Circuit breaker testing

[Desaray]

Hi Guys
Just been wondering, why dont we test circuit breakers? There's testing equipment that does this on an industrial scale but how come its not applicable in the household? Do we just have to trust the manufacturers guarantee, as ive recently fitted a CB new and it wasnt functioning correctly, ie it wastripping too soon.
Thanks

 

[Desaray]

Woops scrap this post ive just found a similar one giving an answer, sorry!

 

[Knobhead]

as ive recently fitted a CB new and it wasnt functioning correctly, ie it wastripping too soon.

Out of interest how did you test it to confirm it wasn't conforming to the time curve?

 

[Desaray]

It was tripping at half its rated value, basically it was a 30A CB and was tripping at 16A. I had an ammeter measuring the current draw and just used appliances like kettle and toaster as I was also checking to see if these were faulty.

 

[Simonslimline]

It was tripping at half its rated value, basically it was a 30A CB and was tripping at 16A. I had an ammeter measuring the current draw and just used appliances like kettle and toaster as I was also checking to see if these were faulty.

How long did it take to trip at 16Amps?

 

[Engineer54]

The test equipment to test MCB's would cost far more than the most expensive MFT you can buy. Seeing as MCB's are generally going to be cheap to just replace, it makes far more sense to go down the replacement route!! Unlike say RCD devices, MCB's are generally taken as being a very reliable protective device.

 

[Deleted member 72666]

What brand of mcb and what part of the cct was the reading taken?

 

[Engineer54]

If you consider the MCB to be faulty just change it out for a new one. Why muck about with it?

The existing unit may have taken a short circuit condition in it's past and now no longer functioning to it's type/rating specification....

 

[Desaray]

It was a brand new board i had put in and it was the kitchen circuit that was tripping so I first assumed it to be a faulty appliance. I had every part of the installation switched off except for that circuit and had a clamp ammeter on the mains tail as it was easiest to get the clamp onto.
I wasnt taking times when it was tripping but I would say it varied between 5 and 14 seconds.
And yes its what the other post(under the same title) said that it is too expensive for the equipment when its generally easier and cheaper to replace what are normally very reliable.

 

[Knobhead]

You also have to take in to account that to correctly test a MCB it wouldn’t be fit for continued use. Testing the MCB would involve using several points on the exponential time curve. OK at the lower currents although it could take several hours, at the maximum prospective short circuit current the MCB wouldn’t be fit for continued reliable use afterwards.

The manufacturers do batch testing, say 1 in every 50.

There's also the minor point, they can afford to throw them away, can you?