Rating of Fire Pump Disconnect Switch

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Sparky2791

Sparky2791

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Electrical Design
Feeding a fire pump directly from the customer owned outdoor pad mounted utility transfomer as the building has a MV service. Per 230.70 & 225.31 a disconnect switch is required to disconnect all ungrounded service conductors that enter the building. NEC 695.4 indicates sizing the OCP for LRC but if I do not have OPC in the switch would the rating of the disconnect switch itself still need to be sized for this? I would prefer to leave the OCP out of the disconnect switch to avoid sizing it for locked rotor current keeping the disconnect switch much smaller because in my case 404.13(B) would apply so I would need to dive further into that

Looking for the section of the code that indicates the disconnect (not the OCP) must be sized for this if it exists. Am I missing something on this?

Thanks!
 
LibertyEngineering said:
Feeding a fire pump directly from the customer owned outdoor pad mounted utility transfomer as the building has a MV service. Per 230.70 & 225.31 a disconnect switch is required to disconnect all ungrounded service conductors that enter the building. NEC 695.4 indicates sizing the OCP for LRC but if I do not have OPC in the switch would the rating of the disconnect switch itself still need to be sized for this? I would prefer to leave the OCP out of the disconnect switch to avoid sizing it for locked rotor current keeping the disconnect switch much smaller because in my case 404.13(B) would apply so I would need to dive further into that

Looking for the section of the code that indicates the disconnect (not the OCP) must be sized for this if it exists. Am I missing something on this?

Thanks!
Click to expand...
Disconnects are sized to the load that is supplied. When used as fire pump disconnects, they should be listed as such and should be locked at the closed position, with required markings so that inadvertent opening is not possible. LRCs are just about 8 to 20 seconds depending on the type of motor, size, and the mechanical load. The provision on the sizing of OCP to LRC is done to allow the fire pump motor to continue running and not trip as pumping duty is more important during fires.
 
tom baker said:
You are better off without a disconnect. Use a listed fire pump controller and connect the service conductors to its line side terminals
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230.70 prohibits me from not having a disconnect switch since it is fed directly from the utility transfomer is is considered a service (?), otherwise I agree.
 
topgone said:
Disconnects are sized to the load that is supplied. When used as fire pump disconnects, they should be listed as such and should be locked at the closed position, with required markings so that inadvertent opening is not possible. LRCs are just about 8 to 20 seconds depending on the type of motor, size, and the mechanical load. The provision on the sizing of OCP to LRC is done to allow the fire pump motor to continue running and not trip as pumping duty is more important during fires.
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My goal is to leave the OCP out of the disconnect and size it just as you mention, to the load that is supplied. My question is if that is acceptable. If there is no OCP than my disconnect switch for a 480V 3phase, 50HP motor is 100A. But even if there is no OCP do I still need to size the rating of the switch for LRC. Meaning the switch ampacity rating must be 400A?
 
packersparky said:
Service conductors underground from the transformer directly into the bottom SUSE rated fire pump controller is code compliant.
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Thanks but the problem with this project is they added a fire pump after the buildings floor was poured and frankly at the end of the project so the conductors will not be underground the whole way. They will come from the transfomer UG over to the exterior wall of the building stub up from UG along the exterior of the building to enter the building than run through the building , using 2 hour fire rated circuit protective system, over to the fire pump controller. So again thinking the disconnect switch is required. Thoughts?
 
packersparky said:
Service conductors underground from the transformer directly into the bottom SUSE rated fire pump controller is code compliant.
Click to expand...
Also, I am curious where would NEC allows the service disconnect to be deleted if the feed is UG the whole way to the controller? I would like to tuck that in my back pocket for future use.
 
LibertyEngineering said:
Thanks but the problem with this project is they added a fire pump after the buildings floor was poured and frankly at the end of the project so the conductors will not be underground the whole way. They will come from the transfomer UG over to the exterior wall of the building stub up from UG along the exterior of the building to enter the building than run through the building , using 2 hour fire rated circuit protective system, over to the fire pump controller. So again thinking the disconnect switch is required. Thoughts?
Click to expand...

In this case a service disconnect would be required either outside or inside nearest the point of entrance of the service conductors.
 
LibertyEngineering said:
Also, I am curious where would NEC allows the service disconnect to be deleted if the feed is UG the whole way to the controller? I would like to tuck that in my back pocket for future use.
Click to expand...

The service disconnect is not being deleted. The service disconnect is the fire pump controller as long as it is SUSE rated. The service conductors never enter the building until they come through the floor directly into the fire pump controller.
 
LibertyEngineering said:
Thanks but the problem with this project is they added a fire pump after the buildings floor was poured and frankly at the end of the project so the conductors will not be underground the whole way. They will come from the transfomer UG over to the exterior wall of the building stub up from UG along the exterior of the building to enter the building than run through the building , using 2 hour fire rated circuit protective system, over to the fire pump controller. So again thinking the disconnect switch is required. Thoughts?
Click to expand...

After thinking about this a little more, I have a few more thoughts. If the disconnect you are asking about does not contain overcurrent protection, the conductors cannot be fun through a building unless they are compliant with 230.6. A fire rated circuit protective system is not listed in 230.6. If the disconnect in question does contain overcurrent protection, it is a feeder and a dedicated feeder can supply a fire pump in accordance with 695.3(A)(3), and you can use the fire rated circuit protective system per 695.6(A)(2)(4)(c). As always, I would run it by the electrical inspector first.
 
packersparky said:
After thinking about this a little more, I have a few more thoughts. If the disconnect you are asking about does not contain overcurrent protection, the conductors cannot be fun through a building unless they are compliant with 230.6. A fire rated circuit protective system is not listed in 230.6. If the disconnect in question does contain overcurrent protection, it is a feeder and a dedicated feeder can supply a fire pump in accordance with 695.3(A)(3), and you can use the fire rated circuit protective system per 695.6(A)(2)(4)(c). As always, I would run it by the electrical inspector first.
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So without the OCP it is still considered a service, good point. Now here is a curve ball. Since the building has a medium voltage service and the transformer is in fact customer owned would that make a difference? Probably not, but per definition of a service in NEC the pad mounted transfomer is not fed directly by serving utility company.
 
LibertyEngineering said:
So without the OCP it is still considered a service, good point. Now here is a curve ball. Since the building has a medium voltage service and the transformer is in fact customer owned would that make a difference? Probably not, but per definition of a service in NEC the pad mounted transfomer is not fed directly by serving utility company.
Click to expand...

That most definitely does make a difference. The fire pump supply is now a feeder and it is not a dedicated feeder per 695.3(A)(3). The only way this could work is if it is a multi-building campus style complex and the AHJ accepts it being installed as such per 695.3(C).
 
What is the voltage and HP of the fire pump?
I had a 460 v 100 hp fire pump and a service disconnect sized for locked rotor current was the size of a VW bug.
 
LibertyEngineering said:
Also, I am curious where would NEC allows the service disconnect to be deleted if the feed is UG the whole way to the controller? I would like to tuck that in my back pocket for future use.
Click to expand...
Yes, all full service rated fire pump controllers are SUSE rated. For most garden variety installs of fire pumps the preferred method is to simply run service conductors directly from the meter underground and/or outside to the fire pump controller room. This makes for a compliant and economical install.
 
tom baker said:
You are better off without a disconnect. Use a listed fire pump controller and connect the service conductors to its line side terminals
Click to expand...
Hi Tom, I would like to know if NFPA allow this? And actually I met this case there is no disconnect means before control fire pump conrol panel and cable connected directly to secondary side of service transformer.
Also the fire pump transforer primary side incoming cable directly fed from 13.2KV MV bus without any fuse or breaker. Is this NFPA allowed and is normal US practice?

Below photo for your reference.

Thanks !
 

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A relevant consideration is that service conductors with a minimum (4"?) of concrete and/or brick cover are considered to be outside the building. But un-encased service conductors any distance below the floor of an elevated building, if they are inside the building footprint, are considered to be inside.

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LibertyEngineering said:
So without the OCP it is still considered a service, good point. Now here is a curve ball. Since the building has a medium voltage service and the transformer is in fact customer owned would that make a difference? Probably not, but per definition of a service in NEC the pad mounted transfomer is not fed directly by serving utility company.
Click to expand...
If the transformer is customer owned and maintained then the service is in the supply to that transformer. everything on secondary is feeders or feeder taps, though you still have similar rules for disconnecting means and overcurrent protection when entering a building as you do for services.

If customer paid for said transformer but POCO still maintains it - then secondary might very well considered to be service conductors, especially if customer does not have access to the transformer.
 
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