Cable Calc Question

[viperrowe2606]

60898 type c 1s? by following the graph?

 

[Phoenix]

If it was 1s, we wouldn't meet the 0.4second maximum allowed. Where are you looking?

 

[viperrowe2606]

Fig 3a5

 

[Phoenix]

Red line is your 400A fault current, so you read up to find where it meets the curve for your selected breaker.

Just for comparison, I've put on a blue line at 60A, and that first meets the line at the 0.1sec point.

So what do you think its telling you about the time of a 400A fault. Clue: It might be better to think of the lines on the graph as  a solid shape (green line rather than a single line)

 

[viperrowe2606]

Mate i'm lost not gona lie 

 

[viperrowe2606]

0.7s?

 

[viperrowe2606]

Does this mean as my fault current is higher than the 60A recommended for 0.1s disconnection time i can assume 0.1s in my calculation?

 

[Phoenix]

Edit, Just seen the latest post, Yes, once you get past 60A the operation is near instantous and we take that to be 0.1s (It can actually be faster, but other factors become significant and it gets complicated, etc), so we take 0.1. You'll find that the 60A is 6A x 10 and your'll notice something if you do (230*0.95)/60 ....

 

[viperrowe2606]

Again, thanks so much for your help, I thought I was gonna go mad as my tutor just finds it funny that it’s driving me crazy so throws bits in to confuse me now I can do I* X 0.1 / K? What’s that 0.95? Is this a factor for something?