Installing a quick disconnect

[Sigo]

I'm in the process of installing a mini-split (ductless) AC in my pole building. Unit is rated at 18.5 amps total so I'll be installing a 2-pole, 20A, 240V circuit breaker in the panel and using 12/2 NM-B romex to get power to a 240V, 60A-rated quick disconnect within line of site of the condenser. My question is how best to run the romex through the steel siding to the quick disconnect. What is the recommended way to seal the resulting hole, etc? Any input would be appreciated. Thanks.

 

[woodzy]

I think you should be installing a 10-3 with ground and a 30 amp breaker. On a piece of equipment that run 18.x amps you would not want it to be on a 20 amp circuit.

 

[Sigo]

Thanks for the input. I'm really interested in understanding the best method to seal up the hole in the metal siding once I run the romex to the back side of the quick connect. I believe I can use NM-B for the run since the path of the wire will all be inside until it exits the building straight into the quick disconnect. I've read that I will need to caulk the top and sides of the quick disconnect box But how best to seal up the hole? I guess the answer would apply to just about any part of the building where a cable leaves through the exterior wall.

 

[ishiboo]

I think you should be installing a 10-3 with ground and a 30 amp breaker. On a piece of equipment that run 18.x amps you would not want it to be on a 20 amp circuit.

In this application he would go off whatever the piece of equipment states. For an AC, it probably only calls for 12-2. Also, why are you suggesting an extra wire?

 

[ishiboo]

Thanks for the input. I'm really interested in understanding the best method to seal up the hole in the metal siding once I run the romex to the back side of the quick connect. I believe I can use NM-B for the run since the path of the wire will all be inside until it exits the building straight into the quick disconnect. I've read that I will need to caulk the top and sides of the quick disconnect box But how best to seal up the hole? I guess the answer would apply to just about any part of the building where a cable leaves through the exterior wall.

I fill the hole with closed cell expanding foam, and around the box gets some quality exterior caulk.

 

[woodzy]

If you have something that has a rating of 18.5amps and runs continuously, my concern is that a 20 amp circuit (everything has tolerances) could be just on the edge to run it safely. If you run a 30 amp circuit, and 10 gauge wire would be safer. If for some reason, down the road you wanted to replace the unit with a slightly larger one (global warming), you would be already be at the next breaker size. The additional cost up front is only slightly higher.

Remember the breaker protects the wire and not the appliance.
Just a recommendation – he doesn’t need to follow it, but I don’t like working on the edge of tolerance which is more prone to failure.


As my relations said “Failure is not an option” and I usually try to do the best job I can without wasting too much money.

 

[MTW]

For the wall penetration use an electrical fitting or conduit ****** just as you would going into a metal appliance, foam and caulk offers no protection to the cable from the sharp metal edges.

Drill a 7/8" hole in the siding to line up with the 7/8" knockout in the back of your disconnect. If the siding is flat enough where you mount the disconnect, a two screw romex connector could be used to go through both layers of metal.

If the siding has bumps that don't allow the normal 2 screw romex connector, use a short 1/2" conduit ******. Put locknuts and plastic bushings on both sides of the ****** to secure it and protect the wires from it's edges. After the wire is installed, plug the inside of the conduit with some wadded up plastic bag, to eliminate air transfer, better than caulk because it's removable for service if required.

With a conduit ****** there is no need to caulk around the disconnect, the wire will be protected from weather inside the ******.

MTW Ω

 

[Sigo]

MTW, Thanks. Just what I was looking for.

 

[wyliesdiesels]

What is the min ckt size and max breaker rating of the condensor?

Dont forget you will also need a service receptacle...

 

[RickP]

MTW, Thanks. Just what I was looking for.

MTW's suggestions were good ones. In addition, I usually add something around the outside of the conduit to seal the hole in the metal siding. I picked up a package of gray putty in the electrical section of Home Depot. It's the same stuff the electricians used to seal all the boxes on the outside of my house when they were originally installed. The putty still looks the same now as it did when it was new 10 years ago.

 

[DSMR]

Just installed a 24k btu mini split and the correct opd was 20a. 12 awg to disconnect, then out to your whip. I did not believe it should be so small but did the load calc and it was right. These new units are very efficient.

Oh, and you should never go larger with opd just to do it. That is dangerous.

 

[rburke65]

What is an opd?

 

[wyliesdiesels]

Its suppose to be OCPD= overcurrent protection device...he obviously forgot a C

 

[Kmt803]

MTW's suggestions were good ones. In addition, I usually add something around the outside of the conduit to seal the hole in the metal siding. I picked up a package of gray putty in the electrical section of Home Depot. It's the same stuff the electricians used to seal all the boxes on the outside of my house when they were originally installed. The putty still looks the same now as it did when it was new 10 years ago.

Yeah the grey stuff is called duct seal and does a good job of keeping water out