Branch ckt question

[Bob Anchorite]

I am a student in code classes. Regarding 210.19(A)1 [2002 NEC] and the exception. The instructor gave a complex explanation that I did not get.

From (1): Branch-circuit conductors shall have an ampacity not less than the max. load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and non-continuous loads, the min. branch circuit conductor size , before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

So, if I have a non-continuous load of say 10 amps and an appliance for a continuous load of 18 amps, then I would take 10 amps plus (18 amp x125%) for a total of 32.5 amps... is this part correct or not?

Then the exception: Where the assembly, including the overcurrent devices protecting the branch ckts, is listed for operation at 100% of its rating, the allowable ampacity of the branch circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

Now what's the difference??? Please give a few examples.

Bob

 

[Pierre C Belarge]

Bob
Yes, you are correct.



100% rating of overcurrent devices is really a specialty item (my opinion).

These devices are not for 120 volt rated BCs. Also I believe the smallest size overcurrent 100% rated device is somewhere around 225 amps or larger. And the biggest kicker- VERY EXPENSIVE

 

[templdl]

And an even bigger kicker is that a 100% rated breakers that I have sold were identical to a standard breaker except that it has been tested and listed for a 100% application when applied with properly sized and rated cable.
If applied correctly it is ment to save money overall when the cost of the cable if considered. The 100% comes from how the cable is allowed to be sized by the NEC. The instructions the are supplied with the 100% breaker will reflect this also. It's all about being able to apply a smaller cable but maintain a given temperature rise at the termination of the breaker.