# Thread: Questions on 120v loads on a 120/208 3 phase panel with NO 3 phase loads? Panel size?

1. Originally Posted by infinity
Never mind
You can, but it is a single shot scenario for getting kVA here.

We know that 208 x 1.732 = 360 and 120 x 3 = 360, so 90 x 120 is the same as 30 x 208 x 1.732 or (360) works because we know the variables.

But later with any 208V loads it does not. Cannot just continue add amps.

It is a limited method that can easily lead to future errors, so I prefer not to even present to people just learning.

OP keeps getting confused and uses that number thinking he needs a 100A panel like his supply guy.

It is simply bad methodology to present it to noobs IMO.
Last edited by infinity; 01-05-18 at 06:54 PM. Reason: Removed confusion

2. Originally Posted by jumper
You can, but it is a single shot scenario for getting kVA here.

We know that 208 x 1.732 = 360 and 120 x 3 = 360, so 90 x 120 is the same as 30 x 208 x 1.732 or (360) works because we know the variables.

But later with any 208V loads it does not. Cannot just continue add amps.

It is a limited method that can easily lead to future errors, so I prefer not to even present to people just learning.

OP keeps getting confused and uses that number thinking he needs a 100A panel like his supply guy.

It is simply bad methodology to present it to noobs IMO.
After thinking about it I'll just leave it alone.

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One last thing to add: the 60A panel must be 3ph. If it were 1 phase, supplied by just 2 of 3 legs of a 208V 3ph system, the voltage would be 208V, but the amperage would be ~56A vs ~32A. And tho most know this as well, I'll write it out for the OP: because you have 1ph 120V loads, you will need a grounded (neutral) conductor to your panel in addition to three ungrounded (hot) phase conductors, and a grounding conductor as well if metal raceway isnt used.

4. Originally Posted by JFletcher
One last thing to add: the 60A panel must be 3ph. If it were 1 phase, supplied by just 2 of 3 legs of a 208V 3ph system, the voltage would be 208V, but the amperage would be ~56A vs ~32A. And tho most know this as well, I'll write it out for the OP: because you have 1ph 120V loads, you will need a grounded (neutral) conductor to your panel in addition to three ungrounded (hot) phase conductors, and a grounding conductor as well if metal raceway isnt used.

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JFletcher

You have brought this back to original post...was it not stated his UL listing will be violated if he changes to 3-phase.
Don't intend on swinging discussion at UL...but if unknown I say keep it 120/208v single phase and don't risk it.
We know this will be a load center just behind a sliding door. Not a fan, don't like placing an EC on the floor with his/her face in a panel.
You could probably use #10's and feed all cct's through same conduit the feeder was going in....NO panel needed.

Tell customers engineer 120/208V-1P (UL issue, can't be changed to 3 phase), load on panel, size of panel lugs and let him decide what to feed with.
You are building this in your shop....you know the CBer's need to be GFCI ? Yes ?

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Originally Posted by MyCleveland
JFletcher

You have brought this back to original post...was it not stated his UL listing will be violated if he changes to 3-phase.
Don't intend on swinging discussion at UL...but if unknown I say keep it 120/208v single phase and don't risk it.
We know this will be a load center just behind a sliding door. Not a fan, don't like placing an EC on the floor with his/her face in a panel.
You could probably use #10's and feed all cct's through same conduit the feeder was going in....NO panel needed.

Tell customers engineer 120/208V-1P (UL issue, can't be changed to 3 phase), load on panel, size of panel lugs and let him decide what to feed with.
You are building this in your shop....you know the CBer's need to be GFCI ? Yes ?
My understanding is he is not modifying a 1ph panel to be 3ph, but rather using an off-the-shelf 3ph panel vs the 1ph originally planned:

"My main question is in sizing the panel (biding the right panel), when converting to amps as per normal the total is 97.1 amps @ 120v this was originally a 125amp single phase panel that the engineer now wants to change to a 3 phase 60amp panel."

If for some reason he has to stick with the 125A panel originally planned, he can still use it, noting my math in previous posts. 125A 1ph panel either 208V or 240V is more than adequate, it's overkill.

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Originally Posted by JFletcher
My understanding is he is not modifying a 1ph panel to be 3ph, but rather using an off-the-shelf 3ph panel vs the 1ph originally planned:

"My main question is in sizing the panel (biding the right panel), when converting to amps as per normal the total is 97.1 amps @ 120v this was originally a 125amp single phase panel that the engineer now wants to change to a 3 phase 60amp panel."

If for some reason he has to stick with the 125A panel originally planned, he can still use it, noting my math in previous posts. 125A 1ph panel either 208V or 240V is more than adequate, it's overkill.
I see your concerns on correct sizing, but if changing entire design to 3P violates UL then discussion was not helpful.
Price of a 125mlo 1P vs 3P load center a real concern.

Something is telling me this is a build from a UL approved design and modification change direction should be coming from the internal factory engineer or designer, not from the guys building it on the plant floor.

8. As far as UL goes, rereading OP, it almost seems that the listing is just for the counter top, receptacles, and kitchen equipment as an assembled package.

The guy seems to be just trying to spec a minimum supply. Since it is all 120V, a variety of options are available. Not sure if type of supply would be part of listing other than it would have to be adequate.

120/240V
120/208V
208Y/120V

All three work if sized correctly.

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Originally Posted by jumper
As far as UL goes, rereading OP, it almost seems that the listing is just for the counter top, receptacles, and kitchen equipment as an assembled package.

The guy seems to be just trying to spec a minimum supply. Since it is all 120V, a variety of options are available. Not sure if type of supply would be part of listing other than it would have to be adequate.

120/240V
120/208V
208Y/120V

All three work if sized correctly.
Agree completely, but wouldn't a factory have a set of options already built-in with the factory designs. This is more a question for the folks who generate the Build Sheets...Yes ?

10. Originally Posted by MyCleveland
Agree completely, but wouldn't a factory have a set of options already built-in with the factory designs. This is more a question for the folks who generate the Build Sheets...Yes ?
Prolly.

I am waiting for OP to come back so we can explain that most if not all his loads are not continuous per the NEC.

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