Cannot get RCD test to work?

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HappyHippyDad

HappyHippyDad

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Evening chaps..

I have just fitted some downlights in a bathroom and needed to give them RCD protection as there was none. I fitted the following:

rcd unit.jpg

The test button works fine and the unit trips when a fault occurs (touching neutral to earth) but I cannot get the MFT to test it for trip times which I need for the MWC. Its a fairy decent MFT and I've never had any trouble with it testing RCD's before but I have never tested this sort of RCD before, it has always been in the CU. I make contact with the live/neutral/earth of something which the RCD is feeding, I get the little 'tick' on the MFT and then it just wont test.

Am I missing something simple here? Is this unit tested in the same way as you would an RCD in a CU?
 
In addition to Howards post above ^^^^ Have you tested the ELI prior to fitting the RCD ?, because if the earth loop is high resistance/non-existent, the tester will inhibit the test if the CPC rises above a pre-set touch voltage, usually set @ 50V, some testers allow this to be set @ 25V, so check this too.
 
spark 68 said:
In addition to Howards post above ^^^^ Have you tested the ELI prior to fitting the RCD ?, because if the earth loop is high resistance/non-existent, the tester will inhibit the test if the CPC rises above a pre-set touch voltage, usually set @ 50V, some testers allow this to be set @ 25V, so check this too.
Click to expand...

I forgot that bit, thanks. prior to carrying out a RCD test, the earth fault loop impedance value must be confirmed as compliant. That is an answer in the 2394/5 exam as well.

Cheers............Howard
 
happyhippydad said:
Evening chaps..

I have just fitted some downlights in a bathroom and needed to give them RCD protection as there was none. I fitted the following:

View attachment 23855

The test button works fine and the unit trips when a fault occurs (touching neutral to earth) but I cannot get the MFT to test it for trip times which I need for the MWC. Its a fairy decent MFT and I've never had any trouble with it testing RCD's before but I have never tested this sort of RCD before, it has always been in the CU. I make contact with the live/neutral/earth of something which the RCD is feeding, I get the little 'tick' on the MFT and then it just wont test.

Am I missing something simple here? Is this unit tested in the same way as you would an RCD in a CU?
Click to expand...
Yes, test the same way, it is just and RCD incorporated into a Switched Fused Spur. Double check polarity and ZS on load side of unit. Also prove your meter on another RCD. You may have a faulty unit.
 
Murdoch said:
Did you test on the outgoing terminals or at the end of the circuit?
Click to expand...

The RCD feeds a junction box which feeds the lights and also a fan in the bathroom. I tested at the triple pole switch which I fitted. I tested on the coductors coming from the junction box and the MFT gave a tick 'measurement can be performed'.
 
spark 68 said:
In addition to Howards post above ^^^^ Have you tested the ELI prior to fitting the RCD ?, because if the earth loop is high resistance/non-existent, the tester will inhibit the test if the CPC rises above a pre-set touch voltage, usually set @ 50V, some testers allow this to be set @ 25V, so check this too.
Click to expand...

Zs was 0.9, I'll have a look at the pre-set touch voltage.. Thanks Spark68
 
Meggerman said:
Yes, test the same way, it is just and RCD incorporated into a Switched Fused Spur. Double check polarity and ZS on load side of unit. Also prove your meter on another RCD. You may have a faulty unit.
Click to expand...

Have triple checked polarity (as I was tired!), Zs is ok and I proved the meter on another RCD in the same house.
 
If the Zs is 0.9 then I don't see the touch voltage being set @ 25V being the problem, I would check the continuity of the CPC all the way through the circuit though.

I would also try the test at the outgoing terminals of the RCD with the outgoing circuit disconnected first too, to narrow down where the problem may lie, it maybe simply that the RCD is faulty.
 
I too think the device is being tested on the input side ,as Trev says , also don't forget to isolate the outgoing circuit if pos to avoid false readings ,,LOL,,,
 
as above. try it again. might be a duff rcd.
 
however....you say it works on the test button.....but not at the load...

whip that RCD fcu off and make sure the outgoing CPC is connected....it may have come out when you pushed the front on...

or it may be that you didn`t connect it at all....as if the sleeving moved over the conductor then it could have given the impression that a secure termination had been acheaved....when in reality its not...
 
Last edited:
GLENNSPARK said:
however....you say it works on the test button.....but not at the load...

whip that RCD fcu off and make sure the outgoing CPC is connected....it may have come out when you pushed the front on...

or it may be that you didn`t connect it at all....as if the sleeving moved over the conductor then it could have given the impression that a secure termination had been asheaved....when in reality its not...
Click to expand...

Should have proven all that if he's done the EFLI test before RCD test ,,
 
spark 68 said:
If the Zs is 0.9 then I don't see the touch voltage being set @ 25V being the problem, I would check the continuity of the CPC all the way through the circuit though.

I would also try the test at the outgoing terminals of the RCD with the outgoing circuit disconnected first too, to narrow down where the problem may lie, it maybe simply that the RCD is faulty.
Click to expand...

Continuity of CPC was proved.

That is a very good idea Spark68 and I should have done that.

trev said:
Which implies that he has not tested at the load terminals of the device. You test the device not the circuit
Click to expand...

Would you not test the circuit as well Trev? When you test an RCD in a CU you test that on the circuit somewhere, generally a socket?
 
I have had one of those units duff before. Would not trip at 30ma. Did 100ma Ramp test and it operated at 70ma. After that it operated at 23Ma. Still returned it as felt it could be unreliable.
 
I don't know what all the fuss is about, i once spent and age trying to find out why an RCD wouldn't trip, i was testing on the supply side, took a while for the penny to drop, and not before i had stripped the bloody thing out before i realised what i had done.

So maybe i am a waste of space after all! :dunce2:
 
SirKit Breaker said:
I don't know what all the fuss is about, i once spent and age trying to find out why an RCD wouldn't trip, i was testing on the supply side, took a while for the penny to drop, and not before i had stripped the bloody thing out before i realised what i had done.

So maybe i am a waste of space after all! :dunce2:
Click to expand...
I never inferred that about you. This OP seems to get a lot of grief and I felt he was about to get a load more when he just wanted some help. I guess I was wrong.
 
SirKit Breaker said:
I don't know what all the fuss is about, i once spent and age trying to find out why an RCD wouldn't trip, i was testing on the supply side, took a while for the penny to drop, and not before i had stripped the bloody thing out before i realised what i had done.

So maybe i am a waste of space after all! :dunce2:
Click to expand...
Howard you have over 720 Thanks from us members here, your no waste of time M8, there are numties here though, and shhh, Don't tell anyone but there may be one in this thread hehe, I said maybe lol
 
Meggerman said:
Yes, I would for a dead accurate reading of device not affected by earth leakage out on the circuit.
Click to expand...
I'm completely at a loss to understand what you're saying here. A bit back you're backing his method when it was pointed out (calmly and respectfully) that he was carrying out the test wrongly now you appear to be backing up what I said but only to get "a dead accurate reading"
Why would you not want a dead accurate reading?
 
trev said:
I'm completely at a loss to understand what you're saying here. A bit back you're backing his method when it was pointed out (calmly and respectfully) that he was carrying out the test wrongly now you appear to be backing up what I said but only to get "a dead accurate reading"
Why would you not want a dead accurate reading?
Click to expand...
Is he not just trying to confirm if unit is faulty. Probably only a got a bathroom light and a fan on load of this unit. He done I/R and ZS and said it was good. Why disconnect load in this case? just more for him to do? That was where I was coming from.
 
happyhippydad said:
Continuity of CPC was proved.

That is a very good idea Spark68 and I should have done that.



Would you not test the circuit as well Trev? When you test an RCD in a CU you test that on the circuit somewhere, generally a socket?
Click to expand...
does this mean you carried out a Zs?

and if so have you disturbed anything sinse then....but before attempting RCD testing?
 
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