugely ..say 36c .. rcbos are 2 x 6A B 30ma 2 x 20A C 30ma and 2 x 32A B 30ma .. fitted in 2014 by the looks of it.
All connections are good..fly leads good..circuit's are just for sockets and lighting..standard stuff.
Anyone had this before..
Any ideas

Ta
Vito

Sorry, just seen this thread.
I had exactly the same situation recently. I found you needed to push the test button to one side or wiggle it (just a little bit) for the button to work. Mine also tested out fine.

 

[Lucien Nunes]

I have had a batch of RCDs (not RCBOs and not Hager) with failed test buttons although the RCD operation was fine. Every one of about 40 identical units was affected, after use in cabinets outdoors for a couple of years.

Agree the best test is to disconnect L & N load. If they then start working normally, N-E fault likely.

 

[ukiri]

Had this several years ago doing periodic tests in Comet stores.
Had 30 ish SqD rcbos giving trip times on the meter but not disconnecting the supply. There was a very quiet recall in progress for sticking mechanisms ,Schneider provided free replacements and paid for labour.

 

[phillipdj]

I've just come across 4 hager rcbo in an old peoples' home. the test button doesn't work, but they trip fine on the tester. they look clean, but it's blummin hot in there and has been non stop since they were fitted (10+ years) plus they are close to the ceiling.