1-phase 1-horse motor.........#6 conductors?

edlee

Senior Member
I did an emergency repair today , a hookup to a replacement compressor motor for a dry sprinkler system in a small mixed-use building. The old circuit was 15a 240v single-phase, 14-gauge copper, and the conduit run was about 25' long. The new motor draws nominally 7.35a @ 230v and the installation instructions called for minimum #6 copper conductors.

This seems offhand kind of crazy because I know it will operate on a much smaller wire. But the installers were concerned that if I used something smaller than #6 it might void the warranty. I talked to the local wiring inspector to see if there is something in the NEC referring specifically to sprinkler systems that I didn't know about and he didn't know of anything.

So we wired it in #6 thhn and put it on a 20a breaker.

Any thoughts about why they spec'd that?
 
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John120/240

Senior Member
Location
Olathe, Kansas
Fire sprinkler pumps are designed to run forever or until the fire is out. Being that it is a dry sprinkler system I don't see the need to oversize the supply conductors. The dry sprinkler compressor is used to charge the sprinkler pipe with compressed air only.
Others more experienced will chime in.
 

tom baker

First Chief Moderator
Staff member
My handy Sq D Motor Data Slide rule:
Min copper wire size 14
TM breaker 15 amp

Its a motor load and the rules are in Art 430. I have not seen any other section that would change this.
I would run 12 AWG as I feel 14 is a bit small to work with
 
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