Ring Final Zs question

[Booyaka]

Hello

I work on occasions with an old school spark who doesnt use a PC much so i said i will ask the expert brains on here regarding this issue

Upon doing a Zs test on the ring final using the usual plug on lead from the MFT1552 tester, He applied the non trip Zs due to the ring final being RCD protected, and for some reason it kept reading Trip because even though using the no trip selection the RCD still kept tripping out!

Any ideas from the land of expert minds?

Many thanks

 

[Spark123]

Everything else unplugged from the circuit?

 

[Booyaka]

Yeah when i spoke to him on the phone he said everythin was unplugged. what are the list/range of possibilities that can trip the RCD on a non trip and i will run through them with him next time?

Many thanks mate

 

[Spark123]

What were the test results for the RCD like? What rating RCD, was it ramp tested? What make and model, what type RCD (A or AC)?

 

[Booyaka]

unfortunately i do not know the exact details of the rcd, he did all the relevant tests for the rcd ans it was fine and also did no trip zs tests on other circuits and it didnt trip so it must be something to do with the ring im guessing?

 

[Spark123]

I'm wondering if it was a type A RCD (AC and DC pulse).
One sure way to tell if it was the RCD or the circuit causing it would have been to test the RCD in isolation.

 

[Booyaka]

unfortunately that part is beyond my knowledge at the moment, i know that its a block of flats he is testing so its a general 30mA rcd i know he ran the test on the rcd ans it was fine

out of interest how much current does a circuit take when Zs tested? i take it the ramp test will prove whether the RCD is tripping due to the test current?

all the other circuits did not trip under non trip but the ring, any ideas on the ring like polarity etc?

 

[Spark123]

It depends on the technology of the tester, DLOC uses DC to lock an RCD, Megger iirc uses a method employing a low current to earth to not trip an RCD. A ramp test will tell you the minimum amount of current required to trip the RCD which can help pinpoint a nuisance tripping RCD, however it shouldn't be tripping at 15mA as that is one of the normal checks.

 

[Booyaka]

so if he carries out the ramp test and the rcd trips before 15mA then the rcd is faulty

what kind of current does the Zs test put through a circuit?

Plus is there anything the ring final circuit could have wrong with it etc?

 

[Spark123]

There shouldn't be anything wrong with the Ring Final circuit as if he is doing the testing in the correct sequence everything should have already been checked i.e. IR test.
I think the MFT1552 delivers 15mA on the no trip test but am not 100% sure. You would normally do a 0.5I test to ensure the RCD does not nuisance trip anyway.
Has he tried new batteries in the tester?

 

[Booyaka]

Hey spark thanks very much for the info, great help as always

 

[Booyaka]

Hey spark123

just to inform you ive just chatted with him and he gained some advice over the phone.

he did the ramp test and the rcd was tripping at 23mA so all cool there

so he then did the same no trip test by using the martindale plug with the back three holes exposed and used his three seperate leads instead of the built in plug and it didnt trip out and he got a good reading.

 

[Spark123]

Very odd, there shouldn't be much difference in using the plug to using the 3 test leads.
Just tried it with mine and get the same results using both the 3 leads and the plug. It is sounding like the instrument which is causing it, 1st thing I'd try is new batteries.

 

[Booyaka]

many thanks mate for your time on this issue

 

[securespark]

When my Alphatek 61557 has a lower than normal voltage, an EFLI test comes back with "RCD" (the usual display if the RCD has tripped).

What was the measured voltage?