A/C Disconnect install


Old 10-12-09, 12:59 PM
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A/C Disconnect install

Hi - I'm installing a fusible A/C disconnect (Eaton / Cutler-Hammer DPF221RP) on the outside of my house where exposed to direct precipitation. This is being done (while I am rewiring the rest of the house) in preparation of a future central air install by a HVAC contractor, likely next year.

I want to mount it to the wood lap siding and use a EMT compression connector through the concentric circle knockout on the back of the box with a short piece of EMT extending just into the open and exposed 2x4 wall cavity, enough to maintain a 1 1/4" distance from the outside and inside stud faces. Then wired with 10/2 NM-B from the service panel, through the EMT sleeving it for protection, and then into the disconnect box. The EMT would be caulked where it goes through the siding.

1.) Is this acceptable?
2.) Is there a better/easier way?
3.) Is 1/2" EMT large enough for the 10/2?
4.) Do I need a NM clamp on the end of the EMT in the wall cavity?
5.) Are there any issues with the future contractor and this already being completed? I'm doing it now mainly because it makes sense while I am rewiring the rest, I'm picky and I'm sure that the HVAC contractor would not adhere to my anal wiring methods, and so that I can hopefully save a bit money as it will already be done. Even if it won't save me money, I'd still rather do it myself...

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Old 10-12-09, 01:28 PM
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Your plan is okay. I'd probably use PVC so the open end of the conduit doesn't cut the cable. The hole should be sealed with caulk or expanding foam. The install should be okay for a future HVAC contractor -- #10 wire is sufficient for most high-efficiency A/C units these days. Most units also don't need to be fusible.
Old 11-01-09, 07:38 PM
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Since you are using a 30 amp fused disconnect the largest breaker allowed by the NEC for feeder protection will be a 30 amp. You are also limited to 30 amp fuses. This may present future problems. If you use a non-fused disconnect the 10 awg romex is rated to 40 amps and can be protected at the panel at whatever the maximum HACR breaker protection on the A/C unit label calls for. If the unit only allows fuses, you are limited to 30 amp fuses in a fused disconnect.

Also the NEC requires a connector where the romex enters the conduit. It is called a "transistion in wiring methods". 1/2" conduit can handle 3 #10 awg conductors.

If you know which model unit you are going to use, get the information off the unit and size everything correctly the first time.

Good luck!

Last edited by electures; 11-01-09 at 07:41 PM. Reason: Added info
Old 11-03-09, 10:40 AM
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My location mods the NEC to add a MAX seperation of unit to disconnect of 6 feet. Check you local code. Don't forget provisions for the control cable; and delete the fuse option if allowed.
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