Fire Pump Service Size

EESparky

Member
Location
Windber, PA
I have a fire pump, 3-phase, 208 volts, 25 hp, with a control panel with a packaged 150 amp circuit breaker in the panel. There are no other loads (jockey pumps...) beside one small light and on receptacle.

According to 695, the conductors shall be 125% of fire pump FLA loads + 100% of miscellaneous loads. This calculates out to about 96 amps. I would think that I would then need a (minimum) of a 100 amp service with #3 conductors (service is close by fire pump so voltage drop is negligable). BUT....my question is, how does the 150 amp circuit breaker in the Fire Pump Controller affect this? Do I need a "150 amp" service size with 1/0 wires and if so, what is the code reference for this?
 

GoldDigger

Moderator
Staff member
I have a fire pump, 3-phase, 208 volts, 25 hp, with a control panel with a packaged 150 amp circuit breaker in the panel. There are no other loads (jockey pumps...) beside one small light and on receptacle.

According to 695, the conductors shall be 125% of fire pump FLA loads + 100% of miscellaneous loads. This calculates out to about 96 amps. I would think that I would then need a (minimum) of a 100 amp service with #3 conductors (service is close by fire pump so voltage drop is negligable). BUT....my question is, how does the 150 amp circuit breaker in the Fire Pump Controller affect this? Do I need a "150 amp" service size with 1/0 wires and if so, what is the code reference for this?
If the fire pump documentation says that it must be supplied by a particular minimum circuit ampacity (MCA), then your service and service equipment as well as your wires will have to be rated for that amount or more.

If they just put a 150A breaker on the pump because they had some lying around, then if it were not a fire pump it would have no effect on the calculated circuit size that you need to provide.
But since there should not be any other overcurrent protection on your end between the pump and the primary protection of the service, POCO will almost certainly have something to say about the required service size based on the 150A breaker. Their requirements can be totally separate from the NEC requirements.
 

RUWired

Senior Member
Location
Pa.
). BUT....my question is, how does the 150 amp circuit breaker in the Fire Pump Controller affect this? Do I need a "150 amp" service size with 1/0 wires and if so, what is the code reference for this?
I would think 230.90(A) would apply to your service conductors for the fire pump controller.
 

kwired

Electron manager
Location
NE Nebraska
Any motor can and usually has conductor overcurrent protection higher than the conductor ampacity, this ensures the motor will start without tripping the overcurrent device, the conductor is protected from overloading by motor overload protective devices fire pumps just happen to have some differences over other motors though, as the idea with a fire pump is the overcurrent protection should be able to hold even during a locked rotor condition, if there is a fire they want that pump to take one for the team if it has to, chances are it is not getting used again if it comes to that kind of demise anyway.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I have a fire pump, 3-phase, 208 volts, 25 hp, with a control panel with a packaged 150 amp circuit breaker in the panel. There are no other loads (jockey pumps...) beside one small light and on receptacle.

According to 695, the conductors shall be 125% of fire pump FLA loads + 100% of miscellaneous loads. This calculates out to about 96 amps. I would think that I would then need a (minimum) of a 100 amp service with #3 conductors (service is close by fire pump so voltage drop is negligable). BUT....my question is, how does the 150 amp circuit breaker in the Fire Pump Controller affect this? Do I need a "150 amp" service size with 1/0 wires and if so, what is the code reference for this?
You'll need to consider a number of things here. Normally a fire pump controller is SUSE rated (I've never seen one that is not), and for very good reason. This allows you to connect directly to a POCO meter socket or CT meter can without having a service disconnect. The conductors to the fire pump are then service conductors (not a feeder) and terminate directly to the fire pump controller. The service conduit routing would have to be outside the building all the way to the fire pump controller room.

If you choose not to do it this way, things will get more difficult. For starters, if you have a service disconnect ahead of the fire pump controller, it will have to be rated and fused to carry the locked rotor current of the fire pump indefinitely. This can get quite large and expensive. Then you will have a feeder to the controller, but it will still have to be outside the building or be 2 HR fire rated (very expensive).

There is more to this, but this will get you started to think. The jockey pump also has some issues if you choose to supply it with the same service or feeder as the fire pump. It is generally much easier to supply the jockey from a separate normal source as this is allowed.
 

EESparky

Member
Location
Windber, PA
Thanks for the replies - now a little more information:

The service enters the Fire Pump Controller - no disconnect switch ahead of controller. The controller is listed as suitable for use as service equipment. The service is a dedicated service and the fire pump is in a separate building so wiring is outside of building until getting to controller.

The issue is, the code says to size wire per FLA amps (* 1.25) of fire pump loads. This is less than 100 amps. The circuit breaker in the controller itself (part of packaged fire pump controller from manufacturer) is 150 amps. The question is do I need to size wires for the 150 amps or 100 amps? I know it only is 50 amps, but here is the kicker....this is an existing fire pump that is just exchanging for a new fire pump, therefore, #3 wires (100 amp) service is already there! IF I have to size for 150, everything needs to be ripped out!

Here is the other question that I don't see explained anywhere...695.3 (A) (1) states that if it is a single utility service (like I have) the service must be "capable of carrying indefinitely the sum of the locked-rotor current..." Does this mean that my service would need to be rated at at least 404 amps (from Table 430.251 (B))? Is it up to the power company to tell me that they can carry locked rotor current on a 100 or 150 amp service or is it up to me to size the service for 404+? Again, if I have 404+ amp service, are the wires to be sized for 100 or 150 - I wouldn't think it would need to be sized for 404+.....?

Again, thanks for help!
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
If the Fire Pump controller (manufacturer) does not require 150 amp rated conductors then you are fine. In fire pump installations you are not worried about overcurrent protection for these conductors, only short circuit protection.


With that said, I see most designers showing 1/0 conductors for this size pump, I think it is simply a CYA.

Roger
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Here is the other question that I don't see explained anywhere...695.3 (A) (1) states that if it is a single utility service (like I have) the service must be "capable of carrying indefinitely the sum of the locked-rotor current..." Does this mean that my service would need to be rated at at least 404 amps (from Table 430.251 (B))? Is it up to the power company to tell me that they can carry locked rotor current on a 100 or 150 amp service or is it up to me to size the service for 404+? Again, if I have 404+ amp service, are the wires to be sized for 100 or 150 - I wouldn't think it would need to be sized for 404+.....?

Again, thanks for help!
The OCPD must be able to carry the locked rotor current of the pump indefinitely. I don't think the 150A c/b would do this for a 25HP motor.

The conductors still would only be required to be sized to at least 125% of the motor FLA, not to the OCPD size.
 

EESparky

Member
Location
Windber, PA
I checked with the manufacturer and they told be that basically ignore the the 150 amp rating (why do they have it on there?) and the breaker is basically controlled to allow for LRC.

Anyhow, I called the AHJ with these questions and he agreed on the the #3 wire size IF the fire pump manufacturer would write a letter telling me about the circuit breaker as stated above.

Now, what he also told me was that per NFPA 20, I was going to need a generator in addition to the utility service even if the utility is considered reliable. I told asked him what code section this was in so I can read it and he said he would have to call me back...does anyone know what he is talking about or have anymore input on any of the above?
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
I checked with the manufacturer and they told be that basically ignore the the 150 amp rating (why do they have it on there?) and the breaker is basically controlled to allow for LRC.

Anyhow, I called the AHJ with these questions and he agreed on the the #3 wire size IF the fire pump manufacturer would write a letter telling me about the circuit breaker as stated above.

Now, what he also told me was that per NFPA 20, I was going to need a generator in addition to the utility service even if the utility is considered reliable. I told asked him what code section this was in so I can read it and he said he would have to call me back...does anyone know what he is talking about or have anymore input on any of the above?
IIRC, the requirement is for two reliable sources; if you have a diesel though, you're good with that, which is why they're so popular.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
IDTYRC...If a source is reliable, only one source is needed (695.3(A)). If reliable power cannot be obtained from a source, then multiple sources are required (695.3(B)).
Hmmm, looks like my memory is not as reliable as I thought. Hope I can find my way home tonight. :)
 
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