V
VladM
Miniature circuit breaker (MCB) time-current characteristic has two specific points in the big-times area:
According to the standards and to the manufacturers catalogues:
- current equal or less than 113% will not trip the MCB in a period of 1 hour,
- current equal or greater than 145% will trip the MCB in a period of 1 hour,
- current in between of 113% and 145% may either trip MCB or not.
The question arises how to coordinate MCB and cable: should the cable long-term admissible current be greater than 145% of MCB rated amps?
In other terms the above mentioned feature of MCB (not to trip if less than 113%) makes me very uneasy about specifying cable cross-secion for 100% of MCB rated amps.
What do you think? Isn't it dangerous to size the conductor to 100% of MCB rated amps concerning the fact that MCB will not trip until 113% and may not trip until 145%?
- 113% of MCB rated amps (current of non-tripping),
- 145% of MCB rated amps (current of tripping).
According to the standards and to the manufacturers catalogues:
- current equal or less than 113% will not trip the MCB in a period of 1 hour,
- current equal or greater than 145% will trip the MCB in a period of 1 hour,
- current in between of 113% and 145% may either trip MCB or not.
The question arises how to coordinate MCB and cable: should the cable long-term admissible current be greater than 145% of MCB rated amps?
In other terms the above mentioned feature of MCB (not to trip if less than 113%) makes me very uneasy about specifying cable cross-secion for 100% of MCB rated amps.
What do you think? Isn't it dangerous to size the conductor to 100% of MCB rated amps concerning the fact that MCB will not trip until 113% and may not trip until 145%?
