Single phase appliance on a 3 phase panel?

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wondervamp

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It is my understanding that you can hook up a single phase, 208 / 230V appliance to a 3 phase panel? The appliance is a RTU/Hvac compressor/condensor for a mini-split (heating/cooling) unit.

I think it's correct if I'm going for 240V, to connect between A phase and B phase. And if I have a lot of 120/240V loads on the panel, it will help phase balance to make one of the phases the wild leg (orange) (i.e. don't just pile everything onto the low phases A and B).

The 3 phase panel is: 3 phase, 240V Delta, High leg C - MY CONFUSION comes from determining which lugs in the panel are considered A, B, and C.
 
Joethemechanic

Joethemechanic

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B should be the high leg. Don't use the high leg for any of your single phase loads. Slash rated single phase breakers like 120/240 are not rated for the high leg. In my place I have single phase sub panels for my single phase loads. I only use the high leg for 3 phase loads
 
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wondervamp

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Joethemechanic said:
B should be the high leg. Don't use the high leg for any of your single phase loads. Slash rated single phase breakers like 120/240 are not rated for the high leg. In my place I have single phase sub panels for my single phase loads. I only use the high leg for 3 phase loads
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The panel is marked as in my above thread as C leg being the high leg - posting a picture of the panel info below. So A & B phase will be black and red lugs and C would be high leg? I haven't opened up the dead front yet to look inside. Again, my confusion comes from determing which lugs are A B and C phase.

panel.jpg
 
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Strathead

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wondervamp said:
The panel is marked as in my above thread as C leg being the high leg - posting a picture of the panel info below. So A & B phase will be black and red lugs and C would be high leg? I haven't opened up the dead front yet to look inside. Again, my confusion comes from determing which lugs are A B and C phase.

View attachment 2566217
Click to expand...
This is a violation of NEC 408.3(E)(1) B shall be the high leg and orange shall be the color.
 
James L

James L

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Kansas Cty, Mo, USA
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wondervamp said:
I think it's correct if I'm going for 240V, to connect between A phase and B phase.
Click to expand...
Some of your confusion might be coming from bad terminology. It's an industry-wide error, though, so I'm not chiding you for it.

A, B, and C are not phases, those are legs.

A phase is the potential between two of those legs.

So a single phase is what happens between A and B, or between B and C, or between C and A

You can use any two of those hots to get 240 volts.
 
busman

busman

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Northern Virginia
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wondervamp said:
It is my understanding that you can hook up a single phase, 208 / 230V appliance to a 3 phase panel? The appliance is a RTU/Hvac compressor/condensor for a mini-split (heating/cooling) unit.

I think it's correct if I'm going for 240V, to connect between A phase and B phase. And if I have a lot of 120/240V loads on the panel, it will help phase balance to make one of the phases the wild leg (orange) (i.e. don't just pile everything onto the low phases A and B).

The 3 phase panel is: 3 phase, 240V Delta, High leg C - MY CONFUSION comes from determining which lugs in the panel are considered A, B, and C.
Click to expand...
For your purposes (just hooking this up and making it work), it does not matter, since you just want 240V. However, if you don't want to overload the phases supplying 120V or 208V, then it does matter.

Mark
 
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hillbilly1

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North Georgia mountains
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Strathead said:
power companies use C for the high leg. We have to swap and C between the POCO and the service disconnect. At least here in Florida.
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It is for the meter to work correctly. By code, it then moves to “B” phase so that the center buss is always the high leg when viewed from the front or back, if you have a gear with removable rear covers. A lot of installations the electrician did not know to do that, so always be cautious.
 
Joethemechanic

Joethemechanic

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Hazleton Pa
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wondervamp said:
It is my understanding that you can hook up a single phase, 208 / 230V appliance to a 3 phase panel? The appliance is a RTU/Hvac compressor/condensor for a mini-split (heating/cooling) unit.

I think it's correct if I'm going for 240V, to connect between A phase and B phase. And if I have a lot of 120/240V loads on the panel, it will help phase balance to make one of the phases the wild leg (orange) (i.e. don't just pile everything onto the low phases A and B).

The 3 phase panel is: 3 phase, 240V Delta, High leg C - MY CONFUSION comes from determining which lugs in the panel are considered A, B, and C.
Click to expand...
Basically you have one of these

hlo.jpg

Never trust the colors or labeling. I don't even look at it. Cover comes off and first thing I do is check voltage. I think I see more unmarked or incorrectly marked than I see right

Z_-utzfo5oz.jpg

If you put one of these in and either side lands on the high leg, You will violate the breaker's voltage rating. Also it will damage equipment downstream that uses a neutral
 
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tom baker

tom baker

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Bremerton, Washington
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wondervamp said:
The panel is marked as in my above thread as C leg being the high leg - posting a picture of the panel info below. So A & B phase will be black and red lugs and C would be high leg? I haven't opened up the dead front yet to look inside. Again, my confusion comes from determing which lugs are A B and C phase.

View attachment 2566217
Click to expand...
Nice it was labeled!
 
Joethemechanic

Joethemechanic

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Location
Hazleton Pa
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Electro-Mechanical Technician. Industrial machinery
Here is a better diagram. If you hook a single phase load up using the high leg, Your breaker and all your appliances will be seeing this

hlo incor.jpg
 
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jim dungar

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Wisconsin
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sgtsparky said:
Same here in Oregon, power co likes high leg on C don’t remember why but then we have to move it to B , power co is not regulated by the NEC but premise wiring is.
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You will find the utilities, all across the country, use the C placement for their electromechanical meters.
 
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wondervamp

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SF Bay Area
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Shop technician
Thanks guys - I'm going to meter it out tomorrow. I'm also going to stay away from the "stinger" leg. The appliance I'm hooking up only requires two hots and a ground but I need a Square D double pole 40A breaker and it seems that a breaker without the slash 120/240 rating will be a little harder to source out.

And with regard to the power co. requiring the "high leg" being on the C phase, I'm a bit confused as to where? Are they requiring it out at the meter and/or in the service panel where I'm terminating my branch circuits? I'm pretty sure the reasoning why that picture I posted of the panel reads "high leg" on C was due to the power company dictating that like you guys mentioned. I'm curious to see what I find out in the morning.
 
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