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Thread: How does one measure the voltage on a 230v 3 phase line?

  1. #1
    Join Date
    Sep 2002
    Posts
    1,999

    Default How does one measure the voltage on a 230v 3 phase line?

    Gentelmen:

    I'm installing a 230v 3 phase (phase sensitive) heat pump unit how does one measure the voltage, across L1-L3 or L1-L2???. The unit is a Florida Heat Pump model em 096. Directions state that the unit is wired 230 but if service is 208v we must move a wire over (provided in panel in ac unit.) Does anyone have any experience with this type of a unit.

    Thanks

    Tom

  2. #2

    Default

    You need to be careful concerning what type three phase you are being served.

    208/110
    240 only
    240 corner grounded
    240 hot leg
    480/277
    480 only


    There are many different types of three phase. Open you main service rated panel. Look to see if you have a neutral bare and four wires coming in from utility company.

    If only three wire service you need to test from phase 1 to phase 2 then phase 2 to phase 3 then phase 3 to phase 1. Then test from each phase to your equipment grounding conductor separately.

    If with four wire service you need to test from phase 1 to phase 2 then phase 2 to phase 3 then phase 3 to phase 1 then each phase to the neutral bar separately.

    Tell us the voltages you find in each test then we should be able to tell you if delta or wye or wye/delta or hot leg or corner grounded delta or open delta service.

    Then you can adjust your a/c unit to match your type three phase service supplied.

    Curious

    Wg

  3. #3

    Post

    Quote Originally Posted by Wgoodrich View Post
    You need to be careful concerning what type three phase you are being served.

    208/110
    240 only
    240 corner grounded
    240 hot leg
    480/277
    480 only

    Tell us the voltages you find in each test then we should be able to tell you if delta or wye or wye/delta or hot leg or corner grounded delta or open delta service.


    Wg
    This was an interesting post. Too bad anonymous decided not to follow up and answer the above question yet posted many others after this.

    Confused:

  4. #4

    Default How does one measure the voltage on a 230V 3 Phase Line?

    I've read this post and would like an answer to my voltages on what type of outputs they are, Wye, Delta, Star...?

    I read the following:
    L1-L2 = 236VAC
    L2-L3 = 234VAC
    L1-L3 = 240VAC
    L1-N = 118
    L2-N = 118
    L3-N = 205

    L3-N looks excessive...


    Thanks
    Stan

  5. #5
    Join Date
    Dec 2003
    Location
    Kent, WA
    Posts
    8,427

    Default

    This is 240V delta. The one leg on this is "special" as you noticed and is called the high leg. It is typically 208V to ground and it not used by itself. To help ensure you don't accidently use it for 120V loads, that wire is supposed to be colored orange. Sometimes this orange colored wire is required to be in a specific position in a meter or panelboard. Even if you have a single phase 208V load to run from it, I don't think the transformers likes it being used (may overload them). The high leg should only be used in circuit that need all 3 phases.

    On 240V delta, one side of the triangle provides "normal" house power -- 240V from the ends, and 120V from those ends to the center tap (which is where the neutral is). You use all 3 corners in a 3 phase load. Most delta 3-phase doesn't use the neutral, but there is still a grounding wire in all circuits and feeders which goes to that neutral point anyway.
    Mark
    Kent, WA

  6. #6
    Join Date
    Dec 2003
    Location
    Springfield
    Posts
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    Default

    Since a pic is worth a thousand words, here's a 4-wire Delta transformer secondary.

    B is the high leg in this pic.

    The "high", or "wild" or "crazy" leg is supposed to be colored orange in the US.

    Homer
    Attached Images Attached Images  
    Depending on your skills, doing your own electrical work may risk the health and safety of the community. Always find out how to do things safely before beginning.

  7. #7

    Default

    Thanks for the quick answers. Now I know I can use this source for the power supply testing I need to do.

    Thanks again,
    Stan

  8. #8

    Default do mine, do mine

    This is a great thread started, although a bit old.
    I found it by google - and so far I can not find anywhere else that has examples to identify types of 3 phase.

    I am setting up a machinists mill that came with a variable frequency drive, but it is 3ph 380-460v and I have 220 3ph, so I am looking for a transformer.

    In calculating transformers I have found you need to know the type of 3phase.

    My 3ph measures:
    L1-L2 = 212VAC
    L2-L3 = 212VAC
    L1-L3 = 213VAC
    L1-N = 122
    L2-N = 123
    L3-N = 121

    After reading for many hours, I believe I have a good grasp on 3phase, just a workout understanding all the types, I have found no less then 8 different types. The difference in Wye vs Delta and combinations of the two.....sheesh.

    What really baffles me is trying to apply a correct transformer, understanding KVA, yet factoring in the coil ratio. The problem I have is trying to obtain the specs from manufactures is difficult.

    Probably end up getting a 220-240 VFD.

    any help would be electrifying

  9. #9
    Join Date
    Dec 2003
    Location
    Welland Ontario
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    Default

    You shouldn't need to be concerned about coil ratio. Input voltage, output voltage, KVA and delta or wye are you concerns.

  10. #10
    Join Date
    Dec 2003
    Location
    Kent, WA
    Posts
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    Default

    You have 208Y 3-phase. You can change from wye to delta if you want via the transformer. Just depends on whether that mill needs a neutral or it just uses 3 phase wires. I also don't believe there is a problem powering a delta load from a wye source (as long as the voltages match). The main consideration is if you will have other 480V things in your future that may need wye, or if you need 277V volts for something.
    Mark
    Kent, WA

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