Electrical ?

I've been working with a three phase fuse panel in school with 3 legs of 120 volts. But I'm trying to understand it more. If I'm using 1 hot leg and a neutral then that is 120 volts (single phase) and if I'm using 2 hot legs and a neutral then it is 240 or 208?

4 Answers

  • 9 months ago

    IT IS 208V.


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  • 9 months ago

    Are you in India?

    Look at the Panel data Plate and find out if it is really three phase or just three legs of a 120/240V two phase Panel. It must say somewhere on it. Take a picture and post it with the question.

    If it really is three phase it is probably 208V three phase between legs and ground.

    If you are in the USA it is 120/240 V two phase and You are looking at three legs of a 120V supply. Each is 120V AC to ground.

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  • 9 months ago

    It's 208 volts between any 2 phases. Actually 120 x √3

    Most 220-240 volt appliances are designed to operate also at 208 volts, although possibly at reduced capacity.

    Homes tend to get 120-240 volt service where a 240 volt CT secondary is used. But apartment buildings and small commercial buildings tend to have 120 volt 3 phase service where each unit gets two of the 3 phases so they have 120 volt and 208 volt lines available. 

    Larger buildings have higher voltage service, such as 240 volt 3 phase or 480 volt 3 phase, with, for example, each floor having transformers to reduce the voltage.

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  • 9 months ago


    The three phases are equally 120 degrees apart.

    Think of three equal spaced points around the circumference of a circle. The radius is voltage and each is 120V from the centre - but between any two points, it's rather less than twice the radius.

    (vs. Single phase spit supply, where the two points are directly opposite).

    Or just look at the voltage waveforms:


    When any one phase is at a peak of either polarity, the other two are well away from their peaks.

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