According to NEC 695.6 the conductor size shall be not less than the sume of 125% of the motors and 100% of the accessories. Fine with that. But...if the overcurrent protection is sized to carry the locked rotor current, does the conductor need to be upgraded to have the same ampacity rating as the ocpd?
Fire Pump Conductor Size
- Thread starter lizzie14
- Start date
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charlie
Senior Member
- Location
- Indianapolis
Re: Fire Pump Conductor Size
The quick answer is no. The conductors will not have enough time to get hot enough to be damaged; they will be protected by the fire pump controller. However, the controller must have the ability to allow the fire pump to run to failure. In other words, the winding of the motor will burn up before the conductors are damaged.
The OCPD (if provided) must carry LR indefinitely. The service disconnect (if provided) must carry 115% of the running amperes of the largest motor plus 100% of the rest of the load. The motor circuit conductors must carry 125% of the running amperes of the largest motor plus 100% of the rest of the load. The overloads are in the fire pump controller and will allow the motor to run to failure before opening up to protect the motor circuit conductors and other upstream equipment. Under LR conditions, the controller OL's will open after about 20 seconds.
Sorry, I didn't expect to get that long winded.
The quick answer is no. The conductors will not have enough time to get hot enough to be damaged; they will be protected by the fire pump controller. However, the controller must have the ability to allow the fire pump to run to failure. In other words, the winding of the motor will burn up before the conductors are damaged.
The OCPD (if provided) must carry LR indefinitely. The service disconnect (if provided) must carry 115% of the running amperes of the largest motor plus 100% of the rest of the load. The motor circuit conductors must carry 125% of the running amperes of the largest motor plus 100% of the rest of the load. The overloads are in the fire pump controller and will allow the motor to run to failure before opening up to protect the motor circuit conductors and other upstream equipment. Under LR conditions, the controller OL's will open after about 20 seconds.
Sorry, I didn't expect to get that long winded.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: Fire Pump Conductor Size
Lizzie, Charlies post is right on. By the way, the 1999 NEC clarified that fire pump conductors do not have to be sized to carry locked rotor current, only 125% of motor FLA.
Lizzie, Charlies post is right on. By the way, the 1999 NEC clarified that fire pump conductors do not have to be sized to carry locked rotor current, only 125% of motor FLA.
charlie
Senior Member
- Location
- Indianapolis
Re: Fire Pump Conductor Size
UH . . . Thanks . . . UH . . . I think.
UH . . . Thanks . . . UH . . . I think.
roger deas
Member
- Location
- North_Carolina
Re: Fire Pump Conductor Size
Given that there is no mention of "Wye Start Delta Run" motors in Article 695, what are the opinions of using Article 430.22(C)if using a "Wye Start Delta Run" motor.
Roger
Given that there is no mention of "Wye Start Delta Run" motors in Article 695, what are the opinions of using Article 430.22(C)if using a "Wye Start Delta Run" motor.
Roger
roger deas
Member
- Location
- North_Carolina
Re: Fire Pump Conductor Size
Charlie,
Roger
Charlie,
I must agree if you're talking about this.
Roger
charlie
Senior Member
- Location
- Indianapolis
Re: Fire Pump Conductor Size
Hey Roger, where in NC are you located? I spent five years in Goldsboro (three in Seymore Johnson AFB, two working for Hevi Duty Electric).
I am inclined to think that the rules in Chapter 6 modify the rules in Chapters 1 through 4. Therefore, Section 430.22(C) stands since Article 695 is silent on the subject. "For a wye-start, delta-run connected motor, the selection of branch-circuit conductors on the line side of the controller shall be based on the motor full-load current. The selection of conductors between the controller and the motor shall be based on 58 percent of the motor full-load current."
Hey Roger, where in NC are you located? I spent five years in Goldsboro (three in Seymore Johnson AFB, two working for Hevi Duty Electric).
roger deas
Member
- Location
- North_Carolina
Re: Fire Pump Conductor Size
Charlie, I'm in the Asheville area. We do work as far away as the coast however.
Roger
[ May 06, 2003, 03:16 PM: Message edited by: roger deas ]
Charlie, I'm in the Asheville area. We do work as far away as the coast however.
This is the way I see it too.
Roger
[ May 06, 2003, 03:16 PM: Message edited by: roger deas ]
Re: Fire Pump Conductor Size
More conductor sizing questions - going from transformer, to fused disconnect, to fire pump. on the line side (from transformer to disconnect) does this conductor need to be sized for the size of the fuse (in this case 400A which is the locked rotor current, plus etc.) ??? i know it doesn't on the load side but am still confused about the line side.
thanks!!
More conductor sizing questions - going from transformer, to fused disconnect, to fire pump. on the line side (from transformer to disconnect) does this conductor need to be sized for the size of the fuse (in this case 400A which is the locked rotor current, plus etc.) ??? i know it doesn't on the load side but am still confused about the line side.
thanks!!
charlie
Senior Member
- Location
- Indianapolis
Re: Fire Pump Conductor Size
You still size the conductors to carry 125% of the running amperes of the largest motor plus 100% of the rest of the load.
You still size the conductors to carry 125% of the running amperes of the largest motor plus 100% of the rest of the load.
- Location
- Illinois
- Occupation
- retired electrician
Re: Fire Pump Conductor Size
Don't forget that you have to size the system for a maximum 15% voltage drop at the pump controller line terminals under the motor starting load. See 695.7. This, may in some cases, require larger conductors.
Don
Don't forget that you have to size the system for a maximum 15% voltage drop at the pump controller line terminals under the motor starting load. See 695.7. This, may in some cases, require larger conductors.
Don
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