I have a question regarding metering of an electric fire pump. I am designing a multifamily residential condominium using multiple meter stacks to meter each unit individually. There now is a requirement for a 30HP, 208V electric fire pump. I do not have a main switchboard in which I could add a fire pump section. I want to tap off of the existing utility transformer with another service to specifically feed the fire pump. The local AHJ is allowing us to do this without a backup generator but I need to know how to size the meter for the fire pump. Article 695 addresses how to size the feeder (125% of fire pump + 100% of all associated loads) and how to size overcurrent protection if desired (600% or LRA) but does not address meters. Should I size the meter with the feeder and put in a 200 amp, 3 phase meter, or do I need to provide a CT cabinet and a 600 amp meter which can carry the locked rotor amps indefinitely? Thanks!
Fire Pump Metering
- Thread starter cpainter
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charlie
Senior Member
- Location
- Indianapolis
Re: Fire Pump Metering
Size everything for the fire pump service the same as you would for the same size electric motor and the various extras like the jockey motor. Next, remove the overload protection you were going to install (the controller that is set up for your motor will take care of that part). Lastly, size the short circuit and ground fault protection for locked rotor. That is fire pump service 101.
I don't understand why you are installing the metering but sizing it for the motor and associated loads is fine. If the motor goes to locked rotor for a while, the meter will not be 100% accurate for that period of time. If it is self contained or a bar type CT, the meter will not stop the current flow. Therefore, I would not be concerned about the metering under those conditions.
Size everything for the fire pump service the same as you would for the same size electric motor and the various extras like the jockey motor. Next, remove the overload protection you were going to install (the controller that is set up for your motor will take care of that part). Lastly, size the short circuit and ground fault protection for locked rotor. That is fire pump service 101.
I don't understand why you are installing the metering but sizing it for the motor and associated loads is fine. If the motor goes to locked rotor for a while, the meter will not be 100% accurate for that period of time. If it is self contained or a bar type CT, the meter will not stop the current flow. Therefore, I would not be concerned about the metering under those conditions.
Re: Fire Pump Metering
Thanks for the info...I am providing metering because the utility requires it. I do not have a traditional switchboard with a metering section and a main section which I could slip in a fire pump section between. This main section is before the meter with two 1200 amp breakers that serve meter stacks for individual condo units. I called the power company and asked about providing an unmetered tap just for the fire pump and the guy just laughed and told me that they don't give electricity away for free.
Thanks for the info...I am providing metering because the utility requires it. I do not have a traditional switchboard with a metering section and a main section which I could slip in a fire pump section between. This main section is before the meter with two 1200 amp breakers that serve meter stacks for individual condo units. I called the power company and asked about providing an unmetered tap just for the fire pump and the guy just laughed and told me that they don't give electricity away for free.
charlie
Senior Member
- Location
- Indianapolis
Re: Fire Pump Metering
No, we don't give the power away but we do provide our own meters. The meter cabinet/fitting is normally furnished and installed by the customer (depends on the electric utility).
No, we don't give the power away but we do provide our own meters. The meter cabinet/fitting is normally furnished and installed by the customer (depends on the electric utility).
Re: Fire Pump Metering
The service switch needs to have overcurrent protection sized to carry INDEFINITELY the locked rotor current of the fire pump. You cannot omit overcurrent protection, you just simply size it at 125% or more of the locked rotor current.
The meter has to carry the locked rotor current of the meter indefinitely. This means that the class size of the meter would need to be 100% or more of the locked rotor current. This so that the meter will not explode if an iron bacteria clump from the mains clogs up the pump and the pump has to grind that up.
The conductors also need to carry the locked rotor current for a reasonable amount of time and also need to meet voltage drop performance at locked rotor. The conductors need to provide 15% or less voltage drop at locked rotor and 5% or less drop at 115% of full load current. Since the motor is subject to overloads due to iron bacteria or inadequate ( just a few springler heads going off ) water flow or excessive water flow, table 430.22(E) could be interpreted as requiring conductors rated at 200% of nameplate current. This is a good selection so that the motor will burn up and blow the short circuit protection before the wires have a chance to hot glue themselves to the inside of the conduit. The wires do not have to carry locked rotor current indefinitely but you would want the motor to burn up first so that you can change the wires after a fire.
If the motor is locked rotor code letter F, G, or H you would need current transformer metering that can take 600 amps, an 800 amp service switch with 800 amp fuses or circuit breaker, and at least 176 read 200 amp wiring. General Electric type JAK-O, JCW-O, or JCR-O current transformers rated 200:5 nominal, 600:15 maximum thermal rating would do the trick for the metering and the meter would have to be Class 20 form 9s. If the electric utility insists that the service wires that supply the service switch for house loads must go through these CTs, then you would 400:5 CTs that have a thermal rating of 1600:20 amps. You would need to have #10 wire from the current transformers to to meter - most utilites do not allow shared conductors in the portion of the CT circuit that runs from the CTs to the test switches in the meter socket.
The motor controller is NOT allowed to have overload protection for the motor or the wires. See 430.31 and NFPA 20. Wires are also prohibited from having overload protection.
The service switch needs to have overcurrent protection sized to carry INDEFINITELY the locked rotor current of the fire pump. You cannot omit overcurrent protection, you just simply size it at 125% or more of the locked rotor current.
The meter has to carry the locked rotor current of the meter indefinitely. This means that the class size of the meter would need to be 100% or more of the locked rotor current. This so that the meter will not explode if an iron bacteria clump from the mains clogs up the pump and the pump has to grind that up.
The conductors also need to carry the locked rotor current for a reasonable amount of time and also need to meet voltage drop performance at locked rotor. The conductors need to provide 15% or less voltage drop at locked rotor and 5% or less drop at 115% of full load current. Since the motor is subject to overloads due to iron bacteria or inadequate ( just a few springler heads going off ) water flow or excessive water flow, table 430.22(E) could be interpreted as requiring conductors rated at 200% of nameplate current. This is a good selection so that the motor will burn up and blow the short circuit protection before the wires have a chance to hot glue themselves to the inside of the conduit. The wires do not have to carry locked rotor current indefinitely but you would want the motor to burn up first so that you can change the wires after a fire.
If the motor is locked rotor code letter F, G, or H you would need current transformer metering that can take 600 amps, an 800 amp service switch with 800 amp fuses or circuit breaker, and at least 176 read 200 amp wiring. General Electric type JAK-O, JCW-O, or JCR-O current transformers rated 200:5 nominal, 600:15 maximum thermal rating would do the trick for the metering and the meter would have to be Class 20 form 9s. If the electric utility insists that the service wires that supply the service switch for house loads must go through these CTs, then you would 400:5 CTs that have a thermal rating of 1600:20 amps. You would need to have #10 wire from the current transformers to to meter - most utilites do not allow shared conductors in the portion of the CT circuit that runs from the CTs to the test switches in the meter socket.
The motor controller is NOT allowed to have overload protection for the motor or the wires. See 430.31 and NFPA 20. Wires are also prohibited from having overload protection.
Re: Fire Pump Metering
Why are you trying to size metering? The utility will most likely provide the CT's and meter. They and/or the distributor or manufacturers rep would know the utility standards for the CT cabinet.
I'll bet the CT's are sized for normal full load amps x 125%. Who cares if they saturate for 30 sec or so until the controller shuts down the pump during locked rotor. Like the wire, they just need to carry the locked rotor current for a short time.
Why are you trying to size metering? The utility will most likely provide the CT's and meter. They and/or the distributor or manufacturers rep would know the utility standards for the CT cabinet.
I'll bet the CT's are sized for normal full load amps x 125%. Who cares if they saturate for 30 sec or so until the controller shuts down the pump during locked rotor. Like the wire, they just need to carry the locked rotor current for a short time.
charlie
Senior Member
- Location
- Indianapolis
Re: Fire Pump Metering
The service switch needs to have overcurrent protection sized to carry INDEFINITELY the locked rotor current of the fire pump.
The service is not required to have additional overcurrent protection if a SUSE rated fire pump controller is used for the service.
You cannot omit overcurrent protection, you just simply size it at 125% or more of the locked rotor current.
Where do you find 125%? All that is required is to carry the LR current and it is not overload protection but only short circuit and ground fault protection.
The meter has to carry the locked rotor current of the meter indefinitely.
It will but it will lose accuracy, no big deal.
The service switch needs to have overcurrent protection sized to carry INDEFINITELY the locked rotor current of the fire pump.
The service is not required to have additional overcurrent protection if a SUSE rated fire pump controller is used for the service.
You cannot omit overcurrent protection, you just simply size it at 125% or more of the locked rotor current.
Where do you find 125%? All that is required is to carry the LR current and it is not overload protection but only short circuit and ground fault protection.
The meter has to carry the locked rotor current of the meter indefinitely.
It will but it will lose accuracy, no big deal.
Re: Fire Pump Metering
But you do not want the meter to catch on fire or explode. That could cause further liability. With modern electronic meters a high ratio CT that can carry locked rotor current indefinitly will not cause an accuracy problem and is definitely safe.
In the case of a large electrical service metering capacity for fire pump locked rotor current is not a big issue. The problem is that meters and current transformers are not as robust as wires and motors. In fact, the vast majority of revenue meters are NOT listed by a nationally recognized testing laboratory. I would challenge you to find a revenue meter that has a UL or Factory Mutual listing.
Sizing the service switch fuses at 125% of locked rotor current makes absolutely sure that they will carry locked rotor current indefinitely.
The only time that I have seen a fire pump that could use the controller as the service switch is when the fire pump is in a shed that has its own service.
I would also rather that the wires NOT hot glue themselves to the inside of a conduit while the pump is grinding up iron bacteria. Most of the water mains around here are infested with iron bacteria and flushing it out causes them to grow back with a vengence if the pipeline is not relined with sand mortar. I wrote my term paper for freshman English in college about metal corrosion bacteria. There is also a company named the Tate Pipelining Process Company that cleans out water mains and relines them with sand mortar all over the world.
But you do not want the meter to catch on fire or explode. That could cause further liability. With modern electronic meters a high ratio CT that can carry locked rotor current indefinitly will not cause an accuracy problem and is definitely safe.
In the case of a large electrical service metering capacity for fire pump locked rotor current is not a big issue. The problem is that meters and current transformers are not as robust as wires and motors. In fact, the vast majority of revenue meters are NOT listed by a nationally recognized testing laboratory. I would challenge you to find a revenue meter that has a UL or Factory Mutual listing.
Sizing the service switch fuses at 125% of locked rotor current makes absolutely sure that they will carry locked rotor current indefinitely.
The only time that I have seen a fire pump that could use the controller as the service switch is when the fire pump is in a shed that has its own service.
I would also rather that the wires NOT hot glue themselves to the inside of a conduit while the pump is grinding up iron bacteria. Most of the water mains around here are infested with iron bacteria and flushing it out causes them to grow back with a vengence if the pipeline is not relined with sand mortar. I wrote my term paper for freshman English in college about metal corrosion bacteria. There is also a company named the Tate Pipelining Process Company that cleans out water mains and relines them with sand mortar all over the world.
charlie
Senior Member
- Location
- Indianapolis
Re: Fire Pump Metering
It is interesting that we now have meters that are exploding all over the place. We don't care about the electronics or even the coils in a meter under fire conditions. However, the bus that goes through the meter or bus bar will carry whatever current is necessary without blowing up for a period of time until the motor is taken out by the controller. We purchase thousands of meters and metering transformers that are built to our specifications. We don't care (and neither do most other electric utilities) if they have a listing. We have tested the meters in our shop and in the field for years.
Why not oversize the motor circuit wire with the short circuit and ground fault protection? The overcurrent devices are already inverse time unless you are using magnetic circuit breakers and will hold over 100%. I don't feel like over sizing something on a whim is a good idea.
I have seen several fire pump controllers that have the SUSE rating and be used as service equipment that were not "in a shed." I am trying to think of a reason why they would need to be in a separate structure to be used as service equipment. It is not like you have to group your disconnecting means that includes the fire pump.
I would like to hear more about iron bacteria and sand mortar lining as I have heard of neither.
It is interesting that we now have meters that are exploding all over the place. We don't care about the electronics or even the coils in a meter under fire conditions. However, the bus that goes through the meter or bus bar will carry whatever current is necessary without blowing up for a period of time until the motor is taken out by the controller. We purchase thousands of meters and metering transformers that are built to our specifications. We don't care (and neither do most other electric utilities) if they have a listing. We have tested the meters in our shop and in the field for years.
Why not oversize the motor circuit wire with the short circuit and ground fault protection? The overcurrent devices are already inverse time unless you are using magnetic circuit breakers and will hold over 100%. I don't feel like over sizing something on a whim is a good idea.
I have seen several fire pump controllers that have the SUSE rating and be used as service equipment that were not "in a shed." I am trying to think of a reason why they would need to be in a separate structure to be used as service equipment. It is not like you have to group your disconnecting means that includes the fire pump.
I would like to hear more about iron bacteria and sand mortar lining as I have heard of neither.
- Location
- Massachusetts
Re: Fire Pump Metering
CTs have even larger busing.
The lack of a listing does not mean an item is not a safe product.
I have never heard of that happening. Any plug in type meter I have seen has very large bus bars.
CTs have even larger busing.
Neither are motors, does that worry you also?
The lack of a listing does not mean an item is not a safe product.
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