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Old 11-07-2012, 12:26 AM   #1
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Is voltage rating of 4-pole disconnect switch per pole?


I have a tankless electric water heater running on two 30-amp 240 volt circuits. I want to add a 4-pole disconnect switch near the heater but I can't figure out if I need a disconnect rated at 120V (because 120V is passing through each pole of the switch) or 480V (because 480V is the total passing through all four poles).

The biggest standard 4-pole disconnect I can find is only rated at 400 volts. Anything with a higher rating seems to only be available as a custom-build special order from various companies. If I need a 480V disconnect, does anyone have a good source?

I've read some sites suggest using two 2-pole disconnects but someone over here interprets a section of the national electric code that seems to imply that's not okay because the two 30-amp circuits aren't coming from separate sources.

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Old 11-07-2012, 04:26 AM   #2
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Is voltage rating of 4-pole disconnect switch per pole?


There is a 240 volt potential on your switch legs, that's the number to work with.


Last edited by zappa; 11-07-2012 at 04:30 AM.
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Old 11-07-2012, 05:22 AM   #3
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Is voltage rating of 4-pole disconnect switch per pole?


The voltage rating is the smallest maximum voltage sustainable between any two terminals (including the ground terminal) plus a safety margin.

Given two 240 volt branch circuits from the same panel feeding the heater, the maximum voltage between any two of the hot lines or between any one hot line and ground is 240.
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Old 11-07-2012, 06:22 AM   #4
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Is voltage rating of 4-pole disconnect switch per pole?


Quote:
Originally Posted by CDragon View Post

I've read some sites suggest using two 2-pole disconnects but someone over here interprets a section of the national electric code that seems to imply that's not okay because the two 30-amp circuits aren't coming from separate sources.
This is NOT true. Post #15 in that thread, along with others, is INCORRECT.
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Answers based on the 2008 & 2011 NEC.
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Old 11-07-2012, 01:14 PM   #5
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Is voltage rating of 4-pole disconnect switch per pole?


Wow, thanks for the fast responses!

I may just go with two 2-pole disconnects, but I'd rather use a 4-pole for a little extra safety (no chance of one getting switched off with the other left on). Unfortunately I've only found one 4-pole that looks like it might work here. Does anyone know if that disconnect can be safely mounted on its own, or does it need an enclosure? It seems like I could leave some wire insulation going into the holes but there wouldn't be much distance between the end of each hole and bare wire so I don't know if that meets code. If not, could I just buy a metal box and mount it inside?

I guess another problem is I don't think there's a place for the ground wires to pass through the box. Although I would think the box would have to have a place for the ground to connect to ground the box... If there's a connection it isn't obvious. Maybe the rail it mounts on is meant to be grounded?
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Old 11-07-2012, 02:31 PM   #6
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Is voltage rating of 4-pole disconnect switch per pole?


That is a din rail mounted switch and it needs and enclosure.
Just go with the 2 2 pole disconnects.

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