No announcement yet.

3 Phase or Just Single?

  • Filter
  • Time
  • Show
Clear All
new posts

  • 3 Phase or Just Single?

    Looking for opinions here, the world has changed a lot since I've considered my electrical needs.

    The building that I'm renovating needs to be completely rewired, Three phase is available (240/120V) and can be brought into the building at no cost from the electrical company. I'm responsible for everything beyond the meter base socket. Regardless of the service type, I'll be running a 100 Amp branch circuit upstairs to the living area.

    I have an Arco rotary phase converter capable of 20 running horsepower, no one motor over 7 ½ hp. This was set up right with a 100 Amp load center downstream for use with several machines. It’s always worked well for me in the past, but I think it’s an inefficient way to power three-phase equipment.

    I currently have three major pieces of three-phase equipment; a series one Bridgeport (1 ½ hp), a Sharp 13” X 40” geared head lathe (3 ½ hp), and Shizuoka CNC kneemill (1 ½ hp). I’ll probably have a surface grinder in the future, but I’m not planning on a lot of big equipment in the future.

    Here’s where things start to get muddy for me. A three-phase load center is a lot more money than an equivalent single phase panel, I’m looking for used, and watch eBay, but often the shipping is huge as well, new three-phase breakers are outrageous – now if I get a Cutler-Hammer load center I can use my existing breakers, but otherwise I’d have to get the breakers I need for my machines. Does anyone see a problem with running a 100 Amp single-phase branch off the three-phase? Most other single-phase loads will me minimal and typical of any other shop environment – lighting, 20 Amp 120v outlets, 50 Amp 240v for a welder, 30 Amp 240v for a compressor.

    I understand that I could easily resell my rotary phase converter to offset the additional cost of the three-phase installation.

    What do you all think the best approach would be?



  • #2
    Go three phase wiring! When you sell/rent the building later it'll be much more appealing. Nothing like true 3-phase!


    • #3
      That's going to give you 208 volt single-phase for the house rather than 240 volt, isn't it?


      • #4
        In some residential areas in Austin, you can actually get 3 phase, 240V, but I've been told it's really expensive (for the install).

        One thing I've found with my foray into home shop machining: get as big a breaker box as you can! I've run out of every possible 208 breaker, and I'd like to have several more. Most of my HSM friends have had the same problem.
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."


        • #5
          First off you can check with some of your local electrical contractors if they have a “used” 3 phase panel they would be willing to sell and or install. It takes permission to use “used” equipment from the code enforcing authority, but you shouldn’t have too much problem if the equipment is in good working order.

          Now when you say 240/120 volt service to me, you are saying the utility is servicing your building with a grounded Delta transformer. This would give you “true” 240 volt service for your living area.

          Just for the fact of having 1 less thing to go wrong I say go for it on the 3 phase power.


          • #6
            did i miss something ? have you considered how the power company charges for 3 phase usage ? seems i remember its dam expensive compared to regular old single phase. . . .


            • #7
              Go with the 3 phase, like the others said. You might check with the power company and see about 2 meters: one for single-phase for the living quarters, another for the 3-phase for the shop. Our power company charges "commercial rate" for 3-phase, or for a second single-phase meter on the same property, such as for a horse barn. You might find that your power company is the same.

              Whatever, there's nothing like Factory 3 Phase power.


              • #8
                I've just got quotes in to run power to my shed, and the 3ط will be 50% dearer than 1ط, 1ط is all I need for the equipment I have.

                The difference would buy a fair bit of tooling, but its no contest really.

                While I'm doing it, and for just in case, and for future resale (honey, this one's got a shed AND 3ط) I'll go for 3ط.


                • #9
                  Keep in mind you will loose some energy in the rotary converter. Maybe enough to offset 3 phase electric rate and the increase in equipment costs depending how much you use it.

                  I'm not sure why you ask but theres no problem running 100 amp single phase off of 3 phase. But watch out for the high leg on the delta. The voltage is the same between all three phases, but phase B to neutral will be 240 volts not 120.


                  • #10
                    EVERYTHING cost more for 3-phase. I have 3-phase at my car wash and I try to buy breakers from ebay. A double-pole breaker by square-D for your stove or dryer at home might cost $12-$15; a 3-phase 20 amp breaker can cost $70 from your local electrical supply house - and they'll have to order it!

                    Check the rates! 3-phase here, means demand metering. If you don't understand the ramifications of that, you better get electrical savvy. One hour of heavy welder use can send your rate soaring for the whole billing cycle. I got 3-phase, I use it, and I hate it. I would never build a car wash with 3-phase again. Yes the motors are simpler and cheaper, but everything else is a pain. Bottom line is that it depends on your unique situation; I don't think anyone here can tell you what is best for you. If your electrical draw (demand) is fairly level, it is just simply comparing the cost per kwh. If you are going to have large swings, then you have to do some analysis.

                    If you had to purchase gasoline for your vehicle the way the utilities charge for "demand metered" electricity, you would go ballistic the first time you got your monthly gasoline bill.


                    • #11
                      Originally posted by davidh
                      did i miss something ? have you considered how the power company charges for 3 phase usage ?
                      Depending on your useage he could be coming way out ahead

                      First off - The power company around here only has Kvar and Peak Demand charges. Kvar shouldn't apply as long as his motor loads are properly balanced. Peak Demand charges need not be even a worry for services of less the 1000amps

                      Second - Three phase power is much more efficient then single phase. Far less line loss and better starting currents.

                      So go by the Kw charge

                      Here residential is .13 per Kw. .11 if you can prove your home is "all electric"
                      Commercial customers are paying .11 per Kw and Industrial can pay as low as .045 per Kw

                      Jim Cuadill

                      That lowest bid is best electrical contractor some one hired to build your carwash probably put some long term screws to you with a shoddy installation. Might want to consult an electrical engineering firm that specializes in Energy Conservation. Typically these guys operate in a 6 - 24 month pay back for the customer
                      Last edited by JoeFin; 06-08-2008, 07:58 PM.


                      • #12
                        Demand metering may or may not come into play. My 200-amp 480 volt service does NOT have a demand meter on it. It does have a montly "meter charge", which doesn't buy any electricity, I think it's $5.00 or thereabouts.



                        • #13
                          Well at my car wash, demand metering is ALWAYS in effect (not just some peak time) and I have 400amp service (IIRC). I just checked some of my records; when I used 3,000kwh with a demand reading of "5", I paid 7.4 cents per kwh. When I used 3,800kwh with a demand reading of "20", I paid 15 cents per kwh.

                          Historically the highest demand reading I ever had was "30", but that was a few years ago. The utility engineer said that I had the potential to hit "47" if I ran everything at the same time for 1/2 hour! I was complaining, and they thought I was doing good to keep my demand as low as I did.

                          My house electric rate is about 7cents per kwh any and all the time, regardless of how much or how little I use.


                          • #14
                            Yes apparently the utility provider in Ohio has everyone by the short hairs.

                            Jim – I’ve surmised you have already checked and tested to insure all your motor loads have not diminished the power factor of your electrical service. Any thing less then .90 would be very costly and contribute to an increased demand factor. The fix is a simple addition of correction capacitors on the load side of the motor starters.

                            Also as I’m sure since you have already talked to the Utility Engineer, you had the utility provider place a charting 3 phase power quality meter on your service to insure some business next door is not pumping harmonic distortion and or decreased power factor into YOUR electrical service as well. Found that once on a nice little food processor located directly across the river from the city water wells – which as you can guess were running 3ea 500hp DC Drive motors.

                            Other then that Energy Conservation measures begin to get quite costly given the necessary operations of the car wash.

                            But back to the subject at hand –

                            Your experience with 3 phase power can be vastly different then the majority of people using 3 phase power depending on your Utility Provider, the size and composure of your utility needs, and even that of your neighbors.