Original message
| Rooky
 |  "Three phase compressor but contactor's2pole"
, posted Wed 13 Aug 16:52  
I have gone to commercial sites. to do maintenance work the roof top units. I come from a residential background.I got started on thi about 2 months ago. I'm very new at commercial. I've seen single pole contactors to energize the compressor and the outdoor fan ( residential , again. They use this wiring to energize the crank-case heater at the base of the compressor. No harm to the compressor. Compressor is'n energized.
Now, I saw the other day this unit Bryant: model # 561CE036-B and serial # 2198E07521. It's a 3 tonsR-22 unit installed at this RV place on the roof. It's a 480 volts and three phase compressor and a single phase condenser fan. What got my attention and interest , it's the fact that the contactor was a two pole contactor. The disconnect had the orange and brown connected to the contactor and the Yellow phase/leg was directly connected to the blue wire of the compressor. My surprise and interest is that , why the compressor's motor does'nt burn or go bad. Is'nt one phase always connected to it. I know that the phase monitors we install in these units ( by the way this one did not have one installed ) is to protect the compressor's motor in case one leg/phase is missing. But again in this unit , I think that ( 2 ) two legs/phases are missing.However, the compressor does'nt get burned.
Plz! could you share your knowledge and experience to help me understand this.
Thanks to everyone.
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Replies:
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| stantec
| "Re(1):Three phase compressor but contactor's2" , posted Tue 26 Aug 11:45
please send the photograph
STANTEC HVAC CONSULTANT
A-222 Popular Plaza, Someshwar complex–1
satellite,Ahmedabad – 380 015
India
Tel.: - 91-79-30125691, Tel Fax: - 91 79 26752305
e-mail :- stantec.con@gmail.com
Mobile :- 9825024651
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| Jojo98
| "Re(1):Three phase compressor but contactor's2" , posted Thu 14 Aug 22:33
They call it "The Stinger Leg" and that's self explanitory.
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| theduke03
| "Re(1):Three phase compressor but contactor's2" , posted Thu 14 Aug 20:27
Rooky, it is OK to have comp. wired like that. When 2 legs are disconnected then the 3rd will energize the compressor, but since there are no other legs connected, there's no difference across the windings. You can verify this by checking volts between the live leg and the other terminals on compressor. You will read 0 volts. Your real concern is "single phasing". This is when only one leg is missing. There will still be a difference of 208 or 460 with 2 legs energized and the compressor will suffer or trip a breaker.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | Rooky
| "Re(2):Three phase compressor but contactor's2" , posted Fri 15 Aug 17:14
Thanks again, guys. I really appreciated the fast responses. I'll measure these voltages next time.
Thanks a lot.
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