Testing circuit breakers..Theory

[Jimmy Boy]

Apologies again if this is an old question but new to the forum what a fantastic forum it seems to be as well wish I had signed up years ago so much info on here it's unreal.. anyway .........

Theoretical question should we/ can we test circuit breakers for tripping ?

Take a typical rewirable fuse it does it's job day in day out OK it has a higher fusing factor compared to a 'B' breaker and offers less protection against overload but it does it's job.

Now take a typical Domestic breaker it sits there for possibly a decade between inspections with no testing, unlike it's big brother the RCBO or an RCD it has no 'test' button to check for mechanical function, and cannot be subjected ( As far as I am aware ) to any kind of simulated overload test either ramped or short circuit, so the big question is...will a 10 + Year old CB actually work when required ?

I am probably not alone in having 'sticky' RCD'S that trip better after a firm operation of the switch.

so are mechanical protective devices the bee's knees or an accident waiting to happen ?

 

[Deleted member 9648]

I think this is something that crosses all sparkies minds at some time or another, given the testing to destruction of the circuits supplied by the mcb it seems strange that the first link in protecting the circuit is just 'assumed up to the job".....that said the next one I see which doesnt trip will be the first.

 

[Jimmy Boy]

Does it not strike you as odd tho that we ( Quite rightly ) jump through hoops for EEBADS now ADS for protection and yet we will never know if a gradual overload of a circuit will actually make a CB trip ? The old CB's had a Bi-Metal strip in them are the new one's all mag field ?

 

[robsparky1975]

Very good point,i suppose they are factory tested,but suppose it may be difficult to get a tester to put 600amps down through mcb to make it trip in under 0.4s(rough guess on current)

 

[robsparky1975]

Does it not strike you as odd tho that we ( Quite rightly ) jump through hoops for EEBADS now ADS for protection and yet we will never know if a gradual overload of a circuit will actually make a CB trip ? The old CB's had a Bi-Metal strip in them are the new one's all mag field ?

I thought they still were,bi-metal for thermal overload,magnetic side for fault of negligable impedence,any one else clear this one up?

 

[Jimmy Boy]

I guess it's quite easy to wire a plug top up to simulate a short circuit scenario what concerns me is gradual overload

Lets say for example a B breaker has fusing factor of 1.4 ( from memory ) how are you going to test it ?....You can't

So you do all your testing all the readings but you can't guarantee that in the event of overload the CB is going to operate ?

So.....Has this been overlooked in the scheme of things ?

 

[robsparky1975]

Wonder what any mods think about this?

 

[Des 56]

We aren't expected to test Mcbs,they are covered by the manufacturers data
They are injection tested in the factory
Some testing is done on the network and oil platforms and such,but the general electrical installations are reliant on those manufacturuers
(Not very reliable I know considering the mass recall on the go)

I would think there could be little change in the characteristic of the Mcb from the date of manufacture
I suppose a continuity test could be done,but what reading would we expect
The injection test would possibly be more harmful than helpfull

A lot easier and cheaper to throw a suspect one away and plonk another in

Watch out for ideas like this because, there would be more money involved buying the test gear
The parasites who thrive on our occupation have enough of our hard earned for the time being as it is

 

[chiplard]

If there ever is a requiremnt to test MCB's, then who will buy the tester?

I dont think i would, i'd just swap out the MCB's and charge for it. At £5 a go they are almost disposable.

 

[pushrod]

I thought they still were,bi-metal for thermal overload,magnetic side for fault of negligable impedence,any one else clear this one up?

Yup you are correct. (mind not with the spelling of negligible impedance mind )