View Full Version : 3rd phase "add a leg" deal

02-22-2005, 03:48 PM
sounds like a chicken commercial!

called utility today. Sales lady was unfamiliar with process of adding 3ph to what exists currently as residential 1ph 200 amp 240v service.

I realize as did she that a new meter was required. as well as a new breakout box in my house.

but asside from that I can just use 1 leg for 120, two legs for 240, and all three legs for 240 3ph? Right?

I don't nee any other special equipment in my house do I?

3 Phase Lightbulb
02-22-2005, 03:56 PM
Sorry, I'm not for sale....


02-22-2005, 04:04 PM
But the third leg might come in handy. You never know when you might need a spare.

02-22-2005, 04:07 PM
The wife already says I have a 3rd leg.

John Stevenson
02-22-2005, 04:14 PM
Move to the Isle of Man

02-22-2005, 04:18 PM
I seriously doubt the utility company will be willing to bring three-phase to your residence. Even if they do, I've heard the hookup cost is pretty steep (on the order of thousands of dollars)

One way that many people get around this problem is through the use of phase converters. I built a Rotary Phase Converter (RPC) myself from instructions on the internet. It was a fun project and now I have three-phase power from 2-phase 220V input(often called single phase). It's not balanced as nicely as what you would get from the utility company, but for running electric motors, it does great. The usual disclaimer of "don't try this if you're not confortable working with electrical circuits" applies, as you are dealing with electricity that could kill you.

If not building one, I know you can buy them for $300+. If well-balanced line voltages are a must in all load conditions, one company makes a RPC that uses a DSP to ensure the lines are balanced regardless of load. I believe those are in the $1200+ range however. Go to


for more info on them.

For more general information on RPC's, look up rotary phase converters on the internet, or even from past posts in this forum I believe. I really enjoyed building mine -- my control panel even has twist lock receptacles for the 3-phase outputs. It's kind of goofy, but I put mine on wheels since I currently rent and will need to move it around. At least it's portable enough to move with me to the next location though.

02-22-2005, 04:21 PM
So maybe you could just have 2 meter bases on the shop, pay 2 light bills and mix-n-match those big wires for 3 phase? Maybe tap into a leg on your neighbors house?
I be thinkin on this one... http://bbs.homeshopmachinist.net//eek.gif

Hoffman in Warner Robins Ga

02-22-2005, 04:47 PM
I asked Phila. Electric that ? once, and didn't like the answer. So I bought a Cederburg 1-3 horse static phase converter. Upgraded to a 7-1/2 horse rotory when I moved and snagged a used GE 3phase breaker panel w/breakers from a demolition sight for a small fee(1 case of beer for the night watchman). PECO would run the lines from the transformer and install a new transformer on the pole behind my old house for the nominal cost of $5,000.00 (this was in 1984). All I had to do was garuntee them a minimum number of kilowatt hours a month, I forget the number, but there was no way a home based part time 1 man shop could do it, or pay a minimum fee each month of around $800.00 for the transformer plus the regular electric bills for both the residential and 3phase services. Oh and by the way, the 3phase is to be billed at your peak demand rate for all hours regardless of your actual usage. This means if you have a machine that draws, say 180 kw on start-up, but once running, only uses 35 (Flywheel effect on a press or big lathe)you get billed at the 180kw rate even if you only use it once a month for all your usage or non-usage,whatever the case may be. I did not even bother to ask when I moved, as the nearest 3phase was almost a mile away, and then I would need to put poles on my lot for it to cross the wet lands on the back side to reduce the run costs and direct burial to come in the front. I love my rotory phase converter. just wish it was bigger like 15 hp and better balanced for CNC. Wife says no way so I'm stuck.

Bruce Griffing
02-22-2005, 04:49 PM
You presently have only one leg. Though your transformer gives you two sources of 120 volts, they are out of phase by 180 degrees. Three phase requires three legs each 120 degrees apart. No way to add one leg to what you have and get three phase.

bernie l
02-22-2005, 05:33 PM
The is a type of common electrical system that is sort of what you describe, but it's pretty much reserved for commerical applications, retail stores, resturants, maybe appartment complexes. It's usually referred to as a 120/208V Y system. Each phase wire is 120 V to neutral, and 208 V between any pair for either single phase use (2 wires) or 3 phase (all three wires). Most 220 V single phase equipment will run okay on 208 and most 240 3 phase equipment will run okay on 208, will draw more current though. It would be a fairly major change for a residential application.

take care

02-22-2005, 06:46 PM
My utility wanted $5,000 to run 50 feet of three-phase,,,must be the going rate.

Static phase convertors are cheap but reduce motor output by 33%. Rotary phase convertors (homebuilt or bought) give full power.

02-22-2005, 07:56 PM
Unless you have 3-phase power on the pole outside your house -- and, unless you live on a major highway, odds are extremely against it -- there is basically NO WAY to do it. Even if you have 3-phase outside on the pole, the cost of running 3-phase to your house will be "thousands."

Buy a VFD for 300 bucks and get an excellent approximation of 3-phase plus speed control.

02-23-2005, 10:59 AM
I use my third leg to lean on posts while resting.

Sprague M
02-23-2005, 11:13 AM
I hope it's not leaning on this post.

02-23-2005, 11:52 AM
hey Webbch
what plans did you use? just curious.
could you send me a copy?


02-23-2005, 12:28 PM
<font face="Verdana, Arial" size="2">Originally posted by SGW:
Unless you have 3-phase power on the pole outside your house -- and, unless you live on a major highway, ......... if you have 3-phase outside on the pole, the cost of running 3-phase to your house will be "thousands."

I do.

and I want to run a 5hp cnc mill. so I am alraeady looking at a $1000 balanced, non restarting, rotary phase cinverter.

so, I called. I figured if the cost were to be ONE thousand. and they didn't have a minimum monthly deal, and everything were just perfectly in my favor, That it might make sense. worth a shot.

02-23-2005, 12:44 PM
Check out VFDs. www.dealerselectric.com (http://www.dealerselectric.com) is one place. Other sources have been discussed in past threads. 5hp is starting to get "big," but may still be cheaper than a rotary phase converter.

In fact, see http://www.dealerselectric.com/ma7200.html

[This message has been edited by SGW (edited 02-23-2005).]

02-23-2005, 12:47 PM
I have three pase right outside my building, and my neighbors on three sides all have three phase. Still going to cost me big bucks to get it setup however. Seems the pole in front is already fully loaded so the pole to the east would need three new 'pigs' that I would have to pay for. Then there is the new 3 phase meter box and main disconnect, etc. I am doing a second 200 amp service instead, just to run a phase converter. Total cost a few hundred bucks.

James Kilroy

02-23-2005, 02:28 PM
Power company did it FREE for me. When you want something, ask in a way that makes the other side WANT to provide it - ie. stress what is in it for them.

In my case, we wanted to install larger (more electricity sold) air conditioner compressors at the house. I requested that the utility provide 3-phase at the meter. I told them that the new units would be more energy efficient than the old ones - that got their attention. Cost about $1,000 for my electrician to pull 4-wires about 100' underground from the meter to the box on our house. Utility company set two pole pigs and did the wiring to the meter (new also). All FREE.

Of course, the ulterior motive was to get the 3-phase into the garage for my Sheldon lathe. We did get two new 3-phase A/C compressor units and see a drop in our electrical bills.

Good luck - give it a second try! A.T.

Bruce Griffing
02-23-2005, 04:26 PM
If you really want three phase for your shop that is of very high quality check out this link


A little expensive, but much better than the cost of real three phase in most places. And it is not limited like a VFD - you can run multiple machines and use standard contactors.

02-23-2005, 04:39 PM
Around here,if there isn't 3 phase power out on the street, you're out of luck. Another thing to consider, our Elec. company uses peak / demand meters on all 3 phase services. Then you get to pay for the part of the power that you used to get for "free" on a single phase service. Depending on the kind of kind of load you have (large motors, etc) the demand charge can be significant. If it was me, I'd go with a rotary convertor.

Michael Moore
02-23-2005, 04:44 PM
I've got a 10hp Phase Perfect. I think the current model in that size is about $2700.

I've got 238 or 239 (I can't recall which at the moment)volts measured across any pair of the three wires - they are dead even.

It is not an inexpensive way to go, but I wanted a high-quality solution for the long term. And if I ever move, it moves with me, unlike a 3 phase line from the pole.


02-23-2005, 09:44 PM
The plans I used to build my phase converter were originally developed by Matt Isserstedt. Here's the link:


This illustrates an auto-start RPC using a time-delay relay. It can cause problems if you set the time delay for too long. On the third leg starting circuit, I actually put about 5 ohms resistance with 250W capacity in series with the starting cap in an attempt to limit inrush current and "protect" the start cap. It's not financially practical to do so, as the 50W power resistors, purchased new, would cost over $50 and a new start cap costs about $3.50. I just had some power resistors that I picked up for dirt cheap. It only seems to make a small difference.

There's another design that uses an autotransformer and potential relay (some guy made a phase converter to power some heavy duty siren). Go to:


I'd like to try that design sometime, but I've already got mine up and running.

Hope this inspires someone else to build one.


02-23-2005, 09:59 PM
Here's some pics of my results. This is my first attempt at posting pics.





Michael Moore
02-23-2005, 10:02 PM
Chad, could you please resize those images significantly downwards? They are far to big to be of much use as you can't see the whole thing at once.


02-23-2005, 10:06 PM
Sorry -- forgot to resize. Here it is again




02-23-2005, 10:07 PM
They're still a little big, but good enough for now. Sorry bout that.

02-24-2005, 04:25 AM
<font face="Verdana, Arial" size="2">Originally posted by IOWOLF:
The wife already says I have a 3rd leg.</font>

AKA: Stumpy, Lumpy or... Limpy? http://bbs.homeshopmachinist.net//biggrin.gif http://bbs.homeshopmachinist.net//biggrin.gif

cheers, Ken