Questions regarding AC shutoff

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Old 06-27-13, 02:12 PM
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Questions regarding AC shutoff

I'm about to install an AC shutoff box for a new AC condenser that will be installed shortly, and just want a sanity check on a few items.

The shutoff box will be mounted on a brick wall (about a foot thick), well above grade and flood levels.

I was planning on drilling through the masonry and mounting the box directly over the hole, so my conduit run will be entering the box from behind.

My first question, can I run EMT to the shutoff box in this case, since very little (essentially none) of the emt will be 'exposed' outside, or do I have to run a segment of rigid for the piece that runs through the wall and terminates in the box? Remember, I am going straight into the back of the switch box flush with the wall. Do I need a waterproof box connector?

I don't mind the extra expense of the rigid conduit, and the additional rigid->emt transition connector, but the biggest masonry bit I have is 1" thick, making the install of 3/4 rigid (1.05" OD) a little more difficult, or will require a new expensive bit. If EMT is ok, I'd like to stick with it.

Next, I have a 40 amp breaker in my load center and am running #8 wire (I guess in retrospect I could have gone with #10). I have a green, black, red, and white for the ground, two hots, and neutral. Total run will be about 35'. Do I need to pull all four wires, or are two hots and a ground sufficient for an outside AC condenser? Should I just pull the neutral since I have it anyway? This house is conduit throughout, if that matters.
 
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Old 06-27-13, 04:55 PM
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Yes it's a 3 course brick exterior wall approx 1 foot thick. I can drill through it where I want, exactly where the shutoff switch will be, so the conduit will go directly into the back of the shutoff box through one the provided knockouts. The issue is not about drilling the whole in another location. Anywhere I drill it will have to go through the same thickness of brick.

My question is can I use emt for the section that goes through the wall and into the shutoff box, or do I need to use rigid conduit? It's not exactly 'exposed' but it's not exactly 'internal'. Also, I'm not sure if connections to the shutoff require a watertight box connector.

The point about the size if my drill bit is about diameter, not length. Rigid has a larger outside diameter, so if I need to use rigid vs emt I will need a larger diameter bit.
 
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Old 06-27-13, 05:16 PM
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EMT is fine for that application. It wouldn't hurt to put some silicone around the connector before installing the disconnect in case any water runs down the back.
 
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Old 06-27-13, 05:31 PM
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Probably the dumbest question ever, but do I need a separate ground inside the conduit run or can I use the conduit and box as ground given that I have a continuous metallic raceway all the way to the service head? Also, if I need a separate ground do I need a #8 size?
 
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Old 06-27-13, 06:11 PM
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The metal conduit if continuous can be your grouding means.

For up to a 60 amp circuit you can use #10 for the ground also.
 
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Old 06-28-13, 11:10 AM
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You don't have to have it but I always pull a ground in pipe. Particularly EMT with set-screw couplings and connectors. Only exception I make is threaded rigid or IMC.
 
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Old 06-28-13, 12:33 PM
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The Neutral Conductor may not be needed: most AC compressor sections are wired for 220 volts. Check the nameplate to determine the specified voltage.
 
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Old 06-28-13, 05:20 PM
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Of course, you don't have 220 volts available. you have 120V and 240V.

Check the name plate information. Two hots and ground may be all you need. BTW, the conduit can only serve as ground if it's continuous. All the way to the unit. Or do you have an idea for bonding between the disconnect and the unit?
 
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