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    jwdodson's Avatar
    jwdodson Posts: 5, Reputation: 1
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    #1

    Dec 12, 2006, 08:28 AM
    Single Phase 208??
    Greetings,
    I'm about to purchase a Suspended unit heater for a carpentry shop. I'd like to use a service I previously used for a table saw, being 208v 30A, (2 hots at 120(120degs opposed) and a ground). The fixtures I'm looking at, in the catalog, state that they are Single/3 phase 208 or Single phase 208. My real confusion here is that I have no idea what single phase 208 is since 208 is derived from 2 legs of a true 3 phase system. Any ideas?

    Thanks
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
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    #2

    Dec 12, 2006, 11:31 AM
    So I am assuming that you currently have a 3 phase 4 wire 120/208 volt system?

    For 208 volt single phase, use a two pole breaker, which can connect to any two of the three legs in a phase panel, to get 208 volt 1 phase.

    If you truly have three phase 208 volt, then I would suggest you get a 3 phase heater. But if your circuit you want to use is only as you say two hots and the ground, then you need a single phase 208 volt heater.

    Did this answer your question?
    jwdodson's Avatar
    jwdodson Posts: 5, Reputation: 1
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    #3

    Dec 12, 2006, 11:38 AM
    I see, so something listed as "single phase 208v" is still actually from 2 legs of a 3phase 120v system.
    What is the difference from a single phase 208v and a 3phase 208v if both would ultimately only be using 2 of the hot legs?

    And yes, I do have true 3phase in the building, it's just that when we install the table saw, years ago we ran 10/3 to the branch panel and used a 30A double pole, so on the level where the Heater is going is only 2 hots/ground of a 3phase system.

    It seems like I just got hung up on a nomenclature thing.
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
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    #4

    Dec 12, 2006, 11:44 AM
    Single phase 208 circuit will use two hot legs, and a three phase circuit needs all three hot legs.

    All circuits will need the ground.

    If any circuits need 120/208, either 1 phase or 3 phase, then the neutral is needed.
    jwdodson's Avatar
    jwdodson Posts: 5, Reputation: 1
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    #5

    Dec 12, 2006, 11:53 AM
    Okay, that's what I figured (as far as what was meant by 3phase 208v). I was just unsure of what was meant by the single phase 208v. Now I know, thank you much.
    gup93488's Avatar
    gup93488 Posts: 1, Reputation: 1
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    #6

    Aug 28, 2012, 09:04 AM
    I need a little clarifictaion on this subject.

    If single phase voltage is 120. What is the two phase voltage? Is it 208 V or 240V.
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
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    #7

    Aug 28, 2012, 09:34 AM
    Two hot legs of a three phase system is still single phase, and would be 208 volts.
    Stuartg46's Avatar
    Stuartg46 Posts: 2, Reputation: 1
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    #8

    Nov 2, 2012, 04:58 PM
    2 phase or polyphase is rarely used, don't even concern yourself with this.
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