How to find out if OCPD comply with 695.4 (B)(2)(a)(2)

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binwork91

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new york
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electrical engineer
How to find out if OCPD comply with 695.4 (B)(2)(a)(2)?
I think (d) is the easiest to verify, as long as the breaker is non-adjustable.

(a) and (c) should be checked using the Time-Current Characteristic (TCC) curve.

What about (b)? A re-start transient of 24 times the full-load current is a large number — but is there any specified time range?





695.4 (B)(2)(a)(2)
(2) Overcurrent protection shall be provided by an assembly listed for fire pump service and complying with the following:
a. The overcurrent protective device shall not open within 2 minutes at 600 percent of the full-load current of the fire pump motor(s).
b. The overcurrent protective device shall not open with a re-start transient of 24 times the full-load current of the fire pump motor(s).
c. The overcurrent protective device shall not open within 10 minutes at 300 percent of the full-load current of the fire pump motor(s).
d. The trip point for circuit breakers shall not be field adjustable.
 
I think that only applies to the OCPD in the listed fire pump controller, and if the controller is listed the OCPD will comply.
Notice the difference in trip time for (1) and (2). In one, it must carry locked rotor current forever and in (2) it can trip after 2 minutes at 600% of motor full load current. The common assumption is that 600% is locked rotor current.
 
don_resqcapt19 said:
I think that only applies to the OCPD in the listed fire pump controller, and if the controller is listed the OCPD will comply.
Notice the difference in trip time for (1) and (2). In one, it must carry locked rotor current forever and in (2) it can trip after 2 minutes at 600% of motor full load current. The common assumption is that 600% is locked rotor current.
Click to expand...
I don't think it is applies to the OCPD in the controller.
Because 695.4(A) is talking about the controller.
however, 695.4(B) Connection Through Disconnecting Means and Overcurrent Device is talking about the disconnect means between the fire pump source and controller. Per 695.4(B)(1).
(1) Number of Disconnecting Means

(a) General. A single disconnecting means and associated overcurrent protective device(s) shall be permitted to be installed between the fire pump power source(s) and one of the following: [20:9.1.2]

1. A listed fire pump controller

2. A listed fire pump power transfer switch

3. A listed combination fire pump controller and power transfer switch

(b) Feeder Sources. For systems installed under the provisions of 695.3(C) only, additional disconnecting means and the associated overcurrent protective device(s) shall be permitted.

(c) On-Site Standby Generator. Where an on-site standby generator is used to supply a fire pump, an additional disconnecting means and an associated overcurrent protective device(s) shall be permitted.

​

 
I am seeing (1) and (2) as different rules. If they are the same, you cannot comply as (2) requires a trip sooner than (1) does....forever vs 2 minutes, so there has to be some difference.
 
don_resqcapt19 said:
I am seeing (1) and (2) as different rules. If they are the same, you cannot comply as (2) requires a trip sooner than (1) does....forever vs 2 minutes, so there has to be some difference.
Click to expand...
I think 600% FLA is large than locked-rotor current.
For example 208 3p 30HP: lock-rotor current is 481A per table 430.251(B), size OCPD 500A. 88FLA per table 430.250, 600% x 88 =528A
528A may trip 500A OCPD within 2 mins (Maybe? depend on the TCC?).

Addition information: In NYC 2025 electric code. NYC added following at the end of 695.4 (B)(2)(a)(1)
The provisions of this section shall be used for sizing overcurrent protective devices for a Limited Service Fire Pump.
 
binwork91 said:
I think 600% FLA is large than locked-rotor current.
For example 208 3p 30HP: lock-rotor current is 481A per table 430.251(B), size OCPD 500A. 88FLA per table 430.250, 600% x 88 =528A
528A may trip 500A OCPD within 2 mins (Maybe? depend on the TCC?).

Addition information: In NYC 2025 electric code. NYC added following at the end of 695.4 (B)(2)(a)(1)
The provisions of this section shall be used for sizing overcurrent protective devices for a Limited Service Fire Pump.
Click to expand...
6x full load current is a very commonly used rule of thumb for locked rotor current, however it is just a rule of thumb.

Tables 430.251(A) & (B) have very limited uses as specified in the tables. You need to use the locked rotor code letter from the nameplate along with Table 430.7(B)

I would expect the trip time for a 500 amp OCPD to be way longer than 2 minutes for a 528 amp load. One curve I looked up shows a trip time of between 300 seconds and never for a 528 amp load on a 500 amp breaker.
 
don_resqcapt19 said:
Tables 430.251(A) & (B) have very limited uses as specified in the tables. You need to use the locked rotor code letter from the nameplate along with Table 430.7(B)
Click to expand...
Thank you.


So, the fire pump OCPD should be sized based on the locked rotor current per table430.7(B), which sets the minimum size. There is no maximum size requirement for the fire pump OCPD.

Is there anything else I need to consider when sizing the OCPD for the fire pump?
 
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