Rcbo test buttons not working - but works ok when tested

vitoboy · Oct 24, 2018

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

Octopus · Oct 24, 2018

Did you test them with the circuits disconnected?

vitoboy · Oct 24, 2018

SparkyChick · Oct 24, 2018

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???

vitoboy · Oct 24, 2018

Ramp tested fine 23 mA 25mA normal sort of range to me.
Just found it amazing that it was all 6 ..

Octopus · Oct 24, 2018

vitoboy said:
No

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

Sintra · Oct 24, 2018

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)

SparkyChick · Oct 24, 2018

vitoboy said:
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.

vitoboy · Oct 24, 2018

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 .

Andy78 · Oct 24, 2018

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.

vitoboy · Oct 24, 2018

SparkyChick said:
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..?

vitoboy · Oct 24, 2018

Not an IP rated db ., just a standard Hager tpn db from about 2008

vitoboy · Oct 24, 2018

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.

johnduffell · Oct 24, 2018

I'm on the faulty contact side of suspicion, ramp test would surely be high if there was a neutral to earth fault.

SparkyChick · Oct 24, 2018

vitoboy said:
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.

Wilko · Oct 24, 2018

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.

johnduffell · Oct 24, 2018

Quick question, when you rcd test a three phase and neutral RCD which phase does it leak the current to earth from?

SparkyChick · Oct 24, 2018

Andy78 said:
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?

simpson93 · Oct 24, 2018

Was the power on when you tried the test button?

Taylortwocities · Oct 24, 2018

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..

johnduffell · Oct 24, 2018

I think I have an answer

[ElectriciansForums.net] Rcbo test buttons not working - but works ok when tested

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 · Oct 24, 2018

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 · Oct 24, 2018

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 · Oct 24, 2018

vitoboy said:
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 · Oct 24, 2018

Murdoch said:
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.

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