Fire Pump Feeder

[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

 

[don_resqcapt19]

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.

 

[mshields]

How about if...

How about if...

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%?

 

[gadfly56]

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.

 

[ron]

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.

 

[mshields]

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

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?