General Breaker Questoion

[leighm]

Hi,

Can anyone please explain the difference between an 'MCB' a 'B Type Breaker' and a 'C Type Breaker'

Are they one in the same, just varying quality or do they do different/specific things?

Thanks,
Leigh.

 

[Adam_151]

the magnetic trip is different, but the thermal trip is the same

Type B trips at between 3-5 labeled rating instantly, for type C its between 5 and 10, and for type D between 10 and 20.

You have to make sure the ELFI is low enough for the breaker you use, the elfi dictates the size of the current that will flow in a phase-earth fault and this must be sufficent to trip the breaker instantly, the reason you don't use type Bs all the time is because some equipment (things like motors and loads incorporating capacitors) takes a surge on start up and this can trip breakers even though there isn't a fault.

Generally speaking, Type B is general purpose, Type C is used where there are motors, and sometimes on circuits supplying lighting and power supply cicruits. Type D are rarely used and are for things like welding machines, X ray machines, etc

 

[leighm]

Thanks Adam.

Cheers,
Leigh

 

[JohnD]

Looking at the trip curves, I see they all trip in about 40 seconds at 1.5x overload, so if you have (for example) plugged in too many electric hetaers, the reaction will be the same, it's the very big currents, that should trip in a second or less, where the more industrial ones will accomodate a bigger current for a short time before tripping.

I've been trying to think if a type C is OK in a domestic environment when spotlight bulbs burn out and trip a 6A MCB, there's a formula somewhere to work it out. A type C 6A would be better than a type B 10A as it would react to the overload situation better.

 

[Spark123]

Max efli is given by 240/(6A x 10) and then multiplied by 0.8 for temp correction (10-20degC for a 70degC cable).
10 is for a C type breaker, B type 5, D type 20.

 

[cozycats]

Type c are perfectly acceptable on a 1.5/1.0 lighting circuit.

 

[securespark]

Crabtree and Wylex RCBO's are all C types........

 

[Spark123]

Type c are perfectly acceptable on a 1.5/1.0 lighting circuit.

Yes, providing the circuit has been checked for compatability with a type c breaker, which is why imo changing an mcb for one with a higher current rating or magnetic setting type should only ever be carried out by a competent person with the correct test equipment.