3-pole disconnect switch on a 2-pole circuit

[Shujinko]

I see this done all the time. Using a 3-pole maintenance disconnect switch for a piece of equipment that is fed by a 2-pole circuit. One of the wire lugs is just not landed on. Is there anything in the NEC that would not allow this?

 

[Jraef]

No. It only hurts your pocketbook.

 

[Leespark57]

I seem to remember seeing in the instructions for a 3 pole disconnect switch that when doing this you must use the 2 outer poles of the switch. Might have been specific to that manufacturer.

 

[GoldDigger]

I seem to remember seeing in the instructions for a 3 pole disconnect switch that when doing this you must use the 2 outer poles of the switch. Might have been specific to that manufacturer.

Another potential reason to use specific pole combinations is when putting two contacts in series to obtain a higher interrupting or withstand voltage value for the switch. Particularly when trying to increase DC interrupting voltage.

 

[augie47]

Supplier told me that on some fusible and non-fusible safety switches the demand is so low for the 2 pole style the manufacturer just supplies 3 pole when a 2 pole is requested and 2 pole versions are not available.

 

[petersonra]

Supplier told me that on some fusible and non-fusible safety switches the demand is so low for the 2 pole style the manufacturer just supplies 3 pole when a 2 pole is requested and 2 pole versions are not available.

kind of like 2 pole MCCB. It is usually less expensive to just buy a 3 pole breaker and usually a lot faster too.

 

[kwired]

kind of like 2 pole MCCB. It is usually less expensive to just buy a 3 pole breaker and usually a lot faster too.

For anything other then 225 amp and less @ 240 volts I can agree. There are a lot of 2 pole 240 volt breakers out there of smaller frame sizes.

 

[jaggedben]

I seem to remember seeing in the instructions for a 3 pole disconnect switch that when doing this you must use the 2 outer poles of the switch. Might have been specific to that manufacturer.

It was probably specific to the voltage and current type as well. For example I'm pretty sure that Square D Heavy Duty switches can be used as 3 pole switches for 600VAC but only 2-pole at 600VDC, and the outer poles requirement that you mention applies to the latter. If you used it as a 2-pole for AC it wouldn't matter which poles you used.

 

[brantmacga]

Supplier told me that on some fusible and non-fusible safety switches the demand is so low for the 2 pole style the manufacturer just supplies 3 pole when a 2 pole is requested and 2 pole versions are not available.

I ordered some 2-pole Eaton disconnects once that came labeled as 2-pole, but were actually 3-pole with a jumper wire from line-2 to load-3.


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[jaggedben]

I ordered some 2-pole Eaton disconnects once that came labeled as 2-pole, but were actually 3-pole with a jumper wire from line-2 to load-3.

You sure it wasn't sold as single pole?

What they can do is take a 3 pole disconnect thats designed for 300V and by factory wiring it that way create a single pole 600V disconnect, because with the two poles in series they can each handle half the voltage.