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480V 3 phase to 240V single phase

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Bob - MI
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PostPosted: Thu Jul 18, 2013 4:35 pm    Post subject: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

My electrician is on vacation and I need to order a transformer to go from 480V 3ph to 240v single phase. I have been reading lots of posts on the 'net and there is confusing information about what type of transformer to get. I realize that we have to size it for the load but my question is really where to start looking.

I do have an option to pull new wiring for it because I have room in a single phase box but it's in another section in the plant and the run would be about 150'. I would also like to keep the breaker as close as I can.

Thanks for your help on this guys!
 
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Charles (in GA)
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PostPosted: Thu Jul 18, 2013 5:20 pm    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

This would be a box about the size of a dishwasher. The facility I work in has several of them around, hanging from the structure or mounted in the hall way and protected by Bollards. I even see them on Craigslist here in ATL sometimes. But yes, it depends on your loads.

http://atlanta.craigslist.org/atl/tls/3920431347.html

http://atlanta.craigslist.org/nat/tls/3895040781.html

http://atlanta.craigslist.org/nat/tls/3847754132.html

Charles
 
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Jimmytheelectrian
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PostPosted: Thu Jul 18, 2013 5:58 pm    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

Wait till your electrician comes back from vacation. Some questions just can't be answered on an antique tractor website....
 
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sflem849
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PostPosted: Thu Jul 18, 2013 6:14 pm    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

Why would you need a transformer? Just pull power off one leg.
 
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Deere Mark
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PostPosted: Thu Jul 18, 2013 6:33 pm    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

I second the suggestion to wait for your electrician.
Only a qualified electrician could determine what is right for your plant.
Usually with 480 volt three phase, you would have 480 volts between the three hot wires and 277 volts from each hot wire to neutral.
You could use a single phase transformer with 480 volt primary and 240 volt secondary.
Or you could use a single phase transformer with a 277 volt primary and 240 volt secondary.
The KVA of the machine to be powered would determine the KVA of the transformer.
 
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David G
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PostPosted: Thu Jul 18, 2013 6:45 pm    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

You would use one of the phases on 480V to get 240V single phase.

How many watts do you need?

480V is VERY dangerous, it will cause 3rd degree burns if arc flashed. It is NOT recommended that any NOT trained person touch it.

The primary and secondaries should be fused. The primary fuse protects the wiring and primary side of transformer, the secondary fuse protects the secondary side of the transformer and the wiring out.
 
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Billy Shafer
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PostPosted: Thu Jul 18, 2013 7:03 pm    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

I have been a generator tech since 1968. I have seen the damage 480 can do if you get wrong. I have seen guys killed and guys with skin blown off to the bone. Best thing you can do is wait until your guy gets off vacation. If you just have to have it now. Find someone that knows what they are doing.
 
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John T
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PostPosted: Fri Jul 19, 2013 3:38 am    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

Okay Bob, here are a few comments that may help: CAUTION I suggest you consult local trained professional electricians or engineers on this one, this is DEFINITELY NOT a question to trust untrained lay Billy Bobs to answer and I'm NOT saying trust me either, as I'm rusty on the latest codes having been retired from electrical engineering wayyyyyyy toooooo longggggg lol That being all said and with NO Warranty here is my "rusty" yet professional OPINION:

PS where to start looking??? Local electrical supply houses, Graingers etc. for a 480 to 240 volt single phase transformer of sufficient wattage.... IFFFFFFF all you need is straight 240 VAC, SEE BELOW for 120/240 or grounded systems!!!


1) If you already have 480 volt three phase, it may be Y or Delta?

a) If its Y its likely configured as 480 Y 277 Volt Three Phase Four Wire (and likely a GrounDED system). In that case you can get 480 volts Single phase from any leg to any other leg (but its only 277 from any leg to Neutral, well DUH). Then if you had a single phase transformer OF SUFFICIENT WATTAGE that can step 480 down to 240, just wire two legs fed from the 480 Y to its Primary input and the Secondary output would be the 240 volts single phase you need.

b) If its straight 480 volt (NO 277) three phase three wire thats a DELTA configuration and likely its a floating NON grounded system (Unless it was corner grounded which I doubt). Similar to the above, its 480 volts across any 2 of the 3 legs. Soooooo take a 480 to 240 step down single phase transformer and wire its Primary input to any 2 of the 3 480 delta legs and on its Secondary output you have 240 volts single phase as needed.

IN SUMAMRY ALL YOU NEED IS A SINGLE PHASE 480 TO 240 VOLT STEP DOWN TRANSFORMER (a 2 to 1 turns ratio transformer) OF SUFFICIENT WATTAGE

NOTES AND MORE CAUTIONS:

1) This gets you straight 240 volts (NO 120) and the output (unless you do otherwise) is a NON grounded floating 240 volts remember. If the load requires 240 only and no 120 and the non grounded floating 240 is okay???? this will work.

2) If the load requires BOTH 120 and 240 this will NOT work. But can still be done, see below.

Your post mentioned 240 ONLY so I wont address what you need to get BOTH 120 and 240 other then it can still be done.

Again, either of the above results in 240 volts non grounded floating, the transformer operates as an isolation transformer and the 240 volts is present ONLY line to line NOT any voltage line to mother earth or line to building steel etc as would be in a grounded system. However, for yearsssssss many industrial plants were wired straight floating NON grounded 480 or 240 and many still are and all is well. When I was a desing engineer our facility and myself preferred a grounded system but floaitng non grounded work fine. There are ways to turn your 480 (Y or Delta) into a 120/240 volt single phase three wire GrounDED system, about as simple as the above, it just requires establishment of a GroundING Electrode to ground the transformers secondary (center tapped)output at the mid point establishing a Neutral.


Sooooooo this is ONLY my OPINION but hopefully it helps you understand why if you dont know what youre doing or whats actually required YOU MAY WANNA CONSULT TRAINED PROFESSIONAL ENGINEERS OR ELECTRICIANS, Your money your risk your choice, be safe.....

ANOTHER PS If theres a need for a few 240 volt circuits and some 120 (single phase), I would probably use a 480 to a 120/240 dry transformer with the center tapped secondary such that I could establish a GrounDED Neutral and use a Grounding Electrode and feed a 120/240 volt single phase three wire sub panel.......


Got it now????????

John T Too dern long retired and rusty grrr EE
 
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Sparktrician
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PostPosted: Fri Jul 19, 2013 5:37 am    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

How big of a xfmr do you need? That is a big part of this. It will be sized in kVA. If you know what you need.....Primary voltage and Secondary voltage, and kVA......call a supply house and they will order what you need.

Are you just trying to get it acquired so your electrician can install it when he returns, or are you looking to do this yourself?

No disrespect meant here....but if you don't know how to size/order a xfmr....you likely shouldn't be installing it. ESPECIALLY with 480V.

Good luck!
 
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Russ from MN
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PostPosted: Fri Jul 19, 2013 5:40 am    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

It seems there is as much bad advice as good! I would go with John T, it's not as simple as just using one leg!
 
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John T
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PostPosted: Fri Jul 19, 2013 6:06 am    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

In our facility in an industrial building served ONLY by 480 3 phase yet where we needed standard 120/240, I tried to balance the loads and the three phases by feeding three seperate dry transformers one fed from each of the three phases of 480........ each would then in turn serve three different parts of the building

BALANCE BALANCE BALANCE was my motto

John T
 
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dr sportster
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PostPosted: Fri Jul 19, 2013 8:23 am    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

Normally [whatever that could mean] the transformer would be 480 3 ph stepping down to 3 ph 120 volt each leg. If you are going to derive the 240 off a single phase do you mean one phase or 2 poles of 120 to get to 240. I too have seen the movies where the 480 [only ten guage wire size] blows the skin off the HVAC apprentice's hands. Sorta sounds like "wait for the electricians vacation to end". Or get a Square D catalog and start reading specs.
 
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dr sportster
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PostPosted: Fri Jul 19, 2013 8:27 am    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

Also as Sparktrician posted ---" How many KVA do you need.? If you undersize you will just burn up your equipment as the transformer will try to supply more load than it is capable of. If you don't know the KVA don't bother trying to order one.
 
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buickanddeere
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PostPosted: Fri Jul 19, 2013 8:32 am    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

There is lots of 347/600V around too.
Then again in Europe there is no 120. It"s 110/380 to 240-416.
 
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dr sportster
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PostPosted: Fri Jul 19, 2013 8:47 am    Post subject: Re: 480V 3 phase to 240V single phase Reply to specific post Reply with quote

David , It is also recommended that trained persons don't touch it either, lol. Most people are suffering a 277 volt shock as unless you fell inside a panel or welder its hard to touch 480[ both phases] by mistake.
 
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