Breaker question

[scofo]

I'm replacing the central HVAC furnace, evap, line set and condenser in my mobile home. 22 years ago I supplied and wired the breaker and external disconnect for the comp/condenser. It was supposed to be protected for 60amps @230v. It never tripped for the life of the old unit. I can't recall what led me to choose the pictured breaker.

The new comp/condenser calls for 40amps @230v protection. Do I need a breaker that is labeled 20a on each leg instead of the current ;-) breaker's 30a on each leg or did I just get lucky and the old unit ran fine on a severely under spec'd breaker? Thanks in advance

 

[dcg9381]

Buy the look of the wires on that breaker, the wires are not rated for 60A. They look like solid 10GA wire to me, which is good for 30A.

Post up the data plate on the HVAC unit. You'll get more help that way. The way you are thinking about it (split current per leg) is not correct.

 

[scofo]

Good eyeball caliper there.

 

[rannoch]

The minimum is 23.4 amps.
You should be fine with your current breaker and wiring (30 amps).

 

[mike93lx]

40a @240v requires a breaker with two 40a legs

 

[scofo]

Well hell, I bought this one the other day thinking this would be 40amps of protection at 230v. Thinking the new unit would draw less current than the old one. I didn't even see a double pole 40 on the shelf for a square D homeline box. Still a bit confused maybe the 22year old r22 condenser required less current. I left the cover off the old one when i diagnosed the old compressor motor had windings shorted, so the old info sticker is gone.

If I truly need a double 40a to meet spec I would need to update wire size it would seem. I sure didn't want to buy wire right now.

 

[Norcal]

That unit could be wired with 12 AWG THWN or 10 AWG NM cable with a 40A breaker. Since 10/2 NM cable is existing it’s fine with a 40A breaker.

 

[sparky 1971]

The 10/2 wire is fine. You will probably be ok using the 30 amp breaker too. If the breaker does trip, you can install a 40 amp breaker. It will look just like the breaker you posted, but have a 40 in place of the 20.

 

[wyliesdiesels]

I'm replacing the central HVAC furnace, evap, line set and condenser in my mobile home. 22 years ago I supplied and wired the breaker and external disconnect for the comp/condenser. It was supposed to be protected for 60amps @230v. It never tripped for the life of the old unit. I can't recall what led me to choose the pictured breaker.

The new comp/condenser calls for 40amps @230v protection. Do I need a breaker that is labeled 20a on each leg instead of the current ;-) breaker's 30a on each leg or did I just get lucky and the old unit ran fine on a severely under spec'd breaker? Thanks in advance

60a @ 240v would be a double pole breaker with 60a on both sides
40a @ 240v would be a double pole breaker with 40a on both sides

the 20a DP breaker you have is NOT 40a, it is 20a..... you dont add up the ampacity rating of each pole on the breaker....

Well hell, I bought this one the other day thinking this would be 40amps of protection at 230v. Thinking the new unit would draw less current than the old one. I didn't even see a double pole 40 on the shelf for a square D homeline box. Still a bit confused maybe the 22year old r22 condenser required less current. I left the cover off the old one when i diagnosed the old compressor motor had windings shorted, so the old info sticker is gone.

If I truly need a double 40a to meet spec I would need to update wire size it would seem. I sure didn't want to buy wire right now.

well we dont know how much current the old one drew as the breaker rating is not the load rating.... but if it required a 60a DP breaker, then it most likely drew more current than your new unit....

no you dont need to upsize the wire

AC circuit wiring is size by the MCA- minimum circuit amps. for your case the 10/2 is just fine since its rated for 30a. the breaker is oversized to stop nuisance tripping and it doesnt protect the wire from overloads. thats the job of the integral overloads in the motor....

 

[scofo]

Okay, got it. Thanks guys. 10/2 cable will stay and I'll trade my newly purchased 20a for a brite and shiny 40a breaker.

I guess I dont recall clearly what the old compressor was suppose to be protected at. Maybe I was thinking of the service disconnect. Its rated at 60a. Maybe that's where I pulled that figure out of the 22year old recollection.

Anyhow much oblighed

 

[mike93lx]

The thing outside is a disconnect. The breaker in the panel protects the wire

 

[theoldwizard1]

The thing outside is a disconnect. The breaker in the panel protects the wire

TRUE ! But not all disconnects are fused or have breaker?

 

[rawen2]

I'm not an electrician but isn't the max breaker size for 10 ga wire 30 amps?

Oops. Meant to quote scofo:
"Okay, got it. Thanks guys. 10/2 cable will stay and I'll trade my newly purchased 20a for a brite and shiny 40a breaker."

 

[wyliesdiesels]

I'm not an electrician but isn't the max breaker size for 10 ga wire 30 amps?

Oops. Meant to quote scofo:
"Okay, got it. Thanks guys. 10/2 cable will stay and I'll trade my newly purchased 20a for a brite and shiny 40a breaker."

For general circuits yes. For motor and air conditioner condensor circuits no... have to read the exceptions to the ampacity rules in 240

 

[Bert_]

I'm not an electrician but isn't the max breaker size for 10 ga wire 30 amps?

Oops. Meant to quote scofo:
"Okay, got it. Thanks guys. 10/2 cable will stay and I'll trade my newly purchased 20a for a brite and shiny 40a breaker."

In this case you're limited to 30A of load. The AC in question pulls about 19A +125% so #10 is fine. It needs the 40A breaker for startup.

 

[rawen2]

Thanks for the clarification guys. Learn something new just about every day on this forum.

 

[Jim greengo]

Okay, got it. Thanks guys. 10/2 cable will stay and I'll trade my newly purchased 20a for a brite and shiny 40a breaker.

I guess I dont recall clearly what the old compressor was suppose to be protected at. Maybe I was thinking of the service disconnect. Its rated at 60a. Maybe that's where I pulled that figure out of the 22year old recollection.

Anyhow much oblighed

No need to use a 40a breaker,30a 2p is plenty.

 

[Terry D]

Minimum circuit ampacity is 23.4 amps, so a # 10 is required. Maximum fuse/breaker is 40 amps . Nothing wrong with a 40 amp breaker on a #10 wire when it is a motor/AC circuit. It is allowed to be oversized for start up current. If you have a 30 amp already. Then you could try it, but personally if this was me installing this circuit for a customer, i would use a 40 amp to prevent a possible call back.

 

[wyliesdiesels]

No need to use a 40a breaker,30a 2p is plenty.

a 30a breaker may work or it might nuisance trip... theres a reason the manufacturer calls for a 40a

 

[Bert_]

Yea, maybe if you already had a 30 I'd say try it. If you're going to buy a breaker anyway why wouldn't you get what it calls for.

 

[Jim greengo]

a 30a breaker may work or it might nuisance trip... theres a reason the manufacturer calls for a 40a

I install install lots of condensing units ,a 30a 2p is by far the most common breaker I ever come across in the field.
Unless you're installing a 4-5t condensing unit.

 

[Bert_]

I install install lots of condensing units ,a 30a 2p is by far the most common breaker I ever come across in the field.
Unless you're installing a 4-5t condensing unit.

No one's saying it can't work. Just that if he's got to go out and buy a breaker why wouldn't you get what it calls for.

 

[Terry D]

I have wired a lot of condensers on a 30 amp. But I always check the plate and size the breaker per that. A lot of them now still need a #10 but only have a maximum breaker of 25 amps. So now I keep a few 25 amp breakers on the truck.