Branch Circuit Rating Delima in My Head.

Merry Christmas
Status
Not open for further replies.
frizbeedog

frizbeedog

Senior Member
Location
Oregon
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.
 
iwire said:
That phrase only applies to the sentence it is in.

It does not apply to last sentence.
Click to expand...


....and that sentence does not apply to the paragraph it's in? :confused:

It has no relevance to the whole paragraph?

It's a lone ranger in a sea of words?


If I strike that phrase am I still confused by my question?


Was that too many questions?
 
frizbeedog said:
It's a lone ranger in a sea of words?
Click to expand...

This sentance...

"The rating for other than individual branch circuits shall be 15, 20, 30, 40, and 50 amperes."

...tell us unless it's individual branch circuit a branch circuit will have one of those ratings. You could not have a 10 or 60 amp general purpose branch circuit.

The last sentence applies to any branch circuit, the breaker rating determines the rating of the circuit and it had better fit the requirements above.
 
iwire said:
This sentance...

"The rating for other than individual branch circuits shall be 15, 20, 30, 40, and 50 amperes."

...tell us unless it's individual branch circuit a branch circuit will have one of those ratings. You could not have a 10 or 60 amp general purpose branch circuit.

The last sentence applies to any branch circuit, the breaker rating determines the rating of the circuit and it had better fit the requirements above.
Click to expand...

Okie dokie.... so much for the nutshell theory. :smile:

Does the OCPD still determine the rating of the circuit I'm refering to?
 
I would say the overload protection determines the rating or the short circuit protection. Whichever is lowest amps. That would be my guess.
 
wireman71 said:
I would say the overload protection determines the rating or the short circuit protection. Whichever is lowest amps. That would be my guess.
Click to expand...

Lets say residential heat pump. 40 amp Circuit breaker, #10 wire, to non-fused disconnect, to equipment terminations. overloads not installed in circuit.

30 amp circuit rating? or 40 amp circuit rating?
 
frizbeedog said:
Lets say residential heat pump. 40 amp Circuit breaker, #10 wire, to non-fused disconnect, to equipment terminations. overloads not installed in circuit.

30 amp circuit rating? or 40 amp circuit rating?
Click to expand...


IMSO, it would be 30 amps or whatever the nameplate states as the minimum circuit ampacity since the 40 amp breaker is not providing overload protection.
 
wirebender said:
IMSO, it would be 30 amps or whatever the nameplate states as the minimum circuit ampacity since the 40 amp breaker is not providing overload protection.
Click to expand...

I'm leaning that direction. Thanks for your input.
 
wirebender said:
210.3 states that the BC rating is determined by the OCPD. In this case the OCPD is integral to the heat pump. If the 40 amp breaker was the OCPD you couldn't use #10.
Click to expand...

So 210.3 does not apply to my question? I'm thinking.
 
frizbeedog said:
So 210.3 does not apply to my question? I'm thinking.
Click to expand...
Can't tell yet... you're not being specific enough.

If the circuit in question is an individual branch circuit, i.e. supplies only one outlet, the rating is that of the OCPD in the panel. The conductors must have a corresponding ampacity, in most cases*, regardless of the amperes drawn by the load. *Some circuits, such as those with a motor load, may permit an OCPD rating higher than the ampacity of the circuit conductors.
 
frizbeedog said:
Lets say residential heat pump. 40 amp Circuit breaker, #10 wire, to non-fused disconnect, to equipment terminations. overloads not installed in circuit.

30 amp circuit rating? or 40 amp circuit rating?
Click to expand...

Like this....I'm just running circuit conductors and installing the larger breaker as allowed for this. What's the circuit's rating?
 
Last edited:
frizbeedog said:
Lets say residential heat pump. 40 amp Circuit breaker, #10 wire, to non-fused disconnect, to equipment terminations. overloads not installed in circuit.

30 amp circuit rating? or 40 amp circuit rating?
Click to expand...


Just use a 30 amp breaker. 40 amp is the maximum. Nothing says you have to use the max.
 
wirebender said:
Just use a 30 amp breaker. 40 amp is the maximum. Nothing says you have to use the max.
Click to expand...

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.
 
frizbeedog said:
What's the circuit's rating?
Click to expand...

I say it is a 30 amp circuit.

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...

I believe this is referring to the maximum OCPD you may normally use. For #10 this is 30 amps.

If this isn't the case then the last sentence:

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...

would not be necessary.

IMSHO :D
 
Status
Not open for further replies.
Top