Main rcd tripping even though its 100 ma

[Yr ys]

Hi

There's a workshop outside the main building with a couple of sockets protected by a 30ma rcd. Even though the rcd inside the main fuse box is 100ma the 100 ma rcd trips without the 30ma not tripping. Changed 30ma rcd still same. How can I get the rcd in the workshop to trip without tripping the main rcd?

 

[telectrix]

change the 100mA RCD to a S type. (delay)

 

[Yr ys]

But they are also protecting other circuits.

 

[Toneyz]

Tel is correct regarding changing the 100mA to a timed delayed (S type) to give discrimination ( sorry selectivity) however there must be a fault or collective leakage to make the rcd trip in the first place.

 

[Yr ys]

The rcd is tripping because the workshop is used to fix faulty fridges washing machines etc.

 

[stevethesparks]

Maybe consider a 1:1 low power isolating transformer.
Foster Transformer | 1:1-2:1-1:2 Isolation Transformers - https://www.foster-transformer.com/page/1-1-2-1-1-2-isolation-transformers

 

[stevethesparks]

Carroll & Meynell, 3kVA CM3000/230 Single Phase Isolation Transformer, 230V ac | eBay - https://www.ebay.co.uk/itm/Carroll-Meynell-3kVA-CM3000-230-Single-Phase-Isolation-Transformer-230V-ac-/163611847193

 

[Yr ys]

Thank you for your suggestions

 

[marconi]

If you opt for the 1:1 iso transformer to provide isolation from the mains and 100mA RCD, I'd recommend you take the secondary output and link N-E (-mark this up), then pass LN through a 30mA RCBO to supply LNE to dedicated and marked up sockets to use for testing and running the fridges and washing machines in for repair. This way you continue to protect these sockets with an RCD and be able to detect any problems with their earth leakage before return to their owners. You get the gist.

 

[Richard Burns]

Oddly I had a 100mA type S tripping before a 30mA RCD, but only after a new washing machine was installed, I believe the washing machine was generating a waveform to which the RCD was sensitive.
All tests on both RCDs were normal.
Changing the make of 100mA type S RCD resolved (or covered) the problem (The RCD was in a separate enclosure!)

 

[Toneyz]

The rcd is tripping because the workshop is used to fix faulty fridges washing machines etc.

Are there any other facts we need to know regarding this setup?

 

[Yr ys]

6 mil wire about runs to the workshop about 10 meters away from main fuse box. The wire is protected by a 30 a mcb.

In workshop it goes into a 30 ma rcd and then goes into 20 a mcb which supplies 2 sockets used for testing refrigerators, washing machines, deep freezers general white goods. It trips main rcd due to heating element faults and compressor faults which causes havoc in the office upstairs.

 

[Toneyz]

I think Marconi's idea would be the best solution.

 

[Deleted account]

6 mil wire about runs to the workshop about 10 meters away from main fuse box. The wire is protected by a 30 a mcb.

In workshop it goes into a 30 ma rcd and then goes into 20 a mcb which supplies 2 sockets used for testing refrigerators, washing machines, deep freezers general white goods. It trips main rcd due to heating element faults and compressor faults which causes havoc in the office upstairs.

Not sure I fully understand your set up.
Am I correct in thinking you use the sockets in the workshop to test The fridges and other white goods for faults?

 

[Yr ys]

Not sure I fully understand your set up.
Am I correct in thinking you use the sockets in the workshop to test The fridges and other white goods for faults?

Yes, that is correct.

 

[Deleted account]

We call that the bang test.

 

[Yr ys]

Bang test?

 

[EalingBadger]

Bang test?

Bang Test - as in you plug it in, switch it on and then there is a loud "BANG!".

 

[Toneyz]

My bang tester is due for calibration any suggestions where I can take it?

 

[Bellendian]

Time to invest in a PAT tester by the sound of it...

 

[Marvo]

Did you do a full ramp test on both RCD's? What were the trip times? Was the 100mA RCD faster than the 30mA?