Circuit breaker testing

[i=p/u]

jibberish malcolm, it will make sense someday

 

[Engineer54]

Yeah, maybe 'days' was overstating it somewhat but even at 1.5 x the rated current which would be a sensible lower point you'd probably be in for an hour or so test time depending on the curve.


According to this document kindly pinned by Lenny on this thread the UK regs state that where two or more faults have occurred between the Ics and Icu values of the MCB the continued operation of the circuit breaker must be verified? Do they outline the verification procedure anywhere?

Not aware of any set verification procedures, but it's generally taken that testing MCB'S, MCCB's, ACB'S and the like, measuring at least 2 points on it's thermal protection curve, will verify that, that side of unit is in good condition for service, then of course a test(s) on the magnetic side of things. Obviously where adjustable parameters are present more tests would be prudent. But then with such breakers, internal/external current coils would likely be the case and then the tests, will generally be conducted through the coils with secondary injection test equipment...

Most larger frame size MCCB / ACB / etc Breakers, will generally have test provision for a manufacturers own protection proving unit!!

 

[DNS1]

If MCB testing was mandatory, where would we stop? Test the DNO fuse to make sure it's going to blow?

Fuses can't be tested, but are still considered safe as the manufacturing processes are so tight.

Personally never heard of an "incident" caused by an MCB failing to trip (although I am new to the game)

The OPs point about second hand is perfectly reasonable though, you'd never know with a pre-owned MCB... It could be brand new and just have been taken out the packaging by mistake, or it could have been dropped in a bucket of water...

 

[Engineer54]

If MCB testing was mandatory, where would we stop? Test the DNO fuse to make sure it's going to blow?

Fuses can't be tested, but are still considered safe as the manufacturing processes are so tight.

Personally never heard of an "incident" caused by an MCB failing to trip (although I am new to the game)

The OPs point about second hand is perfectly reasonable though, you'd never know with a pre-owned MCB... It could be brand new and just have been taken out the packaging by mistake, or it could have been dropped in a bucket of water...

Don't worry, it's never going to be mandatory to performance test MCB's for domestic installations!! lol!!!

 

[Knobhead]

Don't worry, it's never going to be mandatory to performance test MCB's for domestic installations!! lol!!!

Pity, I know where there’s a store room full of 2[SUP]nd[/SUP] hand load banks

 

[Engineer54]

Pity, I know where there’s a store room full of 2[SUP]nd[/SUP] hand load banks

Save them, for all those over sized stand-by generators that Mechanical Engineers have specified!!! lol!!