Rcbo test buttons not working - but works ok when tested

[vitoboy]

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]

Did you test them with the circuits disconnected?

 

[vitoboy]

No

 

[SparkyChick]

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]

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

 

[Octopus]

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]

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]

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]

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]

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]

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]

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

 

[vitoboy]

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]

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

 

[SparkyChick]

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]

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]

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

 

[SparkyChick]

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]

Was the power on when you tried the test button?

 

[Taylortwocities]

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..