I need to size a Transformer for a building that has 480 volt 3 phase AC condenser and air handler, both have a nameplate rating of 8.4 amps but the building has a 120/208 3 phase 150 amp panelboard, Ac guys set wrong units so now we have to change circuits for units, panel has plenty of spares , only using about 6- 20 amp circuits, please advise.
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- Thread starter ketoe
- Start date
- Status
- Occupation
- Licensed Electrician
Why is replacing the unit with one that is 208V not an option?
sparkyrick
Senior Member
- Location
- Appleton, Wi
Tell the AC guys to get the right damn unit. I hate it when their mistake becomes our problem.
End of little rant.
End of little rant.
That's what I said but we are charging the hell out of them to fix the problem
the 8.4 amps includes the moter, these are small ac units, I am more concerned about overcurrent protection for the two units with adding a small transformer, what are my options, can I go to J box with 480 circuits and feed the ac"s and use the overcurrent protection of the transformer? Or on the secondary side go to fusable disconnects
Last edited:
- Location
- Massachusetts
I am sure Gus understood that, what he is saying is that when supplying a motor load with a transformer you do not want to cut it close or you may have trouble getting the motor to start.
The inrush / starting current is much higher than the marked motor load and with a small transformer that can cause a lot of voltage drop, so much so the motor won't start.
You are going to have to set up an entire SDS, along with the over current protection requirements of article 240 for conductors and article 450 for transformers you need a grounding electrode system.
Are you going to use a delta to delta transformer with a 480 volt corner grounded output or are you going to use a delta to wye transformer and just ground the neutral?
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