Understanding what this means on the megger 1731

[HappyHippyDad]

I am in the process of hunting for another difficult fault (intermittent tripping RCD, absolutely no faults showing on any circuits and only 2mA fault current in Main earth).

My question does indirectly relate to this... perhaps.

When testing the RCD with my megger 1731 I am not getting a reading in mS. All I get is 'trp'. The RCD trips, but it does it so quickly and just states 'trp'.

The above was testing at a socket so I tried testing at the RCD itself and got the same.

The RCD is protecting 3 circuits, 2 socket circuits and the cooker. When i test at the RCD with the 3 breakers up the RCD trips and says 'trp'. When I switch off the cooker breaker and test I then get a proper reading (27mS). When I switch the sockets off and the cooker on I get a proper reading also (27mS). What does this mean?

Reading through the megger download does not give any useful info. It just says (under RCD testing), "if the RCD trips it will show 'trp'!!!!! (see pic below)

 

[TJ Anderson]

Did you determine the 2mA with an earth clamp meter?

 

[westward10]

I would guess the rcd is tripping prior to the test sequence starting hence no time is recorded.

 

[buzzlightyear]

the reason for that is the probes or the socket is showing its not connected .

 

[James]

I suspect that you have a higher leakage than you think.
this is causing the rcd to trip almost as soon as the current is starting to ramp up from the meter.

have you tried IR testing the oven and grill elements?

 

[Wilko]

Hi - 2 thoughts as per above really - check you’ve set the test to AC (or what have you) and I think it’s tripped at less than 15mA, a fail. So maybe try a ramp test and see.

 

[Charlie_]

How did you test the earth leakage?

 

[Lucien Nunes]

The first test the MFT does is the 0.5 IΔN test (15mA in this case) to prove that the RCD does not trip at that current (which is must not, if it is in spec.) But when the circuits are live, the test leakage is adding to the existing leakage, taking it over the 15mA and causing a trip. So the test aborts alerting you to the fact it tripped when it was not supposed to.

2mA fault current in Main earth

This tells you little, as there are probably many parallel paths for the leakage to take.

 

[SparkyChick]

Have you ramp tested the RCD with nothing connected? How did you determine you have 2mA in the main earth (if you just clamped the main earth, you're missing what's disappearing down the main bonding)?

I've been in a similar situation, very low leakage across the whole installation, but I couldn't even get a 1/2Ideltan result. Ramp tested the RCD and it was tripping reliably at 10mA.

 

[James]

ah, sorry I thought you were getting that error when doing a ramp test, not the 50% test.
sparky chick is probably spot on.

 

[AJshep]

As above when have you measured earth leakage by clamping around L-N conductors together ?
This way you're measuring what an RCD sees. You can do this on your outgoing tails of the RCD in your CU.

 

[HappyHippyDad]

Did you determine the 2mA with an earth clamp meter?

I would guess the rcd is tripping prior to the test sequence starting hence no time is recorded.

Hi - 2 thoughts as per above really - check you’ve set the test to AC (or what have you) and I think it’s tripped at less than 15mA, a fail. So maybe try a ramp test and see.

How did you test the earth leakage?

Have you ramp tested the RCD with nothing connected? How did you determine you have 2mA in the main earth (if you just clamped the main earth, you're missing what's disappearing down the main bonding)?

I've been in a similar situation, very low leakage across the whole installation, but I couldn't even get a 1/2Ideltan result. Ramp tested the RCD and it was tripping reliably at 10mA.

£648 is an odd total of a quote, I'd have just rounded it off to £650

Classic sale tactic to price like that. £645 instead of £650, £695 instead of £700 and so on..honestly try it, it works.

I should have been more clear, sorry!
The RCD test is at xI
The earth leakage was with a earth leakage clamp meter around the main earth and 2 x bonding cables at the same time.

 

[HappyHippyDad]

The first test the MFT does is the 0.5 IΔN test (15mA in this case) to prove that the RCD does not trip at that current (which is must not, if it is in spec.) But when the circuits are live, the test leakage is adding to the existing leakage, taking it over the 15mA and causing a trip. So the test aborts alerting you to the fact it tripped when it was not supposed to.



This tells you little, as there are probably many parallel paths for the leakage to take.

Sorry Lucien, this is a test at x 1

 

[ipf]

Said before...…. have you tried ramp testing?

 

[HappyHippyDad]

Said before...…. have you tried ramp testing?

I did try ramp testing but only when it was plugged into a socket or at the RCD when all circuits were still down, therefore it still did the 'trp' thing at x1. I should have done a ramp test at the RCD with circuits up but I didn't. Even if it did allow me test I'm still not sure why it would just immediately go to 'trp'.
I'm a bit unsure if Lucien's explanation was based on testing at x 1/2 or not.