120VAC for two panels with one transformer
120VAC for two panels with one transformer
(OP)
I want to use a control panel enclosure with three compartments to house the main power in one, and two independent panels that get their power from the main compartment but have their own disconnect switch. They will power VFDs but also provide 120 VAC for other controls along the machines.The main panel would be Panel 1, the others Panel 2 and Panel 3.
I also want to use only one 3-phase, 480 to 208 transformer to provide the 120VAC to the two independent panels (Panel 2, Panel 3) This transformer would be connected to Panel 1.
When Panel 2 is switched on, Panel 2's 24VAC transformer will energize the coil in a 3-pole contactor (housed in Panel 1)) and power would be transferred to feed the three 120VAC lines for Panel 2 only. Panel 3 would have its own dedicated contactor, also in the Panel 1, that would energize only when panel 3 is on and provide three lines.
My question is: The secondary of the 480/208 transformer has one neutral. How do I handle this?. I think that if the neutral is shared by panels 2 and 3, even if one panel is off, the neutral will still be carrying current. Should I use a 4-pole contactor and run one neutral wire to each of the contactors? Is it better to use one 480/208 transformer for each panel? Please see attached drawing.
Thank you.
I also want to use only one 3-phase, 480 to 208 transformer to provide the 120VAC to the two independent panels (Panel 2, Panel 3) This transformer would be connected to Panel 1.
When Panel 2 is switched on, Panel 2's 24VAC transformer will energize the coil in a 3-pole contactor (housed in Panel 1)) and power would be transferred to feed the three 120VAC lines for Panel 2 only. Panel 3 would have its own dedicated contactor, also in the Panel 1, that would energize only when panel 3 is on and provide three lines.
My question is: The secondary of the 480/208 transformer has one neutral. How do I handle this?. I think that if the neutral is shared by panels 2 and 3, even if one panel is off, the neutral will still be carrying current. Should I use a 4-pole contactor and run one neutral wire to each of the contactors? Is it better to use one 480/208 transformer for each panel? Please see attached drawing.
Thank you.





RE: 120VAC for two panels with one transformer
RE: 120VAC for two panels with one transformer
RE: 120VAC for two panels with one transformer
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 120VAC for two panels with one transformer
Putting aside the obvious conundrum, I'm scratching my head trying to figure out a purpose for all this complexity. You don't want power to go to one panel unless it is going to the other? Are you trying to create an interlock, i.e. Motor A must not be running unless Motor B is available and vice versa? There are a lot simpler ways to accomplisgh that if true.
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RE: 120VAC for two panels with one transformer
Why not just put a 3-pole disconnect switch in panel 2 and panel 3 to turn-on the power to panel 2 and panel 3?
RE: 120VAC for two panels with one transformer
I don't see that any of that applies here. Use a solid (unswitched) neutral.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 120VAC for two panels with one transformer
So, here is how it works:
Panel 1 would be on all the time. It contains a 3-phase, 480 to 208 VAC, 30KVA transformer and other supervisory circuits. out of this transformer, 120VAC go to the inputs of two contactor, one for Panel 2, and one for Panel 3.
If I want one machine 2 to run, I turn on Panel 2. This feeds the motors for machine 2, but also, through a 24VAC control transformer, energizes the coil for Contactor for Panel 2.
When this coil is energized, 120VAC would transfer to the outlets
in machine 2.
If I want machine 3, same principle as above. Panel 3 also has a 24VAC transformer. I can have one machine or two running at the same time.
My concern at this point is that both machines outlets would have the same neutral, so if they want to service one machine, even though is off, there might still be current flowing from the other machine.
Again, I apologize for the confusion. I did not mean to waste everybody's time. You guys are a great source of knowledge and I appreciate your help.
Thank you.
Pls. see new drawing.
RE: 120VAC for two panels with one transformer
Thanks for your help.
RE: 120VAC for two panels with one transformer
If you are going to work on the lights in your house, you go find the breaker for those lights and turn it off, correct? That of course only opens the Hot side of the circuit right? Is not the neutral for those lights then also connected to the neutrals of every other circuit in the house? So by your thinking then, you have potential "current" flowing in the neutral wires in your light fixtures while you are working on the circuit that you have de-energized with the open breaker, is that right?
If you think you do, describe the path of current flow to someone who accidentally makes contact with that Neutral circuit.
"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies
RE: 120VAC for two panels with one transformer
RE: 120VAC for two panels with one transformer
It took me so long to post that I didn't see yours. I'm thinking the situation is analagous to a multi wire circuit in a house. I'd want both breakers open when I'm working. I'm no expert, so forgive me if I've got it wrong.
John
RE: 120VAC for two panels with one transformer
that if you share a neutral, and you switch off one of the circuits, all circuits using that neutral should be switched off. I don't remember if this is for residential or control panel wiring.
RE: 120VAC for two panels with one transformer
This should not be an issue with separate panels. Don't work on the panel feeds unless both feed breakers are open.
Bill
--------------------
"Why not the best?"
Jimmy Carter