Generator Sizing with Fire Pump

[faresos]

Hello Everyone:

I’m working on a project that will have a 300KW generator to back-up the entire facility. The building service is 800A at 480/277V. The building is designed to have 125HP fire pump (it went up from 60HP at last minuet). I’m trying to understand the operation/testing of the fire pump so we can keep the same generator size. The fire pump will be powered form the secondary side of the utility transformer and a separate 250A breaker in the generator. This is a new building and under design phase. My questions:
1. When you size the generator, do we always account for the building load AND the fire pump?
2. Is it common to do a load shedding for the mechanical system in case of fire?
3. I assume in fire pump testing mode when using the emergency power, the generator fire pump breaker will only be used but the generator building breaker will not be running, correct?

Thanks,

 

[gadfly56]

Hello Everyone:

I’m working on a project that will have a 300KW generator to back-up the entire facility. The building service is 800A at 480/277V. The building is designed to have 125HP fire pump (it went up from 60HP at last minuet). I’m trying to understand the operation/testing of the fire pump so we can keep the same generator size. The fire pump will be powered form the secondary side of the utility transformer and a separate 250A breaker in the generator. This is a new building and under design phase. My questions:
1. When you size the generator, do we always account for the building load AND the fire pump?
2. Is it common to do a load shedding for the mechanical system in case of fire?
3. I assume in fire pump testing mode when using the emergency power, the generator fire pump breaker will only be used but the generator building breaker will not be running, correct?

Thanks,

1. Yes
2. If necessary.
3. You won't have a generator fire pump breaker. You tap the generator directly and feed the fire pump controller/ATS. They can switch the fire pump to generator at the ATS during testing if necessary.

 

[Ingenieur]

Verify gen sizing
60 to 125 hp is a big change on a 400 hp genset
genset starting kva > fire pump starting kva + any bldg load kva

a 300 kw / 375 kva genset typically has 1000 kva starting at 35% v drop
the pump requires on the order of 700 kva
does it have a reduced voltage starter? Wye-delta, autoxfmr, etc?

have the genset supplier run calcs

 

[gadfly56]

Some additional info from NFPA 20:

9.6.1.1 Where on-site generator systems are used to supply
power to fire pump motors to meet the requirements of 9.3.2,
they shall be of sufficient capacity to allow normal starting and
running of the motor(s) driving the fire pump(s) while supplying
all other simultaneously operated load(s) while meeting
the requirements of Section 9.4.

9.6.2.1 On-site standby generator systems shall comply with Section
9.4 and shall meet the requirements of Level 1, Type 10,
Class X systems of NFPA 110, Standard for Emergency and Standby
Power Systems.
9.6.2.2 The generator shall run and continue to produce
rated nameplate power without shutdown or derate for alarms
and warnings or failed engine sensors, except for overspeed
shutdown.
9.6.2.3 The generator fuel supply capacity shall be sufficient
to provide 8 hours of fire pump operation at 100 percent of
the rated pump capacity in addition to the supply required for
other demands.

Section 9.4 is about voltage drop, wiring methods and connections.

 

[publicgood]

You won't have a generator fire pump breaker. You tap the generator directly and feed the fire pump controller/ATS. They can switch the fire pump to generator at the ATS during testing if necessary.

This does not meet code. 240.4(A)

 

[publicgood]

Ingenieur is headed down the right path. 695.7 limited to 15% voltage drop at starting. Reduced voltage started will limit to 300%, but you may still not make the 15%. Remember, you also have some amount of voltage drop across the feeder during starting. You can ask gen manufacturer or if they have free software on their website check yourself.

1. No. It is a 700 load. You may prioritize and shed.
2. Yes, if the are not 700/701.
3. More info needed.

 

[m sleem]

3. You won't have a generator fire pump breaker. You tap the generator directly and feed the fire pump controller/ATS. They can switch the fire pump to generator at the ATS during testing if necessary.

No, it'll have OCPD per 695.4(B)(2)(b)

 

[m sleem]

3. I assume in fire pump testing mode when using the emergency power, the generator fire pump breaker will only be used but the generator building breaker will not be running, correct?

Thanks,

It could be, but still you've to size your generator to carry building load + F.P fla

 

[faresos]

Thank you all for the replies. I have been using Kholer generator software to size the gen set. When I have changed the fire pump size to 125HP it went from 275KW (I said earlier 300KW) to 350KW. As we all know, the VD for fire pump should be limited 15% at starting. The generator will have three breakers( building, fire pump, and loadbank) because we are required to have a separate OCPD to power the fire pump per the NEC. The sizing was based on two steps to reduce the size of the generator. The clients in the past always complain about the generator size is always oversized in the past which leads to wet stacking issues. I'm very sure the generator is not going to see that load in reality just like the utility transformer they always sized in half based on the demand load given to them.

 

[gadfly56]

No, it'll have OCPD per 695.4(B)(2)(b)

You have a choice.

695.4(A)
The supply conductors shall directly
connect the power source to a listed fire pump controller,
a listed combination fire pump controller and power
transfer switch, or a listed fire pump power transfer switch.

You are permitted to install an OCPD under 695.4(B) et seq.

 

[gadfly56]

Ingenieur is headed down the right path. 695.7 limited to 15% voltage drop at starting. Reduced voltage started will limit to 300%, but you may still not make the 15%. Remember, you also have some amount of voltage drop across the feeder during starting. You can ask gen manufacturer or if they have free software on their website check yourself.

1. No. It is a 700 load. You may prioritize and shed.
2. Yes, if the are not 700/701.
3. More info needed.

Fire pumps are not 700 loads. Sprinklers are not considered life safety devices, just like heat detectors. Otherwise, you could never get approval for a diesel operated fire pump.

 

[gadfly56]

This does not meet code. 240.4(A)

Did you happen to notice the informational note about "See NFPA 20-2013 for the Installation of Stationary Pumps for Fire Protection"? Or Table 240.3 that points you to article 695 for fire pumps?

 

[steve66]

The 2011 code says you are permitted to do automatic load shedding of optional standby loads in order to comply with the capacity requirements.

Unless that has changed, if you automatically shed optional loads when the fire pump ATS kicks in, you don't have to include those loads for sizing the generator.

695.4D1.

You have a choice.

695.4(A)
The supply conductors shall directly
connect the power source to a listed fire pump controller,
a listed combination fire pump controller and power
transfer switch, or a listed fire pump power transfer switch.

You are permitted to install an OCPD under 695.4(B) et seq.

But you still have to comply with other parts of the code for a direct connection. For example, 225.31 requires a disconnecting means for any feeders that supply a building.

 

[gadfly56]

Thank you all for the replies. I have been using Kholer generator software to size the gen set. When I have changed the fire pump size to 125HP it went from 275KW (I said earlier 300KW) to 350KW. As we all know, the VD for fire pump should be limited 15% at starting. The generator will have three breakers( building, fire pump, and loadbank) because we are required to have a separate OCPD to power the fire pump per the NEC. The sizing was based on two steps to reduce the size of the generator. The clients in the past always complain about the generator size is always oversized in the past which leads to wet stacking issues. I'm very sure the generator is not going to see that load in reality just like the utility transformer they always sized in half based on the demand load given to them.

If you have a breaker for the fire pump, make sure it complies with all the requirements in 695.

The NEC does not require an OCPD for the fire pump, it permits one. It's why it treats the conductors to the fire pump as service entrance. See 695.6(A)(1).

 

[m sleem]

You have a choice.

695.4(A)
The supply conductors shall directly
connect the power source to a listed fire pump controller,
a listed combination fire pump controller and power
transfer switch, or a listed fire pump power transfer switch.

You are permitted to install an OCPD under 695.4(B) et seq.

I'm still on my point per 695.3 D 2

(2) Connection. A tap ahead of the generator disconnecting
means shall not be required. [20:9.6.1.2]

 

[gadfly56]

The 2011 code says you are permitted to do automatic load shedding of optional standby loads in order to comply with the capacity requirements.

Unless that has changed, if you automatically shed optional loads when the fire pump ATS kicks in, you don't have to include those loads for sizing the generator.

695.4D1.



But you still have to comply with other parts of the code for a direct connection. For example, 225.31 requires a disconnecting means for any feeders that supply a building.

230.82(5) is your get-out-of-jail-free card.

 

[gadfly56]

I'm still on my point per 695.3 D 2

(2) Connection. A tap ahead of the generator disconnecting
means shall not be required. [20:9.6.1.2]

Your post at #7 suggests the OCPD is mandatory. It's not. I may have given the impression you had to make the tap ahead, but I was probably influenced by the usual practice at my last company. We found that it was usually better practice to forego the external OCPD and rely on the controller OCPD.

 

[publicgood]

Fire pumps are not 700 loads. Sprinklers are not considered life safety devices, just like heat detectors. Otherwise, you could never get approval for a diesel operated fire pump.

700.2 Definitions.
Branch Circuit Emergency Lighting Transfer Switch. A device connected on the load side of a branch circuit overcurrent protective device that transfers only emergency lighting loads from the normal supply to an emergency supply.
Informational Note:  See ANSI/UL 1008, Transfer Switch Equipment, for information covering branch circuit emergency lighting transfer switches.
Emergency Systems. Those systems legally required and classed as emergency by municipal, state, federal, or other codes, or by any governmental agency having jurisdiction. These systems are intended to automatically supply illumination, power, or both, to designated areas and equipment in the event of failure of the normal supply or in the event of accident to elements of a system intended to supply, distribute, and control power and illumination essential for safety to human life.
Informational Note:  Emergency systems are generally installed in places of assembly where artificial illumination is required for safe exiting and for panic control in buildings subject to occupancy by large numbers of persons, such as hotels, theaters, sports arenas, health care facilities, and similar institutions. Emergency systems may also provide power for such functions as ventilation where essential to maintain life, fire detection and alarm systems, elevators, fire pumps, public safety communications systems, industrial processes where current interruption would produce serious life safety or health hazards, and similar functions.

 

[publicgood]

Did you happen to notice the informational note about "See NFPA 20-2013 for the Installation of Stationary Pumps for Fire Protection"? Or Table 240.3 that points you to article 695 for fire pumps?

I see an informational note, yes. I also see code verbiage that specifically calls out the need for short circuit protection of a fire pump circuit.

(A) Power Loss Hazard. Conductor overload protection shall not be required where the interruption of the circuit would create a hazard, such as in a material-handling magnet circuit or fire pump circuit. Short-circuit protection shall be provided.
Informational Note:  See NFPA 20-2013, Standard for the Installation of Stationary Pumps for Fire Protection.

 

[publicgood]

Did you happen to notice the informational note about "See NFPA 20-2013 for the Installation of Stationary Pumps for Fire Protection"? Or Table 240.3 that points you to article 695 for fire pumps?

I might find your 695 logic agreeable as “permitted,” rather than required, if 445.12 and 445.13 are followed.