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Old 02-07-2010, 03:03 PM   #16
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Originally Posted by frenchelectrican View Post
...keep in your mind all the NM and UF cable are use with 60C rating...
I didn't understand it just listing conductor type, but when you add this fact with my note about the chart listing a temperature rating and it all make sense.

Thanks
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Old 02-07-2010, 03:13 PM   #17
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Originally Posted by micromind View Post
The type of wire matters only because 334.80 states that the ampacity of type NM cable (Romex) shall be based on a temperature rating of 60C.

Basically, conduit and THHN/THWN will use the 75C column in table 310.16, while NM and UF cable will use the 60C column.

Rob
correct and is exactly the point of my post whether I got it across as such or not.
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Old 02-07-2010, 03:19 PM   #18
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Originally Posted by brons2 View Post
I have 2x30 amp breakers dedicated to my AC unit, but the wire is 10/2! Should I consider replacing it with 6/2? The walls are currently open to do so, so it would be pretty easy to do so at the present time.
could you clarify a few things before an answer?

what does 2X30 breakers refer to? If you mean you have 2 30 amp single pole breakers feeding a 240 volt appliance, you need to change that to a 2 pole 30 amp breaker.

If you believe you could possible upsize the AC unit in the future, there would be nothing wrong with installing a larger sized conductor now while you have access to the pathway but #10 is fine for the 30 amp breakers you now have.


you seem to be thinking of this backwards. With AC/s and other motor loads, the breaker is often allowed to be oversized as compared to the ampacity ratings of the wire BUT there are documented limits that must be followed. You seem to be concerned about over sizing the wire.
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Old 02-09-2010, 05:11 AM   #19
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Originally Posted by pomelo View Post
What is the Min Circuit Ampacity rating referring to on the data plate on the side of an A/C unit? I've always used the max fuse rating to size the breaker, but there is a huge difference between Mn Circuit Ampacity and the max fuse rating on my new unit.

35 Min Circuit Ampacity
60 Max Fuse

What type of breaker would an electrician put in? The panel is not overloaded.

If it really says "Max Fuse", you can't use a circuit breaker for the short circuit protection. It must be a fuse.
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Old 02-09-2010, 12:52 PM   #20
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Quote:
Originally Posted by nap View Post
could you clarify a few things before an answer?

what does 2X30 breakers refer to? If you mean you have 2 30 amp single pole breakers feeding a 240 volt appliance, you need to change that to a 2 pole 30 amp breaker.

If you believe you could possible upsize the AC unit in the future, there would be nothing wrong with installing a larger sized conductor now while you have access to the pathway but #10 is fine for the 30 amp breakers you now have.


you seem to be thinking of this backwards. With AC/s and other motor loads, the breaker is often allowed to be oversized as compared to the ampacity ratings of the wire BUT there are documented limits that must be followed. You seem to be concerned about over sizing the wire.
It's two 30 amp breakers with a rectangular bridge that connects the two switches.
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Old 02-09-2010, 03:22 PM   #21
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This is called a two-pole breaker. It's used to supply 240 volt loads, or 120/240 if the neutral is involved.

For a 30 amp, #10 is the minimum wire size. You can go bigger, but not smaller.

About the only reasons to go bigger are because you might want to increase the circuit size at some point in the future, or for a very long run. Like more than 150'.

Other than the above, #10 is fine.

Rob
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Old 02-09-2010, 05:49 PM   #22
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Originally Posted by micromind View Post

About the only reasons to go bigger are because you might want to increase the circuit size at some point in the future, or for a very long run. Like more than 150'.


Rob
I was thinking if they might believe they would be installing a larger unit in the future. If the current one is too small or they might add on to the house, they might end up with a larger unit and need a larger conductor.

Now, guessing what you might need is...well, it is just a guess.
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Old 02-09-2010, 06:50 PM   #23
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The exact thought I had too.

More than once I've had to run something larger after the house is completely done.

Rob
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Old 02-09-2010, 11:03 PM   #24
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The AC unit in my house is plenty big enough, never had a problem cooling on 105F days with single pane windows and substandard insulation.

Of course, I'm trying to remediate those issues as part of the current project...
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Old 02-10-2010, 12:01 AM   #25
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I recently had a 3 ton 10 seer A/C unit replaced with a 4 ton 16 seer unit (HELLO TAX CREDIT!). The new unit required upgrading the #10 wire run to #8.
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