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Mattja

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This is a new RCD, came in the CU. The max disconnection time I need to comply with is 400ms (Table 41.1 TN ac 230V). From a new RCD I'd expect something roughly in the region of 30ms (for a 30mA fault test). What I'm getting is 234ms (x0.5 there's no disconnection and x5 it's a 13ms disconnection).


TLDR: Meets the regs but a bit ---- compared to expectations.

Replace or use it?
 
try testing with it;s circuit/s dissed before replacing.
 
I tested at nearby socket to find the problem first, then turned off the MCBs and disconnected the RCD from its neutral bar and tested again, high 30mA disconnection time persisted.
 
Replace it. They aren't that expensive and its job is to trip before a shock current is reached. With a time like that I'd worry how it will perform in years to come.
 
Myself, I don't like it as it's an outlying result for a new device. Assuming it's a split load board, does the other one test as expected?
 
What I'm getting is 234ms (x0.5 there's no disconnection and x5 it's a 13ms disconnection).
You can't really say that its faulty when it disconnects within 300mS as required by the standard. Why do you feel uneasy about that? The 40mS required at 5I delta n for an RCD providing additional protection is easily met by the device.
 
Have you done a ramp test?
To what end?

He has verified that it doesn't operate at half its rated residual operating current and does operate at the full current already. Precisely what current between those parameters isn't really relevant.
 
We don't know whether it's faulty because we don't know the manufacturers' acceptance criteria. If they stipulate a new unit should trip in 200ms for example, then it's faulty even though it complies with the requirements of BS7671. The fact that it takes six times longer to respond than a supposedly identical unit (that has what I would consider 'normal' performance) would concern me, therefore I would replace it if possible. Obviously in an EICR one would accept it, but this is new work with the OP's name on, and there is more to quality work than achieving minimum regulatory compliance.
 
complies with the requirements of BS7671.

I was thinking more of the requirements of BS EN 61008 for an RCCB or BS EN 61009 for an RCBO.

I doubt you will have a manufacturer tell you that their device should operate quicker than the requisite time but feel free to contact them if you feel it will get you somewhere.
 

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