I just saw this,
Originally Posted by
stanfortyman
Read it again, and don't use logic. You canot use logic when reading the NEC.
So true.
Some confusion comes from the NEC where it states
"shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load." that is applied in various locations. This statement comes from the UL listing of circuit breakers.
From the 2003 UL white book
CIRCUIT BREAKERS, MOLDED-CASE AND CIRCUIT BREAKER ENCLOSURES (DIVQ)
MAXIMUM LOAD
Unless otherwise marked, circuit breakers should not be loaded to exceed 80 percent of their current rating, where in normal operation the load will continue for 3 hours or more.
This is difficult to apply to the typical general purpose lighting circuits. Since no one really knows how the circuit will be used or rarely used more than 3 hours.
From NEC 2008 Edition:
Article 210
II. Branch-Circuit Ratings
210.19 Conductors — Minimum Ampacity and Size.
(A) Branch Circuits Not More Than 600 Volts
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum 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.
And:
210.20 Overcurrent Protection.
Branch-circuit conductors and equipment shall be protected by overcurrent protective devices that have a rating or setting that complies
With 210.20(A) through (D).
(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.
While
Table 210.24 states Maximum Load under each circuit rating column,
each column refers to specific paragraphs of Section 210.23 A thru D
210.23 Permissible Loads.
In no case shall the load exceed the branch-circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it is rated. A branch circuit supplying two or more outlets or receptacles shall supply only the loads specified according to its size as specified in 210.23(A) through (D) and as summarized in 210.24 and Table 210.24.
(A) 15- and 20-Ampere Branch Circuits.
A 15- or 20- ampere branch circuit shall be permitted to supply lighting units or other utilization equipment, or a combination of both, and shall comply with 210.23(A)(1) and (A)(2)
(1) Cord-and-Plug-Connected Equipment Not Fastened in Place.
The rating of any one cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80 percent of the branch-circuit ampere rating.
(2) Utilization Equipment Fastened in Place.
The total rating of utilization equipment fastened in place, other than luminaires, shall not exceed 50 percent of the branch circuit ampere rating where lighting units, cord-and-plug connected utilization equipment not fastened in place, or both, are also supplied.
This is why we always need to know the purpose of the circuit.
Unless the circuit is a general purpose lighting circuit, the circuit should not be loaded more than 80%.