1ph panel 240/120V on a 3ph 208Y/120V system?

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peterwire

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los angeles, california
There is a distribution transformer 45kVA, 3ph, 4w, 480-208Y/120V, feeding three separate disconnect switches (fused) 100AS 70AF. (Assumption:
disc SW 1: AB;
disc SW 2: BC;
disc SW: AC)

One of this disconnect switches is a spare and they want to feed an old office trailer with it. The trailer needs a brand new panelboard (loads on that trailer: A/C unit + lighting). I was going to order a 1 phase, 240/120V, 100A main, (1) 2-pole 60A CB and (10) 1-pole 20A CB. However, I just want to make sure I’m doing things right:

- Is my assumption that each disconnect switch is AB, BC and AC?

- Can I have a 1ph 240/120V panel even though the upstream transformer is a 3ph 208Y/120V? This question comes because I can’t understand how to go from a 208V (line-to-line), 3 ph panel to a 240V (line-to-line), 1 ph panel.
I would understand that with a single phase transformer you can get 120V or 240V on the secondary depending how you wire the terminals X1, X2, X3, X4, but I can’t get my head around how you get 240V when the transformer is a 3ph 208Y/120V. what am I missing?
The HVAC unit is 240V so i would need that voltage after all.
thank you!
 
peterwire said:
One of this disconnect switches is a spare and they want to feed an old office trailer with it. The trailer needs a brand new panelboard (loads on that trailer: A/C unit)

- Can I have a 1ph 240/120V panel even though the upstream transformer is a 3ph 208Y/120V?
The HVAC unit is 240V so i would need that voltage after all.
thank you!
Click to expand...

You are going to end up with 208/120V at the office trailer. Sounds like the only problem will be the AC unit.

The AC unit may work with 208V.
You could use a buck/boost trasformer to bump the 208v up to 240V.
If the AC unit's as old as the trailer spend the money on a new AC unit that is designed for 208V.
 
peterwire said:
There is a distribution transformer 45kVA, 3ph, 4w, 480-208Y/120V, feeding three separate disconnect switches (fused) 100AS 70AF. (Assumption:
disc SW 1: AB;
disc SW 2: BC;
disc SW: AC)

One of this disconnect switches is a spare and they want to feed an old office trailer with it. The trailer needs a brand new panelboard (loads on that trailer: A/C unit + lighting). I was going to order a 1 phase, 240/120V, 100A main, (1) 2-pole 60A CB and (10) 1-pole 20A CB. However, I just want to make sure I’m doing things right:

- Is my assumption that each disconnect switch is AB, BC and AC?

- Can I have a 1ph 240/120V panel even though the upstream transformer is a 3ph 208Y/120V? This question comes because I can’t understand how to go from a 208V (line-to-line), 3 ph panel to a 240V (line-to-line), 1 ph panel.
I would understand that with a single phase transformer you can get 120V or 240V on the secondary depending how you wire the terminals X1, X2, X3, X4, but I can’t get my head around how you get 240V when the transformer is a 3ph 208Y/120V. what am I missing?
The HVAC unit is 240V so i would need that voltage after all.
thank you!
Click to expand...





Sent from my iPhone using Tapatalk
 
peterwire said:
...
- Can I have a 1ph 240/120V panel even though the upstream transformer is a 3ph 208Y/120V? This question comes because I can’t understand how to go from a 208V (line-to-line), 3 ph panel to a 240V (line-to-line), 1 ph panel.
Click to expand...
120/208V 1Ø 3W system is rather common in multi-unit housing. AFAIK, no manufacturer makes a panelboard specifically for 120/208. 120/240 is all that they offer and it is acceptable to supply it with 120/208.

I would understand that with a single phase transformer you can get 120V or 240V on the secondary depending how you wire the terminals X1, X2, X3, X4, but I can’t get my head around how you get 240V when the transformer is a 3ph 208Y/120V. what am I missing?
Click to expand...
Nothing. You do not get 240V. You only get 208V line-to-line.
 
As Growler said, you get 120/208 single phase, and the panel you would use will indeed be a 120/240V rated panel. The only issue , as he mentioned, is whether the AC unit will work in 208V. It likely will, or you can use it until it fries then replace it with a 208V version
 
thank you for all your responses. It really clarified things up. It seems that the A/C unit will take 208 or 240V, so it will be ok in the end.
@ jaggedben: the disconnect switches are 2-poles.
Thanks again!!
 
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