I2 for Circuit breakers and fuses

[captaincargo]

Hi guys
Could someone please help me with the calculations of ...
1. The fusing current (which trips the thermal side of the cb)
my understanding is it`s 1.45 x the nominal setting of the device
I.E 32A TYPE B would trip for overload at 1.45x32A=46.4A?

2.What do fuses to BS3036 trip at?

Many thanks.

 

[Adam_151]

Its accepted as being 2xIn

I.e. a 30A BS3036 would clear in a reasonable time at 60A (yeah...thats why they are discouraged these days )

If you had an MCB of X amps and a 3036 of Y amps, and the current that caused them both to operate in the conventional time was Z amps

If 2 times the 3036 rating is equal to to 1.45 times the mcb rating rating, then it follows that the 3036 rating is equal to 0.725 times of the MCB rating, and that number should look familiar