480V 3-phase to 240V single phase question

[dcg9381]

OK, I know nothing about wiring 480V, nor am I going to be wiring 480V...
But for a shop that has 480V (delta, I assume) feed. What's the easiest / most practical way to get 240V single phase out of it? Lets assume we have to drive moderate 240V loads, 15-40A.

Simple (not cheap) transformer needed? Frequency OK?

 

[Innovate1]

If it was a Y feed it would be 277 from line to ground. You could buck that down to 240 with a 36V transformer rated for 40A which is a LOT smaller than a transformer that has to handle all the power. But with delta you don't have many options. You need a transformer. Frequency doesn't change so that's not an issue. Ideally you would have several transformers to distribute the load to all the phases.

 

[wyliesdiesels]

OK, I know nothing about wiring 480V, nor am I going to be wiring 480V...
But for a shop that has 480V (delta, I assume) feed. What's the easiest / most practical way to get 240V single phase out of it? Lets assume we have to drive moderate 240V loads, 15-40A.

Simple (not cheap) transformer needed? Frequency OK?

How many wires coming in on the service? If its delta then its either ungrounded (should have 3 light bulbs for ground fault indication) or corner grounded, where one leg is bonded to ground.

On either delta system you really need to know what youre doing because straight rated breakers are needed, etc

If its 480Y/277, its easier to deal with....

in either case i would get a small step down transformer

10KVA will give you 40a @ 240v

Acme T2535163S :: Transformer, 10KVA, 1P, 240/480V, 120/240V, Isolation :: PLATT ELECTRIC SUPPLY

10 KVA, 1-Phase, 240 x 480 Primary Volts - 120/240 Secondary Volts, NEMA 3R, Shielded Isolation Transformer, Encapsulated, 50/60 Hz. HxWxD: 15.19" x 13.50" x 10.84". ***Reverse Feed Capable and for Use with 3-Phase Source by Connecting Primary to Any Two Wires of a 3-Phase System***, Cat #...

www.platt.com

or for a little more headroom get a 15KVA

Sola Hevi-Duty ES5H15S :: Transformer, Dry Type, 15KVA, 240 x 480 - 120/240, 1PH, NEMA 2 :: PLATT ELECTRIC SUPPLY

15 KVA, 1-Phase, 240 x 480 Primary Volts - 120/240 Secondary Volts, NEMA 2, Dry Type, Transformer, General Purpose, Cat #: ES5H15S, Mfr: Sola Hevi-Duty

www.platt.com

If it was a Y feed it would be 277 from line to ground. You could buck that down to 240 with a 36V transformer rated for 40A which is a LOT smaller than a transformer that has to handle all the power. But with delta you don't have many options. You need a transformer. Frequency doesn't change so that's not an issue. Ideally you would have several transformers to distribute the load to all the phases.

that would create quite an imbalance on one leg. better to run a step down transformer..

 

[Bert_]

Straight 240? Or 120/240?

 

[Innovate1]

that would create quite an imbalance on one leg. better to run a step down transformer..

That's true but no worse than a 277 to 240 step down transformer.

 

[rlitman]

That's true but no worse than a 277 to 240 step down transformer.

Exactly. The imbalance is from the load, not from the transformer. The buck transformer is an interesting and kinda smart idea at getting away with less hardware.

To the OP, why exactly do you need 240V single phase? Are you aware that lots of 240V equipment will work on 208V?

 

[Norcal]

That's true but no worse than a 277 to 240 step down transformer.

480V primary 240V secondary 1Ø transformers are off the shelf items, another option is a 480V pri, 208Y/120V X-former, another off the shelf item.

 

[wyliesdiesels]

That's true but no worse than a 277 to 240 step down transformer.

why bother with an odd ball transformer? get a 480 to 240x120 transformer

 

[rlitman]

why bother with an odd ball transformer? get a 480 to 240x120 transformer

One reason would be the standby losses of the far bigger transformer.

 

[dcg9381]

Exactly. The imbalance is from the load, not from the transformer. The buck transformer is an interesting and kinda smart idea at getting away with less hardware.

To the OP, why exactly do you need 240V single phase? Are you aware that lots of 240V equipment will work on 208V?

Just so I understand, all of these configurations 480v are 60hz (in the US), correct? The delta is just the potential difference between legs? Someone explain it to me...

Not my project, but yea, he has a bunch of equipment that still runs on 240V single phase. We're aware that "some" equipment wont care about voltage range (maybe like a big electrical motor) - but some may care, like a TIG welder.

 

[ycgoat]

I would do a 3 phase 480 to 3 phase 240/120 step down transformer. You will also need to fuse the line and load sides of the transformer. Why do you think its a Delta feed? Around here I usually only see Delta configurations on Medium Voltage systems , or 208/120 on some very old auto shops (these would have a high leg that would be around 150v on B phase if i remember correctly)

 

[ArcReactorKC]

Just so I understand, all of these configurations 480v are 60hz (in the US), correct? The delta is just the potential difference between legs? Someone explain it to me...

Not my project, but yea, he has a bunch of equipment that still runs on 240V single phase. We're aware that "some" equipment wont care about voltage range (maybe like a big electrical motor) - but some may care, like a TIG welder.

Depending on the welder it may also be multi-tap. Meaning it could be run on 3phase 240, or 480.

 

[ycgoat]

D on the right Y on the left. D is typically 3 phase only,

 

[alfredeneuman]

208/120 on some very old auto shops (these would have a high leg that would be around 150v on B phase if i remember correctly)

That would be a 240/120 center tapped delta connection. The BØ is 208V to neutral or ground.

 

[ycgoat]

That would be a 240/120 center tapped delta connection. The BØ is 208V to neutral or ground.

would swear they were 208 phase to phase, and 120v A or C to ground and around 150v on B to ground. I do not remember seeing a 240 Delta, I have recently specified a 3 phase 5K to 120 Delta to power meters on an MCC.

Not saying you are wrong I have not seen everything and its been a long time since I worked on an old Delta, building distribution system.

 

[fitter30]

There are companies that sell surplus and used electrical equipment. Just do a search.

 

[wyliesdiesels]

Exactly. The imbalance is from the load, not from the transformer. The buck transformer is an interesting and kinda smart idea at getting away with less hardware.

To the OP, why exactly do you need 240V single phase? Are you aware that lots of 240V equipment will work on 208V?

yes and delta connected transformers dont behave well when there is an imbalance... youll see fluctuation in the voltage

One reason would be the standby losses of the far bigger transformer.

every transformer has losses but imbalancing a delta bank is not a good idea

Just so I understand, all of these configurations 480v are 60hz (in the US), correct?

yes

The delta is just the potential difference between legs? Someone explain it to me...

Not my project, but yea, he has a bunch of equipment that still runs on 240V single phase. We're aware that "some" equipment wont care about voltage range (maybe like a big electrical motor) - but some may care, like a TIG welder.

no, it describes how the transformers are connected. it doesnt describe the potential between legs but if you have a voltage factor, then you can calculate the voltage potential between the hi-leg and neutral, if present.

I would do a 3 phase 480 to 3 phase 240/120 step down transformer. You will also need to fuse the line and load sides of the transformer. Why do you think its a Delta feed? Around here I usually only see Delta configurations on Medium Voltage systems,

If its 3-wire 3Ø 480v almost can guarantee its delta connected, unless someone forgot to run the neutral into the MDP.

there is plenty of 3Ø 240D/120 and 480v, around here still but our PoCo will no longer install it for new service

or 208/120 on some very old auto shops (these would have a high leg that would be around 150v on B phase if i remember correctly)

negative. 208/120 is wye connected. there is no hi-leg as all 3 phases are 120v to neutral. the hi-leg you speak of (which is 208v to neutral not 150v) is found on 240D/120 service

would swear they were 208 phase to phase, and 120v A or C to ground and around 150v on B to ground. I do not remember seeing a 240 Delta, I have recently specified a 3 phase 5K to 120 Delta to power meters on an MCC.

Not saying you are wrong I have not seen everything and its been a long time since I worked on an old Delta, building distribution system.

if you did the math you would see that isnt possible. 208v phase to phase means phase to neutral is 120v on all 3 phases.

 

[Norcal]

If 220V 3 phase still existed the high leg would be 190V, in reply to the 150V comment. Anything that can run on 480V should be rather then paying for a bigger X-former & the losses of it.

 

[dcg9381]

Thanks guys.. I think I get it.

It wasn't obvious to me that the WYE configuration (4-wire) is 277V from high leg to ground, but I understand how you can step that down in a less expensive manner with a 36V transformer.

And yea, 120V will be needed too. The 240V single phase loads are "moderate" in the 30A range.

Is there a panel type that is "more available" for 480V (comparing Delta vs Wye)?

 

[Terry D]

Thanks guys.. I think I get it.

It wasn't obvious to me that the WYE configuration (4-wire) is 277V from high leg to ground, but I understand how you can step that down in a less expensive manner with a 36V transformer.

And yea, 120V will be needed too. The 240V single phase loads are "moderate" in the 30A range.

Is there a panel type that is "more available" for 480V (comparing Delta vs Wye)?

Its not 277 from High leg to ground, its 277 volts from any phase to neutral/ground. The High leg is on a 240 volt Delta system where one transformer is center tapped to create 120/240. Going from the opposite phase, usually "B", you would get 208 from that to the center tap/neutral or ground.

You will need a single phase panel for your 120/240 volt

I would go with the 15 KVA step down transformer 480 to 120/240 . It is good for 62 amps. A little extra for the future.

 

[dcg9381]

Got it.

 

[Norcal]

Got it.

Are you 480V or 480Y/277V? There is a number of flavors of straight 480V.

 

[wyliesdiesels]

Thanks guys.. I think I get it.

It wasn't obvious to me that the WYE configuration (4-wire) is 277V from high leg to ground, but I understand how you can step that down in a less expensive manner with a 36V transformer.

And yea, 120V will be needed too. The 240V single phase loads are "moderate" in the 30A range.

Is there a panel type that is "more available" for 480V (comparing Delta vs Wye)?

hold up. there is no hi-leg on a wye connected transformer bank. a hi-leg is a phase that has higher voltage to neutral/ground than the other 2 phases. a hi-leg is ONLY found on delta connected transformer banks....

on a 480Y/277v service all 3 phases are equally 277v to neutral/ground... so there is no hi-leg....

 

[dcg9381]

You guys are great. Thanks for the correction.

 

[McRat]

Necro-posting in case anyone needs it:
You determine if you are 480 Wye by looking if you have a neutral. You are 277v single phase to neutral. Volts between phases is 480v nominal (±3%?).
I created 240 1ph two different ways:

First way, I used 277v to neutral to feed a 252>230 buck transformer. This will not give you a neutral, so it won't work for certain devices. This is now sitting on shelf since I upgraded.

Second way, I found a real isolation transformer on Ebay for $400 used, there are lots of them around. This give true split-phase 240vac with a neutral just like a normal house.

Pics of the devices attached. I use them to charge EVs.

Trivia -
Teslas are the only EVs in the US that will accept 277 single phase power. You need to locate a discontinued HPWC to do it, it is undocumented now.
Many overhead lights will accept 277v if you read the specs carefully. Most commercial buildings that have 480 3-ph Wye use troffer and parking lot lighting that is 100v-277v or 277v. It is easier to wire, and saves money.

 

[walta]

If you own the building and there is no 480V equipment or 277V lighting seems like getting the provider to change out the pole transformer to 208 would be the smart move.

Often when they do a 3 phase 480 service there is also a second single phase service for the type of loads you are describing.

If not then you can buy a 480 to 208 transformer and install a panel.



Walta