Daisy Chained Disconnect Switches

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georgeshall

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I'm working on a design for a wastewater treatment plant where I've daisy chained the 480V power feed to three disconnect switches (non-integral) for three motor operated valves from an MCC, so these three valves are all powered from one circuit.

A person reviewing the design said that I need to specify that the disconnect switches be UL listed for the "daisy chain" application, but he wasn't anymore specific than that. Does anyone know of a UL listing for this type of application?

Also, I was looking at catalog cuts (square d specifically) for disconnect/safety switches and didn't see any options for lugs that would accommodate this type of design. Can the contractor just wire an incoming feeder and an outgoing feeder to standard lugs on the line side of the disconnect switches?

Thanks in advance.
 
Let's just ask: George, how are the feeders tapped at the first two switches?


(When I first saw "daisy-chained", I thought you meant in series. I couldn't believe anyone had an issue with that. :rolleyes:)
 
LarryFine said:
Let's just ask: George, how are the feeders tapped at the first two switches?


(When I first saw "daisy-chained", I thought you meant in series. I couldn't believe anyone had an issue with that. :rolleyes:)
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Same here. Daisy chain is a reference to one after another, not one beside another. That would be a string.

Anyway, you didn't state the size but for MOVs, I can assume they are small. I don't know of any small safety switches which have lugs rated for more than one wire per terminal. Starting at 400A you can get lugs that accommodate multiple conductors, but that would have to be the mother of all MOVs to require a 400A disconnect!

But I agree with the comment about using splitter boxes. Nothing wrong with that idea, it's done all the time.
 
I am certain that the issue is this is an explosionproof area you could put a pullbox in and tap single conductors down but in an explosionproof area could get expensive quickly. Maybe an oversized conduit body would work??
 
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The MOV's are not in a hazardous location.
If the contractor can't get a disconnect switch with lugs that take two conductors per phase on the line side, then he can just use a junction box ahead of the disconnect. I've used junction boxes before for this application but I figured we could save the owner a little bit of money by eliminating them.
 
Pierre C Belarge said:
George
What size is the conductor/disconnects?

Why not take advantage of 312.8 and use the disconnecting means enclosure as your tap/splice location?
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The conductors are all #12AWG. The disconnects are 30A with 5A fuses.
The owner does not allow splices in the disconnect enclosure. I must use the line side lugs to accomplish this, or a junction box ahead of the disconnect.
 
georgeshall said:
The owner does not allow splices in the disconnect enclosure. I must use the line side lugs to accomplish this, or a junction box ahead of the disconnect.
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Go with the junction box. You would need to change the lugs on your switch, and I not aware of any UL Listed switch with ratings for multiple conductors in one lug.
 
georgeshall said:
The conductors are all #12AWG. The disconnects are 30A with 5A fuses.
The owner does not allow splices in the disconnect enclosure. I must use the line side lugs to accomplish this, or a junction box ahead of the disconnect.
Click to expand...


Because the conductor are relatively small, I would use a junction box and move on.
I thought we may have been discussing larger conductors.
 
I agree with the J-boxes. This also helps in the future if you need to change out one of the disconnects, the rest can stay up and running.
 
I will go with a ckt for each MOV. Its more money for the client but can't really go cheap with wastewater treatment.:)
 
georgeshall said:
The conductors are all #12AWG. The disconnects are 30A with 5A fuses.
The owner does not allow splices in the disconnect enclosure. I must use the line side lugs to accomplish this, or a junction box ahead of the disconnect.
Click to expand...

You are going to have to put a pull box in anyway. Put the splices there, or use a jbox as a pull box.
 
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