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Thread: 3 phase Delta High Leg Single Phase Load

  1. #151
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    Quote Originally Posted by Smart $ View Post
    So are you saying Monica's error was the reason for your's...

    Finding it in hindsight don't count
    Nup! Monica asked the question; someone else answered it, and this proves that the word means different things. Strictly speaking, I think the word means horizontal line or something like that. They quit teaching Latin just before I started high school, so it's all Greek to me. Natheless,

    1/2/2 = ?

    (1/2)/2 = 0.25?

    1/(2/2) = 1?
    Last edited by rattus; 01-30-10 at 04:59 PM. Reason: Expand
    Don't mess with B+!
    (Signal Corps. Motto)

  2. #152
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    By the way:

    BTW, here we have an excellent example of the voltage phasors, Van and Vcn, being 180 degrees out of phase. Then,

    Van + Vba = Vcn + Vbc = Vbn

    or,

    120V@0 + 240V@120 = 120V@180 + 240V@60 = 208V@90

    If one draws the phasor diagram it is immediately obvious that the equation above is correct.
    Don't mess with B+!
    (Signal Corps. Motto)

  3. #153
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    High leg use

    I have seen the high leg (wild leg) range from 180 to 215 volts to ground.
    This is just a cheap way for the utility company to build transformers.
    This is the can you see used in Residental area's a lot around here.
    They just drop that tap, and send the 240volt phases to the residence.
    I always tell my men, If you are on a commercial job and measure 240 volt expect a high leg.
    I have seen this use on lighting circuits, expecially now that electronic ballasts are in fixtures.
    They have auto sensing and will work just fine on the wild leg as long as it is between 100-277volt. you just have to use 277 volt switches, and mark everything well.
    This is becoming common place. due to panel space limitations with the high leg taking 1/3 of the spaces, and only being able to use with a 2 pole operation.
    I would be concerned about using this to run a motor load, or some other equipment, because the voltage may not be stable.
    Because the NEC is only concerned with clearance for rated voltage, and equipment rated to voltage, I don't think this would be addressed in the NEC.
    Tony
    OK Contractor.

  4. #154
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    Quote Originally Posted by TonyEEINC View Post
    ...I would be concerned about using this to run a motor load, or some other equipment, because the voltage may not be stable...
    What do you base this on?
    BB+/BB=?

  5. #155
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    I have a question to ask. The type of load wasn't really specified. Wouldn't it have to be a load designed to be connected phase to neutral? Otherwise you would be using the neutral as an ungrounded conductor; then 240.22 would apply?

  6. #156
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    Quote Originally Posted by Stopmoving View Post
    I have a question to ask. The type of load wasn't really specified. Wouldn't it have to be a load designed to be connected phase to neutral? Otherwise you would be using the neutral as an ungrounded conductor; then 240.22 would apply?
    208V 1ō equipment is designed to connect across a 208V source. Typically line-to-line connected, but phase to neutral on the system under discussion is also 208V. AFAIK, this class of equipment has never had a requirement that both conductors be ungrounded or that one not be grounded.

    240.22 would only apply if there was an OCP inline with the neutral conductor. For example, if the utilization equipment had a two-pole "one handle" breaker, you could still connect it, but if it had two handle-tied single-pole breakers you could not both connect and be compliant. Also, if the equipment has only one integral OCP, it cannot both be connected and compliant if the OCP is on the neutral side of the load(s).
    Last edited by Smart $; 02-07-10 at 04:55 PM.

  7. #157
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    Quote Originally Posted by mivey View Post
    Sounds like a legend to me as they will just charge for what you use. Like with any load, you should tell them your loading so they can size the transformer correctly.
    Depending on the type of metering the POCO is using, they may not be charging for this use. If I remember metering correctly from my POCO days, a 2 stator meter will not see the usage on the high leg. A 3 stator meter would have to be used and, since it is more expensive, they are not typically installed. Where I worked, we used all 2 stator meters and prohibited connection of load to the high leg.

  8. #158
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    Quote Originally Posted by egoy View Post
    Depending on the type of metering the POCO is using, they may not be charging for this use. If I remember metering correctly from my POCO days, a 2 stator meter will not see the usage on the high leg. A 3 stator meter would have to be used and, since it is more expensive, they are not typically installed. Where I worked, we used all 2 stator meters and prohibited connection of load to the high leg.
    I think you did not remember it quite right and must have prohibited the use because of other reasons (probably having to do with transformer sizing).

    When you meter a 3-phase 4-wire delta service, Blondel's Theorem does indeed state using three stators is the way to make an accurate measurement. As a refresher, Blondelís Theorem states that for correct measuring of N conductors, you can use N-1 measuring elements as long as the voltage coils have a common tie to the conductor without the current coil. In the 2-stator case, there is a compromise in accuracy that is similar to the compromise made with a single stator 1-phase meter (voltage unbalance in the 120 volt legs), but it has nothing to do with the high leg not being measured.

    The high leg has it's own stator and the power is correctly metered. The 120 volt legs are the ones that share a stator, like in a single-phase meter. The voltage is taken line-line and one of the currents is reversed through the meter to make the current fluxes additive with respect to each other. Since the voltage flux is doubled, the current coils are reduced by 1/2 to produce 1/2 the current flux and results in a proper reading for the lighting legs.
    BB+/BB=?

  9. #159
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    Smile

    Assuming that the source is a GROUNDED system 3 phase DELTA:

    In a "2 wire" circuit that is composed of one GROUNDED conductors, it is best (a code requirement no less) to install the circuit protection in the NON-GROUNDED conductor only.
    In this case A 208V. 2 wire circuit is composed on one GROUNDED conductor same as a 120V 2 wire circuit. The circuit breaker or fuse should be installed only in the NON-GROUNDED conductor or "high-leg".

  10. #160
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    Vin, welcome to the forum!

    Quote Originally Posted by vinform View Post
    The circuit breaker or fuse should be installed only in the NON-GROUNDED conductor or "high-leg".
    As long as the protection in the grounded conductor cannot open independently (i.e., by use of a 2p breaker), it is permitted.
    Code references based on 2005 NEC
    Larry B. Fine
    Master Electrician
    Electrical Contractor
    Richmond, VA

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