Branch Circuit Rating Delima in My Head.

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Branch circuits recognized by this article shall be rated in
accordance with the maximum permitted ampere rating or
setting of the overcurrent device.
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The maximum permitted for the example is 40. If this installation is recognized by this article (210) then......
 
frizbeedog said:
Read 210.3 please. (I'm reading 08)

..in a nut shell the size of the Overcurrent device determines the rating of the branch circuit even if the concutors they protect have a higher ampacity.
.....for other than individual branch circuits.

I hope I got that right.

For an air conditioner circuit where the overcurrent device is larger than the conductor rating what determines the rating of the circuit here?

This is important becuase a certain type of permit we use has limitations on the rating of the branch circuit.

Am I over thinking this? Feels like there is a simple anwser that I'll kick myself for.
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I think to make this simple people get motor circuits (as in A/C compressors) confused with regular power circuits. On a motor circuit #12 Thhn in conduit is good for 25 amps. #10 wire is good for 35 amps. Look at the motor nameplate. Among other things it will list the RLA (Running load amperage), the minimum circuit ampacity, which is the RLA X 1.25 (which is how you calculate the conductor size of a motor and the maximum fuse size which is the breaker size that can go way up to just start the motor. Sometimes it will list the minimum circuit fuse size which you will find is the minimum circuit ampacity. RLA X 1.25 the same as the conductor size. You can have a A/c compressor that has a MCA of 22 amps and a max fuse of 35. So the circuit would be #12 wire in conduit (not romex) and fuse it at 35 amps. A perfect motor circuit.

Hope this helps
Steve Simpson
 
benaround said:
The a/c circuit is not recognized by 210 it is recognized by 440.
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Back up and read 210.2 and see the corosponding table for it. If it's not recognized by this article I'll eat my cat...or get the dog to do it.
 
frizbeedog said:
The maximum permitted for the example is 40. If this installation is recognized by this article (210) then......
Click to expand...

The maximum normally permitted for #10 is 30 amps.

Where conductors of higher ampacity are used for
any reason, the ampere rating or setting of the specified
overcurrent device shall determine the circuit rating.
Click to expand...

This sentence would not be necessary if you simply used the breaker to determine the rating anyway. Therefore, IMSO, the maximum OCPD normally allowed is what determines the rating.
 
wirebender said:
The maximum normally permitted for #10 is 30 amps.



This sentence would not be necessary if you simply used the breaker to determine the rating anyway. Therefore, IMSO, the maximum OCPD normally allowed is what determines the rating.
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For the example given, installling a larger breaker is what is normally done....and is the maximum permitted for the application.

Where conductors of higher ampacity are used for
any reason, the ampere rating or setting of the specified
overcurrent device shall determine the circuit rating
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.

This sentence refers to a higher ampacity conductor, like a voltage drop situation for example.
 
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frizbeedog said:
Back up and read 210.2 and see the corosponding table for it. If it's not recognized by this article I'll eat my cat...or get the dog to do it.
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Table 210.2 Specific-Purpose Branch Circuits

...right at the very top of the list...

Air-conditioning and refrigerating equipment 440.6, 440.31, 440.32

...and if it isn't subject to Article 440 and has a motor, it would then be subject to Article 430...
 
The provisions for branch circuits supplying equipment listed in table 210.2

AMEND or supplement the provisions of this article----

Table 210.2 AIR CONDITIONING see 440.6

440.6 - 440.6(A)ex.1

Also 440.31 and 440.32

To me the above all say the branch circuit rating is what the MNFCR 's have

listed on the nameplate ( mca )
 
Smart $ said:
...and if it isn't subject to Article 440 and has a motor, it would then be subject to Article 430...
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... and amend or supplement the provisions of 210. And I have found no rating for branch circuits in 440 that amends 210.3....The fist sentence that is.
 
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benaround said:
The provisions for branch circuits supplying equipment listed in table 210.2

AMEND or supplement the provisions of this article----

Table 210.2 AIR CONDITIONING see 440.6

440.6 - 440.6(A)ex.1

Also 440.31 and 440.32

To me the above all say the branch circuit rating is what the MNFCR 's have

listed on the nameplate ( mca )
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....And all of that information is used to size all of the components for that branch circiut. But the manufacturer is not determining the rating of the branch circuit, but the components in the circuit required to supply the equipment. The NEC is dertemining the rating of the branch circuit.

:smile:
 
wirebender said:
But that is not what is normally allowed for #10. See 240.4(D).
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240.3 trumps your rationale...

again....210.3
Branch circuits recognized by this article shall be rated in
accordance with the maximum permitted ampere rating or
setting of the overcurrent device
Click to expand...

You can't throw in the phrase normally allowed, becuase I'm not seeing that phrase pop up in any of these articles.

...but I understand why you keep saying it.

For the example in question, it is permitted, it is allowed and it is something that is normally done.
 
frizbeedog said:
... and amend or supplement the provisions of 210. And I have found no rating for branch circuits in 440 that amends 210.3....The fist sentence that is.
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Please READ 440.6 !!!
 
frizbeedog said:
240.3 trumps your rationale...

again....210.3


You can't throw in the phrase normally allowed, becuase I'm not seeing that phrase pop up in any of these articles.

...but I understand why you keep saying it.

For the example in question, it is permitted, it is allowed and it is something that is normally done.
Click to expand...

So, explain why this sentence is even there.

Where conductors of higher ampacity are used for
any reason, the ampere rating or setting of the specified
overcurrent device shall determine the circuit rating.
Click to expand...


Or, just pay the higher fees, you seem convinced that it is a 40 amp circuit.:grin:
 
wirebender said:
Or, just pay the higher fees, you seem convinced that it is a 40 amp circuit.:grin:
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After all this I am convinced that 210.3, the first sentence, is what determines the rating on the branch circuit for the given example. AHJD seems to agree.

.....and life goes on.

Can someone close this thead....wait a sec., the jury's still out... My brain hurts.
 
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frizbeedog said:
After all this I am convinced that 210.3, the first sentence, is what determines the rating on the branch circuit for the given example. AHJD seems to agree.

.....and life goes on.

Can someone close this thread. My brain hurts.
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Mine too. At risk of further damage to my neurons I vow to suffer with box and ceiling fans and resort to a cool shower when we encounter our three days a year of unbearable heat.

If that don't work, running through the sprinklers and taking the T-tops off the Z-28 and heading to the beach at Lake Michigan sure would to much to mitigate a heat stroke and put the math on hold until I no longer needed it.

A/C? We don't need no stinking A/C!!
 
I would think that the 'weakest link' determines a circuit's rating. A #10 circuit supplying an AC unit, supplied by a 40a breaker, is a 30a circuit.

It is an exception that allows using a larger-than-T310.16 breaker rating.
 
frizbeedog said:
Right..... That's what we do when we're unsure how to call it, but I still would love to know.

If you were an inspector would you say that this is a 30 amp circuit or a 40 amp circuit? The difference in permit fees could be an additional 40 to 50 dollars.
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Thats easy. Put the 30 in. When the inspector leaves replace with 40! :D
 
I agree with Larry if the there is an overload rated @ 30 amps then regardless what the short circuit and gfound fault protectionis set at ,.. the rating that the circuit is protected at is 30 amps
 
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