Another C&G level 2 question

[rich1]

This is another test question. Mulitple choice.

Which circuit breaker operates fastest with a 300A fault current.
1. 32A Type B
2. 32A Type C
3. 32A type D
4. 32A Type C RCBO.

I am thinking, as it's not been in any of the handouts, that a type B would see 300A as a short circuit and operate megnetically instantly (or in mS) where as a type D would take a few seconds for the thermal trip to operate?

 

[Fleeting]

Look at figures 3A1 to 3A6 in Appendix 3.
Don't worry it is not on the hand outs you are learning how to navigate BS7671.

 

[binky]

Nice to see the question writing hasn't improved

 

[rich1]

Look at figures 3A1 to 3A6 in Appendix 3.
Don't worry it is not on the hand outs you are learning how to navigate BS7671.

Sadly we won't have the Regs book to hand in the exam, only the on site guide.

Looking at the charts I see that 300A is just at the point on the 32A line where the magnetic trip meets the thermo trip on a class C and is nowhere near the line on a 32A Class B.

Am I right in reading that charts that Class B 32A breakers open instantly at 160A and above where as Class C open instantly at 320A and above?

 

[NozSpark]

Look at figures 3A1 to 3A6 in Appendix 3.
Don't worry it is not on the hand outs you are learning how to navigate BS7671.

Definitely look at these, but also think about how fast the RCD component of the RCBO needs to operate during fault conditions