Too much electricity!!!!

[Peter Meacham]

Lots of people would like this problem, I suspect.

I moved into an industrial condo for my workshop.

Unfortunately, it has some 240VAC, 50 amp, three phase power. I only need single phase 240VAC for my ShopBot CNC.

Is there a way to get single phase power from a three phase panel?

Can I do it with a three phase to single phase converter (is there such an animal)?

Thanks for any advice.

Pete

[Leo Graywacz]

Just use 2 of the three hots. Most likely it will be 208 volts. And depending on if you have a delta or a wye 3PH you may have a high leg which will have a much higher voltage than the other two. If your bot need 230 VAC you may need a boost transformer to add the extra voltage to the line.

I have a 100 amp 3PH system and all but one pc of equipment is single phase.

[Dan Friedrichs]

Leo is on the right track - depending on exactly what you have, you may be able to just connect between two phases (or between one hot and a neutral, if available) and get 230V. Take an AC voltmeter and check the voltage between the available wires (are there 3 wires available or 4?) and see if you have 230V anywhere.

[Peter Meacham]

Thanks for the replies.

The meter I took with me this AM was broken - so I could not measure betweens legs, etc. I will do that next and see what voltages I can find.

I do have three wires (phases) plus a netural and ground, I believe - I am not in front of the panel at this time.

Thanks.

[Phil Thien]

Just be careful working in any high voltage, three-phase panels. If you have never worked on three phase before, and aren't familiar with the term "arc flash," I'd suggest reading up before proceeding.

[Charles Lent]

There several versions of 3 phase 208-240 volt power commonly available in the USA and I'll try to explain them below. Each may be more common in any one locale, but you could find all of them almost anywhere that 3 phase power is available in the USA. The power companies decide which one they want as standard and then let the customers convert from this to whichever version they would rather have via large transformers.

3 phase Y connected power - will measure about 208 volts between each of the 3 phases and 127 volts from each phase to Neutral or ground.

3 phase Delta connected power - will measure about 240 volts between each of the 3 phases and it will not have a neutral. 2 of the phases will read 240 volts from each phase to ground and one will read zero volts to ground. 120 volts is not available from this system without installing a transformer.

3 phase high leg (commonly called split phase or sparker leg delta) - measures about 240 volts between each phase but there is a center tap between two of the phases with neutral connected at this center point. From each of these two phases to neutral or to ground you will get about 120 volts, but from the third (high leg)
to neutral you will see about 280 volts. In this case 120 volt single phase equipment should only be connected to one of the center tapped phases and neutral with the neutral also grounded. The third (high leg) phase is only used for one of the three required phases to supply 3 phase equipment and is not used to supply any 120 volt equipment.

If you only need single phase 208 or 240 volt power you can connect your equipment between any two of the three phases, but if you have many single phase needs you should spread the load by connecting some machines between different phases. If you need 208 and the incoming power is 240 or vise-versa there are transformers available to raise or lower the incoming power to meet the needs of a particular machine or to lower it if it is too high.


Single phase power- like what you have in your home was initially created to replace Edison's 110-220 volt DC system with comparable AC power so the conversion to AC would be as painless as possible. The power company runs one phase through the primary of a transformer to ground. The secondary of this transformer is 240 with a center connection. It's still only one phase, but the center connection is grounded and also used as neutral. From each hot wire to neutral or ground you will see 120 volts, but from hot wire to hot wire you will read 240 volts.

I hope this helps you all understand the single and 3 phase power systems that are available in the USA better

Charley

[Anthony Whitesell]

There several versions of 3 phase 208-240 volt power commonly available in the USA and I'll try to explain them below. Each may be more common in any one locale, but you could find all of them almost anywhere that 3 phase power is available in the USA. The power companies decide which one they want as standard and then let the customers convert from this to whichever version they would rather have via large transformers.

3 phase Y connected power - will measure about 208 volts between each of the 3 phases and 127 volts from each phase to Neutral or ground.

3 phase Delta connected power - will measure about 240 volts between each of the 3 phases and it will not have a neutral. 2 of the phases will read 240 volts from each phase to ground and one will read zero volts to ground. 120 volts is not available from this system without installing a transformer.

3 phase high leg (commonly called split phase or sparker leg delta) - measures about 240 volts between each phase but there is a center tap between two of the phases with neutral connected at this center point. From each of these two phases to neutral or to ground you will get about 120 volts, but from the third (high leg)
to neutral you will see about 280 volts. In this case 120 volt single phase equipment should only be connected to one of the center tapped phases and neutral with the neutral also grounded. The third (high leg) phase is only used for one of the three required phases to supply 3 phase equipment and is not used to supply any 120 volt equipment.

If you only need single phase 208 or 240 volt power you can connect your equipment between any two of the three phases, but if you have many single phase needs you should spread the load by connecting some machines between different phases. If you need 208 and the incoming power is 240 or vise-versa there are transformers available to raise or lower the incoming power to meet the needs of a particular machine or to lower it if it is too high.


Single phase power- like what you have in your home was initially created to replace Edison's 110-220 volt DC system with comparable AC power so the conversion to AC would be as painless as possible. The power company runs one phase through the primary of a transformer to ground. The secondary of this transformer is 240 with a center connection. It's still only one phase, but the center connection is grounded and also used as neutral. From each hot wire to neutral or ground you will see 120 volts, but from hot wire to hot wire you will read 240 volts.

I hope this helps you all understand the single and 3 phase power systems that are available in the USA better

Charley

As I have recently learned, three phase Y is typically used in strict office buildings (ie., buildings not intended to include manufacturing areas that may and typically run 3 phase equipment). It allows the PoCo to send 50% more wattage and only run one more wire.

[Doug Palmer]

With a three phase 240 volt system, you should see 240 volts between phases. However when you measure phase to ground or phase to neutral you will probably see some odd readings. If I remember correctly you will usually see 120v phase to neutral on two legs and something like 258 volts phase to neutral on the third leg. This is because you have a grounded delta setup. If you see this with you meter, use the two 120v legs and you will have a single phase 240v setup and you will be able to use the 120 volt legs individually for your other needs.

[Charles Lent]

Anthony and Doug,

You have not read my post very closely.

3 phase Y systems exist in many places, not just office buildings, and it is fast becoming the favorite system for many new manufacturing facilities that are being built today, because of it's flexibility. There are many manufacturing facilities in the US that use it, and some even have more than one type or voltage of 3 phase system in the same building. 480 volt Y type 3 phase systems are commonly used for lighting in many commercial systems where the phase to neutral voltage is 277 volts. You will find many surplus fluorescent fixtures with 277 volt ballasts because of this. These fixtures are unsuitable for home use unless the ballast is replaced, which usually costs 80% of what a whole new fixture sells for. A 277 volt fixture will not work properly, if at all, on 230-240 volts without a new ballast. All of the IBM manufacturing facilities that I have been in use 208 volt Y systems for powering their manufacturing lines and 480 volt 3 phase Y systems for lighting.

The most prevalent 3 phase system in the USA is the 240 volt high leg (sparker leg) Delta system, but 208 Y has been becoming much more popular over the past 60 years, mostly because it can provide for balanced loading of mixed 120 volt single phase and 3 phase 208 volt loads. This is very important for high current electrical power consumers because the power company bill is based on the highest loaded phase. As an example, if all of your loads are 120 single phase and all of them are connected to only one phase, the electric bill will be 3 times higher than it will be if those same loads are distributed equally over all 3 phases.

Smaller facilities tend to use whatever type of 3 phase power that the local power company provides in that area. Larger facilities usually provide their own transformer substations to convert what the power company provides into whichever type of 3 phase system that they want to use. There are some advantages and disadvantages to using each 3 phase system, and the user company needs to determine which is best for them, or live with what is provided and save the cost of transformers to convert it.

I'm a semi-retired EE with 40 years of automated machine development experience and I hold an electrical contractors license. In one of my positions I was the only USA factory electrical service rep for a European manufacturer of printing equipment, with a territory of all 50 states, the Caribbean Islands, and I occasionally assisted my counterpart in Canada. Much of this job entailed figuring out how to convert the different 3 phase power systems to allow this European printing equipment to be connected in the USA, Caribbean Island, or Canadian power systems, wherever this equipment was being installed, and to resolve problems that resulted from poor installations by others.

Charley

[Peter Meacham]

Well, thanks to all who responded.

I have the CNC up and running - Kind of wish I had remembered the emergency off switch got pushed during the move, would have saved me a couple of hours of troubleshooting wondering why the control box would not power up!!!!

Charles, you hit the nail on the head. I have a 3 phase high leg system. So, I used the two 113VAC (low voltage area, I guess) legs to meet my requirements.

Thanks, Pete

[Doug Palmer]

Thanks Charley, I'm not so sure that we have disagreed on anything. I have accepted Peter's original post as accurate. He stated he had 240v 3 phase, not 208 3 phase. He later posted that he also had neutral and ground conductors. Hence the 4 wire grounded delta 240v. (Perhaps there is a 240v wye system out there somewhere, but I have never seen or heard of such, nor have you mentioned one.) You said 280v on the high leg, I said around 258, which is a calculated number. I just tried to answer his specific question. If you are a EE, then we both know there are many other available power delivery options. What exactly do you disagree with in my post?

[Anthony Whitesell]

I'm not sure that I disagree either. Nothing anyone has said is incorrect. I'm following in your shoes Charles, I'm a MSEE with 16 years of the same experience. Until recently (little over 2 years ago) I never gave much thought to why or how the various supplies exist. Just over two years ago, I was involved in a major refit at a facility that included every voltage I had ever heard of. We installed equipment that was 120, 220, 277, 208 3 phase, 240-380-480 and 600 3 phase plus 12, 24, 48, 120VDC. It was a sub project just to keep straight what was being installed where and the power it required. We mandated an un-lock-out/un-tag-out procedure that required the equipment to be present and photos of the name plate and voltmeter readings before the equipment was attached or plugged in with three people present for a sign off. It was a good thing too, because some of the equipment nameplates turned out not to match the requirements on the "inventory list". It was during the setup for a factory acceptance test that was to take place in an office building that all of the differences and reasons for being sunk in about the different phase options. It turned out that the office building had three phase but only 208 as it had no manufacturing or high powered motors, it had no requirement for the higher voltage.

Since hindsight is 20/20, I can look back and say with confidence, that most of the places I have worked have had either 220V single phase or 208 3 phase for their 120V supply and 480 delta for equipment (only 4 wires) or had 208 3 phase and 480 Y for their equipment. Interesting that our experience differs that way. I wonder if it is a regional thing?

I wholly agree with everything you have said, with maybe one exception. I'm not sure about the high leg delta being that popular (again reagional?). Until I started WWing (within the last 5 years), I had not heard of it and to frost the cake (in a bad way) it's not even mentioned in my undergraduate power and motors book (c)1992.