Heat pump disconnect questions

[46MGTC]

I just realized that we forgot to rough-in the electrical for a future mini-split HP in the garage. I need to get this done before insulating the walls. I've got no probblem running the 220 line but I'm unsure of how to install the outside disconnect box now that the vinyl siding is up. I'd rather not cut up or remove the siding if possible.

Can I just run the wire through a hole in the wall into the back of the disconnect box and use a siding "light block" mounted on the vinyl siding to hold the disconnect? Is it OK to just use NM wire through the wall into the disconnect?

I noticed that the directions for the HP (LG 18K btu) gives a wire size of #14 AWG but spec. a 20A breaker. I thought that #12 was required for 20A? Since I have some #10 left is it OK to use this on a 20A circuit?

Thanks for any help.
Dave
'46 MGTC
'59 MGA

 

[ghnl]

I'm no electrician so wait for more learned replies...

1) It is easy to remove a panel or two of vinyl siding if you want to put the electrical box 'in' the siding. Don't try it on a very cold day however as the vinyl will tend to be brittle then. There is a tool to help unhook the bottom of a panel. Looks like a bent putty knife.

1a) I'll have to go outside but it look like the electrician just put the disconnects on top of the siding. See photo attached below.

2) Is the unit 20 amps at 110V or 220V?

3) Should be OK to use a larger than required wire gauge. The heavier gauge wire will be harder to bend & snake into place however. And make sure it'll fit into whatever device you plan to use.

4) Tell me about your MG's. I have a 1960 MGA (bought it in 1971) & 1978 MGB (bought it a few years ago to replace the '72 MGB my wife had before we were married).

 

[Aceman]

Can I just run the wire through a hole in the wall into the back of the disconnect box and use a siding "light block" mounted on the vinyl siding to hold the disconnect? Is it OK to just use NM wire through the wall into the disconnect?

Yes, that fine. You also need an outside receptacle within 25' of the unit as well. Siemens makes a combination GFCI receptacle/AC disconnect that comes all in one that works well for this.

I noticed that the directions for the HP (LG 18K btu) gives a wire size of #14 AWG but spec. a 20A breaker. I thought that #12 was required for 20A?

Motors and welder have different rules.

Since I have some #10 left is it OK to use this on a 20A circuit?

Yes.

 

[Norcal]

Art. 440 allows one to use table 310.16 ampacities so 14 is 20A 12 is 25A & 10 AWG is 35A (Note: these values do not apply to NM cable, "Romex®" since it still limited to 60 degree ampacity). Since the A/C has overload protection the fuse/circuit breaker is only for short circuit protection and the label on the equipment will show what one needs to know 1) the min ampacity , for example 22.3 amperes, and 2)the maximum fuse or circuit breaker for example 40A means one can wire it w/ 12 AWG and a 40A breaker, and be code compliant.....

10 AWG will be fine, as for vinyl siding I stay away from it, thank goodness it's rare around these parts.....

 

[Aceman]

Art. 440 allows one to use table 310.16 ampacities so 14 is 20A 12 is 25A & 10 AWG is 35A (Note: these values do not apply to NM cable, "Romex®" since it still limited to 60 degree ampacity).

The 60 degree ampacity is still 20 for #14 and 25 for #12.

 

[46MGTC]

Thanks for the replies.

Aceman:

I didn't think of the GFCI outlet needed but I see that I do have one of the combined disconnect/GFCI boxes on the main house heat pump. I'll hit up the local electric supply as I can't find one on the big box web sites.

Can I just run 12/3 with ground and bring the neutral over and use one of the 110v legs for the GFCI? To use up my # 10 I'd have to run another wire anyway.

ghnl:

From your picture it looks like you have Dutch lap siding which has a nice flat face. We've got double 4" so there is no real flat face so I think I'll need a light block. It's been cold enough here in Lenoir that I'm afraid to touch the siding.

For MGs we just have the two. I've owned the TC for almost 20 years and the A for about 12 years. We moved to the Lenoir, NC area from New Hampshire last September to get away from the cold and snow
Not worked out too well so far!
We've joined up with the Catawba Valley club and have gone to a few meetings. Hope to get some drives in this spring.
I guess I should have used HDR43 as my screen name!

Dave

 

[Norcal]

Thanks for the replies.


Can I just run 12/3 with ground and bring the neutral over and use one of the 110v legs for the GFCI? To use up my # 10 I'd have to run another wire a....

Dave

You cannot connect it to the load side of the disconnect*, it would be wise for it to be independent of the A/C unit circuit since it is there for servicing the unit, such as a recovery machine & a vacuum pump....

*See NEC section 210.63.

 

[46MGTC]

Thanks,

I realized after I pressed submit that running off one of the legs would probably not be allowed and probably not a good idea. I've got a 20 amp outlet circuit nearby that's already fed by a GFCI outlet. I can pigtail off of it to the outside. Can I feed a GFCI outlet in one of the combo disconnects without confusing the first GFCI?

Dave

 

[Norcal]

Thanks,

I realized after I pressed submit that running off one of the legs would probably not be allowed and probably not a good idea. I've got a 20 amp outlet circuit nearby that's already fed by a GFCI outlet. I can pigtail off of it to the outside. Can I feed a GFCI outlet in one of the combo disconnects without confusing the first GFCI?

Dave

Just feed it from a GFCI protected circuit & install a standard receptacle in it. (Decora® type).