Diesel and Electric fire pumps in same building

[brigadier_92]

Greetings to all:

A question has come up in reference to the fire pumps installed at a high rise building 30 floors

Background:

Each of three pumps is controlled via its own UL approved fire pump controller.

The building is presently equipped with three fire pumps as follows:

200 HP diesel fire pump with its own dedicated fuel source. This pump serves the upper floors.

200HP electric fire pump connected via a separate utility service feeder with a 600AMP fused disconnect. The fire pump controller is a primary resistor reduced voltage type. This pump serves the upper floors as an alternate.

60HP electric fire pump with connected via the same 600 AMP fused disconnect. The fire pump controller is a primary resistor reduced voltage type. This pump serves the lower floors of the building.

Both of the electric fire pumps are also connected to the building?s emergency generators via a 600 AMP automatic transfer switch.

The fire pump controller for the 200HP electric requires replacement as parts are no longer available for its maintenance.

As a result of the replacement of the fire pump controller, an electrical contractor is alleging that the current installation does not comply with the provision requiring the electrical service disconnecting means to be able to carry the locked rotor currents of the motors indefinitely.

In the case of the 200 HP motor, the amounts to 1450 AMPS. Our present utility service disconnecting means is 600 AMPS.

And now, our question. Does the fact that the building is equipped with a diesel fire pump, in any way allow for the alternate pump with two sources of available energy mitigate the apparent requirement for such a large electrical service disconnecting means and larger service capacity?

Thoughts?

 

[milemaker13]

What article are you quoting? That seems like a silly idea... Since the 600a disconnect is fused, it will never ever see 2400 amps. If the motor locks, the fuses will blow at 600, right? If the disconnect was NOT fused it may be an issue. I assume the fire pump controller does not have overcurrent protection of its own (better the pump burn out than shut down to protect itself in case of fire).

 

[brigadier_92]

What article are you quoting? That seems like a silly idea... Since the 600a disconnect is fused, it will never ever see 2400 amps. If the motor locks, the fuses will blow at 600, right? If the disconnect was NOT fused it may be an issue. I assume the fire pump controller does not have overcurrent protection of its own (better the pump burn out than shut down to protect itself in case of fire).

200HP motor is 480 Volt. Locked Rotor is 1450 AMPS. Fire Pump Controllers that have overcurrent protection typically have the NFPA curve which allows LRA for 8-20 Seconds before trip. See article 695 in NEC

 

[don_resqcapt19]

What article are you quoting? That seems like a silly idea... Since the 600a disconnect is fused, it will never ever see 2400 amps. If the motor locks, the fuses will blow at 600, right? If the disconnect was NOT fused it may be an issue. I assume the fire pump controller does not have overcurrent protection of its own (better the pump burn out than shut down to protect itself in case of fire).

If you use a disconnect with fuses, the fuses must be sized to carry the locked rotor current forever. 695.4

 

[gadfly56]

If you use a disconnect with fuses, the fuses must be sized to carry the locked rotor current forever. 695.4

Yep. They'd rather have the pump burn up (literally) than stop running on overload. And unless you want to get into the sprinkler system design business, I wouldn't try suggesting that the second pump isn't really needed. That's my job :lol:! And it's usually a pretty tough sell. Once a fire protection system is installed, most jurisdictions are loath to let you remove it.

 

[milemaker13]

But how would it ever see 2400 amps? Are you saying they want you to put in a 2400 amp disconnect switch? Wouldn't you then have to up your service to match? Is that the issue in question? Wow.

I see why they would rather let the pump keep pumping til it just burns up, but at 600 amps isn't it pretty much toast aleady?

Just curious. I have no real knowledge to input here:happyno:

 

[milemaker13]

I mean, do they want the wire and everything else sized for 2400 amps? Otherwise, what will prevent the fire pump system from starting its own fire?

 

[milemaker13]

Again, sorry.... 1450 amps but still....

 

[Joethemechanic]

The service and the feeders are encased in a material that allows them to pretty much melt. I believe one specification is surrounded with 2 inches of brick. Maybe Lady Engineer will chime in on this, she just did a couple electric fire pumps.

Also the service and feeders do not have to be sized to carry LRA, But the service disco does have to be sized for LRA and fused for LRA

 

[iwire]

Also the service and feeders do not have to be sized to carry LRA, But the service disco does have to be sized for LRA and fused for LRA

I agree but the conductor must be sized to limit voltage drop as well, one of the few times the NEC addresses voltage drop.

695.7 Voltage Drop. The voltage at the controller line terminals
shall not drop more than 15 percent below normal
(controller-rated voltage) under motor starting conditions.

The voltage at the motor terminals shall not drop more than
5 percent below the voltage rating of the motor when the
motor is operating at 115 percent of the full-load current
rating of the motor.

Exception: This limitation shall not apply for emergency
run mechanical starting.

 

[Joethemechanic]

I agree but the conductor must be sized to limit voltage drop as well, one of the few times the NEC addresses voltage drop.

Although typically from the installations I have seen, the service and feeder runs are as short as possible limiting voltage drop by just having less wire. The shorter buildings I have worked on had the fire pumps located probably less than 20 feet from the transformers that served them.

Although in taller buildings there is an advantage in having booster pumps located at higher elevations. Typically you need 0.5 PSI (rule of thumb and not taking into account friction head) to overcome each foot of elevation, and there are practical design limits to each single stage of centrifugal pumps. (each stage consistes of an individual impeller and volute)

For example a 1,000 foot building would need 500 PSI of water pressure just to get a trickle (and I do mean a trickle) out of the sprinkler heads on the top floor

 

[iwire]

Although in taller buildings there is an advantage in having booster pumps located at higher elevations. Typically you need 0.5 PSI (rule of thumb and not taking into account friction head) to overcome each foot of elevation, and there are practical design limits to each single stage of centrifugal pumps. (each stage consistes of an individual impeller and volute)

For example a 1,000 foot building would need 500 PSI of water pressure just to get a trickle (and I do mean a trickle) out of the sprinkler heads on the top floor

Yes, Joe, water has weight, we got that. :lol:

 

[Joethemechanic]

Yes, Joe, water has weight, we got that. :lol:

But because of the weight of water, it influences the placement of the booster pumps, and therefore the length of the conductors.

When people first hear about the need to carry FLA at a 15% voltage drop it sounds very extreme and very expensive. Until you realize that good design practices place the fire pump very close to it's supply. Although when dealing with taller buildings with longer runs of conductor. it gets a lot more expensive in a big hurry

 

[iwire]

Typically electricians nor electrical engineers have any input at all where the pumps are located.

We are told where they are going and where the source is, at that point it becomes our job to supply it correctly. If that takes larger conductors because the pump is located remotely than that is what it takes.

 

[iwire]

Until you realize that good design practices place the fire pump very close to it's supply.

Let me expand on that.

An electricians view may be that good design places the Fire Pump near the electrical source.

The sprinkler fitters view will likely be that a good design places the pump near the water source.

The Fire departments view may be that a good design places the fire pump in an easy to access location

The building owners view may be that a fore pump room takes up a lot of good space and may want it located in a un-rentable / ugly area of the building.

It will always come down to compromise between, wants, wishes and requirements.

 

[Joethemechanic]

Most I've seen, and my experience has been limited to municipal buildings have been very good designs. Near the pad mount, in the basement, and very close to the same elevation or slightly below the water main. If the pumps are located above the water main, you take a chance of cavitation.

Then again, I'm from Philly. We have water mains in operation that are well over 100 years old. Now and again a crew will dig up a section of wooden pipe still in use.

 

[hurk27]

But because of the weight of water, it influences the placement of the booster pumps, and therefore the length of the conductors.

When people first hear about the need to carry FLA at a 15% voltage drop it sounds very extreme and very expensive. Until you realize that good design practices place the fire pump very close to it's supply. Although when dealing with taller buildings with longer runs of conductor. it gets a lot more expensive in a big hurry

5% at 110% of FLA, 15% of start up current or LRA which could amount to over sizing conductors on longer runs.

I will add that this is very open to interpretation of what the normal voltage rating of a given motor is, does it include the +-10% allowed by NEMA? a 230 volt motor could have a range 207-253 volts?

 

[Joethemechanic]

5% at 110% of FLA, 15% of start up current or LRA which could amount to over sizing conductors on longer runs.

I will add that this is very open to interpretation of what the normal voltage rating of a given motor is, does it include the +-10% allowed by NEMA? a 230 volt motor could have a range 207-253 volts?

Sorry I think I meant LRA in that post.

I will mention that many times I see design voltage ratings of fire pump motors that are somewhat below nominal line voltages. Such as a 200 volt design voltage that is meant to run from a 208 nominal line voltage. I would think that would allow you a 38 volt drop over your entire circuit at LRA.

I've always wondered how long the armature windings hold at LRA. I've only ever tested general purpose T and U frame motors and they fry pretty fast.

 

[brigadier_92]

Fire PUMP hi-rise

Fire PUMP hi-rise

Thanks to everyone for their replies.

This is what I know so far.

200 HP 460 Volt LRA = 1450 Amps per NEC 430.150B, FLC = 240 per NEC 430.150
50 Hp 460 Volt LRA = 362 Amps...... FLC = 65.....

Total LRA = 1812 Amps

Feeder Conductors = 1.25*240+65 = 365 Amps so a minimum of 500kCmil with 380 Amps @ 75?C.

Disconnecting means = 1450+65 = 1515 Amps so next size up is 1600 Amps?