New connection for central AC

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  #1  
Old 09-16-11, 10:29 PM
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New connection for central AC

I will be adding Central AC to my home and all the estimates exclude the cost of what they call HV (High Voltage) wiring. I have always done all my own electrical work and I have not problem with it but I do have a few questions.

I have a wall mounted GE main panel. That is mounted in the plaster wall. It has plenty of space but there is no access to the outside of the panel. I can open a knockout and fish a wire down but I have no way to put a clamp in. Is there a special type of acceptable clamp for this type of situation? Having only access to the inside.

The circuit will be either 2-10/wg or 2-8/wg and either a 30A or 40A DP breaker as per the furnace installers specs. There will be a 60A disconnect mounted outside where the compressor is to be installed. I will use raintight flexible conduit from the disconnect to the compressor.

I will also be running a 2-12/wg for an outside GFCI receptacle within reach of the compressor.

Does code require a ground rod at the compressor site? Is there anything else I need to know about this install?
 
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Old 09-17-11, 04:42 AM
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As for the "clamp" if you can fish the cable through the appropriately sized hole, then, likewise an appropriately sized snap in cable "keeper" will be fine. Their main purpose is not to be so much a strain relief, but to keep the cable from chafing on the sharp edges of the hole in the box. Sample below. Again, check for the correct size for the cabling you are using.
No grounding rod, unless some local building code requirement calls for it.

OK, bad focus, but the original pix was as small as a pin head.
 
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Old 09-17-11, 06:30 AM
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If you strip the outer sheathing from the NM cable before you fish to the panel, a typical romex connector can be installed on the cable. All you would have to do is install the locknut after the cable is fished and seated in the knockout. You will need to use separate conductors, such as THHN/THWN, in liquidtight flexible conduit between the disconnect and the condsensing unit, do not use NM cable. In some areas you are also allowed to run your thermsotat cable inside the liquidtight to the unit too, but other areas require the thermostat wiring in the liquidtight to be #16 THHN/THWN.
 
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Old 09-17-11, 08:28 AM
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Thanks for the tips on the wire entry. I am sure one or the other will work fine.

Is there a minimum or recommended height for mounting the outside disconnect? I will be coming out of a crawl space so the maximum height if I come directly into the back of the box owuld be about 1 1/2 to 2 feet above ground. Otherwise I would need to come out and do a 90 with conduit up to the bottom of the box. If I need to do this it would be a short run of hard conduit. I assume I can run the romex thru it to the box?
 
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Old 09-17-11, 08:32 AM
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There is no minimum height. I would try to come directly into the back of the disconnect with the cable. Be sure to seal the opening with caulk or duct seal to prevent water leaking into the house.
 
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Old 09-17-11, 09:34 AM
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I assume I can run the romex thru it to the box?
Not if the conduit is outside. While it would be OK to come straight in to the back of the box from inside with Romex any thing in conduit outside must be weather proof. You could transition to UF or THWN before coming out. Simplest would be run UF or conduit all the way. Some would say conduit because critters sometimes like to chew on cable.
 
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Old 09-17-11, 01:27 PM
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Mount the disconnect above the expected snow level.
 
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Old 09-18-11, 10:51 PM
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Can the stranded THHN in the flexible conduit to the AC be two blacks and a green or must it be black, red, and green?
 
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Old 09-18-11, 11:18 PM
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The two "hot" wires can be any color other than white, gray or green. They don't even need to be different colors.
 
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