277 single phase single pole to, 208-230 single phase 2 pole

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mon6am

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I need to change out a heat pump that was sized to big. The old heat pump is a 277v single phase on a single pole breaker 22 amps. The new heat pump, a smaller unit does not come 277v single phase single pole, it only comes in a 230v-208v and would need 2 poles 18.8 amps. How can I do this without going broke, I already have to eat the costs of the new heat pump????
 
You will need to supply a transformer to step down from your existing 277V down to the required 240V or 208V.
 
I guess what I am asking is the 277v is from a single leg and the 208v-230v I need, would come from 2 legs. So would I need a 480v to 208v transformer?
 
mon6am said:
I guess what I am asking is the 277v is from a single leg and the 208v-230v I need, would come from 2 legs. So would I need a 480v to 208v transformer?
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...or a buck-boost xfmr 240 x 480 Primary, 24/48V Secondary configured as an autotransformer to buck 48 volts (277 in, ~230 out).

For example, a SolaHD HS22F750B (search model# in pdf).
 
You might want to double check the parameters on your 230 v unit, but, as Smart$ states, a buck and boost will take you down to 230 volt but if your 277 is running high your 230 will also (proportionally) so you might want to check some actual voltages.
 
Question: What power is available at what price? Is there already a 208V or 240V source close enough that you don't need to add a transformer? Also if doing the buck-boost double check the heat pump (especially compressor) to make sure it allows more than 125 volts to ground... many don't.
 
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Why do you need another transformer?

If you've got 480/277 on-site, is there not already a transformer supplying a 120/208 panel?

Could you re-route the circuit into that panel to feed the pump?
 
mon6am said:
I need to change out a heat pump that was sized to big. The old heat pump is a 277v single phase on a single pole breaker 22 amps. The new heat pump, a smaller unit does not come 277v single phase single pole, it only comes in a 230v-208v and would need 2 poles 18.8 amps. How can I do this without going broke, I already have to eat the costs of the new heat pump????
Click to expand...

Curious, and at a loss in understanding why the replacement? I realize you said it is oversized, but in which way, physical, btu, or some other way? I can understand if it just won't fit physically in an allotted space, but if oversized by cooling/heating capacity, it would be cheaper to just leave the current one in place... wouldn't it?
 
The heat pump is over sized for the room in cooling mode minimum run time cools the room down below the set temp and the temp swing is causing people to be uncomfortable.
 
The heat pump is part of a geothermal system that is metered seperate with the d17 rateing. That meter feeds 1 panel witch is 480 3 phase. What I have is one leg 277v or 2 legs 480 and I need 2 legs 208v or 230v each leg being 120v I am thinking a buck-boost will not work for me. am I wrong?
 
The heat pump is part of a geothermal system that is metered seperate with the d17 rateing. That meter feeds 1 panel witch is 480 3 phase. What I have is one leg 277v or 2 legs 480 and I need 2 legs 208v or 230v each leg being 120v I am thinking a buck-boost will not work for me. am I wrong?
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BRIAN,New Baltimore,Michigan
 
If you have 277 available, a buck & boost can be used to provide you with 230 volts.
 
Ok so you are saying If I have one 277v leg a buck-boost will give me 2 legs 120v and 230v across the 2 120v legs
 
close, no cigar:), a buck and boost can be wired into a 277 volt circuit in such a manner as to provide you with 230 volt output.
There will not be any 120v leads.
You need to look at the wiring diagram for the buck and boost. Unlike a standard step-down transformer, they are wired, for lack of a better term, in series with your supply.
277 in, 230 out
 
In no particular order:

A. A load does not care which, if any, conductor is grounded. We can use 1p breakers when one circuit conductor happens to be grounded, and we must use 2-pole breakers when both circuit conductors are hot to ground.

2. If you use a buck-boost, which becomes an auto-transformer when wired that way, must have the grounded circuit conductor be maintained as a grounded conductor all the way to the load, so a 1p breaker still works.

D. You can use a 277-to-240v 1ph transformer. 240v is not too high for a 208-to-230v motor load, and is actually better. You will need to establish a secondary grounding electrode connection with a 'real' transformer.
 
I would like to thank everyone for the help, I do not have much experance with transformers. This is a great place for imformation and its because of the people that use it.

Thank you everybody!!
Brian
 
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