NFPA 20 versus NEC

[hhsting]

NFPA 20 says for fire pump 10.4.3.3.1 "The circuit breaker shall have the following electrical characteristics:
(I) A continuous current rating not less than 115 percent of the rated full-load current of the motor"

However NEC 2014 Article 695.4(B)(2)(a)(1) which says to size per 6x FLA= LRC or 695.4(B)(2)(a)(2) assembly listed for fire pump.

Am I missing something. Is their a difference between two? Why is their discrapency?

Sent from my SM-G935U using Tapatalk

 

[hhsting]

NFPA 20 says for fire pump 10.4.3.3.1 "The circuit breaker shall have the following electrical characteristics:
(I) A continuous current rating not less than 115 percent of the rated full-load current of the motor"

However NEC 2014 Article 695.4(B)(2)(a)(1) which says to size per 6x FLA= LRC or 695.4(B)(2)(a)(2) assembly listed for fire pump.

Am I missing something. Is their a difference between two? Why is their discrapency?

Sent from my SM-G935U using Tapatalk

Post #1 really confusing how to size fire pump breaker one code says one thing and other says something else.

Appreciate your input in resolving if anyone knows what is going on.

 

[steve66]

I'm not 100% sure, but I always thought the 6x rated current or locked rotor current rating was required for the additional service disconnecting means permitted by 695.4(B)(1)(a).

The other specs including the 115% are specifically for a listed fire pump controller.

 

[david luchini]

I agree with Steve. The NEC is permitting you to install a circuit breaker as a disconnecting means between the source and the fire pump controller...and basically saying to size it so that it will never trip because the controller required by NFPA 20 will provide the required protection to the circuit.

 

[hhsting]

Please see attached sketch showing fire pump controller, ats, breaker all in one and the 50 hp, 208v three phase fire pump fla of 172.5A.

Bkr #1 on POCO side shown is sized per NFPA 20 115 percent of fire pump full load amps which comes to 200A. Same with Bkr #2 Generator side 200A.

Should not the BKR #1 be sized per 6x the full load to 1200A and Bkr #2 be sized per NEC 2014 Article 695.4(B)(a)(2)(b) pickup of full lpad amps but not greater than 430.62?

Sent from my SM-G935U using Tapatalk

 

[david luchini]

Should not the BKR #1 be sized per 6x the full load to 1200A and Bkr #2 be sized per NEC 2014 Article 695.4(B)(a)(2)(b) pickup of full lpad amps but not greater than 430.62?

NEC 695.4 doesn't say anything about sizing BKR #1 or BKR #2...only BKR #3.

 

[hhsting]

NEC 695.4 doesn't say anything about sizing BKR #1 or BKR #2...only BKR #3.

Who or what code determines sizing of Bkr #2 or Bkr #1 size?

 

[Jraef]

I believe the issue has to do with the fact that NFPA 20 now allows the Fire Pump Controller mfrs to use Instantaneous Trip (aka MCP) breakers in the controllers. They do not have thermal / long time trips at all, only the mag trips, which cant be set at up to 13x the motor FLA. Nothing unusual here except that normally an MCP cannot be used in a motor starter unless there is an OL relay, but there is no OL relay in a Fire Pump Controller so they had to make a special exception. This section in NFPA 20 is just re-emphasizing that this breaker must be sized at 125% of the motor FLA as far as the continuous current rating, probably because someone tried getting away with something smaller.

The NEC section is, as mentioned, about any ADDITIONAL OCPD in the circuit being sized to allow the FP to "run to destruction".

 

[david luchini]

Who or what code determines sizing of Bkr #2 or Bkr #1 size?

NFPA 20.

 

[hhsting]

I have re-attached the sketch except fire pump Ats, controller, breakers is service rated so has service grounding electrode system and added Fdr #1.

If Bkr #1 or Bkr #2 is sized per NFPA 20 then how would then one size Fdr #1 equipment grounding conductor or is it even equipment grounding conductor?

 

[david luchini]

If Bkr #1 or Bkr #2 is sized per NFPA 20 then how would then one size Fdr #1 equipment grounding conductor or is it even equipment grounding conductor?

I think 250.122(D)(2) would apply.

 

[hhsting]

I think 250.122(D)(2) would apply.

Ok but exact size of Bkr #1 is not know. NFPA 20 says shall not be less than 115 percent of motor full load amps. So their is no maximum.

Also what would be the service disconnect the Bkr #1 sized by NFPA 20 or need additional breaker as service disconnect?

 

[david luchini]

Ok but exact size of Bkr #1 is not know. NFPA 20 says shall not be less than 115 percent of motor full load amps. So their is no maximum.

Size of BKR #1 is not relevant to 250.122(D)(2).

You know motor HP, figure the maximum permitted dual-element fuse for that HP, and size the EGC per that fuse size.

 

[hhsting]

Also what would be the service disconnect the Bkr #1 sized by NFPA 20 or need additional breaker as service disconnect?

Sent from my SM-G935U using Tapatalk

 

[hhsting]

Sketch attached in post#10: If its service rated fire pump/controller/breaker all in one then should not their be another breaker other than Bkr #1 which is sized per NFPA 20 for service disconnect in the equipment or outside or can Bkr #1 sized per NFPA 20 be used as service disconnect? Anyone here know? Appreciate your input

 

[hhsting]

Size of BKR #1 is not relevant to 250.122(D)(2).

You know motor HP, figure the maximum permitted dual-element fuse for that HP, and size the EGC per that fuse size.

David luchini what if their is another breaker upstream of fire pump ATS controller per 695.4(B)(2)(a)(2) then how should you size the EGC?

Sent from my SM-G935U using Tapatalk