HVAC system circuit breaker.

[The motor guy]

I'm looking at having an hvac system installed in my shop. It's going to be a 5 ton AC/heat pump system and the installer said I need a 50 amp for the air handler and then a 40 amp breaker for the outside condenser unit. I willl clarify in the morning with the installer, but he said I needed to upgrade the wiring in the panel. Is he saying I just need to have room in the panel for a 50 amp breaker, then the 40 amp will be outside in the disconnect for the condenser?

 

[ondarvr]

Yes, 50 in the panel and disconnect box with 40 amp fuses outside near the unit.

 

[The motor guy]

I just checked my disconnect at the house and it doesn't even have a circuit breaker in their for the condenser. What's up with that?

 

[mk378]

You need 90 amps from the panel -- a 50 amp circuit and another 40. The 50 runs the electric reserve heaters and the 40 is for the compressor. They can both be on at the same time. A 5 ton system requires a significant amount of power.

The little box outside is typically only a switch. This is required so a service person can pull that switch to definitely de-energize the outdoor unit without having to track down which breaker it is inside.

Edit: There is a breaker-- somewhere. Thus the requirement for the outdoor disconnect.

 

[The motor guy]

I thought the smaller outside condenser breaker is just inline with the air handler and it will trip before the rest of the system does to protect the condenser.

 

[zzyzzx]

You need 90 amps from the panel -- a 50 amp circuit and another 40. The 50 runs the electric reserve heaters and the 40 is for the compressor. They can both be on at the same time. A 5 ton system requires a significant amount of power.

This!! If it were just an "air handler" no way anywhere near 50A for it. There is an electric heater in the air handler.

 

[mk378]

There's supposed to be a separate dedicated feed from the house panel to each unit. There are a lot of "unconventional" installations out there though, ranging from mere code violations to downright dangerous.

 

[The motor guy]

Well that sucks. I may need to go directly to the panel on the pole.

 

[zzyzzx]

I thought the smaller outside condenser breaker is just inline with the air handler and it will trip before the rest of the system does to protect the condenser.

The outside disconnect switch, complete with lockable position, is so that anyone servicing the compressor unit can be 100% sure that it has no electricity going to it. The disconnect serves no other purpose. That is also why the disconnect switch is always very close to the compressor.

 

[Oildudeny]

Sounds like you need room for a 2 pole breaker in the breaker panel.. 50a should be 6 gauge wire. Outside disconnect is “fused” at 40a therefore your disconnect would trip before the breaker in the breaker panel.

yes the disconnect also is a service junction to break power from the electrical service.

 

[The motor guy]

Yes the heat pump system will still have heat strips that come on only if the outside temp gets to around 40 or lower.

 

[The motor guy]

Sounds like you need room for a 2 pole double throw breaker in the breaker panel.. 50a should be 6 gauge wire. Outside disconnect is “fused” at 40a therefore your disconnect would trip before the breaker in the breaker panel.

yes the disconnect also is a service junction to break power from the electrical service.

This is the part I don't understand. Is the smaller 40 amp just to protect the condenser and it will only need a 50 amp breaker for the airhandler/heater portion?

 

[Oildudeny]

Yes the heat pump system will still have heat strips that come on only if the outside temp gets to around 40 or lower.

Heat strips is the emergency heat to assist the heat pump

 

[mk378]

Breakers are primarily to protect the wiring, not the load. Thus they are installed at the source end (panel) and sized to match the maximum safe current for the wire size installed.

 

[Oildudeny]

Sounds like your total system will be on the 50a In theory you want to not exceed 80% of the breaker. That may be why he’s using a 40a in the disconnect

 

[The motor guy]

Sounds like your total system will be on the 50a In theory you want to not exceed 80% of the breaker. That may be why he’s using a 40a in the disconnect

That's the way I understood it when he was explaining I think he also said an air handler would only need like 20 amps, but since mine is a heat pump system with the backup heat strips to keep the compressor from freezing up and requires more like zz was saying. I find it hard to believe a system pulls 80-90 amps everyones electrical bill would be $500/month.

 

[ondarvr]

The installation manual will tell you whats needed for your exact unit. Look it up online.

I just installed several systems, 3 ton was 40 amp panel breaker and 30 amp fuses at the discount near the unit.

Smaller ones were 30 at the panel and 20 at the discount.

 

[ondarvr]

Its not two separate breakers and circuits, same circuit with with a breaker and discount.

 

[Oildudeny]

That's the way I understood it when he was explaining I think he also said an air handler would only need like 20 amps, but since mine is a heat pump system with the backup heat strips to keep the compressor from freezing up and requires more like zz was saying. I find it hard to believe a system pulls 80-90 amps everyones electrical bill would be $500/month.

As mentioned pull up the manual for your system it’ll state breaker/disconnect wire gauge etc.

 

[EA82]

You need 2 separate circuits, one for the air handler and one for the condenser, an air handler calling for 50 amp breaker means that they're installing an 8kw back up heater.
Service disconnects dont have to have a breaker, most often they just install a pull plug which is just an on/off switch. You have to run #8 wire to support the amperage for each unit.