Disconnect switch wiring

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Old 08-16-13, 06:26 PM
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Disconnect switch wiring

Hello,

I need to wire a disconnect switch to disconnect 2 circuits. Both of them are 120VAC. The FLA for one circuit is about 18A (12A typical), and the FLA for the other circuit is about 13A (7A typical). I have a 32A/600VAC rated 3P disconnect switch available. Do you think I can wire just the Line of each circuit to the disconnect? Ideally I'd like to disconnect the Line and Neutral of each circuit, but only have 3 terminals to work with. I could wire the Line and Neutral of the higher amperage circuit and just the Line of the lower amperage circuit. Any suggestions? Thanks.
 
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Old 08-16-13, 06:48 PM
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Please supply more details. Disconnect switches, where required, are almost always single circuit switches. Tell us what these two circuits are for and maybe someone can help you. I suspect that what you will need to do is install two separate switches.
 
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Old 08-16-13, 08:03 PM
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A single pole switch might be all you need.

Why do you want to disconnect the neutral?
 
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Old 08-19-13, 04:20 PM
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Hello, thanks for your replies, and sorry for my delay.

One of the power lines is dedicated to a pump drive that requires 120VAC, 12.5A (18.8A max). The other power line is used for a couple AC-DC power supplies that supply DC-powered actuated valves that typically use 1A, but I am sizing for their stall current of 3A, and a few sensors that require a few mA.

I wanted to disconnect the line and neutral wires because I had read for AC circuits especially this may be necessary, as in AC electricity may change direction whereas in DC it is one direction always. I figured switching off the live wire would break the circuit, but I just want to make sure I cross all my t's and dot the i's.

I panel-mounted the 3-pole disconnect switch and space is limited so I'd prefer not to mount another disconnect switch. The supplier I got it from (McMaster-Carr) didn't offer any 4-pole disconnect switches, most of them were 3P.

Thanks.
 
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Old 08-19-13, 04:36 PM
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I wanted to disconnect the line and neutral wires because I had read for AC circuits especially this may be necessary, as in AC electricity may change direction whereas in DC it is one direction always.
Who ever wrote that was confused at least. Actually it changes direction sixty times per second but in a properly wired circuit neutral is always ~0 volts to ground. In fact code prohibits switching the neutral in most cases. All you need is one heavy duty motor rated switch single pole that slightly exceeds the horsepower of your pump (will look like a regular light switch but light switches aren't usually motor rated) and a commercial grade 15a single pole (light) switch.
 
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Old 08-19-13, 04:57 PM
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I wanted to disconnect the line and neutral wires because I had read for AC circuits especially this may be necessary, as in AC electricity may change direction whereas in DC it is one direction always.
The electricity "changes direction" (oscillates) 60 times per second in an alternating current system in the US. That's what alternating current and 60 hertz mean.

I figured switching off the live wire would break the circuit
That's correct, there is no potential on the grounded conductor - the neutral - unless the circuit is closed.

The grounded conductor should only be connected to switch control in certain very rare circumstances. None of those is present here. Do not switch the neutral.
 
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