430.62 Short -Circuit & GF Protection

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Sparky2791

Sparky2791

Senior Member
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Northeast, PA
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Electrical Design
Hello!
When one sizes SC & GFP for a motor per 430.62 are you required to use the maximum percentage of full load current value in Table 430.52 when determining the size of the OCPD

For example 75HP 208V 3 phase motor = 211A per Table 430.250.

Using an Inverse time circuit breaker if Maximum is required 211 x 250% = 527.5A (600A Breaker required)

I am thinking that is not the case but wanted to be certain.

It states ....not greater than the largest rating or setting of the branch circuit short -circuit & ground-fault-protective device for any motor supplied by the feeder.

If maximum value must be used I would think it would state.......... no less than the largest rating or setting of the branch circuit short -circuit & ground-fault-protective device for any motor supplied by the feeder.

In the end you still need the breaker sized to allow starting of the motor.

Thanks in advance for the replies
 
430.62 uses the language "not greater than" so it is clearly providing a maximum allowable size. You can go smaller if desired.

But now take a look at 430.63 and tell me what that means. That one seems like a minimum allowable size. Which is confusing as far as 240.4, as nothing seems to impose a maximum size.

Cheers, Wayne
 
wwhitney said:
430.62 uses the language "not greater than" so it is clearly providing a maximum allowable size. You can go smaller if desired.

But now take a look at 430.63 and tell me what that means. That one seems like a minimum allowable size. Which is confusing as far as 240.4, as nothing seems to impose a maximum size.

Cheers, Wayne
Click to expand...
430.63 does not apply to a single motor load.
 
wwhitney said:
Sure. But it is related to the OP's question by being similar, nearby in the code, and apparently a minimum rather than a maximum.

Cheers, Wayne
Click to expand...
Thanks. Ill take a look. This actually came up because of 695.4.(B) (2) (b) which requires compliance with 430.62 short circuit protection only. I have a gen set with a breaker feeding the fire pump controller ATS. Ironically in that case I would think they want you to use the maximum size breaker which is why I asked in the first place.
 
Good question. I think better clarification would be helpful, with actual example. We are here to learn.
Your patience please. " Everything is easy when you understand it "
 
JEFF MILLAR said:
Good question. I think better clarification would be helpful, with actual example. We are here to learn.
Your patience please. " Everything is easy when you understand it "
Click to expand...
Jeff - You are referring to? Actual example of the installation which prompted my original posted question?
 
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