What is a "Red Leg" panel?

[tonype]

Stupid engineer question - what is a "red leg" panel?

Tony Shupenko, PE

 

[Dennis Alwon]

Stupid engineer question - what is a "red leg" panel?

Tony Shupenko, PE

My guess is a high leg check this out
http://www.pwrm.com/library/technical_documentation/technical_notes/Red_Leg_Delta.pdf

 

[tonype]

What is the benefit?

 

[infinity]

What is the benefit?

One benefit is that if you have a large number of 3 phase loads they can operate at 240 volts vs. 208 volts which will use less current and may allow you to install a smaller service, and smaller feeders etc. This system is only really beneficial when the 120 volt loads are very small vs. the 3 phase loads.

 

[tonype]

One benefit is that if you have a large number of 3 phase loads they can operate at 240 volts vs. 208 volts which will use less current and may allow you to install a smaller service, and smaller feeders etc. This system is only really beneficial when the 120 volt loads are very small vs. the 3 phase loads.

Trevor:

Makes sense to the panel that was present in an industrial building I was looking at yesterday. The only question is how it was labeled (the markings on the panel were "3-Phase Red Leg, 208-v to ground") - the panel contained (3) 20-amp, (1) 60-amp and (1) 100-amp 3-phase breakers, but also contained (2) 20-amp, 120-volt breakers.

Regards,
Tony

 

[iwire]

What is the benefit?

If I recall correctly it is a large benefit to the power company as they can supply this type of service with two single phase transformers in place of three.

 

[iwire]

Here is a diagram of a 3 phase 4 wire open delta connection

 

[tonype]

Thanks for the explanation - much appreciated

 

[brian john]

Tony: The old adage always applies the only stupid question is the one not asked. How else are we suppose to learn!

 

[JohnJ0906]

Here is a diagram of a 3 phase 4 wire open delta connection

408.3(E) Shouldn't the "high leg" be "B" phase? Or is this a local thing?

 

[kbsparky]

Not all high-leg services are open delta.

We have many 3-phase services around here with 3 transformers on the pole feeding a high leg service --> "Closed delta"

Same nominal voltages: 240 Volt delta 3 phase, 120/240 single phase, and the 208 volts to ground high leg. Although we are supposed to mark it orange, instead of red.

 

[Smart $]

408.3(E) Shouldn't the "high leg" be "B" phase? Or is this a local thing?

I have always connected consumer transformers and panels that way, but the diagrams from Cooper Power Systems' Distribution Transformers documentation (below) and American Electricians' Handbook both depict the "high leg" as being "a".

Delta-Delta for Light and Power​

Open Delta for Light and Power​

 

[LarryFine]

We also always make the high-leg B phase, although the POCO meter diagrams show it as C.

 

[russ]

In my area the High leg is the C phase at the utility meter. It's rotated to be the center phase at the main.

 

[Minuteman]

In my area the High leg is the C phase at the utility meter. It's rotated to be the center phase at the main.

Here too. Except the panel I was in last week. It was marked A (blue) B (yellow) C (red) with C as the high leg. Building owner could not figure out why the new lights that he installed kept frying ballast. Yep, he put them on the high leg!

 

[dnem]

Why is this called "red leg" when the only color mentioned in the code is orange [110.15] ?
I know it says "or by other effective means" but I wouldn't understand what this means just by looking at the example below

Here too. Except the panel I was in last week. It was marked A (blue) B (yellow) C (red)

So if you come in cold without any explanation, which of the 3 is the high leg ?

Here too. Except the panel I was in last week. It was marked A (blue) B (yellow) C (red) with C as the high leg. Building owner could not figure out why the new lights that he installed kept frying ballast. Yep, he put them on the high leg!

What if noone had been there to tell you that the high leg was C ?
How is it "effective" if it's not obvious without needing insider information ?
As an inspector I would not consider that installation "effective" so the addition of orange would be needed.

David

 

[dnem]

I have always connected consumer transformers and panels that way, but the diagrams from Cooper Power Systems' Distribution Transformers documentation (below) and American Electricians' Handbook both depict the "high leg" as being "a".

We also always make the high-leg B phase, although the POCO meter diagrams show it as C.

In my area the High leg is the C phase at the utility meter. It's rotated to be the center phase at the main.

So now we have examples of every phase being used for the high leg A, B, + C. . If you need to change the rotation of a 3? motor you change 2 leads. . Industry standard is switching A +C but that?s not code required either. . If you switch A + C you still have your same color code order except that its flipped.

I think it would be less confusing for everyone if high legs were always B and flipped motor leads were always A + C.

David

 

[roger]

What if noone had been there to tell you that the high leg was C ?

His tester or meter

How is it "effective" if it's not obvious without needing insider information ?
As an inspector I would not consider that installation "effective" so the addition of orange would be needed.

David

This might be fine for a small building, but a large facility that has a color or marking already established ( I have been in mills and factories that have used Blue, Red, and even Purple) should not have another color introduced (added) into the system.

Roger

 

[Pierre C Belarge]

Utility companies use the NESC as their code, and electricians use the NEC.

The NESC mandates that the "C" leg is the "high" leg.

The NEC mandates the the "B" leg is the "high" leg.


In our work, all you need to do is transpose the "C" leg to the "B" leg in the service enclosure, with the proper colors.

I believe there is a group who is trying to coordinate which leg should be used for the high leg... I do not believe it is much of an issue as long as the electricians are properly trained.

 

[don_resqcapt19]

Pierre,

The NESC mandates that the "C" leg is the "high" leg.

Are you sure about that? I believe that the high leg is only landed in the meter can on the C phase position so that the older type meters will read correctly. It is my understand that even though this conductor is landed in the right terminal, it is still electriclly B phase, not C phase.
Don