RCD tripping at 1/2 test

[jeremy]

Testing some new cabinets today which had in them a PDU with a 30mA rcd upfront as main switch. ( We build among other stuff, communications cabinets for highways, railways, etc). First one tested tripped on 1/2 fault current. Tried another cab, same thing. Did a ramp test, (tester is Kewtech kt64), tripped at indicated 18mA, though it felt like it was going at 15mA, but the tester indicated 18 before it stopped. ( I think they test too fast for accurate diagnostics?) I would expect a 30mA RCD to hold until about 21-24, from experience, and would have been disappointed with 18, but for 11 to fail at 1/2? One the one hand, I hope I've missed something ever so simple so that we can ship these cabs tomorrow, but I think I've covered everything. Any thoughts?

 

[Sintra]

Did you test at the RCD with no appliances connected? If they are ramping at 18mA then your tester might need calibrating as at 1/2 times it should be outputting 15mA.

 

[thekingiam]

Tried another tester? Try a different make rcd? Disconnect loads and just test rcd?

 

[R G]

Just a thought , was the test carried out with all loads disconnected/ isolated ? , could be some leakage in the equipment connected ..

 

[telectrix]

might be some leakage on the load, as sintra said, can you test with no load connected?

 

[R G]

Did you test at the RCD with no appliances connected? If they are ramping at 18mA then your tester might need calibrating as at 1/2 times it should be outputting 15mA.

Beat me to it ..

 

[trev]

Just a thought , was the test carried out with all lads disconnected/ isolated ? , could be some leakage in the equipment connected ..

The lads were on their teabreak Ray
Sorry mate

 

[R G]

The lads were on their teabreak Ray
Sorry mate

Its those lads again , hahaha,

 

[NickD]

What I think, right, is test it with no loads connected.

 

[jeremy]

Tested with probes, ( there's something not right about the word "probes"!) at RCD load side, tried another tester, same make, 2 years younger, tried a different test supply circuit, tried swearing at it, a lot, ( that usually works). They're A type , in anticipation of a rectifier being fitted by the client, but that shouldn't affect the test. The way I see it is no matter what the circumstances of the test, whether it's a simulated situation or real, it shouldn't trip at 1/2, it should trip at x1 and x5. Trip times for x1 and x5 were the same if that's any use? Shouldn't be too bothered as I've had enough of running a workshop and am going back into the field ( got a job as a scarecrow!), but strangely I care what leaves the 'shop whilst I'm there.

 

[R G]

Although you have tested with probes , was the load completely disconnected , i.e. was the neutral and live to the load disconnected ,

 

[jeremy]

Admittedly, no, there was still an IEC dis strip connected. The only load there in theory is a neon indicator. I'll re-test when I get in early tomorrow. Thanks for all the ideas, sleep well chaps!

 

[Hawkmoon]

Is the RCD definitely 30mA? (easy mistake to make)

 

[thekingiam]

Got caught out by that in the past!

 

[shanky887614]

Is your tester set to 30mA?

A work colleague had his set to 10mA and was wondering why it didnt trip XD