Hi Helpers
When and where do I use the worst case scenario as far as calculating the cable resistance??
Thanks Norm
Please help me
When and where do I use the worst case scenario as far as calculating the cable resistance??
Thanks Norm
Use worst case scenario when calculating prospective short circuit as lower temp means lower resistance = higher current
Hi Gunsparky
The reason I'm asking this question. I am an electrical trades teacher at Wollongbar TAFE and I've had a student asking this question.
When and for what reason do I use the worst case scenario as far as calculating the cable resistance??
I recommend your web site to all of my students and notice that there are some asking questions in you forum.
Look forward to your assistance.
Norm Thomas
When working out your maximum Prospective Fault Current the worst time for this to happen is when the cables are cold, because that's when the resistance will be lowest and you will have the highest current.
When working out fault loop impedance, the worst time for it to occur is when the circuit has been loaded to the max for a while and the cables are hot. The resistance might be so high that the current is not high enough to trip the breaker in time.
Plenty of textbooks and websites use different numbers with no real explanation of why. It just depends on how serious you want to get. What are the chances of having a three-phase bolted short the instant you turn on the main switch? AND. What effect will a fault current limiter have?
It all sounds a bit over the top to me and I would be in favour of cutting students a bit of slack on a question like this. I only put it here because some examiners are a bit serious about it.
Thanks for recommending my site. It makes me feel good.
When working out fault loop impedance, the worst time for it to occur is when the circuit has been loaded to the max for a while and the cables are hot. The resistance might be so high that the current is not high enough to trip the breaker in time.
Plenty of textbooks and websites use different numbers with no real explanation of why. It just depends on how serious you want to get. What are the chances of having a three-phase bolted short the instant you turn on the main switch? AND. What effect will a fault current limiter have?
It all sounds a bit over the top to me and I would be in favour of cutting students a bit of slack on a question like this. I only put it here because some examiners are a bit serious about it.
Thanks for recommending my site. It makes me feel good.