Rcbo test buttons not working - but works ok when tested

[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..

 

[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.