Disconnecting Control Enclosures With Multiple Power Sources

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eurekah

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Hello, I'm currently designing a control enclosure and have come across an issue that I'm unsure exactly what would be the best way to handle. The control enclosure will be powered from a 480V 3Ph feeder. Typically I used 120V control transformers inside the enclosure, but with this design we decided to supply a 120V ~30A single phase line externally to the enclosure.

I'm planning on having an externally operated handle for the 480V supply as usual, but what should I do for the 120V supply disconnect? Ideally I would like to have a system where the single handle will disconnect both the 480V and 120V supply just to be sure that nothing is left live by accident. I know typical contactors can't be used as a disconnecting means, but does someone make devices like 'certified disconnect relays' so that if the 480V supply gets disconnected it would disengage a relay that would remove power from the 120V circuit?

Thanks for the help!
 
So there are auxiliary contacts that you can add to the main disconnect which will operate with the handle position and are typically used for this purpose. The problem is, 30A is way too big for those, 10A is common, 15A maybe. But a 30A 120V circuit is too big for most control circuits anyway, because most control devices will have to be fused at 10-15A even if you do have a 30A circuit feeding it. So what is it you are trying to operate with that 30A 120V circuit anyway? I would have just done it with a CPT but it would have to be a 5kVA to get that much at 120V. Can it be broken up into 3 separate 10A circuits? Because there are some disconnects that will allow you to stack up 3 separate 10A aux contacts.

You may have to go with a separate rotary through-door disconnect switch for the control power if you really have to have 30A on one circuit.
 
There are at least some disconnect switches available with 4 power poles. Not real common though. Never seen a flange mounted one that way though.

I know Mersen makes a thru the door disconnect switch with a 4th power pole as I saw it in their catalog. Never used one though.
 
Jraef said:
So there are auxiliary contacts that you can add to the main disconnect which will operate with the handle position and are typically used for this purpose. The problem is, 30A is way too big for those, 10A is common, 15A maybe. But a 30A 120V circuit is too big for most control circuits anyway, because most control devices will have to be fused at 10-15A even if you do have a 30A circuit feeding it. So what is it you are trying to operate with that 30A 120V circuit anyway? I would have just done it with a CPT but it would have to be a 5kVA to get that much at 120V. Can it be broken up into 3 separate 10A circuits? Because there are some disconnects that will allow you to stack up 3 separate 10A aux contacts.

You may have to go with a separate rotary through-door disconnect switch for the control power if you really have to have 30A on one circuit.
Click to expand...

The need for the extra 120V current is due to a 20A outlet that will need to be controlled from within the enclosure. This enclosure must be able to turn the outlet on/off which is why it isn't wired directly into the facilities 120V distribution panel. When the 120V power enters the enclosure it will be split into 2 circuits, one with a 20A CB for the external outlet and one with ~10A fuse for control power.

I think I'm just going to get a side mounted 120V disconnect. Also, I was considering just having the 120V wired directly into the enclosures fuses without a disconnect because the enclosure will be mounted ~3 meters away from the room that has the 120V panel board.
 
petersonra said:
There are at least some disconnect switches available with 4 power poles. Not real common though. Never seen a flange mounted one that way though.

I know Mersen makes a thru the door disconnect switch with a 4th power pole as I saw it in their catalog. Never used one though.
Click to expand...

I was also looking at this. Is there any reason why I would be unable to use the 4th pole for the hot 120V line disconnect?
 
eurekah said:
I was also looking at this. Is there any reason why I would be unable to use the 4th pole for the hot 120V line disconnect?
Click to expand...

good question.

I can't think of any off hand but the manufacturer would be the person to ask if you want a correct answer. I just don't know.
 
Siemens sells 6-pole disconnect switches. They're normally used for two-winding, two-speed motors, but they sound like exactly what you're looking for. You'd have to size the switch to handle the highest load - either the 480v or the 120v feeder, so the other set of contacts would probably be oversized but it satisfies your desire for a single handle solution.

http://w3.usa.siemens.com/powerdist...switches/4-and-6-pole/pages/4-and-6-pole.aspx

Use two electric interlocks to hold the door shut until power is shut off. One for the 120v feeder and another for the 480v feeder. As the interlocks' coils are 120v, you'll need a small 480v-120v transformer for stepping down.

http://www.automationdirect.com/adc...lectrical_Interlocks_-a-_Defeaters/WAEK115NDH



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