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Old 07-18-2014, 11:33 AM   #16
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Max HVAC Breaker Size


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Originally Posted by Stubbie View Post
Not the proper procedure for determining branch circuit conductor sizing and opcd to a single residential ac unit.
Never said it did. IMO there is no way the circuit described by the OP should be supplied by a 40 amp breaker regardless of whether the disco is fused or not.

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Old 07-18-2014, 11:42 AM   #17
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Think of it this way,

What if I ran a 240V branch cir with #10 thhn in conduit to an outdoor 3r subpanel and then put 30amp fuses or breakers to the A/C unit. Would that be ok?? If so, whats the difference in that v.s. the original case ?
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Old 07-18-2014, 11:54 AM   #18
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Originally Posted by brric View Post
Never said it did. IMO there is no way the circuit described by the OP should be supplied by a 40 amp breaker regardless of whether the disco is fused or not.
We actually don't know how this unit should be supplied since we do not have the information. The OP's suggestion of how he is going to do it is incorrect .

You made a statement how "some" people would look at the ops method. I was simply stating that what you wrote is not how you would approach the installation.

So what was your purpose in stating something that is incorrect ?
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Old 07-18-2014, 12:03 PM   #19
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Max HVAC Breaker Size


Quote:
Originally Posted by Cletis View Post
Think of it this way,

What if I ran a 240V branch cir with #10 thhn in conduit to an outdoor 3r subpanel and then put 30amp fuses or breakers to the A/C unit. Would that be ok?? If so, whats the difference in that v.s. the original case ?
The difference between the 30 amp and 40 amp breaker in the main.
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Old 07-18-2014, 12:06 PM   #20
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Max HVAC Breaker Size


Quote:
Originally Posted by Cletis View Post
Think of it this way,

What if I ran a 240V branch cir with #10 thhn in conduit to an outdoor 3r subpanel and then put 30amp fuses or breakers to the A/C unit. Would that be ok?? If so, whats the difference in that v.s. the original case ?
That would be feeder conductors not branch circuit conductors to the subpanel. As long as these conductors are sized to the calculated load of the panel it would be fine and of course the correct ocpd protecting them.. This is assuming your sizing the ac correctly.

Note you would probably run 120/240 circuit to the subpanel.....
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Old 07-18-2014, 12:40 PM   #21
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Quote:
Originally Posted by Stubbie View Post
We actually don't know how this unit should be supplied since we do not have the information. The OP's suggestion of how he is going to do it is incorrect .

You made a statement how "some" people would look at the ops method. I was simply stating that what you wrote is not how you would approach the installation.

So what was your purpose in stating something that is incorrect ?
We have the information in post #4, 30 amps max. What I said is that some would interpret the installation differently as they (not necessarily me) would say the conductors to the disco are feeders rather than branch circuit conductors as by definition the branch circuit conductors would be those from the load side of the disco to the unit.
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Old 07-18-2014, 12:45 PM   #22
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Originally Posted by JohnDS
Thanks guys.
Iwire, you have raised another question. In this case, Why does installing a fused disconnect as opposed to a non-fused disconnect determine that the wire from disconnect to panel be upsized to 8awg?

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By definition the conductors between the panel and the fused disconnect are feeder conductors. They would have different rules than the branch circuit conductors between the fused disco and the unit.

There has been some argument that the fuses could be supplemental protection and therefore the conductors would not be feeder conductors.
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Old 07-18-2014, 01:39 PM   #23
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Quote:
Originally Posted by brric
Some would say the fuses at the disco make the conductors supplying the disco feeders. Thus limiting the OCPD to 30 amps.
Bingo. Since the disco is fused the conductors supplying it are feeders. Have to protect them at their rated amps cities. #10 romex = 30A. #10 THHN = 35A.
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Old 07-18-2014, 01:40 PM   #24
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Quote:
Originally Posted by Stubbie
Not the proper procedure for determining branch circuit conductor sizing and opcd to a single residential ac unit.
They are not branch circuit conductors to the fused disco. They are feeders.
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Old 07-18-2014, 03:41 PM   #25
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We are talking AC units here, In most cases, you will have a much higher rated breaker than the actual wiring is rated for, this is because the breaker is NOT protecting the wire, the AC unit is... It is not out of the norm to have a #10 AWG protected by a 50 amp breaker, but you have to go off the AC nameplate, the manufacture already did all of the required calculations for you.
The A/C is not protecting the wires.
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Old 07-18-2014, 06:11 PM   #26
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The A/C is not protecting the wires.
The AC provides the overload protection.
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Old 07-18-2014, 06:24 PM   #27
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The AC provides the overload protection.
Only for the condenser fan motor and compressor.

Their internal over loads only open between their common winding and their run and start windings. A partial short to ground can still occur before the internal over load.

Yes, I know the NEC feels its enough protection for the wire.
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Old 07-18-2014, 06:27 PM   #28
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Yo. If I run #10 Thhn in conduit to an A/C disconnect and fuse it with a 40 amp 2 pole hacr breaker and 30 amp fuses in disconnect will this pass NEC code?

Thanks in advance
Cletis what are you doing? I mean really!!!!
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Old 07-18-2014, 08:55 PM   #29
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Cletis what are you doing? I mean really!!!!
You guys are falling for this
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Old 07-18-2014, 09:09 PM   #30
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Cletis what are you doing? I mean really!!!!
Where did he go anyway?

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