FIRE PUMP DISCONNECT

[VENgineer]

I have the following situation. A customer made a mistake in the purchase of a fire pump. The service voltage is 240V, and the fire pump operates at 208V (200V/400V) according to the nameplate.

As a result, when they attempted to start it, the controller triggered an alarm. My suggestion was to replace the fire pump, but the customer wants to install a transformer because, according to them, replacing the pump would take too long.

Therefore, the proposed solution is to install a 150kVA transformer , 240V - 208/120V. On the primary side, a 2000A breaker will be installed to comply with the NEC (National Electrical Code) fire pump requirements, considering a Locked Rotor Current(LRC) of approximately 1800A.

The fire department visited the site and stated that the transformer cannot be installed in the fire pump room. Consequently, it will be installed outside.

My question concerns the 2000Amp breaker.

1. Should it be installed in the fire pump room?
2. Can it be installed outside next to the transformer, with its respective NEMA 3R enclosure?
3. Or should it be installed in the main electrical room (I understand that the code requires it to be sufficiently remote from other disconnects for other loads; correct me if I'm wrong)? Therefore, I am ruling out this option.

(Fire Pump + Jockey Pump 125HP)


I appreciate any guidance on this matter. Thank you.

 

[augie47]

Have you looked at the possibility of a buck-n-boost transformer ?

 

[infinity]

Therefore, the proposed solution is to install a 150kVA transformer , 240V - 208/120V. On the primary side, a 2000A breaker will be installed to comply with the NEC (National Electrical Code) fire pump requirements, considering a Locked Rotor Current(LRC) of approximately 1800A.

Why the additional breaker on the primary? Isn't there already protection?

 

[VENgineer]

Have you looked at the possibility of a buck-n-boost transformer ?

The costumer already have a transformer so that is not the issue.

 

[VENgineer]

Why the additional breaker on the primary? Isn't there already protection?

No, the fire pump controller is directly connected to the service conductor without overcurrent protection (as recommended by the NEC). However, since a transformer needs to be installed now, and it does require protection on the primary side, according to 695.5(B), the breaker must be sized to indefinitely support the Locked Rotor Current (LRC) of the motors. Therefore, for a motor with a Full Load Amps (FLA) of 305A, multiplying it by (LRC)6.5 results in 1982Amps. Hence, a 2000A breaker is needed.

 

[augie47]

No, the fire pump controller is directly connected to the service conductor without overcurrent protection (as recommended by the NEC). However, since a transformer needs to be installed now, and it does require protection on the primary side, according to 695.5(B), the breaker must be sized to indefinitely support the Locked Rotor Current (LRC) of the motors. Therefore, for a motor with a Full Load Amps (FLA) of 305A, multiplying it by (LRC)6.5 results in 1982Amps. Hence, a 2000A breaker is needed.

Can't say that I fully understand 695.5 but (C)(2) also says you need to meet 450.3 which the 2000 amp breaker does not.

 

[infinity]

Since the transformer is outside of the room that contains the fire pump what wiring method are you using for the secondary?

 

[VENgineer]

Can't say that I fully understand 695.5 but (C)(2) also says you need to meet 450.3 which the 2000 amp breaker does not.

But 695.5 specifically indicates that the protection device is selected or set to carry indefinitely the sum of the locked-rotor current of the fire pump and any accessories associated with it.

 

[VENgineer]

Since the transformer is outside of the room that contains the fire pump what wiring method are you using for the secondary?

Two sets of 2.5" EMT conduits will be installed. The transformer will be on the opposite wall from the fire pump controller, so the transformer's secondary side will go towards an auxiliary gutter. From there, it will connect to the fire pump controller located above the auxiliary gutter.

The service conductor currently goes towards the auxiliary gutter, so now I have to place the new breaker and transformer to comply with the new requirement.

 

[MyCleveland]

No, the fire pump controller is directly connected to the service conductor without overcurrent protection (as recommended by the NEC). However, since a transformer needs to be installed now, and it does require protection on the primary side, according to 695.5(B), the breaker must be sized to indefinitely support the Locked Rotor Current (LRC) of the motors. Therefore, for a motor with a Full Load Amps (FLA) of 305A, multiplying it by (LRC)6.5 results in 1982Amps. Hence, a 2000A breaker is needed.

What happens to your 150kVA secondary voltage when your trying to pull 1900amps through it ?
How long of a time [ sized to indefinitely support ] before the tranny fails ?

 

[VENgineer]

The NEC indicates:

• Transformer sized by 125% Fire pump + jockey pump.
• Protection device sized to carry LRC (approximately 6 - 6.5 times FLA).

I understand that the goal is to prevent the fire pump from shutting down due to overload. That's why direct installation without disconnects is recommended, allowing it to be used for the longest possible time during a fire.

Please correct me if I'm wrong. I'm relatively new to the engineering field.

 

[gadfly56]

No, the fire pump controller is directly connected to the service conductor without overcurrent protection (as recommended by the NEC). However, since a transformer needs to be installed now, and it does require protection on the primary side, according to 695.5(B), the breaker must be sized to indefinitely support the Locked Rotor Current (LRC) of the motors. Therefore, for a motor with a Full Load Amps (FLA) of 305A, multiplying it by (LRC)6.5 results in 1982Amps. Hence, a 2000A breaker is needed.

To find the LRC for the fire pump motor you have to go to NFPA 20 and the tables in 9.5.1.1, not just use a rule of thumb. What are the actual HP's for the fire and jockey pumps?

 

[VENgineer]

To find the LRC for the fire pump motor you have to go to NFPA 20 and the tables in 9.5.1.1, not just use a rule of thumb. What are the actual HP's for the fire and jockey pumps?

i am using the LRC provided by the manufacturer on the name plate. Fire Pump 125HP. FLA 320A, 200V, code letter G, (5.9 times FLA) = LRC = 1920A (200V secondary side of T)
1600A (240V primary side of T)

1800A-2000A breaker would be comply.

 

[augie47]

The NEC indicates:

• Transformer sized by 125% Fire pump + jockey pump.
• Protection device sized to carry LRC (approximately 6 - 6.5 times FLA).

I understand that the goal is to prevent the fire pump from shutting down due to overload. That's why direct installation without disconnects is recommended, allowing it to be used for the longest possible time during a fire.

Please correct me if I'm wrong. I'm relatively new to the engineering field.

I'm interested in how you do that and comply with 450.3.

 

[MyCleveland]

The NEC indicates:

• Transformer sized by 125% Fire pump + jockey pump.
• Protection device sized to carry LRC (approximately 6 - 6.5 times FLA).

I understand that the goal is to prevent the fire pump from shutting down due to overload. That's why direct installation without disconnects is recommended, allowing it to be used for the longest possible time during a fire.

Please correct me if I'm wrong. I'm relatively new to the engineering field.

I see now what you are referencing, but perplexed on the transformer rating (size) requirement.
Will wait to see other{s) opinion on what to expect with your transformers expected longevity and secondary voltage when driven to this extreme.

 

[gadfly56]

I see now what you are referencing, but perplexed on the transformer rating (size) requirement.
Will wait to see other{s) opinion on what to expect with your transformers expected longevity and secondary voltage when driven to this extreme.

The transformer sizing is correct, but you have to mind the voltage drop on startup.

 

[MyCleveland]

The transformer sizing is correct, but you have to mind the voltage drop on startup.

I get that from the 695 text, but...

{ On the NEC tab : Topic "NEC 450.3 Transformer sizing"

MOD: augie47
Excerpt from his response as follows....
One of the wiser members of the Forum posted this:
But for "dry type" transformers that we typically see in distribution equipment, the rating is the rating. So unless it specifically STATES a rating higher than it does, you would be in violation of 110.3(B) if you tried to use it that way. However, transformers have a TEMPORARY OVERLOAD capability without being damaged based on NEMA design criteria as follows:

200% nameplate load for one-half hour
150% load for one hour
125% load for four hours
NEMA ALSO requires that there is a 50% load preceding and following the overload. So it's not a good idea to COUNT ON this overload capability unless you can control ALL aspects of the load. }

My concern is what is happening when you are driving the transformer output at 500 or 600% of the rated output current, even though it appears that 695 is allowing it and somehow you can comply with 450.3.

 

[gadfly56]

I get that from the 695 text, but...

{ On the NEC tab : Topic "NEC 450.3 Transformer sizing"

MOD: augie47
Excerpt from his response as follows....
One of the wiser members of the Forum posted this:
But for "dry type" transformers that we typically see in distribution equipment, the rating is the rating. So unless it specifically STATES a rating higher than it does, you would be in violation of 110.3(B) if you tried to use it that way. However, transformers have a TEMPORARY OVERLOAD capability without being damaged based on NEMA design criteria as follows:

200% nameplate load for one-half hour
150% load for one hour
125% load for four hours
NEMA ALSO requires that there is a 50% load preceding and following the overload. So it's not a good idea to COUNT ON this overload capability unless you can control ALL aspects of the load. }

My concern is what is happening when you are driving the transformer output at 500 or 600% of the rated output current, even though it appears that 695 is allowing it and somehow you can comply with 450.3.

I get that; there definitely appears to be some kind of disconnect among the various requirements. I can't imagine a transformer lasting very long at 500 - 600% of rated output, but the disconnect has to be rated for the LRC, but the conductors don't have to be sized that way. I'd like to hear comments from the committee on this, if anyone has a contact.

 

[jim dungar]

I get that from the 695 text, but...

{ On the NEC tab : Topic "NEC 450.3 Transformer sizing"

MOD: augie47
Excerpt from his response as follows....
One of the wiser members of the Forum posted this:
But for "dry type" transformers that we typically see in distribution equipment, the rating is the rating. So unless it specifically STATES a rating higher than it does, you would be in violation of 110.3(B) if you tried to use it that way. However, transformers have a TEMPORARY OVERLOAD capability without being damaged based on NEMA design criteria as follows:

200% nameplate load for one-half hour
150% load for one hour
125% load for four hours
NEMA ALSO requires that there is a 50% load preceding and following the overload. So it's not a good idea to COUNT ON this overload capability unless you can control ALL aspects of the load. }

My concern is what is happening when you are driving the transformer output at 500 or 600% of the rated output current, even though it appears that 695 is allowing it and somehow you can comply with 450.3.

How long can a fire pump motor pull LRA? Why would the TX need to last any longer?
The term Locked Rotor describes a condition where the motor is not turning. The requirement for the OCP to carry LRA indefinitely is so that the motor has every chance of the rotor breaking free and then doing what it is supposed to do. There is no need to supply LRA once the motor, itself, is on fire.

 

[MyCleveland]

How long can a fire pump motor pull LRA? Why would the TX need to last any longer?
The term Locked Rotor describes a condition where the motor is not turning. The requirement for the OCP to carry LRA indefinitely is so that the motor has every chance of the rotor breaking free and then doing what it is supposed to do. There is no need to supply LRA once the motor, itself, is on fire.

Thanks Jim
Based on your comments last sentence, assuming the rotor does NOT break free and the table from "augie47" about tranny overload, is it then a race between the motor and tranny destruction to see which clears the circuit first ?