Question about 3-phase

[doojus]

I had a question about 3-phase and wanted to figure it out before I even bother calling my local POCO about getting the service.

From what I understand, with a 4 wire 3-phase service, any hot leg to neutral is 120v. Like most shops I have a variety of single-phase 120v and 220v machines that I need to power, along with wanting to get a 3-phase mill.

Can I still power my 120v and 220v machines by using 1 and 2 legs of the service like on a normal 1-phase service or does some other arrangement have to be made to power those?

 

[Chris705]

Nope, only 120v across one hot....two hots will equal 208volts. Some (220)240v tools will run on 208v but don't think you want that for any typical machine as it can damage the motor. 3 hots equal 277volt. You can however use a transformer to get true 240v with a 3p service. ( at least this is what I recall from my tech. school days with John Joyce teaching us at Alfred.)

 

[doojus]

Found this on my POCO's site:

"also has available the following four wire three phase voltages: 120/240, 240/480, 120/208, and 277/480. Customers may obtain three phase service at no cost if their forecasted load is sufficient to support the installation of three phase equipment."


Would 120/240 be more preferential in this situation?

I'm also struggling to understand how one hot equals 120v but two equals 208v... but maybe that's for another thread.

 

[Charles (in GA)]

I think you will find that three phase service will cost you a bundle, getting it installed and paying the bill (at commercial rates) each month.

You need to have three phase accessible to your property, meaning it needs to run down the road in front or behind or beside your property, and the POCO has to be willing to give you the service. Three phase requires they place three transformers, not one, and this costs them a bundle, that if they don't forsee recouping this cost and making a profit in the future, they won't do.

Unless you are on a main road, you very possibly don't even have three phase anywhere nearby.

If you need to run one or two pieces of machinery, your best bet is to install a Rotary phase converter, or similar solid state phase converter. Will be much cheaper in the long run.

Charles

 

[doojus]

I think you will find that three phase service will cost you a bundle, getting it installed and paying the bill (at commercial rates) each month.

For sure, I knew in advance it would be much more difficult than just getting single phase, I'm just checking to see if it would even be viable in a shop where you also run a bunch of 120 and 220v machinery.

 

[KenC]

This varies a lot from place to place.
My power is local municipality provided. I was able to change my service from 120/240 single phase to 240 4 wire 'high leg' delta at no cost from the utility.
That gives me 120v and 240 single phase and 240v 3phase. But, one leg is 208v (actual on mine is 218) that is unusable for anything but 3 phase. Keep that in mind when sizing a breaker box as you loose use of 1/3 of the spaces for single phase loads.

They even provided the new meter and base, hung an additional transformer and pulled one new service wire, about 300 feet. No charge! rate is the same also, just usage at the same as single.

All I was out was the breaker box/breakers and wire to the weatherhead.

Of course this was in an older building, zoned agricultural (holdover from when it was just outside the city limits), and the old single phase main breaker failed, so it was a 'repair'.

The even gave me a permit and inspected it even though by the letter of the code owners are not allowed to work on that type of thing.

 

[alfredeneuman]

Nope, only 120v across one hot....two hots will equal 208volts. Some (220)240v tools will run on 208v but don't think you want that for any typical machine as it can damage the motor. 3 hots equal 277volt. You can however use a transformer to get true 240v with a 3p service. ( at least this is what I recall from my tech. school days with John Joyce teaching us at Alfred.)

3 hots don't equal 277 volt. On a wye connected system it's 208 3 phase.

Delta connected 240 systems are rare these days. They produce 240 volts line to line, and 120 volts from line to neutral on 2 legs. The third leg is 208 volts to neutral.

277 volts is produced by a 277/480 volt system. All three legs measure 480 volts line to line, and 277 volts line to neutral.

BTW I'm Alfred and I never taught you THAT

 

[Stuart in MN]

This picture shows the difference between 120/208 wye and 120/240 delta:

If you have 240vac (or 208vac) single phase machines, they can be connected to any one of the three phases.

Also, many electric utilities will provide a 120/240 three phase open delta service, which uses only two transformers instead of three:

240 delta systems are kind of old school, and some utilities are trying to get rid of them and eventually replace them with 208 wye systems - Xcel Energy in the upper Midwest is one example, but I know others are doing it as well.

 

[rockwithjason]

Found this on my POCO's site:

"also has available the following four wire three phase voltages: 120/240, 240/480, 120/208, and 277/480. Customers may obtain three phase service at no cost if their forecasted load is sufficient to support the installation of three phase equipment."


Would 120/240 be more preferential in this situation?

I'm also struggling to understand how one hot equals 120v but two equals 208v... but maybe that's for another thread.

the math has to do with the times at which the waves cross the zero voltage line. vector alebra is used to determine the voltages in these situations and it can be very counterintuitive. suffice to say that in a three phase bank you will always have values that seem off. most modern machinery can run on 208 so a check of the owner's manual or the name plate can be helpful.

some of the configurations listed may not be 4 wire systems. you will have to get more information on that.

 

[ishiboo]

I'm going to come up with a 3.5-phase system, where there is a fourth 120v phase 180 degrees from one of the other ones, as in single-phase system. So that would give you true 240v single-phase, 3-phase, and of course 120v from any phase and neutral.

Perfect for our smaller shops! Going to be a complicated breaker panel though. I guess 120v and 3-phase loads on top, dedicated 120v/240v area on the bottom.

 

[matt_i]

The Power Company is likely to quote you between $5k and $10k just to run 3phase to your meter base, even if you have 3 lines at the top of the pole on your property. They have to supply 2 additional transformers which are costly suckers. Depending on locale, they may also supply materials and labor to pull wire thru a conduit to said meter base. Also, you have to demonstrate need of large amp draws in order for them to recoup their investment in incrementally higher power sales over time, as they are a business attempting to make a very slight profit vs. expenses. You may have a demand meter and a charge related to that, depending on "grid useage". As such, the power company typically discourages 3 phase installs for "advanced residential customers", except those with "advanced budgets", or those running a for-profit business inside their shop.

Then, there is the expense of 3 phase circuit panels and 3 pole breakers, all significantly more expensive than your Square D panel (etc) out of the local big box. Ideally you'd balance single phase amp draw within reason on the A, B, C phases. The power company has to do this balance somewhere in their system but look to 3ph customers to "self police" as they can be big industrial customers drawing as much as a large neighborhood.

I suggest looking at a digital phase converter, such as the Phase Perfect. It is not cheap, but you keep it forever, especially if you ever move again (have to pay the install charges above in a new location). The power quality is on par with what you get from the power company, and it solves all the sink/source issues you'd ever run into with things like braking servo drives. You can protect downstream wiring with a simple old-school fuse block.

Disclosure: I have one which I use to run CNC machines and several other 3 phase machines, it works most excellently, other than a VFD-like buzz which gets drowned out by the fans on the machines. I have no affiliation with the company other than as a customer.

If all you have is simple motors to run without a lot of complex relay-logic controls, computers or servo drives to run, I would recommend buying or wiring up your own rotary phase converter. They are relatively inexpensive and work great for relatively simple machines like lathes or mills. The phase converter, however is a poor choice for a 3ph air compressor due to the reduced power and torque. Stick with single phase air compressors.

 

[mburrus]

for light 3 phase usage with heavy single phase usage (as i assume your load would be), the ideal set up would be an open delta service. uses a large "lighting" transformer and a smaller "power" transformer. lighting transformer gives you a center tapped neutral, which basically makes 2 legs and a neutral behave just like 120/240 single phase. power transformer gives you the third leg, which allows you to have 240 volts between any 2 phases. this would be most ideal for a 240v motor and would likely be the least expensive route to go. if i were you, i would install 2 panels, one for single phase, and a smaller one for 3 phase, that way theres no chance of putting a single phase load on the high leg.

doojus, you just have to accept the math for what it is unless you want to go in to detail learning about EE stuff. 120x1.73=208 1.73 is the square root of 3, and shows up a LOT in 3 phase calculations...

 

[Norcal]

If a 2 pole breaker is rated for 240 volts instead of the normal 120/240 volt slash rated the high leg & any other phase can be used for any straight 240 volt load, such as a motor, water heater, it should not be used w/ neutral present. The only problem is that a 240V rated breaker is expensive & not normally stocked.

 

[BillK]

Dooj,
I sort of scanned all of the other replies, but to give you a real world answer ....... YES you can power all of your 120 and 240 equipment just fine. I have all three here at my business as does just about any other business with three phase service. Most of my large machines are 3 Phase. My compresser and a couple of smaller machines are single phase 240 machines and plenty of other stuff that is 110 or 120 or whatever you want to call it.

I really have to wonder if any of the other guys replying have actually ever been in a shop that has three phase power ? Do you really think that you have to buy special equipment such as computers, light bulbs, hair dryers etc to use in a building with three phase power ????

 

[theoldwizard1]

Dooj,
I sort of scanned all of the other replies, but to give you a real world answer ....... YES you can power all of your 120 and 240 equipment just fine. I have all three here at my business as does just about any other business with three phase service. Most of my large machines are 3 Phase. My compresser and a couple of smaller machines are single phase 240 machines and plenty of other stuff that is 110 or 120 or whatever you want to call it. ...

Measure the voltage at your compressor. I'll bet it is 208V.

They do make 208v - 240v transformers.

Many "modern" motors (especially A/C) are actually designed to run on 200-250V.

 

[MixManSC]

Billk and a couple of other are correct. You power company does NOT need 3 transformers on the pole. For you the ideal would be a Delta configuration which is what we have (ours is 4 wire, 3 phase, high leg Delta service). One additional transformer on the pole is all that is needed by the poco.

Also as another mentioned, for sanity and safety at least 2 breaker panels is ideal. One single phase and one three phase. That way if you are working or messing with anything single phase you have no worries with making certain a single phase 120v circuit does not end up on the high leg.

Pic of our pole and panel setup. I do have a complex setup inside though as this property was an old millwork so I have 4 buildings and 600a service. The main service comes to a 600a disconnect (my wife does not weigh enough to shut if off ) which has a enclosed raceway below it. That distributes to 3 breaker panels for the main shop, a 200a disconnect that goes to a 200a single phase only panel in the mail office part of the building and a 60a disconnect that goes to a small 60a single phase panel in the warehouse building (mostly for lighting). All in all I have two 3 phase panels, and two single phase panels. For this place 3ph is very beneficial since I have 3 HVAC units, a compressor, and a couple of smaller things like my new old grinder and whatnot that are all 3 phase.

Also someone mentioned balancing your loads. To an extent you do want to do this. In other words if you were to put in two single phase panels and made sure to use every other breaker space so that your entire load was only on one of the lines that would not really be a good way of setting things up.... its best to balance the single phase loads as much as possible as you don't want to overload any single line.

On the 4 wires, we also have a ground at the main disconnect so we have 3 hots, neutral, and ground. Most of the grounds are connected via rigid metal conduit. Two of the hots to neutral are 120v, the third hot (the high leg) to neutral is 240v, any hot to hot gives 240v. Our service also runs on the high side, actual voltages average about 253 volts and 128 volts.

One thing I've considered trying (although its probably against code for some reason) is to use the high leg for certain 240v single phase loads like all the overhead lighting. I have not had a chance or time to look at the electrical code and possibly look into using the wild leg for that though. As I said, it might be a code violation but I'd think if can get a non slash rated single pole 240v breaker why it would not work.

 

[wyliesdiesels]

Wow lots of misinformation in this thread!!

I had a question about 3-phase and wanted to figure it out before I even bother calling my local POCO about getting the service.

From what I understand, with a 4 wire 3-phase service, any hot leg to neutral is 120v. Like most shops I have a variety of single-phase 120v and 220v machines that I need to power, along with wanting to get a 3-phase mill.

Can I still power my 120v and 220v machines by using 1 and 2 legs of the service like on a normal 1-phase service or does some other arrangement have to be made to power those?

As u already found out on your PoCos site, theres actually several flavors of 3-phase. For 4-wire 3-phase theres several options.

Theres 208Y/120v (Wye), which will give u 120v between any of the 3 hot legs and neutral. Line to line(either 2 or 3) will be 208v.

Another 4-wire wye service is 480Y/277v- 277v between any hot and neutral and 480v line to line.

Next is Delta. 240v/120v- 120v between 2 hot legs and neutral. The third leg is the high leg or stinger and its called this because its 208v to neutral. U obviously cant use this leg for 120v loads!

Many PoCos are getting rid of or no longer supplying new service with 240v Delta so many people are limited to 208Y/120v service. Delta services are inherently imbalanced and Ive been told can end up providing dirty power due to the imbalance.

Theres also some other varieties of 3-phase that wouldnt apply to u so i wont go into them.

Now if u have a lot of 120v equipment, a 208Y service might be a better bet for u.

Your equipment may very well be rated for 208v. Check the motor nameplate!

Nope, only 120v across one hot....two hots will equal 208volts. Some (220)240v tools will run on 208v but don't think you want that for any typical machine as it can damage the motor. 3 hots equal 277volt. You can however use a transformer to get true 240v with a 3p service. ( at least this is what I recall from my tech. school days with John Joyce teaching us at Alfred.)

Huh? Theres no such service where u will get 120v across neutral and only 1 hot. And theres NO system that gives u 277v between all 3 hot legs. You are confused! 277v is a line to neutral voltage for a 480Y/277v system.

Found this on my POCO's site:

"also has available the following four wire three phase voltages: 120/240, 240/480, 120/208, and 277/480. Customers may obtain three phase service at no cost if their forecasted load is sufficient to support the installation of three phase equipment."


Would 120/240 be more preferential in this situation?

I'm also struggling to understand how one hot equals 120v but two equals 208v... but maybe that's for another thread.

U the customer needs to figure out what voltage your machines need.

The 240/480 must be a typo because no one provides service like that as there is no point to it. The 480v Delta service is ran as a 3-wire service.

for light 3 phase usage with heavy single phase usage (as i assume your load would be), the ideal set up would be an open delta service. uses a large "lighting" transformer and a smaller "power" transformer. lighting transformer gives you a center tapped neutral, which basically makes 2 legs and a neutral behave just like 120/240 single phase. power transformer gives you the third leg, which allows you to have 240 volts between any 2 phases. this would be most ideal for a 240v motor and would likely be the least expensive route to go. if i were you, i would install 2 panels, one for single phase, and a smaller one for 3 phase, that way theres no chance of putting a single phase load on the high leg.

doojus, you just have to accept the math for what it is unless you want to go in to detail learning about EE stuff. 120x1.73=208 1.73 is the square root of 3, and shows up a LOT in 3 phase calculations...

No the power transformer means u will have 240v between ALL 3 PHASES! U already have 240v between 2 phases with the single phase transformer.

Measure the voltage at your compressor. I'll bet it is 208V.

They do make 208v - 240v transformers.

Many "modern" motors (especially A/C) are actually designed to run on 200-250V.

No it depends on the system! Read above!

Billk and a couple of other are correct. You power company does NOT need 3 transformers on the pole. For you the ideal would be a Delta configuration which is what we have (ours is 4 wire, 3 phase, high leg Delta service). One additional transformer on the pole is all that is needed by the poco.....

....On the 4 wires, we also have a ground at the main disconnect so we have 3 hots, neutral, and ground. Most of the grounds are connected via rigid metal conduit. Two of the hots to neutral are 120v, the third hot (the high leg) to neutral is 240v, any hot to hot gives 240v. Our service also runs on the high side, actual voltages average about 253 volts and 128 volts.

One thing I've considered trying (although its probably against code for some reason) is to use the high leg for certain 240v single phase loads like all the overhead lighting. I have not had a chance or time to look at the electrical code and possibly look into using the wild leg for that though. As I said, it might be a code violation but I'd think if can get a non slash rated single pole 240v breaker why it would not work.

yes, u can get delta service with just 2 transformers. However, your 3-phase power is limited to about 58% of what u would get with a 3 transformer bank so an open delta configuration is for limited power loads.

And the high leg is ~208v to neutral NOT 240v! If u have a 240v high leg, then the voltage on the primary side of the transformer is TOO high!

And yes people have tried using the high leg for single phase loads. Your lighting would need to be rated for 208v NOT 240v. Using the high leg with neutral does create some weird imbalances in the transformer bank and u could possibly overheat it. Also, the voltage on the high leg varies and isnt stable. I dont recommend using the high leg for line to neutral loads!

 

[MixManSC]

.................
yes, u can get delta service with just 2 transformers. However, your 3-phase power is limited to about 58% of what u would get with a 3 transformer bank so an open delta configuration is for limited power loads.

And the high leg is ~208v to neutral NOT 240v! If u have a 240v high leg, then the voltage on the primary side of the transformer is TOO high!

And yes people have tried using the high leg for single phase loads. Your lighting would need to be rated for 208v NOT 240v. Using the high leg with neutral does create some weird imbalances in the transformer bank and u could possibly overheat it. Also, the voltage on the high leg varies and isnt stable. I dont recommend using the high leg for line to neutral loads!

Correct - error on my part. Yes the high (stinger, wild, etc) leg is actually around 218 or so to neutral here. A little on the high side but not bad.

I've not tried it as I said. However about a year ago I retrofitted the 40 or so dual F96 T12 strip fixtures to dual T5HO. The new ballasts are labelled as 120/277 input so they "might" work okay. But yeah I can see where that might cause some weirdness running the high leg directly with neutral on a single phase load. Really it all works fine as is so I'll probably leave well enough alone.... if it aint' broke dont fix it and all...

 

[alfredeneuman]

Good luck trying to get a new 120/240 3Ø Delta Service.

In my service area (SoCA Edison) they haven't installed any new Delta services since the early '60s.
All new services are 120/208Y.

 

[mburrus]

it depends on your utility. i wouldnt say open delta gives you any kind of dirty power... you just dont have the 3 phase loadability you would have with a wye or closed delta bank. here in florida (FPLs territory to be exact), open delta banks are very common and are still installed on a regular basis.

as for wylies diesels, i think what you are calling me on is a matter of semantics and wording. correct with the lighting transformer you already have 240 between phases, but the power transformer gives you the third phase... which allows you to have 240v between any 2 of the 3 phases (as opposed to wye which will only ever give you 208).

the statement of not loading the high leg with single phase to ground loads is valid and it will cause some imbalance.

technically open delta witha. center tapped lighting transformer is 3 phase 4 wire, and 120/y208 is also 3 phase 4 wire... you have to be concerned with the 3 phase connection so that you know what you are dealing with.

in a wye system you should balance all single phase loads across the 3 phases as much as practical, a 3 phase load should be naturally balanced already. in an open delta you would balance single phase loads across the 2 legs with the center tap (not the high leg), and again a 3 phase load will already be balanced.

many modern motors are dual rated for 208/230 volts, but again, check the nameplate. you may have to connect the leads in the motor differently dependinv on voltage.

and i am certianly not giving you misinformation, i am an EE for a utility...

 

[Stuart in MN]

it depends on your utility.

The only thing consistent from one utility to the next is their inconsistency. I regularly deal with a half dozen different utilities in my area, and they each have their own set of rules and standards.

 

[Rookie2]

OK , Now explain how he will have a demand meter and how the charges are tiered . LOL
I'm not even going to go there.

 

[doojus]

^I'm all ears, I'm just doing some initial research to see if it's worthwhile, so sharing the ways it differs from standard service other than the obvious helps me.

 

[Rookie2]

For 1 or two machines just use a phase converter. When you call your power company you will be floored at their fees to install 3 phase let alone how they have to charge for anticipated use of power rather than your actual use. It's so complicated and not worth it unless you have a large use of three phase.

 

[KenC]

^I'm all ears, I'm just doing some initial research to see if it's worthwhile, so sharing the ways it differs from standard service other than the obvious helps me.

As I said in my first post above: It is not the same everywhere and anything anyone tells you here is a guess based on our local experience. Mine was free install and no billing penalty.

Others aren't so lucky.

Just contact your provider and find out your local situation.

 

[Falcon67]

For 1 or two machines just use a phase converter. When you call your power company you will be floored at their fees to install 3 phase let alone how they have to charge for anticipated use of power rather than your actual use. It's so complicated and not worth it unless you have a large use of three phase.

This. I have a 3 phase mill and use a 2 HP TECO converter from 240 single to run it. May not be completely trivial because a converter like that has to be wired directly to the motor. A rotary phase converter would let you produce self contained 3 phase if there was more need. There is a farm not 300' from me and he may well get 3 phase (not sure how to tell from the poles) but I ain't asking about it. $$$ easy.

 

[mburrus]

and i sure agree with above... get a teco single to 3 phase vfd for each machine, or use a rotary converter... much cheaper than getting 3 phase installes by the utility... there may or may not be demand charges... we have some 3 phase residences here (elevators, well/pool pumps, boat lifts etc) and im not sure that they have to deal with a demand pricing structure... some commercial accounts sure do though...

 

[MixManSC]

Its not demand based here and we are in a heavy industrial zoned area. No idea of what (if any) extra SCE&G charges on new 3 phase installations. I'm going to be finding out very soon though. The warehouse building - I'm converting about 4000sf of the front of it into finished office space that I'm going to be leasing out. The current 60a feed from my main building is not going to cut it so I'm just about to be calling SCE&G in the next week or so to see what my costs are going to be and I'm undecided on having it connected as 3 phase. Probably will though but it might not be much extra since we already have transformers in place on the pole for 3 phase service but I really dont know much about that end of things and if they will just run the other building off the same transformers or not. I'll update in here once I find out if this thread is still going. It might be a few weeks though. Not sure yet because I'm getting the city to assign a separate street number to the other building and I want to have that done before I call the utility.

 

[theoldwizard1]

.
.
.

Measure the voltage at your compressor. I'll bet it is 208V.

They do make 208v - 240v transformers.

Many "modern" motors (especially A/C) are actually designed to run on 200-250V.

No it depends on the system! Read above!

Not sure what you are responding "NO" to ? I made 3 statements.

1) Speculation
2) Acme T279741S Primary 120/208/240/277 Secondary 120/240 and 240 w/neutral.
3)Most mini-splits have "wide" input voltage ratings.

 

[Nortonscustom]

Not sure why this board is always doom and gloom when it comes to 3 phase. OB your best bet is to talk to local electrician and your utility provider.

It didn't cost me a dime to have 3 phase run to my shop. I just had to provide the pole, weather head and meter box. City also required a master disconnect be installed. Told them what I needed and they set me up on a delta. One 200amp breaker in my 3 phase panel feeds a second single phase panel. As far as paying commercial utility rates? Thank goodness! My shop cost a fraction of what my house does for the same usage.

 

[Stuart in MN]

Not sure why this board is always doom and gloom when it comes to 3 phase.

You didn't mention where you live, but your situation is the exception to the rule - it's not normally that easy or inexpensive.

 

[theoldwizard1]

Not sure why this board is always doom and gloom when it comes to 3 phase. OB your best bet is to talk to local electrician and your utility provider.

It didn't cost me a dime to have 3 phase run to my shop.

3 phase is typically only available in "commercial" areas and (maybe) on farms.

Rotary phase converters are not extremely efficient, fine if you are only going to use it infrequently. VFD are more efficient, but they get expensive fast.

Most hobby shops are better off swapping out 3 phase motors for single phase.


(I learned about 3 phase "back in the day" when computers used it ! Some had power cables that were as big as your bicep ! Ran into a few "sparkies" who could not understand why you need both ground and neutral !!)

 

[Rookie2]

Its not demand based here and we are in a heavy industrial zoned area. No idea of what (if any) extra SCE&G charges on new 3 phase installations. I'm going to be finding out very soon though. The warehouse building - I'm converting about 4000sf of the front of it into finished office space that I'm going to be leasing out. The current 60a feed from my main building is not going to cut it so I'm just about to be calling SCE&G in the next week or so to see what my costs are going to be and I'm undecided on having it connected as 3 phase. Probably will though but it might not be much extra since we already have transformers in place on the pole for 3 phase service but I really dont know much about that end of things and if they will just run the other building off the same transformers or not. I'll update in here once I find out if this thread is still going. It might be a few weeks though. Not sure yet because I'm getting the city to assign a separate street number to the other building and I want to have that done before I call the utility.

For anyone contemplating moving into a commercial lease space :
If a lease space has 120/208 3ph your fine, if it's an old industrial lease space with 277/480 3ph then run away unless you have heavy use for 480. These spaces use dry transformers to make the 120/240 for offices and some lighting and waste about 9% of the rated kw while sitting there unused (night time) 24/7 365 days a year. I've seen a local small business struggle to make a profit and pay the electric bill until they went under.

 

[BillK]

waste about 9% of the rated kw while sitting there unused (night time) 24/7 365 days a year

I am not an electrician but my training is as an electronic tech and I do not understand how a transformer can use power if there is no load on it ? If there is no current flowing through the secondary than there cannot be current flowing through the primary. I can maybe understand their being inefficient during use and costing more in that way but not when they are just sitting there ????

Not logical.

 

[Rookie2]

I am not an electrician but my training is as an electronic tech and I do not understand how a transformer can use power if there is no load on it ? If there is no current flowing through the secondary than there cannot be current flowing through the primary. I can maybe understand their being inefficient during use and costing more in that way but not when they are just sitting there ????

Not logical.

Primary windings with # 8 or #10 wire 10-15 KW transformer.
clamp on amp meter ! And I called the transformer manufacturer and talked to an EE.

 

[Steve from Socal]

For anyone contemplating moving into a commercial lease space :
If a lease space has 120/208 3ph your fine, if it's an old industrial lease space with 277/480 3ph then run away unless you have heavy use for 480. These spaces use dry transformers to make the 120/240 for offices and some lighting and waste about 9% of the rated kw while sitting there unused (night time) 24/7 365 days a year. I've seen a local small business struggle to make a profit and pay the electric bill until they went under.

I have 600amp 480 service at my shop with 3-100KVA transformers for my 240/120 service. I pay demand charges and even with all that the freight to keep the transformers warm is about 100.00 a month. I have a 100KVA dry delta transformer to install someday! It should drop the parasitic load on the transformers by about 2/3rds. Death Star power AKA Weststar is mercenary in pricing to small industrial users!

I wouldn't have any qualms about recommending 480 service if available and priced near 240 service. I really dislike 208, but that is just my own bias.

Steve

 

[mburrus]

its still a coil of wire that makes a circuit... ALL transformers have a no load loss figure, even though the there is no current flowing in the secondary, the transformer still hums right? there is still some current flowing to excite the windings. i doubt that the no load loss is 9% of the nameplate, but i wouldnt doubt that the full load losses (lost as heat) would be 9%...

 

[My Old Tools]

I've been spinning my own 3 phase with a rotary converter for years. Much cheaper than a bunch of motor swaps, and you get to keep the smooth 3 phase motor your mill and lathe were born with. Lathes don't generally like single phase power if you want a good finish. You don't have to talk to the POCO or pay through the nose for commercial rates.

 

[MTW]

Just for some further confusion on the subject.

In my area SE Michigan, High leg delta (120/240V 3 Φ 4W) is still very common in industrial and commercial use, especially in the previously developed areas.

As a side note for those with 240V phase converters, the output could be converted to 480V 3Φ with another pair of open delta transformers, for some of that old iron you might come across.

MTW Ω

 

[wyliesdiesels]

We still have a lot of existing delta services(either high leg 120v/240v or 3-wire 480v) but the PoCo wont install new Delta service!

And yes a transformer with no load on the secondary still uses energy and spins the meter. This is just the reason why PoCos install undersized transformers.