Can there be two mechanical disconnects on a single industrial control panel

jim dungar

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Staff member
Location
Wisconsin
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Retired Electrical Engineer - Power Systems
Yes, there can be.
In the majority of installations, like this, you also need to include labels warning/alerting there are multiple sources in the panel and multiple disconnects may need to be operated.
 

Peakhunter

Member
Location
Massachusetts, USA
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Engineer
Yes, there can be.
In the majority of installations, like this, you also need to include labels warning/alerting there are multiple sources in the panel and multiple disconnects may need to be operated.
Thanks Jim! Is there a code or regulation regarding this that you know of. It seemed odd to me that there could be two mechanical disconnects on a single panel.
 

Jraef

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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
There is no regulatory limit to the number of disconnect handles on the outside, but there is a PRACTICAL limit, based on the fact that most humans having only two hands. Disconnect handles are interlocked with the door and require being over-traveled from the Off position in order to release the interlock. Then those have spring-return latches as well, so you have to HOLD the handle in the un-latch position. Holding two handles simultaneously seems like it shouldn't be an issue, but if you are holding a drop light, meter, tool etc., it beomes instantly obvious that this is maybe not a great plan.

The better way to do this is to simply put in another contact on the main disconnect that you run the separate control power through. There are also door-operated plunger switches that you can mount so that the door being closed makes the switch and as soon as the door is opened, the power through that switch is interrupted. Think about the type of switch used to turn off your dryer when you open the door.
 

paulengr

Senior Member
You could use cable operated disconnects...much easier.

Aside from the fact that IEC rotary disconnects suck because the stupid rods don’t line up with use and the handles are loose as a goose and are a violation of NFPA 79 which is unfortunately voluntary,

There are lots of pump and hydraulic skids out there with several handles in a row. Opening is a pain. First you unbolt/latch it. Then pull open. Then pull first handle past off until it disengages a little. Then the next handle and the next until you clear them all and the door finally opens.

The older GE version had the rotary handle floating where it just poked through a round door hole. Great as far as you just open the door.

Aside from the fact that there is no rod to wear out or goofy way you have to release the door, the good part of cable operators is:
1. Up is on, down is off. There is no guesswork with worn out faded plastic.
2. NFPA 79 compliant. As in item #1.
3. Mounts anywhere. A “disconnect flange” door is nice but in say a hydraulic skid locking the door is stupidly misdirected except on the main disconnect.
4. Locks can stay ON the disconnect without preventing access. No more tracking down the operator that is on another shift and locked out something you’re not even working on.
5. It’s the American way.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
Most rotary disconnect kits now offer an accessory kit which adds a handle on the inside that stays with the disconnect in order to satisfy NFPA-79 rules.
 
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