1. ## Fire Pump Feeder

To a 100HP fire pump, is an MI feeder emergency feeder (i.e. run from the generator) comprised of 3#1 &1#6.

Per 310.15(B)17 in the 75 deg column, #1's and #6's are rated for 195A and 95A respectively.

They could have gone with just a 3 phase feeder but they didn't. They included the neutral.

My question is that given this feeder does not exceed 200A, by code allowance, would it be permissible to run a neutral that is 50% that of the phase conductors.

Wouldn't the feeder need to be over 200A, per 220.61 to reduce the size of the neutral at all?

By the way, the OCPD is a fused switch with 175A fuses (assuming they are dual element type). A bit low but OK I guess assuming the pump has a soft start or drive.

In any event, what do you think?

Thanks,

Mike

2. If there is no neutral load, there is no need to look at 220.61. It is my opinion that the rule in 215.2(A)(2) would apply to this grounded conductor.

What if there were lets say a small load on the neutral load (lets say it's feeding a mostly 3 phase load DP but with single pole breaker load).

Does 215.2(A)2 still apply. Can I size the grounded conductor/neutral based on 250-122.

And how does that gybe with the 220 rule that says for feeders up to 200A, the grounded conductor needs to be 100%?

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Originally Posted by mshields
To a 100HP fire pump, is an MI feeder emergency feeder (i.e. run from the generator) comprised of 3#1 &1#6.

Per 310.15(B)17 in the 75 deg column, #1's and #6's are rated for 195A and 95A respectively.

They could have gone with just a 3 phase feeder but they didn't. They included the neutral.

My question is that given this feeder does not exceed 200A, by code allowance, would it be permissible to run a neutral that is 50% that of the phase conductors.

Wouldn't the feeder need to be over 200A, per 220.61 to reduce the size of the neutral at all?

By the way, the OCPD is a fused switch with 175A fuses (assuming they are dual element type). A bit low but OK I guess assuming the pump has a soft start or drive.

In any event, what do you think?

Thanks,

Mike
That seems way low. What is the voltage for this pump? Per NFPA 20, the LRA for a 100 HP pump at 460 volts would be 725. No exception for soft start applies.

5. Originally Posted by mshields
To a 100HP fire pump, is an MI feeder emergency feeder (i.e. run from the generator) comprised of 3#1 &1#6.
The #6 is suspiciously / coincidentally the same as the 175A OCPD EGC from 250.122.

Are you sure it is a grounded conductor and not a grounding conductor? Meaning no L-N loads.

6. ## 480V and a clarification on which feeder we're talking about

That's my suspicion as well on the #6 conductor. The voltage is 480V and this, it bears clarifying, is on the generator side not the utility. So utility feeder has an OCPD that is 6 times FLA. On the generator side, max is 2.5 (1.75 for a inverse time fuse; i.e. same as for any motor) which is what I was referring to.

Do you agree?

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