Feeder sizing conflict in code

[eeprom]

Hello,
In article 215.2(A) the code says a feeder has to be size by either (1) 125% of the continuous load plus the non-continuous load OR (2) ampacity adjustment after load correction factors. This implies that if I have a commercial installation and after adjustments I end up with 310A, that I can use a feeder size of #350 MCM at 75C.

However, in 215.3, the feeder overcurrent protection requirements seem to override 215.2(A)(2). It states that if the feeder supplies continuous loads or any combination of continuous and non-continuous loads, then the feeder overcurrent protection has to be sized at 125% of the continuous load plus the non-continuous load, and of course the feeder ampacity needs to be at least as large as that.

Am I mistaken or does 215.3 completely nullify 215.2(A)(2)?

Thanks

 

[LionelHutz]

Well, one is the requirements for sizing wire and the other is the requirements for sizing protection. It's just how it is so each part can have rules.

 

[eeprom]

LionelHutz,
The two are related, as I'm sure you know. I have two choices to calculate feeder ampacity.

215.2(A)(1) 125% of the continuous load plus the non-continuous load
215.2(A)(2) ampacity adjustment after load correction factors

I have one choice to calculate overcurrent protection.
215.3 125% of the continuous load plus the non-continuous load

Clearly 215.2(A)(1) and 215.3 will result in the same number.
Consider that if you use 215.2(A)(2) and you end up with a smaller feeder number than 215.2(A)(2). You are still stuck with overcurrent protection that matches 215.2(A)(1).

I will not install a feeder conductor that has an ampacity less than the overcurrent protection.

So how could I ever use 215.2(A)(2)

 

[eeprom]

I had a typo in that.

215.2(A)(1) 125% of the continuous load plus the non-continuous load
215.2(A)(2) ampacity adjustment after load correction factors

I have one choice to calculate overcurrent protection.
215.3 125% of the continuous load plus the non-continuous load

Clearly 215.2(A)(1) and 215.3 will result in the same number.
Consider that if you use 215.2(A)(2) and you end up with a smaller feeder number than 215.2(A)(1). You are still stuck with overcurrent protection that matches 215.2(A)(1).

I will not install a feeder conductor that has an ampacity less than the overcurrent protection.

So how could I ever use 215.2(A)(2)?

 

[waross]

I will not install a feeder conductor that has an ampacity less than the overcurrent protection.

Good luck designing motor feeder circuits.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[eeprom]

Motor branch circuits are protected by the motor overload.

 

[waross]

Some codes equate overcurrent protection with fault current protection as opposed to overload protection.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[eeprom]

I understand. I'm just trying to understand how a person could reduce a feeder size as allowed in 215.2(A)(2) and then not having to size it up again because of 215.3. I found an article (310.12) that says for a single dwelling the feeder can be 83% of the feeder rating. I don't work on residential so it doesn't apply, but I would assume that is why 215.2(A)(2) is there.

 

[LionelHutz]

So how could I ever use 215.2(A)(2)

100% rated breaker.