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Old 01-27-2013, 09:13 PM   #1
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120/208panel


Will the I'd tag show if delta or wye

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Old 01-27-2013, 10:14 PM   #2
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No it won't. The only way to know for sure is to take voltage readings.

One dead giveaway though is if one of the phases has no single pole breakers on it. Then it's most likely a delta.

Another way is to measure voltage on a known device that uses two phases. If it's close to 208, it's a wye. If it's more like 240, it's a delta.

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Old 01-27-2013, 10:21 PM   #3
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Not unless someone put the label on it.

Measure the voltage between hot and neutral, or between two hots, as needed if you are encountering this panel for the first time.

A 120/208 volt 3 phase system will have 120 volts from any hot leg to neutral (and 208 volts between any two hots).

A wye 3 phase system has hot to neutral voltage the same for all three phases.
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Old 01-28-2013, 12:08 AM   #4
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If it's 120/208, then it's a wye system by definition. If there's no neutral present then it can only be used for delta-connected loads - but it's still a wye system. The square root of three (1.73) ratio of voltages indicates that the grounded conductor is at the "midpoint" of the three hot legs on a phase diagram, which is achieved by connecting the transformer secondaries in a wye configuration.
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Old 01-28-2013, 07:03 AM   #5
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Not always. Ever hear of a stinger?

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Old 01-28-2013, 07:04 AM   #6
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Quote:
Originally Posted by mpoulton View Post
If it's 120/208, then it's a wye system by definition. If there's no neutral present then it can only be used for delta-connected loads - but it's still a wye system. The square root of three (1.73) ratio of voltages indicates that the grounded conductor is at the "midpoint" of the three hot legs on a phase diagram, which is achieved by connecting the transformer secondaries in a wye configuration.
Not always.

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Old 01-28-2013, 08:33 AM   #7
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I personally have never seen a 120/208 as anything but a wye.

Of course i have only seen 1 delta before also.
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Old 01-28-2013, 08:36 AM   #8
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Not always. Ever hear of a stinger?

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Stinger or Hot leg IS evidence of the 120/240 Delta winding. two legs of 120 and a third leg or 208, or 240 across any two legs.
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Old 01-28-2013, 09:46 AM   #9
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There is no raison d'etre for (and no socially redeeming value of, and no easy way of producing) a 120/208 volt system that is not from a symmetric wye configuration.

The reason 208 volts became accepted as a standard is because it is the natural result of configuring a return conductor to have 120 volts potential from each of the 3 legs of a 3 phase system. It combines the advantages of 3 phases with the advantages of 240 volts over 120 volts (fewer or thinner conductors needed), although some appliances come in slightly different versions for 208 versus 240 volts.

Also the high leg, or stinger, is the natural result of configuring a return conductor having 120 volts potential from each of two legs of a 240 volt 3 phase system so as to provide a 120/240 volt feed (or subfeed).
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Old 01-28-2013, 10:48 AM   #10
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Quote:
Originally Posted by busman View Post
Not always.

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What's an example of "not always"? To produce a 208V delta without wye-connected secondaries would require transformers with 208V secondaries - and that's very odd. To produce a 208V delta with 120V from each hot to ground and not use a wye configuration would be... darn near impossible. I can't think of an easy way to do it.

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