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Single phase vs 3 phase power

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  • Single phase vs 3 phase power

    I am building a diesel generator for storms and events and I have a choice between two different power heads. They are both 16KW, one is 120/240 single phase and the other is 120/240 single, 120/208 3 phase, 240 3 phase and 277/480 3 phase. They are both 12 wire units regardless of the different outputs. My question here is can a 3 phase unit be wired up to have different outlets for different power outputs? In other words, have one outlet wired for 120 single phase to run say a hand drill, and another outlet wired for 208 or 240 3 phase to run a compressor and be able to run everything at the same time (assuming the total power draw is within the rated output for the unit)?

    I am familiar with basic electrical systems, but I'm not familiar with 3 phase systems and things more complicated than home wiring. It would be nice to have the 3 phase capability in case I need it, but the unit will mostly be used for 120/240 single phase applications.

  • #2
    Re: Single phase vs 3 phase power


    On the boat I work on, we have a 110/208 32.5KW Generator spitting out 3-phase power. I'm not completely familiar with all the wiring, but we have it setup so that all the 110 is single phase, and the 208 is 3-phase. So, yes, it is possible.

    From what I've seen of the wiring, there are three outputs: L1, L2, L3. I believe that for single phase use, you can take the input off of ONE of those outputs and run the other side to neutral.

    I wish I was at work right now so I could actually take a look at the wiring diagrams. :(

    "You have to go out, you don't have to come back."

    Dredgeisms: "NO! GoNooowwwBARRELROLL!" - "There WILL be NO desync!"


    • #3
      Re: Single phase vs 3 phase power

      From my limited knowledge on the subject, 3 phase power is usually used in large HVAC systems and industrial equipment to reduce the wear on large AC motors by reducing the phase angle of standard 120/240 service by adding the 3rd phase. Unless you own equipment that can make use of the 3 phase power why not stick to the more usual 120/240? For 'home' service, I am unaware of any benefits to having a 3 phase power source. Though my knowledge is limited as stated previously.


      • #4
        Re: Single phase vs 3 phase power

        I am a Journeyman Electrician.

        Yes 3 phase can be wired for different voltages, its a matter of having either single, 2pole, or 3pole breakers feeding the loads. So let's say you have a 6 space 3 phase panel. You essentially then have 6 - 120V circuits or you could have 2 - 3phase circuits.In a residential situation there is absolutely no reason for 3 phase generators. Even with single phase power you can still do 120V for general recepts, and then 240V for anything requiring more welders, motors, pumps. PM me if you have any other specific questions, I am more than happy to help. :)
        "Everyone makes fun of us rednecks with our big trucks and all our guns........until the zombie apocalypse"


        • #5
          Re: Single phase vs 3 phase power

          Great thanks for all the replies!

          Siantis- That about coincides with what I have found doing research, glad you could verify it.

          Dreah- Yes I agree with you there, although the generator heads I am looking at are the same price, same output just one is single and one is 3 phase. I probably wont need the 3 phase capability, but if I can wire it all up like I want to, then it makes sense to have the 3 phase in case I ever need it. My dad has a ranch and his neighbor has a performance shop so you never know when it could come in handy to run something big.

          Venman- Thanks for your expertise. I may take you up on that offer when the time comes that I can order it and get everything wired up :)


          • #6
            Re: Single phase vs 3 phase power

            I am an electrical Engineer with a concentration in Power System Design and Distribution services and technology and Venman is correct. Your house will not require 480vac as in a storm situation you are only going to want essentials which should only reqiure 120vac.

            I do want to stress that if your going to get a 3 phase generator be careful not to overload a single phase. Phase unbalancing can be the end of your generator. If your gonna use a 3 phase system and a power panel with 6 breakers with 2 breakers per phase, plan ahead what items your gonna want to plug in. You don't want all your equipment that require a lot of power on phase C, B, or A. Make sure that you distribute the power draw equally on all the phases.

            You may also want to have a disconnect switch for the incoming power from the generator. You really shouldn't have a problem if lets say your get a short on one of the receptacles as the breaker will trip. If you damage the cable running from your generator to the power panel and short that out, you run the risk of perminantly shutting down your generator unless that has a internal fuse system. The disconnect switch can be rated for the max output in AMPS of the generator or a little more. All it would really be is a 3 pole breaker and if you have a short that exceeds X amount of amps, the breaker trips and you may save your generator.

            Not sure how hardcore you want to get but that's my .02 cents.
            Last edited by viper1986; 01-06-2011, 09:16 PM.

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