main disconnect, industrial machine

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Rob E

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My question is on having two disconnects for a industrial machine. One disconnect will be for auxiliary outlets (200amp) and the other disconnect will be for rest of the machine (800amp - motors, heaters, etc.). The disconnects will be side by side in the cabinet.
Can I supply the two disconnects with one feed where the 200amp disc. can remain energized with the 800amp disc. off and vise versa? In other words jumper the line side of the two disconnects.
In the past we normally have a separate feed for each disconnect. Maybe this is a NFPA issue?
Thanks
Rob
 
Re: main disconnect, industrial machine

Yes you can feed as many disconnects as you want from one feeder.

The only issues I see are how do you intend to do that.

Either order the disconnects with lugs that are cable of two conductors each or you can hit a JB between the two disconnects and tap each way from the feeder to each switch.
 
Re: main disconnect, industrial machine

Consider using the tap rules in Art. 240.21(B) for your installation. We used a similar installation recently and it worked well. A wireway (Art. 376) was used for the taps above the two disconnects.
 
Re: main disconnect, industrial machine

Rob, it is normal to have the line side of a disconnect hot when the disconnect is open. Otherwise, why have the disconnect?

"Why have a door?" - Gary Seinfeld
 
Re: main disconnect, industrial machine

Gary, sorry I did not respond sooner.
I can only answer from my experience as a OEM,
we wire industrial control cabinets on our injection molding machines. Per the NFPA we are
required to have a supply disconnecting means.
It is up to the plant personnel when they work on
a machine if the power is turned off at the machine disconnect or main bus feeding the machine. Perferably have both disconnects off and locked out. Yes, it is normal to have power on the line side when the disconnect is off. This will be the only "live" wiring in the cabinet (with the exception of other power sources, yellow wire). Protective covers are over the live terminals.
I am not sure what you mean by "why have a door".
Most of our cabinets are 6 to 8 doors. The main disconnect handle interlocks the first door. The door can be opened with the disconnect "on" using a tool (screwdriver). Obviously the doors are used for easy access to the cabinet.
Regards
Rob
 
Re: main disconnect, industrial machine

I'm wondering what kind of disconnect opens the line side when the disconnect is opened. Isn't that the point of the disconnect; to open the load side?

Would it be a violation to wire a disconnect backwards so the load is connected to the line side terminals and the line is connected to the load side terminals?

Bob

Rob,

I would imagine that you would want to be very diligent about labeling these disconnects since opening one still leaves live power in the enclosure. Seems like a risky practice.

[ September 23, 2005, 03:40 PM: Message edited by: bthielen ]
 
Re: main disconnect, industrial machine

Originally posted by bthielen:
I'm wondering what kind of disconnect opens the line side when the disconnect is opened. Isn't that the point of the disconnect; to open the load side?

Would it be a violation to wire a disconnect backwards so the load is connected to the line side terminals and the line is connected to the load side terminals?

Bob

Rob,

I would imagine that you would want to be very diligent about labeling these disconnects since opening one still leaves live power in the enclosure. Seems like a risky practice.
Click to expand...
Yes; yes; and yes, you would, which is why there's another disconnect upstream.
 
Re: main disconnect, industrial machine

A little twist to my original design.
The wires coming from the 100amp service to the industrial control cabinet will be 350mcm x4 for each phase. Instead of having a junction box or one main connection point in the cabinet can I simply connect 350mcm x3 wires to the 800amp disc. & 350mcm x1 to the 200amp disconnect?
Rob
 
Re: main disconnect, industrial machine

Do you mean 1000A feeder to the cabinet instead of 100A service to the cabinet?

What you are now proposing would be subject to many NEC rules, not the least of which could be rules for conductors in parallel.
Bottom line - it depends.
 
Re: main disconnect, industrial machine

Sorry, should be 1000amps. I think this would be defined as 1000amp service. The 4 x 350mcm (total 12) wires come directly from a 1000amp circuit breaker (inside plant). The only load connections are the 200amp & 800amp disconnect on the industrial machine. I assume this case would fall under code section 240.21?
Rob
 
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