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#90492 11/23/04 10:10 AM
Joined: Mar 2003
Posts: 849
Y
Member
Large Industrial complex, Several Buildings Several 13.8 ,4160, transformers and switchhgear Dropping dn to 480 several in buildingings. In power plant Transformer 13.8 to 480 volt. They want to add a firepump Aprox. 200 feet from the transformer feeding that building. Can a run be taken off the load side of the transformer run to a disconnect Rated at locked rotor current of the 15 hp fire pump mtr. Then run to a service rated firepump 250 Ft. away. 200 feet of this run could be outside the building.No disconnect at the firepump location?? Also from transformer to ist disconnect must that wire be sized for the locked rotor current disconnect or can thaty also be sized at the 125% of the 15 hp mtr.Also are Two feeders required??(695.3 (b)2 .Locked Rotor current 430.151b 15 hp mtr.460 volts 116 amps.So disconnnect 125 Amps (240.6) Ok.
Feeder run OR runs if required in buiding Must comply with 695.6b. Couple imputs here Please.

2017 / 2014 NEC & Related Books and Study Guides
#90493 11/23/04 03:04 PM
Joined: Feb 2002
Posts: 182
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Bob Offline
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"Can a run be taken off the load side of the transformer"?
695.3 requires that the source be reliable and capable of supplying the locked rotor current to the equipment. Can the transformer
do this?

"Also from transformer to 1st disconnect must that wire be sized for the locked rotor current disconnect or can that also be sized at the 125% of the 15 hp mtr."
The conductor from the source to the firepump per 695.6C shall be rated for 125% of the equipment FLA.
If the source is reliable only one source is required per 650.3A2.

"Locked Rotor current 430.151b 15 hp mtr.460 volts 116 amps.So disconnnect 125 Amps (240.6) Ok?"

According to table 430.150 a 15 hp at 460 volts has a FLA of 21 amps. If the LRA is
6 x FLA the LRA would be 126 amps. How did you get the 116 amps for LRA?

#90494 11/23/04 04:34 PM
Joined: Mar 2003
Posts: 849
Y
Member
Bob
Following the example in the N.E.C. Code handbook I took locked rotor current from Table 430.151(B) 460volts Mtr B.C.D.(116 amps)
Where did you get the six times??(695.4(B)1
The transformer is way larger then required. Also is one feeder ok or are two required???


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