2382 Question

[Markey]

I got this question wrong and would like to know why

A 30Amp Semi Enclosed BS3036 Fuse receiving a prospective fault current of
130A would disconnect in

a. 5.0sec
b. 1.0sec
c. 0.4sec
d. 0.2sec

Please can someone explain the correct answer and how they came to that answer (already knowing doesnt count )

I used FIG 3.2A on P 245 to come to my answer.

 

[ricicle]

It would be slightly longer than 1 sec so I will round up to the next answer at 5 secs. (140A required for 1 sec operation)

 

[ericmark]

I would reckon 2 seconds using graph. Do remember log log scale. Using box you can see 140A takes 1 sec so will have to be more than 1 second and less than 5 seconds.

So answer I suppose would be (a) but really a bad question as it should have been one of the figures in the box.

Really answer is "None of the above".

 

[Markey]

hmm interesting, i also answered a) based on the same reasoning

it was taken from

http://www.djtelectraining.co.uk/questions.htm first 2382 paper Question 40.

They think the answer is C 0.4, me thinks they might be wrong then

 

[Albert]

As already mentioned, if 140A will require 1 sec, less current will require more time. I think that it will be less than 2 sec but as the graph does not give you a precise figure, you should go to the next safest option and I agree that the answer should be 5sec. There is no way that 0.4 sec is correct.

 

[Spark123]

I think they have probably made a slight mistake with the figures, looking at the other sheets i.e. the 2391 there's typing errors too.

 

[securespark]

Maybe they thought it should be 4s and got the dp in the wrong place?

 

[Albert]

I agree that the possible option is that they put the dot in the wrong place, if it is so, I think that the answer should be 2sec.

 

[securespark]

Maybe they thought it should be 4s and got the dp in the wrong place?

As Albert rightly points out, that should read 2s....