# 480V 3ph to 240V 1ph question.



## Jusshatched

Let me begin by saying I have very limited experience with AC systems. I am working for an engineering company and looking for answers for my boss who has much more experience than me in this area. (he should be the one searching for these answers, I know)

At any rate here is what I'm working with:

I need to get 240V single phase power from a 480V 3 phase disconnect in order to run several water pumps that will draw about 1.5KVA. I know there are transformers that convert the power how I need but is there any way to get the power without using a transformer, by grounding a leg or something of that nature?

This is not something I will be attempting myself, just wondering if its possible/safe in theory. Also, if I need to purchase a transformer are there any reputable sites recommended?

Thanks!


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## Jusshatched

Scratch the idea of grounding...

*My question now is:

If I get a 480V 3ph to 240V 3ph step down transformer will I be able to run a 1ph 240V pump between 2 legs?*


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## MDShunk

Jusshatched said:


> Scratch the idea of grounding...
> 
> *My question now is:
> 
> If I get a 480V 3ph to 240V 3ph step down transformer will I be able to run a 1ph 240V pump between 2 legs?*


Yes. You still have grounding and overcurrent protection to contend with, however.

If this is temp, you might consider going phase to neutral on the 480 side (277 volts) if your L-N voltage runs a smidge on the low side. 

Or, buy the right damn motors.


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## Meadow

Are you an electrician?


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## Jusshatched

No I am not, just looking for answers on behalf of someone else.


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## Meadow

Jusshatched said:


> No I am not, just looking for answers on behalf of someone else.


The thread will probably be locked so Ill just give you an answer since you are an engineer (hence professional). 


If you run a neutral to the disco you can use a buck boost transformer (cheaper than an isolation unit) to drop 277 volts to 240. This will save a lot on transformer since a buck boost is smaller. ACME transformer makes low cost buck and boosts. MGM, GE, Square D does as well if looking for something higher grade.


Another option is an isolation transformer hooked 480 volts and then stepped to 240 volts. You will have to go this route if you don't have or cant bring a neutral to the disco.

Several 1.5kva pumps are a fair amount of load. Your boss will have to determine if the feeder to the disco can take that.


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## hardworkingstiff

meadow said:


> Another option is an isolation transformer hooked 480 volts and then stepped to 240 volts. You will have to go this route if you don't have or cant bring a neutral to the disco.


Why would you need the neutral? Are you talking the 480-volt side?


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## Meadow

hardworkingstiff said:


> Why would you need the neutral? Are you talking the 480-volt side?


Its easier to step 277 to 240 then 480 to 240 with a buck boost.


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## bobelectric

Only if the 480 is a Y wound xfmr.


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## Southeast Power

If you have room, see if your boss would consider a Retro encabulator


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## sstlouis03

JMO, this is how jobs get over budget and have to be re-done in most cases. When engineers start trying to "engineer" something they know nothing about. My suggestion, contact the electrician that will be doing the job and let HIM tell you the best method, before it all has to be re-done and you've just wasted you time. 

Sorry if that came off a little harsh.


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## Meadow

bobelectric said:


> Only if the 480 is a Y wound xfmr.


Or center tapped delta:whistling2::jester:


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## power

Jusshatched said:


> Scratch the idea of grounding...
> 
> *My question now is:
> 
> If I get a 480V 3ph to 240V 3ph step down transformer will I be able to run a 1ph 240V pump between 2 legs?*


Yes, that would work. However, the transformer need not be 3-phase. A single phase 480vac to 240vac transformer will work too. You would need a 10kVA minimum transformer, dry-type, 1-phase, 480-240vac, copper or aluminum wound (your preference). Remember to bond your X4 terminal in the transformer, otherwise you've an ungrounded system. The transformer's primary 480vac (at 1-phase) will need to be fused at 30amps, and individual upstream overcurrent protection will be needed for each 1.5kVA pump.


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