fire pump feeder protection

[gfdbiker]

I' have been reading all day on NEC 695 and my brain is getting mushy. I need some assistance in my intepretation. I have a new building being installed on a campus. It's being fed by 2- 13.8kv feeders from distribution gear in another building each from a different utility source. The 13.8 feeders travel approximately 150' through adjacent mechanical rooms were they terminate on a fusible disconnect switches on the transformer primaries. We are planning on tapping the secondary of both sides of a 13.8kv- 480v 2000kva double ended sub for the two feeder sources for the fire pump. The tap will be in it's own section before the main 480v breaker. Each tap would terminate in seperate disconnect with OCPD rated for locked rotor current located in the same electric room approximately 30' away. The fire pump is in an adjacent room. Both rooms are 1hr fire rated.

My questions are:

Does the primary side of each transformer need to be outside the building since it's a feeder not a service entrance(ie under the slab) or be 2 hour rated? My interpetation is no although it may be a wise thing to do.

Does the cable from the tap on the transformer secondary to the OCPD have to be "outside the building"(ie under the slab) or concrete encased? - My interpetation is yes

Does the feeder from the OCPD to the fire pump transfer/ controller have to be 2 hr rated since the fire pump room is adjacent to the electric room?

Can the 2 OCPD devices be in seperate but adjacent enclosures?

Thanks in advance

 

[Joe Villani]

Fire Pump feeder protection

Fire Pump feeder protection

Gfdbiker

Your 13kv feeders will have to comply with 225.52 which refers you to 225.32 nearest the point of entry of the feeders or outside

I think you may be able to use exception 1 with documentated safe switching procedures since your on a campus type facility.

If you route the 13kv feeders through the building I don't think they need to be 2 hr rated based on 695.6(A) exception. As a design choice if possible I would run the 13kv under the slab to the switchgear.

As far as the tap conductors as they are in the electric room 695.6(B) exception I feel the 2 hour rating will not be needed. My concerns are that these tap conductors are too long 30' and will need to be reduced to 25' or run in the slab under 2 inches of concrete.

The real issue will be how your AHJ interperates the tap conductors from the secondaries of the transformers. I do not see any relief from the tap conductors rules. ( I could be wrong) You size fire pump conductors based on the pump not the OCPD, The breakers can get big, now your tap conductors may have to be sized based on that OCPD.

feel the feeders to the fire pump transfer switch will not need 2 hr rating as long as they stay within the electrical room and the fire pump room. 695.6(B) exception

I feel the OCPD can be in seperate enclosures but have to comply with 695.4(2)&(3) and be remote from each other so you cant operate them at the same time.

Joe Villani

 

[gfdbiker]

Joe,

Per 695.6(c) I think says you don't have to adhere to the tap rules (distance) as long as they are underground. My OCPD would need to be 1200 amp (150HP at 460v). Do you know if a motor circuit protector breaker is permissable in this location? Typicallly you can get them to protect for locked rotor current. IE a 200 amp breaker can be set up to not trip until 1200 amps?

 

[gadfly56]

I' have been reading all day on NEC 695 and my brain is getting mushy. I need some assistance in my intepretation. I have a new building being installed on a campus. It's being fed by 2- 13.8kv feeders from distribution gear in another building each from a different utility source. The 13.8 feeders travel approximately 150' through adjacent mechanical rooms were they terminate on a fusible disconnect switches on the transformer primaries. We are planning on tapping the secondary of both sides of a 13.8kv- 480v 2000kva double ended sub for the two feeder sources for the fire pump. The tap will be in it's own section before the main 480v breaker. Each tap would terminate in seperate disconnect with OCPD rated for locked rotor current located in the same electric room approximately 30' away. The fire pump is in an adjacent room. Both rooms are 1hr fire rated.

My questions are:

Does the primary side of each transformer need to be outside the building since it's a feeder not a service entrance(ie under the slab) or be 2 hour rated? My interpetation is no although it may be a wise thing to do.

Does the cable from the tap on the transformer secondary to the OCPD have to be "outside the building"(ie under the slab) or concrete encased? - My interpetation is yes

Does the feeder from the OCPD to the fire pump transfer/ controller have to be 2 hr rated since the fire pump room is adjacent to the electric room?

Can the 2 OCPD devices be in seperate but adjacent enclosures?

Thanks in advance

1. No. 695.6(A) Exception

2. No. 695.6(B) Exception

3. No. 695.6(B) Exception, for both the switch gear room and the fire pump room; also 695.6(A) exception if the ATS is in the fire pump room.

4. Yes, but the two of them have to be remote from the other disconnects in the room. Whether they have to be remote from each other is an interesting question. I assume that the fire pump controller has an integral automatic transfer switch? So if someone is working on the fire pump, they likely want both sources next to one another so they don't forget to turn one off.

Joe, I certainly could be wrong, but don't think the tap rules apply since 695 generally views the supply to the fire pump as a feeder; see 695.6(D).