25kW furnace with 80-amp breaker?!

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sw_ross

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I was told ahead of time that there’d be a 25kW furnace.

I specifically asked if it would be 3 circuits, 2-10 kW’s and 1-5kW circuits. That’s what I normally see in furnaces this big.

When I looked at the furnace it has (1) 50-amp breaker and (1) 80-amp breaker as disconnects factory installed on the unit!

Isn’t a 60-amp branch circuit the largest circuit allowed to be run in residential?
 
424.22...................

(B) Resistance Elements. Resistance-type heating elements in
electric space-heating equipment shall be protected at not
more than 60 amperes. Equipment rated more than
48 amperes and employing such elements shall have the heating
elements subdivided, and each subdivided load shall not
exceed 48 amperes. Where a subdivided load is less than
48 amperes, the rating of the supplementary overcurrent
protective device shall comply with 424.3(B). A boiler employing
resistance-type immersion heating elements contained in
an ASME-rated and stamped vessel shall be permitted to
comply with 424.72(A).
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The 80 amp circuit is not further sub divided with additional overcurrent protection, right?

424.22 that Dennis mentioned has been around and basically sets a design limitation on these types of units. You can go three phase or even up the volts to 480 and get more watts but still are limited to 60 amp max overcurrent protection.

Have seen some that take a larger supply circuit, or even have option for a main lug kit to convert to a single supply circuit but still subdivide into 60 amp or less circuits within the unit.
 
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In regards to the visible disconnects/breakers on the face of the furnace all you’re looking at is the 80 and the 50.

when you open it up you see the the 80 then goes to 2 breakers, a 45 and a 25 amp breakers.
 
kwired said:
The 80 amp circuit is not further sub divided with additional overcurrent protection, right?
Click to expand...

Yes, it does. The 80 then sub divides into a 45 and a 25 amp breaker inside the unit.

Does that mean that what I’m doing to give power to that 80 is really a feeder and not a branch circuit?! (Along with a branch circuit for the 50...?)

I’m kinda frustrated because I pulled 2 runs of 6/2 and one run of 10/2...
Now I basically have to start from scratch.
 
sw_ross said:
Yes, it does. The 80 then sub divides into a 45 and a 25 amp breaker inside the unit.

Does that mean that what I’m doing to give power to that 80 is really a feeder and not a branch circuit?! (Along with a branch circuit for the 50...?)

I’m kinda frustrated because I pulled 2 runs of 6/2 and one run of 10/2...
Now I basically have to start from scratch.
Click to expand...
If you could bypass the 80a breaker, your three feeder cables would be perfect.
 
LarryFine said:
If you could bypass the 80a breaker, your three feeder cables would be perfect.
Click to expand...
Would that be modifying the unit though? The 45-amp and 25-amp breakers that the 80-amp breaker feeds are located inside the unit without the handles readily available.

If I did that I would still have to have a disconnect within sight since the only visible disconnects on the unit are the 80-amp and 50-amp breakers visible with the cover on and the panel that feeds the branch circuits is in a different location of the house.

I agree, I could make it work using the NM cables I’ve run, but the walls haven’t been Sheetrocked yet so I’ll probably just change out the wires and plan on feeding the 80-amp breaker with correct size SER cable.

Lesson learned- don’t always believe information given by HVAC company. Request specifics on paper before running wire (unless it’s a basic common system)!

This wasn’t a basic, or common, system.
 
If you don't have a disconnect or if you have a disconnect without overcurrent protective device then the runs are branch circuits not feeders. Just a small point....
 
Even with an OCPD at both ends if the unit contains supplemental OCPD it is still a branch circuit.
 
infinity said:
Even with an OCPD at both ends if the unit contains supplemental OCPD it is till a branch circuit.
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If there is a breaker in the panel and one at the disconnect then it is a feeder. From the disconnect to the unit is a branch circuit. I assume you are talking about the runs to the unit from the disco
 
Dennis Alwon said:
If there is a breaker in the panel and one at the disconnect then it is a feeder. From the disconnect to the unit is a branch circuit. I assume you are talking about the runs to the unit from the disco
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The point I was making is that an OCPD at the unit does not automatically make the circuit a feeder even though it meets the Article 100 definition of a feeder with an OCPD at each end.

424.22(D) Branch-Circuit Conductors. The conductors supplying the supplementary overcurrent protective devices shall be considered branch-circuit conductors.
Click to expand...
 
Dennis Alwon said:
Gotcha, that is what I was insinuating with my comment. I got confused when you made your statement
Click to expand...
Yes there were a few other posts that mentioned that the branch circuit conductors would actually be a feeder(s) due to the OCPD at the unit.
 
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