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Discussion Starter · #1 ·
I have been trying some take home assignments from my Code class and have realizing I have no idea what I am doing in regards to calculating the size of circuit breakers (using the CEC book).

I was wondering if someone could do this example for me, so that I know which steps to take and which tables to go to. When I have been doing them, my answers are totally off. According to the answer sheet, the correct answer is 60A.

Here's the question:
Calculate the size of circuit breaker that would that would be required to properly protect a 5HP 120 V DC Motor using an FV starter?
 

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Discussion Starter · #3 ·
IF you're dealing with AC, do you just go directly to table 29 then?

There's also questions like:

Calculate the size of circuit breaker that would that would be required to properly protect a 15HP 600 V 3 phase squirrel cage motor using an FV starter?

I know table 44 is for three phase AC. I can go to 15HP and see that at 575V the amperage is 17. The answer sheet says 40 Amps as an answer. I would have thought I go to table 29 and multiply the squirrel cage under 30 amp value of 175%...but that gives 30A...
 

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Surfin-Dead said:
IF you're dealing with AC, do you just go directly to table 29 then? There's also questions like: Calculate the size of circuit breaker that would that would be required to properly protect a 15HP 600 V 3 phase squirrel cage motor using an FV starter? I know table 44 is for three phase AC. I can go to 15HP and see that at 575V the amperage is 17. The answer sheet says 40 Amps as an answer. I would have thought I go to table 29 and multiply the squirrel cage under 30 amp value of 175%...but that gives 30A...
Multiply by 1.75 for time delay fuses. Move across the table and you will see that CBs are 2.5 times fla
 
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