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
 
In essence, the test button just connects a resistor to create an artificial imbalance. Resistors have tolerances and temperature ranges. Could be the raised ambient has damaged them or is causing them to pass less current than expected.

Might be worth ramp testing them as well. If they are running slightly high and the test current created by the test button is slightly low???
 
Did you try the test button again after you're test with the meter? Seen it before where they haven't worked before proper testing but where fine after. (Not necessarily hager though)
 
Ramp tested fine 23 mA 25mA normal sort of range to me.
Just found it amazing that it was all 6 ..

As you say, the fact six have gone...

Is it humid where they are? Is it an IP rated board?

Could be the switch contacts are screwed due to environmental factors.
 
Yes I've had that before .. but then the rcbo or rcd didn't work at all .. these work fine with an auto test .. circuit's still connected .
 
I find Hager RCD devices some of the most reliable out there. I have however, as Murdoch says, had them not trip with the test button when connected N-E faults have been present.
 
As you say, the fact six have gone...

Is it humid where they are? Is it an IP rated board?

Could be the switch contacts are screwed due to environmental factors.

Yep .. this was my guess.. plant room ..2 commercial boilers 3 big water tanks .. all dry in there now .. but they have had multiple problems in there over the past few years..
Just the test button contacts have had it..?
 
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.
 
Yep .. this was my guess.. plant room ..2 commercial boilers 3 big water tanks .. all dry in there now .. but they have had multiple problems in there over the past few years..
Just the test button contacts have had it..?

Could be.. but I'm just floating ideas around. I've had to replace a CU locally that was in a domestic swimming pool plant room. Was in a right state, some MCBs wouldn't turn off, contacts were all corroded or affected by chemicals.

To avoid it happening again, I put a plastic unit, inside an IP rated steel cabinet, with every cable properly glanded through the cabinet.
 
Hi Vito - assuming they have the functional earth lead, perhaps check it's still connected. I don't really see how this could cause it, I'm just thinking out loud. :)
 
I find Hager RCD devices some of the most reliable out there. I have however, as Murdoch says, had them not trip with the test button when connected N-E faults have been present.

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?
 
Are these the type with a functional earth flying lead (cream coloured?)

Is this properly terminated to a known good earth. me too just floating ideas..
 
I think I have an answer
upload_2018-10-24_21-7-42.png
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.
 
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
 
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.
 
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 ?
 
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.
 
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?
upload_2018-10-24_22-37-14.png
  • 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)
 
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.
 
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
 
Last edited:
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
 
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.
 
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.
 
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.
 
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.
 

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Rcbo test buttons not working - but works ok when tested
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