RCD Testing

[s6stu]

Hi All,

I have just tried to test a new cable I have installed and have an odd situation! All dead and live tests have been satisfactory and i've visually checked everything, the only test that does not pass is the RCD @ 1 x milliamp rating. The tester simply returns > 310ms. The 5x test came up below 40ms and the Zs was fine and i've treble checked all these tests again. The other 2 circuits that are on the same side as the RCD in question have both tested out fine at 1x and 5x.

Has anyone seen anything like this, because i'm a bit stumped?

The cable in question is 2.5 SWA 3 core and the sheath is earthed also in 2.5, as I say it has just been installed, so there really shouldn't be any issues. Maximum length of run, 30m, voltage at end of circuit 244.4V.

Thanks in advance,

Stuart

 

[Deleted member 26818]

I imagine that you are testing the RCD at the end of the SWA cable, rather than testing the RCD at the RCD.
Test the RCD at the RCD.

 

[thebigcheese]

Why would that make a difference spinlondon?

 

[s6stu]

I have got to return to the job at 6pm today so I will test the RCD at the board and report back

 

[Engineer54]

Why would that make a difference spinlondon?

Think about it?? The only thing you test with an RCD tester, is the RCD device, NOT the circuit. The circuit has been tested and found compliant. All official RCD testing should be conducted at the disconnected RCD terminals, as per every RCD manufacturers instructions!!!

 

[thebigcheese]

Oh yes I know the requirememts of GN3 but I was just wondering why that would affect the test results...?

 

[Engineer54]

All sorts of reasons, combined leakage from the other protected circuits, long distance affecting the the instruments output or measuring abilities etc, etc... None of which will affect the RCD's fault clearance and tripping in normal conditions. Unless of course the RCD device is a faulty unit, which is not when all said and done, an uncommon occurrence!! lol!!

 

[s6stu]

Hi again, update;

I tested at the board and the same occurred as with the end of the SWA, I didn't have time to re-test the other 2 circuits at the final points, to see if they were still producing a satisfactory result as I assumed they would also fail, plus i'm tired! I will check the 2 circuits again on monday before I change the RCD unit in the board, just to see, because it is strange how the RCD unit produced a satisfactory result in the morning on those 2 circuits, but then once the SWA was connected, decided to fail.

Thanks for the replies, and as Engineer54 says, RCD's do fail from time to time, this isn't the first instance of a failure that i've had, just a first instance of this particular situation.

I'll post back again monday evening.

 

[Richard Burns]

Make sure all circuits are off before you test and perhaps disconnect the SWA as it could be causing a capacitance effect on the circuit that is preventing the RCD tripping.
Since you have had good results from the RCD then I would be tempted to say those are the results.
That said do be ready to change the RCD just in case it has failed in the last day.

 

[s6stu]

Evening all, final report on the situation;

The original RCD still behaved the same when I tested at the board and with all circuit breakers off, I don't think the SWA would have made a significant effect on the capacitance of the system due to the small cable length, this turned out to simply be a case of a faulty RCD. The new RCD tested out correctly. The alarming part that is worrying me slightly, is that the RCD tested ok in the morning and not so in the afternoon, also strange that the RCD tested ok at x5 but not x1?

Anyhow, all sorted now, thanks for all your input

Stuart

 

[Engineer54]

When you have seen as many RCD device failures as i have, and i'm talking about boxes of the things being returned on a regular basis to manufacturer/suppliers for replacement, you don't have as much faith or reliance in them as some clearly have on here...lol!!!

 

[ashrow]

When you have seen as many RCD device failures as i have, and i'm talking about boxes of the things being returned on a regular basis to manufacturer/suppliers for replacement, you don't have as much faith or reliance in them as some clearly have on here...lol!!!

My local wholesaler says i am the only one to return RCD,s for being faulty, i said i must be the only one testing them correctly then !

Never had a faulty RCBO yet though

 

[Pat Tester]

I've had a faulty rcbo, mind you it was an europa

 

[Engineer54]

My local wholesaler says i am the only one to return RCD,s for being faulty, i said i must be the only one testing them correctly then !

Never had a faulty RCBO yet though

Either that, or your local wholesaler's prices are too high and don't therefore sell to many!! lol!! Truth be known, he's just telling you a line of Porky's!! lol!!

Our general site LV final circuit protection equipment (as well as all our systems protection equipment) is all from a top quality manufacturer, and the faulty RCD devices include all types, including RCD's (2/3/4 pole), RCBO's and Vigi units 2/3/4 pole etc. On the last project (as will be the case on this project, eventually) all went through the contractors accredited on-site test laboratory, before being sent back for replacement... It certainly opens your eyes, believe me!! lol!!!