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Old 09-06-2008, 11:03 PM   #16
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connecting a 240v A/C to my 480v box?


If you're having trouble with voltage drop when the A/C starts, check the 120/208 voltage with an accurate voltmeter. It might be low. If it is, most transformers have taps that can be adjusted to bring the voltage back up. Personally, I like to see about 122/212 or so.

If your voltage is OK, you have a couple of options. One is to use a buck-boost transformer and power the A/C unit from the 480 panel. Depending on the size of the unit, figure a couple hundred bucks if you do the work.

The other is to re-connect the equipment for 208. If you do this, you'll need to arrange the panel so as to not have the offending equipment on the same two phases as the A/C unit. For example, if the A/C is on black and red, put the other equipment on red and blue, or blue and black.

The thing I'd try first though is to insure that the offending equipment isn't on the same phase as the A/C. If, for example, the A/C is on black and red, make sure the other equipment is on blue.

One of those options should solve the problem.

Rob

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Old 09-06-2008, 11:13 PM   #17
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connecting a 240v A/C to my 480v box?


unless I missed it, the first thing you need to do is read the data plate on the AC unit. If it states 24o volts, you are going to need a transformer (as MM was saying) to boost the voltage to an acceptable level.

If it states 230, then you need to check your actual voltage to see if it is possible to run it on the voltage you have.

If it states 208/230 or 208/240, you can run it on the supply you have.

So, what does the nameplate list as voltage?
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Old 09-07-2008, 10:48 AM   #18
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connecting a 240v A/C to my 480v box?


even on commercial rooftop or large supply fan motors the motor tag will 99% of the time will state 208-230/460 Voltages and the amps say for example.... will state 15.9/4.5 Amps consider 230-240 the same. if you read on 2 legs at the 240V box 245V then you would have a true 240V.even 115V on a socket will never read an actual 115V all readings are higher then the actual tagged voltages so go with the lower after you read it.the amperage will vary depending on the actual reading range 208....240 you see 208 or even 215 on the 2 legs, that is a chage of 1/2 amp or even 1 amp max the sun swinging on the condenser would change the amps more during a cycle.if you can check the compressor tag for voltage range info tags are general look at the loads for the brand supplier info comp/fan motors etc.
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Old 09-07-2008, 11:57 AM   #19
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connecting a 240v A/C to my 480v box?


Quote:
=biggles;155872]even on commercial rooftop or large supply fan motors the motor tag will 99% of the time
I seem to live in that 1% of the world. I always check nameplate ratings.

Quote:
.even 115V on a socket will never read an actual 115V
the nominal voltage is now 120.

the biggest problem with running a device rated at 240 on 208


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Old 09-07-2008, 04:57 PM   #20
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connecting a 240v A/C to my 480v box?


Ok, I will double check the data plate on the AC unit Monday morning and make sure it says 208/240. If it does not say 208, then I need to boost the voltage with a transformer. Or run it off the 480 panel. Although I was getting the hint that running it off the 480/277 panel isn't a good idea?

I'll also re-arrange the the other equipment to be on a different phase than the A/C unit.

What about trying a hard start kit on the AC?

thanks for all the info!
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Old 09-07-2008, 06:24 PM   #21
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connecting a 240v A/C to my 480v box?


if you run 277V into a 240V rated unit you will burn out the windings on the cond.fan compressor and supply fan as soon as it speeds up and smokes out.
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Old 09-07-2008, 06:51 PM   #22
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connecting a 240v A/C to my 480v box?


no i meant stepping down the 277/480 to 240 like micromind suggested.
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Old 09-09-2008, 01:57 AM   #23
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connecting a 240v A/C to my 480v box?


I don't know why but did the OP ever find out how big the transfomer Between the 480 system to 208Y120 system ?

The transfomer should be able tell you the XX KVA on the nameplate and how big the breaker box you have on 208Y120 side ??

There is other option that can be used from time to time get a single phase 480X240 transfomer and run from there to keep the A/C running

To size that unit need to know how big the A/C due there are quite few differnt size transformer { I rather have this done by electrician due safety reason }

Merci,Marc

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