Electronic – What factors play into choosing type of MCB (Circuit Breaker) which is B16 vs C16 vs D16

automatic-circuit-breakercircuit breakercircuit-protection

Found these discussions and Q&As online around this and am trying to determine how/ when one would decide to choose which way to go?

http://www.theiet.org/forums/forum/messageview.cfm?catid=205&threadid=25220

Type B – trips between 3 and 5 time full load current

Type C – trips between 5 and 10 times full load current

Type D – trips between 10 and 20 times full load current

I will quote more information from the above thread as we begin to understand it more.

A simpler Q&A not as detailed assessment of factors as above discussion thread.

https://uk.answers.yahoo.com/question/index?qid=20130531054018AAVHMEw

Short-circuit relay trip-current setting (Im)

Short-circuit tripping relays (instantaneous or slightly time-delayed) are intended to trip the circuit-breaker rapidly on the occurrence of high values of fault current.

There is some insight on this question but its brief and specific and does not clarify or explain which to choose in other scenarios & why?

Working house main Control Miniature Circuit Breaker(25A) instead of transfuse (16A)?

Also will be sharing photos of existing ELCD/ MCB scenario at location for which the above fundamentals / factors need to be understood and then to arrive at a decision.

Best Answer

Your specifications on type B, C and D MCBs are incomplete. The crucial detail is that these are the overload currents they will tolerate for a maximum of 5 seconds. All of them should trip if they experience a current above their rating for longer.

The MCB type you would choose for a circuit therefore depends on the peak transient current you expect your load to draw. For most applications type B is perfectly adequate, but for circuits that supply very reactive loads such as air conditioners, motors and other machinery, large switch-on currents would force you to use C or D. The manufacturers of such devices will normally specify details such as supply cable size, MCB capacity and type and local wiring regulations may also restrict some of these choices.