Fire pump ocpd

[hhsting]

I have fire pump 40HP 200V three phase with fla of 115A.

The contractor is providing ocpd as main service disconnect. I have not on plans that says ocpd is 400A trip and in compliance with NEC 2017 Article 695.4(B)(2)(a). See below.

The 400A trip is very questionable for 40Hp three phase 200V fire pump of 115A.

How can it comply withNEC 2017 Article 695.4(B)(2)(a)?

 

[wwhitney]

How can it comply withNEC 2017 Article 695.4(B)(2)(a)?

2017 NEC 695.4(B)(2)(a) says that "Overcurrent protection for individual sources shall comply with 695.4(B)(2)(a)(1) or (2)". So you have a choice of subpart (1) or subpart (2). The plans are saying they are going to go with subpart (2).

Why do think there is a problem? Looking at the details of subpart (2), seems plausible that can be achieved with a 400A OCPD for a 115A FLA motor, and I assume the listing standard will ensure that it has been tested to meet all of those requirements.

Subpart (1) would require a higher value OCPD, but that subpart has no listing requirement, so it's not a tested combination. So it makes sense that without specific testing, more headroom would be required to ensure the OCPD doesn't trip when undesired.

BTW, in the 2020 NEC 695.4(B)(2)(a) was changed to say "Overcurrent protection for individual sources shall comply with the following:" which could be read to mean that you have to comply with both subpart (1) and subpart (2). But surely that is just an editing error, as the two subparts are more or less in opposition to each other, and the meaning intended is "shall comply with one of the following".

Cheers, Wayne

 

[hhsting]

2017 NEC 695.4(B)(2)(a) says that "Overcurrent protection for individual sources shall comply with 695.4(B)(2)(a)(1) or (2)". So you have a choice of subpart (1) or subpart (2). The plans are saying they are going to go with subpart (2).

Why do think there is a problem? Looking at the details of subpart (2), seems plausible that can be achieved with a 400A OCPD for a 115A FLA motor, and I assume the listing standard will ensure that it has been tested to meet all of those requirements.

Subpart (1) would require a higher value OCPD, but that subpart has no listing requirement, so it's not a tested combination. So it makes sense that without specific testing, more headroom would be required to ensure the OCPD doesn't trip when undesired.

BTW, in the 2020 NEC 695.4(B)(2)(a) was changed to say "Overcurrent protection for individual sources shall comply with the following:" which could be read to mean that you have to comply with both subpart (1) and subpart (2). But surely that is just an editing error, as the two subparts are more or less in opposition to each other, and the meaning intended is "shall comply with one of the following".

Cheers, Wayne

I posted NEC 2017 Article 695.4(B)(2)(a)(2) below.

For part a 600% i get 690A trip
For part b 24 times fla i get 2760A trip
For part c 300% i get 345A trip

None of them are as stated 400A trip. Thus my question 400A trip correct or incorrect?

 

[wwhitney]

For part a 600% i get 690A trip
For part b 24 times fla i get 2760A trip
For part c 300% i get 345A trip

For a given OCPD with a given single rating, you have a trip curve. That tells you that, to make up some numbers, at 110% of rated current, the OCPD may never open; at 150% of rated current it will open within 60 minutes, and at higher multiples of rated current, the OCPD will open faster. And actually, the curve is really a band; e.g. at 150% of rated current, it will open in 45-60 minutes. [Again, all number made up.]

So the requirements in (a), (b) and (c) are specifying points on that trip curve, not specifying overall trip ratings. You are comparing apples and oranges.

The point is that the listing should cover the necessary testing that ensures that (a)-(d) are satisfied. So if they use a listed product according to its listing, 695.4(B)(2)(a)(2) will be satisfied. If you want to research this further, figure out what the listing standard is, look up the text of that standard at ul.com, and you should find some section in that listing standard that mirrors the requirements in (a)-(d). {This is an assumption on my part, that the NEC and the UL standard are coordinated here, but they are supposed to be, that's why the NEC provides details like (a) through (d) to tell UL what the listing standard should say.]

Cheers, Wayne

 

[don_resqcapt19]

You have to look at the time trip curves for the 400 amp breaker. One I looked at shows the 150 second trip point at 800 amps, and the instantaneous trip point of around 4000 amps. With a full load current of 115, the 400 amp breaker should never open at 300% of the FLC.

 

[gadfly56]

Why is there a separate OCPD? The fire pump controller, which is listed as service equipment, has a breaker meeting all these requirements. If you need a disconnect, just select one for the locked rotor current and be done with it.

 

[hhsting]

Why is there a separate OCPD? The fire pump controller, which is listed as service equipment, has a breaker meeting all these requirements. If you need a disconnect, just select one for the locked rotor current and be done with it.

Short answer I am reviewer not the designer. I can recommend but their is no code requirement to stop designer to placing ocpd if he/she wants to.

 

[jim dungar]

Why is there a separate OCPD? The fire pump controller, which is listed as service equipment, has a breaker meeting all these requirements. If you need a disconnect, just select one for the locked rotor current and be done with it.

I had one installation where the existing FP service was relocated to the secondary side of an customer owned transformer, this necessitated the addition of an upstream feeder protective device. we followed the method outlined by Don in post #5.