Fire Pump CT and Disconnect size?

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olly

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Location
Berthoud, Colorado
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Master Electrician
I am reviewing a one-line diagram that had a CT / Disconnect that was 200A and now its 1000A and the pump size never changed. The Electrical engineer claims that it needs to be 5x larger due to fire code. Is he correct that this disconnect needs to be 5x larger?
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olly said:
I am reviewing a one-line diagram that had a CT / Disconnect that was 200A and now its 1000A and the pump size never changed. The Electrical engineer claims that it needs to be 5x larger due to fire code. Is he correct that this disconnect needs to be 5x larger?
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It has to be sized to handle the locked rotor current for the jockey and fire pumps, plus and auxiliary loads like the controllers. That looks like just under or at 400 amps, not 1,000 amps.
 
olly said:
I am reviewing a one-line diagram that had a CT / Disconnect that was 200A and now its 1000A and the pump size never changed. The Electrical engineer claims that it needs to be 5x larger due to fire code. Is he correct that this disconnect needs to be 5x larger?
View attachment 2554557
Click to expand...
I didn't check the math but that looks about right as that is on the 208 side and it needs to carry locked rotor on the 480 side motor. Note that that transformer will need to be 208 delta X 480Y.
 
texie said:
I didn't check the math but that looks about right as that is on the 208 side and it needs to carry locked rotor on the 480 side motor. Note that that transformer will need to be 208 delta X 480Y.
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I didn't pay attention to that. My bad.
 
gadfly56 said:
I didn't pay attention to that. My bad.
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However, if you apply table 9.5.1.1(a) from NFPA 20, you'll see that the locked rotor current for the fire pump should be 277 at 480v, not 380. The jockey pump goes up to 19.2 amps.
 
texie said:
I would question why he doesn't spec a 208 fire pump and make it less complicated. 40 HP is not unreasonable to run on 208.
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In addition, if you use 208 motors you could also get rid of the 1000 amp disco. as the fire pump controller and the jocky pump controller can/will be service rated and make this much simpler, cheaper and reliable.
 
texie said:
In addition, if you use 208 motors you could also get rid of the 1000 amp disco. as the fire pump controller and the jocky pump controller can/will be service rated and make this much simpler, cheaper and reliable.
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The big problem is that the POCO bills capacity fee's based off of the first disconnect from the transformer. So If he would have went with a 208 pump the disconnect could have been smaller?
 
gadfly56 said:
However, if you apply table 9.5.1.1(a) from NFPA 20, you'll see that the locked rotor current for the fire pump should be 277 at 480v, not 380. The jockey pump goes up to 19.2 amps.
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Does that mean the disconnect off the POCO transform could be smaller? 1000A is still not making sense to me
 
olly said:
The big problem is that the POCO bills capacity fee's based off of the first disconnect from the transformer. So If he would have went with a 208 pump the disconnect could have been smaller?
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No, I'm saying you don't need the disconnect at all. The fire pump controller is rated as service equipment and you run service conductors directly to it from the CT can. The path must be "outside the building" (usually underground to the fire pump room). As for POCO charges you need to have a chat with a capable service planner and explain that this is a fire pump.
You really should have a conversation with the engineer that designed this and ask why he is using 480 for the pump. In this size range I don't see how this can be cost effective. If you use the native 208 voltage you can do away with the 1000 amp disco and the step-up transformer.
 
I am actually in the middle of designing a service for a 40Hp fire pump. I have an 800A fused disconnect because according to NEC the overcurrent is required to handle 600% of the FLA for at least 2 minutes.
My service is also 240 3phase delta... so my numbers will be a little lower, so by the numbers he is looking at 930A so he would need the 1000A
 
Rock86 said:
I am actually in the middle of designing a service for a 40Hp fire pump. I have an 800A fused disconnect because according to NEC the overcurrent is required to handle 600% of the FLA for at least 2 minutes.
My service is also 240 3phase delta... so my numbers will be a little lower, so by the numbers he is looking at 930A so he would need the 1000A
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That 600% is for the fire pump controller, "an assembly listed for fire pump service". This is for the case where you have a tap ahead of the meter or service entrance panelboard and the only disconnecting means for the fire pump is the fire pump controller.
 
Rock86 said:
I am actually in the middle of designing a service for a 40Hp fire pump. I have an 800A fused disconnect because according to NEC the overcurrent is required to handle 600% of the FLA for at least 2 minutes.
My service is also 240 3phase delta... so my numbers will be a little lower, so by the numbers he is looking at 930A so he would need the 1000A
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My question for you is why do you have disconnect ahead of the fire pump controller?
 
texie said:
My question for you is why do you have disconnect ahead of the fire pump controller?
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Because Code says I can. 695.4 "General. A single disconnecting means and associated overcurrent protective device shall be permitted to be installed between the fire pump source power source (in my case the utility) and one of the following.... 1. a listed fire pump controller." I have a very long run and felt it better to have the disconnect.
 
Rock86 said:
Because Code says I can. 695.4 "General. A single disconnecting means and associated overcurrent protective device shall be permitted to be installed between the fire pump source power source (in my case the utility) and one of the following.... 1. a listed fire pump controller." I have a very long run and felt it better to have the disconnect.
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Well, of course you can but all it does is add a lot of cost and reduce reliability.
 
gadfly56 said:
That 600% is for the fire pump controller, "an assembly listed for fire pump service". This is for the case where you have a tap ahead of the meter or service entrance panelboard and the only disconnecting means for the fire pump is the fire pump controller.
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Not to argue you with you but that is not how the code words it. Also, by not including the full statement you are taking the code out context. But if I am wrong, please explain.
 
Yes you can have a disconnect but you are much better off not to, in terms of cost and reliability. Where will the disconnect be, outside? If so someone could tamper with it.
1,000 amp disconnect will be quite large.
Best to keep the service conductors outside and then go straight into the fire pump controller.
You can tap off for the jocket pump controller in the CT Can.
Let the POCO know this if for a fire pump, they may want to increase the size of the primary fuse.
Also watch the voltage drop, this is the one article in the NEC where there is a limit.
 
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