Fused Disco Required for HVAC?

[growler]

I would like to discuss, however, the possibility of the circuit you are working on at some point in the future being required to carry a 40Amp load again. With my limited experience, if I were to look in a main panel and see a 25 amp breaker with 8AWG wire under the terminal screws, I would not automatically assume that I could replace the 25 amp breaker with a 40 amp breaker to bring the capacity of the circuit back up.

However, if I saw a 40 amp breaker with 8AWG in the main panel, and 8AWG coming into a disco with a 25 amp breaker or fuse, I would be quite comfortable returning the load on the circuit to 40 amp.

Please let me know if I am seeing this issue incorrectly.

It's an opinion. Everyone gets one.

I would change out the breaker if allowed by the manufacturer because materials are cheaper.
You charge the same amount and pocket more. That's the name of the game.

 

[Smart $]

I have to read the code as literally as I can. I am not changing the ungrounded conductor size; it is existing wiring. 250.122(B) is simply n/a here imo, tho I'm open to any convincing argument to the contrary. I am not changing the conductor size, regardless of what breaker I may (will) install.

This is why I mentioned intent. The intent has not changed since 2002... only the words have changed.

Here's the 2002 through 2011 version:

(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors.

Here's the 2014 version:

(B) Increased in Size. Where ungrounded conductors are
increased in size from the minimum size that has sufficient
ampacity for the intended installation, wire-type equipment
grounding conductors, where installed, shall be increased in
size proportionately according to the circular mil area of
the ungrounded conductors.

 

[JFletcher]

Don't forget about 250.122(B) in doing so... :slaphead:

As luck would have it, there were no 25A fuses at HD, and the HO wanted a fused disco (they werent as expensive as I thought) 30A max disco with 20A fuses on original CH CH 40A breakers, one of which failed (wouldnt stay closed) during my install.:slaphead: (I figured I had done something wrong; the breaker just died while I was there) So 250.122(B) is intact, tho I probably violated something else by leaving a 40A breaker feeding a 30A max fuse size disco.

David, both are making assumptions about the rest of the circuit. On that job today, there was one such repurposed circuit: originally 240V, the black #6 was on a 15A breaker, the red #6 reidentified white and pigtailed to a #12 going to the neutral bar.

If you wanted to use a #6 on a 40A circuit again, you'd have to verify it isnt tapped off somewhere feeding 120V receptacles, wire size hasnt decreased elsewhere, etc. Either method is viable imo.

btw, the discos were corroded because they had SE cable popped thru the backs and no silicone anywhere, so rainwater got in. They were original to the house, and put on before the siding was painted.

 

[Smart $]

...tho I probably violated something else by leaving a 40A breaker feeding a 30A max fuse size disco.
...

Not a violation.