Sizing a service with a Fire Pump

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Lady Engineer

Senior Member
Location
New Jersey
Hi everyone,

Usually when sizing a fire pump, I spec a separate service. One, because I don't have to make the tap head of the main, and two I don't have two worry about making the service bigger in order to feed the fire pump.

Well, I'm taking off my Utility Power hat, and putting back on my commercial building hat for this new project. (I do utility power now so I need a refresher)

I have a 75hp, 208V/120 which has a FLA of 214A and a LRA of 1246A. If my demand load is 400A, how large should my entire service be if I want to feed the existing demand load plus the fire pump? I can't remember if I use the FLA for LRA when sizing the service. I am going to tap ahead of the main for this, so I need to let the utility (not mine, other local utility) know what size service I'm requesting.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
I believe that the circuit must be designed to carry LRA indefinitely. They want them to run until they have a catastrophic failure.

Is there some reason that you are locked into using 208 instead of 480 or even 416 if possible?
 
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pete m.

Senior Member
Location
Ohio
I believe that the circuit must be designed to carry LRA indefinitely. They want them to run until they have a catastrophic failure.

You could design to that but 695.5(A) would only require a transformer rated at 125% of the FLA of the fire pump motor plus associated loads such as jockey pumps.

Pete
 

Lady Engineer

Senior Member
Location
New Jersey
I believe that the circuit must be designed to carry LRA indefinitely. They want them to run until they have a catastrophic failure.

Is there some reason that you are locked into using 208 instead of 480 or even 416 if possible?

I think they are pre-purchasing a 208V fire pump, and basically they gave me a cut sheet and said, here, I need to run this thing.

I'd be ok with running a separate service to the Fire Pump, because I'd say put in a 1200A Main and feed the Fire pump from a utility transformer. I'm not sure what the size of their existing service is.
 

Lady Engineer

Senior Member
Location
New Jersey
You could design to that but 695.5(A) would only require a transformer rated at 125% of the FLA of the fire pump motor plus associated loads such as jockey pumps.

Pete

Oh, yeah. I guess I can use 695.5 for sizing the transformer needed for the fire pump, then add the demand load. I can beef if up just a little to be safe. I know the LRA used for the main is the combat the in rush, so I think what you said makes sense. Actually, you hit the nail on the head. 695.5.C covers it.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
You may be able to change the connections to take it out to a higher voltage. It all depends on how many leads they have brought out from the stator into the connection box. In order to dumb things down many motors only bring 3 leads out. Then you are stuck with whatever they gave you.

But really you could cut way down on copper costs and make for an easier install if you could go with the higher voltage. I take it this thing is a WYE? Something about the voltage being listed as 120/​208 seems odd. It's been a long time since I dealt with an electric powered fire pump though. Most everything I worked on for the last 10 years or so has been diesel.
 

Lady Engineer

Senior Member
Location
New Jersey
You may be able to change the connections to take it out to a higher voltage. It all depends on how many leads they have brought out from the stator into the connection box. In order to dumb things down many motors only bring 3 leads out. Then you are stuck with whatever they gave you.

But really you could cut way down on copper costs and make for an easier install if you could go with the higher voltage. I take it this thing is a WYE? Something about the voltage being listed as 120/​208 seems odd. It's been a long time since I dealt with an electric powered fire pump though. Most everything I worked on for the last 10 years or so has been diesel.

I know what you mean. I think it depends on what's out there. I think they presently have a 208V/120 service to their building, and they thought oh so I'll just order a 208V/120V fire pump. If I decide to go with a separate service, I could have easily have asked the utility for a 480V service.

I agree that putting in 208V pump seems wasteful. The good thing is, the main will be about 1200A, but I don't need to run 1200A worth of copper to it, just approximately 350Kcmil wires. It depends.

I honestly think this client just wanted something fast and cheap, that's why he told me to just make it work and sign and seal my drawings. Sorry bud, I don't just seal and seal stuff. :p
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
Yeah, I guess if the same guy ordered the controller he probably speced a 208 volt. What a waste. I never understand why buying decisions like that are left up to the least knowledgeable. I have had to so many times spend lots of the customer's money hooking machines up because someone thought that those little details were unimportant.

I wonder how long a 125% FLA transformer will carry the LRA. I'd like to watch and see what fries first.
 
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Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
Lets buy the parts first, and then call the engineer :rotflmao:


The salesman probably had the 208 V unit in stock and wanted to move it so he said "sure it'll be fine"
 
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Lady Engineer

Senior Member
Location
New Jersey
Lets buy the parts first, and then call the engineer :rotflmao:


The salesman probably had the 208 V unit in stock and wanted to move it so he said "sure it'll be fine"

I think that's what happened.

There was this generator guy who came buy and said I need to sell generators, but the state will not let me just install one without drawings. He would sell them 30KW gen sets when they need actually need a 45KW. Well, needless to say, he said well I told the client all I need is to take your demand load x 1.5, isn't that a good rule of thumb.

I told him, well suppose you have multiple motors, I hope can start the gen set with all the in rush. He says...in rush??? :slaphead:
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
I think that's what happened.

There was this generator guy who came buy and said I need to sell generators, but the state will not let me just install one without drawings. He would sell them 30KW gen sets when they need actually need a 45KW. Well, needless to say, he said well I told the client all I need is to take your demand load x 1.5, isn't that a good rule of thumb.

I told him, well suppose you have multiple motors, I hope can start the gen set with all the in rush. He says...in rush??? :slaphead:


Are all these jobs out of NJ? Or are you making drawings for jobs everywhere. I was based out of Trenton for years. I might know this guy.
 

bob

Senior Member
Location
Alabama
Lady
Please check your code book again. It says that the service conductor will be 125% of the FLA of the motor. The over current device will be sized at the LRA of the motor. You may want to install 2 services. Correct me if I am wrong. I have seen the service go right to the fire pump location with out a fused disconnect provided it is install properly. The OC device is at the pump.

http://ecmweb.com/nec/code-basics/electric_power_pump/
 
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lilsparky

Member
Location
Madison, Al
Add a fire pump to existing service

Add a fire pump to existing service

This conversation helped me a ton!! we were just hit from the FP contractor that they need to add in a 100hp fire pump to the system (not even shown on their 35% submittal). I only have one feed to the building through an outdoor 500KVA 12.47/480v transformer , then a through a 600A disconnect before coming into the building. I believe I can tap the transformer before the 600A disconnect to feed the fire pump. I believe that's the only way to go, unless I can convince them to go diesel.
 

Lady Engineer

Senior Member
Location
New Jersey
Are all these jobs out of NJ? Or are you making drawings for jobs everywhere. I was based out of Trenton for years. I might know this guy.

Umm...he's in the Somerville/Bridgewater area, but he's a generator rep. I work in Somerville, so he came by my office with with the "deal of the lifetime". He says, "You give me drawings signed and sealed, and I'll give you work." Ok...seems plausible, but then when I heard he was selling gen sets without calcs, I said wait so how do you know they will start? He says, "Eh, as long as they are sized to 1.5 times the size of the load they start." I said to him, "Ok, so I'll be charging you for calculations too." :D

I live near Trenton, but this guy came to my job. I used to work for a few architects in the city as a side job. I'm going to stop talking now, you maybe have built one of my projects I designed there. :rotflmao:
 

Lady Engineer

Senior Member
Location
New Jersey
This conversation helped me a ton!! we were just hit from the FP contractor that they need to add in a 100hp fire pump to the system (not even shown on their 35% submittal). I only have one feed to the building through an outdoor 500KVA 12.47/480v transformer , then a through a 600A disconnect before coming into the building. I believe I can tap the transformer before the 600A disconnect to feed the fire pump. I believe that's the only way to go, unless I can convince them to go diesel.

Oh no. I did a courthouse in the city where we tapped ahead of the main like you are saying. However, I just couldn't remember how I sized my service! :ashamed:
 

Lady Engineer

Senior Member
Location
New Jersey
Lady
Please check your code book again. It says that the service conductor will be 125% of the FLA of the motor. The over current device will be sized at the LRA of the motor. You may want to install 2 services. Correct me if I am wrong. I have seen the service go right to the fire pump location with out a fused disconnect provided it is install properly. The OC device is at the pump.

http://ecmweb.com/nec/code-basics/electric_power_pump/

I get what you are saying, and the size of the conductor and OCP aren't the problem. I was confused if the pump is tapped ahead of the main, will the utility transformer which feeds the service, (including the fire pump) need to be increased. I think someone said 1.25 plus the other loads.
 

Joethemechanic

Senior Member
Location
Hazleton Pa
Occupation
Electro-Mechanical Technician. Industrial machinery
Lady
Please check your code book again. It says that the service conductor will be 125% of the FLA of the motor. The over current device will be sized at the LRA of the motor. You may want to install 2 services. Correct me if I am wrong. I have seen the service go right to the fire pump location with out a fused disconnect provided it is install properly. The OC device is at the pump.

http://ecmweb.com/nec/code-basics/electric_power_pump/


Yeah, if you sized your conductors to carry the LRA of the motor, why would you need or want additional overload protection in the circuit? How close is this pump to where you would have it's service enter?

Is this a pad mount btw? And who owns the pot?
 

bob

Senior Member
Location
Alabama
Yeah, if you sized your conductors to carry the LRA of the motor, why would you need or want additional overload protection in the circuit? How close is this pump to where you would have it's service enter?

You don't size the conductor for the LRA. It is sized at 1.25 x the FLA of the motor and other equipment.
The service is installed in conduit with 2" of concrete around it(I think it is 2").
It is then considered outside the building so there is no disconnect required. The OC breaker comes with the fire pump and its other equipment. You can see this in the picture at his site.

http://ecmweb.com/nec/code-basics/electric_power_pump/
 
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