thunder15j
Member
- Location
- Cali
I would welcome feedback on the folllowing installation.
Our customer has asked us to run a new circuit to a 5 horsepower, 3 phase speedair air compressor unit that they recently purchased from graingers. It is prewired for 240 volts, 3 phase supply. The electic feed is to run into a 2 pole pressure switch with the 3rd leg going direct to the motor. The mfg went from the pressure switch with a piece of 4 conductor chord going into the motor. The 3 phase motor has some sort of thermal protector that provides motor protection from overloads.
We will install a fuseable disconnect next to unit and run 3 #12's with egc to pressure switch and fuse at 20 or 25 amp TD fuses.
When the customer told me about the job, I was planning on installing a combo starter and use the pressure switch to open and close the starter.
When I first saw the motor on this unit, I saw the manual reset overload button on the back of the motor and automatically thought that it was for a single phase motor. Good thing I went back to the truck and grabbed my specs (glasses) and found, much to my surprise, that the motor was indeed 3 phase.
Finally getting to the point, my thoughts on this unit are: 1) I don't like the idea of using a 2 pole pressure switch to switch the 3 current carrying conductors . One leg is alway hot to the motor. An internal ground fault in the motor on the right leg could cause problems. 2) The thermal protector in the motor more than likely doesn't protect all three legs. 3) Conversley, it must be an approved assembly since graingers is a major industrial supplier (should be in the know). 4) Good luck trying to get a replacement motor for this unit when the motor fails.
Our customer has asked us to run a new circuit to a 5 horsepower, 3 phase speedair air compressor unit that they recently purchased from graingers. It is prewired for 240 volts, 3 phase supply. The electic feed is to run into a 2 pole pressure switch with the 3rd leg going direct to the motor. The mfg went from the pressure switch with a piece of 4 conductor chord going into the motor. The 3 phase motor has some sort of thermal protector that provides motor protection from overloads.
We will install a fuseable disconnect next to unit and run 3 #12's with egc to pressure switch and fuse at 20 or 25 amp TD fuses.
When the customer told me about the job, I was planning on installing a combo starter and use the pressure switch to open and close the starter.
When I first saw the motor on this unit, I saw the manual reset overload button on the back of the motor and automatically thought that it was for a single phase motor. Good thing I went back to the truck and grabbed my specs (glasses) and found, much to my surprise, that the motor was indeed 3 phase.
Finally getting to the point, my thoughts on this unit are: 1) I don't like the idea of using a 2 pole pressure switch to switch the 3 current carrying conductors . One leg is alway hot to the motor. An internal ground fault in the motor on the right leg could cause problems. 2) The thermal protector in the motor more than likely doesn't protect all three legs. 3) Conversley, it must be an approved assembly since graingers is a major industrial supplier (should be in the know). 4) Good luck trying to get a replacement motor for this unit when the motor fails.
