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electric supply to fire water pump
11

electric supply to fire water pump

electric supply to fire water pump

(OP)
i have a controlgear rated for 1200A,480v. one of the feeder is a fire water pump.having a FLA of 240A(locked rotor current 1500A Approx. i am extracting the local std requirement for fire pump unit package.
"QUOTE"
The protection schemes for Fire Pump Unit (FPU) packages shall comply with NFPA 20 and NFPA 70.  In general, these standards require that the motor be allowed to operate under locked rotor condition continuously and is only automatically disconnected under short-circuit conditions.
Exception :
    The exception to these requirements is that where a FPU package is fed from a bus that has ground overcurrent protection on the incomers or supply transformers, the feeder to the FPU package shall have ground overcurrent protection, and all other feeders connected to the same buses or transformers shall have ground overcurrent protection.
"UNQUOTE"

my question is will this controlgear be sufficient to supply the locked rotor condition mentioned? does the exception above mean that by providing groung fault protection i do not have to comply with require that the motor be allowed to operate under locked rotor condition continuously. please comment.

RE: electric supply to fire water pump

My feeling is no it will not be sufficient. Rated 1200A and motor Locked rotor is 1500A. The idea is if you have a fire you do not want the motor to be shut-off in the event of an overcurrent. The fire is more important than the motor. I do not see how installing ground current protection will eliminate the potential need for the motor to run under locked rotor currents. I am certain others will have additional info to add or corrections to make to my assumptions.

RE: electric supply to fire water pump

My feeling is no it will not be sufficient. Rated 1200A and motor Locked rotor is 1500A. The idea is if you have a fire you do not want the motor to be shut-off in the event of an overcurrent. The fire is more important than the motor. I do not see how installing ground current protection will eliminate the potential need for the motor to run under locked rotor currents. I am certain others will have additional info to add or corrections to make to my assumptions.

RE: electric supply to fire water pump

I agree with buzzp.

And if you have other loads on the switchgear (which it sounds like you do), then your situation is even worse.

And to compound the problem even further, there's a voltage drop limit in NEC 695.7 of 15% during starting conditions.  There's a really good chance your gear and feeders and upstream transformer would impose a more severe undervoltage than 15%.

RE: electric supply to fire water pump

Hold on guys. Do not forget that we are talking about an abnormal condition when the motor may be required to run at locked rotor condition. Refer to NEC Section 695. Even the feeders which provide power to the fire pump are sized per the full load current and not per the locked rotor current.Only the overcurrent protective device will be selected & set to carry indefinitely the locked rotor current.

The exception may be related to providing a ground fault protection which is also not required as per NEC.

It may be too early to write off the 1200A Controlgear.  

RE: electric supply to fire water pump

Suggestion to the previous posting:
The feeders to motors are sized higher than the motor FLA, e.g. 125% of FLA by NFPA 70 NEC.

RE: electric supply to fire water pump

Suggestion: Adhere to current NFPA 70-2002 National Electrical Code Article 695 Fire Pumps

RE: electric supply to fire water pump

Hmm, if the OCPD is sized for LR then should not the rest of the control gear be sized for the same (ignoring what the NEC says)? Seems like a potential safety hazard to me. If the OCPD does not shut down at LR then the equipment could potentially run indefinately with LR or near that. Seems like sparks and arcs (fire) may be the result. Maybe I am missing something here. What explanations are there for this reasoning?

RE: electric supply to fire water pump

Suggestion to the previous posting: The intent of such design is to have the pump functioning as much as possible regarding additional fire hazard posed by the fire pump electrical installation run. Apparently, the fire pump is assumed to do more "good" than its feeder being on fire doing more "bad."

RE: electric supply to fire water pump

Yes I understand the need to keep the pump running but why create another fire with undersized equipment?

RE: electric supply to fire water pump

Reposted from response at alternate listing for this subject:

No.  The exception deal with the disconnecting portion of overcurrent protection.  In other words, if you have the ground fault protection, you are 1) required to have it present at all the locations listed, and 2) now allowed to  have the ground fault protection  automatically  disconnect in the ground fault instance and not only in the  short-circuit instance.

With this requirement, the locked rotor "operation" could easily exceed the capabilities of the gear in question,  even without considering the other loads involved.

Consideration should also  be given to emergency requirements for this service.

Also, some locations will allow  you  to have separate service for the  fire pump and associated equipment.

Hope this helps.

RE: electric supply to fire water pump


According to my knowledge LRC is a static condition before the rotor of the motor starts moving. The LRC will last on until the motor has reached full speed and go down to rated current.
Full load current FLC is 240A Means motor will start with about 6 x rated currrent.
Why should a 1200 A rated switchgear not being able to start a 240 A rated current. Also the starting current is a little higher. This is quite normal. All breakers, bus bars and components are designed for continous current. Starting a fire pump will last < 10s.

RE: electric supply to fire water pump

Suggestion to buzzp (Electrical) Oct 17, 2003 marked ///\\\
Yes I understand the need to keep the pump running but why create another fire with undersized equipment?
///Yes, this is an excellent question with no easy answer. Apparently, the smaller size of fire pump motor feeder and inadequately protected with respect to the immediately upstream located protector is viewed as significant cost and labor savings.\\\

RE: electric supply to fire water pump

(OP)
with all the sugestions posted i am convinced that the feeder breaker to the fire pump should be rated for 1500A with short circuit and groung fault protection. the only doubt still remaining is the rating of the controlgear,1200 or 1500A!!!!!!!!!!

RE: electric supply to fire water pump

Suggestion to the previous posting: Would you clarify what you mean by "controlgear"? The feeder to the fire pump shall be rate 125% of the pump motor full load amps (FLA), i.e. 1.25 x 240A = 300A. Obviously, the higher ampacity fire pump motor feeder, the better. The 125% of FLA is a statistically determined number. The actual fire pump installation should have evaluated the motor feeder voltage drop, if the feeder is long, e.g. over 100 feet or so since the motor Locked-Rotor Amps (LRA) do also count.

RE: electric supply to fire water pump

(OP)
controlgear is a term used for motor control centres(MCC).

RE: electric supply to fire water pump

jacphi

What are the other loads on the MCC Bus. Are these continuous or intermittant loads?

RE: electric supply to fire water pump

(OP)
some continuous some intermittant..there are 5 different feeders on this MCC.

RE: electric supply to fire water pump

Difference,
 I am certainly no expert on fire pump controls but I know these controls should allow the pump to run no matter what, hence the locked-rotor current is the maximum it can draw (not just on start-up) under virtually any condition. So under whatever circumstances (single phase, undervoltage, etc..) the pump has to run. Hence, the discussion on locked-rotor current is not just for start-up conditions.

RE: electric supply to fire water pump

The motor will only last around 30 secs running at locked rotor current before it burns out and is useless anyway!

RE: electric supply to fire water pump

2
Having previously been in the fire pump controller business I can address some of these issues.

1) LOOK CLOSELY AT THE FIRST SENTENCE OF THE QUOTE. There is no intention for the equipment to actually PROVIDE locked rotor current continuously, because as others have pointed out the motor will melt down anyway. The references in this section are for the PROTECTIVE device (or lack there of). The intent here is to have the system be void of any running over current protection, i.e. long-time thermal trip elements. Since the code must cover the possibility of fuses or circuit breakers they are covering the worst case scenario, fuses. You may not size the FUSES for any less than Locked Rotor Curent so that they dont blow unless you have a destructive short circuit situation. Circuit breakers with magnetic-only trip elements are typically sized at 1100 - 1300% of FLA anyway.

2) Without knowing all of the other loads connected to the 1200A switchgear there is no way of determining if it is adequate or not. Hire a professional. If you do it wrong and have a fire, the insurance adjuster will be looking for this flaw in your thinking as a way to get out of paying!

3) The exception has to do with using a GF trip device on the entire system. If you use it on one part of the system, you must use it on the FPU as well. This is assuming that a coordinated system where GF protection was put in the incommer or transformer will be relying on that GF protection and not necessarily an instantaneous short circuit device. So to maintain the integrety of that system coordination you cannot have one major component, i.e. the FPU, running without GF because other protective devices may not pick up a short circuit in it. In other words, just because it is a Fire Pump doesn't mean you can get away with not using a GF protective device if your system was designed to have one.

4) For those who don't know, a Fire Pump Controller is SUPPOSED to allow the motor to "run-to-destruction". Remember, it will only come on when there is ALREADY a fire and so creating another one in the motor is the least of your problems. Hence the elimination of thermal protective devices.  Fire Pump Starters must even contain a method of manually forcing the controller closed even if the coil fails, i.e. a mechanical lever! They are very specialized controllers and must be UL / FM listed (in the US) under a completely different set of standards than regular motor controllers. In most jurisdictions you CANNOT use a standard MCC for a fire pump.

It also needs to be in a red box!

Quando Omni Flunkus Moritati

RE: electric supply to fire water pump


1.  I assume that this is the fire water pump and not a jockey pump.

2.  I assume that you are use the MCC to provide a feeder to a UL listed fire pump controller.  If not and your are planning to use a starter in the MCC, that is a code violateion.

3.  The power to the Fire pump controller should normally be tapped ahead of the service entrance.  The feeder becomes in essence another service entrance.  This feeder is generally sized at approximately the locked rotor current of the fire pump motor and, if protect4ed,  is protected with short circut protection only.  

If the rules for service entrance are followed, primary protection is not required on the feeder and it may be run directly to the fire pump controller.  

You should not be feeding the fire pump controller from a MCC unit downstream of the service unless you have a reliable redundant source(s) of power to assure service continuity.  

RE: electric supply to fire water pump

Suggestion: In many local Authorities Having Jurisdiction, the fire pump control is reviewed before it is submitted for construction. However, it is a good idea to have it designed flawlessly.

RE: electric supply to fire water pump

LOL! ..."designed flawlessly"?

Only an engineer could believe in such a fairy tale!

No disrespect intended JB, just a humorous observation of your assertion that such a thing as a flawless design might be achievable without divine intervention.

Quando Omni Flunkus Moritati

RE: electric supply to fire water pump

Suggestion: Visit
http://www.vi.wheeling.il.us/Services/Fire/SprinklerSys...
for:
Village of Wheeling Plumbing fire protection requirements
and for:
Fire Pump Requirements
When sprinkler requirements dictate the need for a fire pump, the installation must comply with the following standard:

NFPA #20: "Installation of Stationary Fire Pumps"

RE: electric supply to fire water pump

Kudos to jraef for a very informative reply!

Trivia question:
When you say water hose it is water that comes out of the nozzle. How about a fire hose? :) :)

God bless!

RE: electric supply to fire water pump

As has been pointed out, the 1200A MCC is not adequate for a 1500A locked rotor current on a fire pump. Also, if the MCC is downstream of the service, you will need a second source of power. You might want to consider a diesel driven fire pump as an alternate. This would eliminate all of the problems of supplying this power through your plant electrical system.

RE: electric supply to fire water pump

Suggestion: The Diesel Driven Fire Pump is more or less a fire truck. This is much too much a mechanical engineering item.

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