Wiring for HVAC

[Miller54z]

New shop building is almost up, so I’m starting to look at HVAC. I’d like to have all the wiring in place for the HVAC guys, and maybe even install the outside and indoor units myself so that all they would have to do is charge the system. My question is about what needs to be in place for wiring: wire size / circuit breaker size / thermostat / etc? I’ve ran some calculators, but I’m looking for some professional expertise and experience to confirm my assumptions.

The building is in central Florida- 50’X60’ concrete block (insulated) with 14’ ceilings (also insulated- R30). Still doing preliminary load calculations, but we are looking at a 5-ton or maybe even a 7.5 ton unit. Most likely no heat; just AC. The cable would run a maximum of 100’ from the breaker box to the AHU and outside unit. Thanks in advance for any advice.

-Matt

 

[Stuff]

Not enough info as equipment determines minimum wire and breaker size. Also when going that big you could do 3 phase. Best to do the wiring after the ductwork is installed as well.

Have you considered all-in-one package roof top units? Zoning/multiple units?

 

[Fixin'Stuff]

Yep, gotta have specs. You could wire for the 7.5 ton and still use those wires for a 5-ton, but not the other way around. The 7.5 almost certainly requires a heavier gauge wire. The installation manual (and the sticker on the outside unit) will list the info you need to feed it properly.

 

[Miller54z]

Not enough info as equipment determines minimum wire and breaker size. Also when going that big you could do 3 phase. Best to do the wiring after the ductwork is installed as well.

Have you considered all-in-one package roof top units? Zoning/multiple units?

Thanks, but I'm not sure what specs you need- maybe you can clue me in. I just want to size the wire big enough to accommodate up to a 7.5 ton unit. Nothing detailed yet- I just want to run a circuit to the AHU/compressor location in the walls/ceiling before everything is finished and closed up. I don't have a specific model in mind, but I assumed certain sizes all have similar requirements.

I've considered rooftop/package units, but the traditional split central system would be easier. 3 phase is not an option. Isn't there a minimum wire size required for up to a 7.5 ton split unit? Minimum breaker size?

Thanks Again,

-Matt

 

[brewchief]

Who makes a 7.5 ton single phase unit? I don't think I have ever seen a unit over 5 tons that's not 3 phase.

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[Miller54z]

Who makes a 7.5 ton single phase unit? I don't think I have ever seen a unit over 5 tons that's not 3 phase.

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Well that is good to know! Had a 'friend of a friend' do a rough calc for me and he said it needs a 7.5 ton. I've never seen one. It's a 50'x60' building with 14' ceiling, so to me that sounds excessive. I did my own online manual J calculation online and came up with 4 ton...so not exactly sure. So the wiring would probably be for the largest available single-phase unit, which sounds like a 5 ton...or maybe even 2X 3 ton units?? Either way, isn't there a standard circuit and wiring size for a 5-ton unit? What do I need to have in place for these units? Surely there is some kind of 'standard'...

 

[justinjoyal]

Get a proper load calc. 7-ton seems excessive.