Rcbo test buttons not working - but works ok when tested

[johnduffell]

I think I have an answer

the test button leaks from phase 1 to phase 2.

Try ramp testing between those two phases rather than to earth and see what happens (assuming your RCD tester is good for 400V)

I bet there is either an imbalanced load (in favour of phase 2 or 3), or there is an imbalance in favour of 1 and a N-E fault. This is assuming the RCD tester leaks to earth from phase 2 or 3.

 

[Leesparkykent]

Are there some circuits not on RCBO’s?
I wouldn’t pee around with a earth leakage clamp meter if there’s only six circuits. I would just disconnect a circuit 1 at a time and find the culprit circuit.

 

[vitoboy]

Yes there are 2 tp mcb's on the other side .. it's a 4 way tpn db.
The rcbos in question are single phase .. just incase anyone was thinking otherwise .
Yes rcbo's with cream fly leads .
Good shout though leesparkykent could well just switch all other circuit's off and check the rcbo's 1 at a time..
Ill report back when I know more.
Seems though from the replys that no one has had a non working test button on a working rcbo..
Bit novelty. ..must get out more!
Ta all
Vito

 

[Octopus]

Seems though from the replys that no one has had a non working test button on a working rcbo..
Vito

What makes you think that?

I have FWIW

 

[123]

That is what you should do next ..... and use your earth leakage clamp meter too

Non fuctioning test buttons can be a sign of N - E faults

To do what? I've asked in the past about these, and yourself included couldn't give me a reason (let alone a good one) to purchase one.

 

[westward10]

@Leesparkykent means disconnect the circuit and not just switch it off, switching off will not isolate the neutral.

 

[Octopus]

To do what? I've asked in the past about these, and yourself included couldn't give me a reason (let alone a good one) to purchase one.

I have identified rcd trips using my clump meter on more than one occasion .... and I often use it before I change a cu ....

They aren’t that expensive ..... why not buy one ?

 

[123]

I have identified rcd trips using my clump meter on more than one occasion .... and I often use it before I change a cu ....

They aren’t that expensive ..... why not buy one ?

Why do I need one? I do approx 150-200 call outs for faults a year as a sole trader and yet to not find to fault/issue. All without the use of one. I asked in a different thread why I'd need one, and iirc no one came up with a reason as to why I'd need one.

 

[johnduffell]

If it's only a single phase, the only electrical difference common across all rcbos is the ramp test used L-E and the RCD button uses L-N.
Have you checked the polarity both before and after the RCBO?

Andy, would that be because some of the created test current flows back through the neutral side of the sense transformer and then down the CPC resulting in less than the expected test current appearing on the sense winding?

• An N-E fault downstream of the RCBO would pass some of the test current through the sense coil again in the same direction, making it more sensitive to the test button. That would also mean some of the RCD tester current would flow back through the neutral and cancel some of the unbalanced live, making it less sensitive to the RCD tester.
• An L-E fault downstream of the RCBO would increase the sensitivity of both the test button and the rcd tester.
• If the polarity was reversed upstream, the test button would still work the same.
• If the polarity was reversed AND there was a N-E fault downstream (L terminal would be N) some of the current coming from the actual L would go to earth rather than the sense coil, reducing the sensitivity of the test button. The RCD tester would work as normal (assuming the polarity was reversed back again before connecting the RCD tester)

 

[Leesparkykent]

My bets is a neutral-earth fault, possibly on one of the two TPN circuits. As above I would disconnect a circuit at a time not just switch them off as the neutral will still be connected.

 

[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.