1 Phase power outage - 3 Phase still operational

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hardworker

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The 1 Phase had a power outage from the power company. The 3 phase was not affected. The building has both power sources.

The 3 phase HVAC system called for A/C, the air handler fan ran properly, but the condenser caused a very loud "buzz" and never would operate.

When 1 phase was restored, all operated properly.

What is your educated guess concerning the reason for the condenser malfunction?
 
Air handler fan single phase? Split system? (seperate air handler with remote compressors) Most commercial packaged roof top units have three phase compressors, three phase indoor fan (air handler), but the condensor fans are almost always single phase (even 480 volt units)
 
The 1 phase and the 3 phase come from different transformers. I did not take a voltage reading.

The air handler fan is 3 phase. The HVAC is a split system. The only power source fed to the roof top compressor is 3 phase.

This is why I am confused? There must be some 1 phase power going to some of the thermostat controls or something. I have not yet investigated that possibility.

Is that normal? If so, what happens to the unit if unattended during a 1 phase power outage?
 
The power company confirmed that Leg B is used for the 1phase system and that the 3phase system uses A,B, and C. (B supplies both)

Leg B went out, so the 1phase system was completely out. This also took down 1 leg of the 3phase system. This is why the HVAC was making noise. It was trying to start with only 1 leg.

The only thing I do not understand is why the elevator was completely down. When it was called, it did nothing. The HVAC condenser made a loud buzz. The elevator motor did nothing.

Any ideas?
 
hardworker said:
The power company confirmed that Leg B is used for the 1phase system and that the 3phase system uses A,B, and C. (B supplies both)

Leg B went out, so the 1phase system was completely out. This also took down 1 leg of the 3phase system. This is why the HVAC was making noise. It was trying to start with only 1 leg.

The only thing I do not understand is why the elevator was completely down. When it was called, it did nothing. The HVAC condenser made a loud buzz. The elevator motor did nothing.

Any ideas?
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We were under the impression that the three phase was still working. The reason the elevator would not work could be two fold, it probably has a phase loss monitor in the control circuits, and the control transformer was probably on "B" phase and one of the other two phases.
 
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