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120 / 240V Service .... Assumed Delta????

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    120 / 240V Service .... Assumed Delta????

    I am reviewing drawings from an Engineer that screwed up big time (undersized equipment, bad calcs etc). The incoming service is 120/240V 3PH-4W. Am I to assume that it is a delta system? I typically see 120/208V system. What made me question it is because the engineer has no loads on the B leg. I checked the new service order from the power company to bring the power into the building and it only says 600A 3PH 4W 120/240V.

    #2
    Sounds like Delta to me. The B phase would only be used for 3Ø or 1Ø 240 volt loads.
    Rob

    Moderator

    All responses based on the 2017 NEC unless otherwise noted

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      #3
      Originally posted by AWinston View Post
      I am reviewing drawings from an Engineer that screwed up big time (undersized equipment, bad calcs etc). The incoming service is 120/240V 3PH-4W. Am I to assume that it is a delta system? I typically see 120/208V system. What made me question it is because the engineer has no loads on the B leg. I checked the new service order from the power company to bring the power into the building and it only says 600A 3PH 4W 120/240V.
      Delta. any single phase 120 volt loads on the B phase will get 208 off the high leg.
      ~New signature under construction.~
      ~~~~Please excuse the mess.~~~~

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        #4
        Is there supposed to be a standard difference in meaning between "120/240" and "240/120" in cases like this? That is, with one being split-phase and the latter being high leg delta?

        I suppose it's fairly hopeless to expect everyone to know and remember it, I'm just asking.

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          #5
          Originally posted by jaggedben View Post
          Is there supposed to be a standard difference in meaning between "120/240" and "240/120" in cases like this? That is, with one being split-phase and the latter being high leg delta?

          I suppose it's fairly hopeless to expect everyone to know and remember it, I'm just asking.
          Yes, and Jim Dungar has mentioned it to me many times. The former being the single phase case and latter being the three phase case. I often just use 120/240 for three phase as well because it was industry standard utility notation for many years and old habits are hard to break.

          Plus, the circumstances usually make it clear enough that I don't care anyway as long as the concerned parties know what is being discussed.
          BB+/BB=?

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            #6
            Officially per ANSI standards, if you list the lower voltage first, it's supposed to denote single phase, if you list the higher voltage first, it denotes 3 phase.

            So "120/240V" automatically SHOULD mean it is a single phase service, if it was listed as 240/120 (with nothing else), one should assume it is 3 phase. Best practice of course is to add "3 phase 4 wire" when talking 3 phase, just to make sure. Think about it, do we say "277Y480V" or do we call it "480Y277V"? That doesn't mean however that people have been doing it wrong for years...

            Also, if it is 3 phase, it HAS to be a delta service with a center tapped leg to get 120V, there is no other way of doing it. If you had a 240V Wye service, the Phase-Neutral voltage would be 139V.
            __________________________________________________ ____________________________
            Many people are shocked when they discover I am not a good electrician...

            I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

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              #7
              Originally posted by mivey View Post
              ...120/240 for three phase as well because it was industry standard utility notation for many years and old habits are hard to break.
              You betcha.
              Just because you can, doesn't mean you should.

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                #8
                Thanks for the replies. Now one more person can do it right.

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                  #9
                  Originally posted by jaggedben View Post
                  Thanks for the replies. Now one more person can do it right.
                  Hopefully
                  but there's still us with age damaged brain cells. Mr. Dungar has corrected me more than once on proper terminology with regard to voltages and fault-current. I actually saved a few of his post, now all I have to to is remember where I saved them (I think he finally gave up on teaching me)

                  For other septuagenarians out there or those approaching, this will bring a smile:
                  https://www.youtube.com/watch?v=0wW-pVp7OZg
                  At my age, I'm accustomed to restaurants asking me to pay in advance, but now my bank has started sending me their calendar one month at a time.

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