How to prove an MCB functions correctly?

RCDs have either a rather delicate mechanical part or an electronic part.  The more rugged MCB seems to be considered more reliable, which I guess is the main part of why they're not tested.  For simply verifying that instantanous tripping happens at a suitable current, a variable autotransformer should do the job without much draw from the mains, and wouldn't have to be very big if only rated for brief currents of <<1s: this makes me suppose that difficulty and expense were not the main reasons for ignoring MCB testing. 

Modern batteries, capacitors and power electronics manage some impressive feats in recent secondary and primary injection testers for relays (as mentioned by OMS and mapj1) so probably one could now get a much lighter and smaller alternative to a transformer if there were a market for testing MCBs as a routine task.


In Paul's situation, if not having fancy things like a strong variac and DC clamp meter, oscilloscope or similar, I'd probably check for 'instantaneous' trip across a healthy car battery, and thermal trip by connecting a cooker and well-loaded ring to the MCB, attaching an AC clamp, and pushing up to 80 A or so.  Even if this doesn't check with good measurement of time at the minimum required currents, it gives confidence that it can trip both quickly and slowly. 

RCDs have either a rather delicate mechanical part or an electronic part.  The more rugged MCB seems to be considered more reliable, which I guess is the main part of why they're not tested.  For simply verifying that instantanous tripping happens at a suitable current, a variable autotransformer should do the job without much draw from the mains, and wouldn't have to be very big if only rated for brief currents of <<1s: this makes me suppose that difficulty and expense were not the main reasons for ignoring MCB testing. 

Modern batteries, capacitors and power electronics manage some impressive feats in recent secondary and primary injection testers for relays (as mentioned by OMS and mapj1) so probably one could now get a much lighter and smaller alternative to a transformer if there were a market for testing MCBs as a routine task.


In Paul's situation, if not having fancy things like a strong variac and DC clamp meter, oscilloscope or similar, I'd probably check for 'instantaneous' trip across a healthy car battery, and thermal trip by connecting a cooker and well-loaded ring to the MCB, attaching an AC clamp, and pushing up to 80 A or so.  Even if this doesn't check with good measurement of time at the minimum required currents, it gives confidence that it can trip both quickly and slowly.