Rooftop A/C units

[jaylectricity]

A customer has a 3 story residential building. He is going to put A/C condensers on the roof. All the rooftop units I've wired before had some sort of wall to mount the disconnect on. So I would use 10-2 Romex and poke through the wall of the doghouse stairway to the roof. Then mount the disconnect on the outside of that wall.

This building is just going to have a hatch going up to the roof. I'll have to put three cables, one for each floor, through the roof.

What do I use? PVC? RMC? Do they need to be in three separate conduits?

Once I have the cables up there, what do I mount my disconnect to? Is there a special kind of disconnect for this application?

The units will all be 30 amp condensers.

Thanks for any help you can give me.

 

[bphgravity]

You will have to use a wiring method and conductors/cables suitable for the conditions of use. (Likely outdoor and wet location)

It may be possible to mount the disconnect on the units themselves. See 440.14 of the NEC.

 

[dezwitinc]

Some rooftop units can be wired from underneath through the curb.
If not, you will need to have a pitchpocket installed through the roof.
With the pitchpocket, you can change over to sealtight and go through the roof to your disconnect which may be mounted on the unit.
Depending on how the curb is built, you may be able to build a unistrut rack to mount the disconnect on if you can't mount it on the unit.
If you are going through the roof, the important thing is to make sure that your roof penetration is as close as possible to where you are mounting the disconnect and that you won't interfere with access panels.
With the disconnect mounted on the unit, just chase nipple through to the wiring compartment.

 

[rcarroll]

Don't forget the service recep. 210.63 :smile:

 

[jaylectricity]

Some rooftop units can be wired from underneath through the curb.

It will be a standard unit that would also be used on the side of a house.

If not, you will need to have a pitchpocket installed through the roof.
With the pitchpocket, you can change over to sealtight and go through the roof to your disconnect which may be mounted on the unit.

Not sure I'm understanding a pitch pocket completely but a few minutes on google produced this:

So it looks like the pipe can come up into that, and the sealant will keep water from seeping into the roof. Then I can change over to liquid-tight. Sounds good, but I don't see this guy putting this in his roof. I'll ask him of course.

Depending on how the curb is built, you may be able to build a unistrut rack to mount the disconnect on if you can't mount it on the unit.
If you are going through the roof, the important thing is to make sure that your roof penetration is as close as possible to where you are mounting the disconnect and that you won't interfere with access panels.
With the disconnect mounted on the unit, just chase nipple through to the wiring compartment.

Maybe I'm not envisioning this completely, but wouldn't the only place to put a disconnect on the unit and still be able to chase nipple to the wiring compartment be on the removable panel?

Picture is rather large, so just click here.

Don't forget the service recep. 210.63 :smile:

I probably would have too! haha, I'll just use combination disconnects.

 

[DaveTap]

If he's not willing to put pitch pot(s) (and/or roof boots) through the roof how's he planning on getting refrigerant lines to the evaporator coils inside the bulding?

You might be able to run up the outside wall in conduit or even sneak through near the corner of the roof hatch curb if properly protected, but HVAC guys need to get 6 copper tubes up there as short and straight as possible.

As to whether you can run all in the same conduit... only if all 3 units are powered from the same source... but I assume each floor is on a seperate panel.

You can put the 3 conduits (and possibly all the refrigerant lines) through the same pot though

Industrial units usually have a frame or fixed panel you can mount to residential we usually have to make a stand-off frame because the top and corner covers have to be accessable for service.

 

[Cavie]

there is no place to mount a disc on that unit. You'll have to build something to mount your disc on.

 

[jaylectricity]

If he's not willing to put pitch pot(s) (and/or roof boots) through the roof how's he planning on getting refrigerant lines to the evaporator coils inside the bulding?

You might be able to run up the outside wall in conduit or even sneak through near the corner of the roof hatch curb if properly protected, but HVAC guys need to get 6 copper tubes up there as short and straight as possible.

As to whether you can run all in the same conduit... only if all 3 units are powered from the same source... but I assume each floor is on a seperate panel.

You can put the 3 conduits (and possibly all the refrigerant lines) through the same pot though

Industrial units usually have a frame or fixed panel you can mount to residential we usually have to make a stand-off frame because the top and corner covers have to be accessable for service.

Yes, each floor will have its own meter. But the owner will probably be fine with putting one pot for all three units, then I can liquid-tight to each unit from each conduit.

Thanks

there is no place to mount a disc on that unit. You'll have to build something to mount your disc on.

Thanks for confirming that.

I think I have this figured out.

 

[peter d]

Just curious, are you sure they require 30 amp circuits? With the new minimum 13 SEER rule, most residential units don't require 30 amp circuits anymore.

 

[jaylectricity]

Just curious, are you sure they require 30 amp circuits? With the new minimum 13 SEER rule, most residential units don't require 30 amp circuits anymore.

I'm using 30 amps as a general example. I am trying to differentiate between your average residential condenser and a big-time commercial unit.

The circuit and over-current device is determined by the nameplate rating on the unit.