2002 NEC for fire pumps

[mpparent]

Hey guys,

In the new NEC, it states in section 695.4B, that overcurrent protection between a standby gen. and fire pump controller shall be selected to provide short circuit protection only. Does this imply that one could use an MCP to protect the circuit from short circuit events?

 

[REDDOG]

MCP (MOTOR CIRCUIT PROTECTORS) ARE NOT LISTED DEVICES THEY ARE RECOGNIZED DEVICES, ONLY USED IN COMBIANATION STARTERS. THERMAL MAGNETIC CIRCUIT BREAKERS ARE LISTED DEVICES AND CAN BE USED FOR BRANCH CIRCUIT PROTECTION.

 

[mpparent]

Reddog,

I agree with what you're saying, but don't a lot of the combination fire pump controllers/automatic transfer switches have motor starters in them, which would allow the use of an MCP?

 

[dpc]

Probably, but the MCP has to be part of a UL-labeled assembly specifically designed for use as a fire-pump motor controller.

If you make any changes to a listed controller, you no longer have a UL-listed device.

You cannot use an MCP as a stand-alone device to protect anything. It might not be logical, but I don't believe the NEC allows that under circumstances.

 

[Ares]

What that means is that you may tap a feeder to Fire Pump right behind a main generator breaker and not be concerned with overload protection, as long as a short in any point of that feeder will trip the breaker.

For example: It may be acceptable to run a 100 Amp feeder from a 400A braker

 

[DRWeig]

Hi, mpparent!

The reasoning behind this statement in the code is that it's preferable to let the fire pump and/or generator run overloaded -- even until one of them stops due to overheating -- rather than stop supplying fire water to the sprinklers & standpipes while a fire is in progress. Sacrifice a machine to possibly save lives and property.

Thus, no overloads are permitted. A magnetic-only instantaneous trip breaker sized to the maximum allowed for the motor horsepower and voltage in question is the answer, and this is basically what an MCP is. However, you'd need to find one enclosed and listed as an assembly to meet the listing requirements. Talk to your favorite circuit breaker rep, I bet they have just the ticket already made up for you.

Best of luck!

Old Dave

 

[mpparent]

Thanks Dave,

That's what I was thinking. I appreciate it...

Mike

 

[dpc]

I may be wrong, but I don't think you will find an MCP or mag-only breaker in a separate enclosure with a UL label on the enclosure.

The fire pump supply is generally tapped directly from the service entrance conductors ahead of the main service disconnecting means. If you run this tap outside the building, you can run it directly to the fire pump controller without an additional breaker. The fire pump controller is the service disconnect for the fire pump.

If you do install an additional breaker at the tap, I still think you will end up using a thermal-mag (or electronic) trip. It will have to be sized to carry the locked-rotor current of the fire pump motor, so it would end up being oversized, as would the conductors. But I've been wrong before.

If you have a special situation, I'd suggest discussing with local electrical inspector and the fire marshall before buying any equipment.

 

[REDDOG]

Don't forget the Meter socket and ct cabinet for the utility service.

 

[Codemaster]

For standard fire pump installation (from utility not a generator) I agree DRWeig and partly with dpc. DRWeig is correct for the reasoning behind the code rule. dpc is correct except that the conductors don't have to be oversized, this is an exception to the overcurrent protection rule (motor will melt down and short circuit before conductors start a fire). For generator installations, I don't know. I think it is far better to provide a diesel driven fire pump then a generator/electric pump combination. If you use the electricity for anything else, you are required to shed other load to prevent inadequate power for the fire pump.