17th Edition Wiring Question

[rustynails]

A question that some of you may be able to help me with:

If an 80 amp B type circuit breaker is required to disconnect the electrical supply in 0.1 seconds how much fault current is required?

A: 80 amps
B: 800 amps
C: 40 amps
D: 400 amps

Where in the green book is the answer for this one?

:banghead:

 

[telectrix]

time/current graphs. near the back of the book

 

[Dan the spark]

400amps mate page 301 brb

 

[rustynails]

Ah yeh - right under my nose. ta

 

[rustynails]

And I'm stuck with the answer to this one as well:

A BS1361 Fuse, rated at 45 A, is carrying a fault current of 240A, the protective device should operate in:

A: 0.4s
B: 8.0s
C: 300s
D: 5.0s

Any ideas where in the book this is?

Thanks

 

[Dan the spark]

I think that bs1361 fuses are now classed under bs88-3 fuses so page 296

 

[Dan the spark]

If you look at appendix 1 page 277 it tells you there about the 1361 being replaced by bs88-3. Hope this helps

 

[rustynails]

Found the answer now, 5 secs I think. Table says 220A not 240A but close enough for a guess and also because of the now redundant fuse type the numbers might be slightly different.

 

[Dan the spark]

I'm guessing you are going thru past papers at the moment. As geeky as it sounds I have just had a look in the red book( the one before the green in case you didn't know) and that has 240amps as the fault current and that was a 5sec disconnection time.
So like you say your answer will be 5secs