If I am correct, most circuit breakers are rated at 80%. That is, they can carry their full rated current for a short time, but for continuous loads that may last for hours, they are only rated for 80% of their current rating.
210.19 (2002 NEC) makes it clear that a branch circuit has to be sized for 1.25 times the continuous load. Since a branch circuit is sized per the breaker, the breaker has to be 1.25 times the continuous load.
215.3 makes the same case for feeders. The overcurrent device shall not be less than 1.25 times the continuous load.
230.42(1) states the minimum size for service entrance conductors. Basically, 1.25 times the continuous load unless the breaker is 100% rated. For a 100% rated breaker, the conductors can be sized at 100% of the continuous load.
Question: Why doesn't 230.42 require the breaker to be sized for 1.25 times the continuous load? Also, why are smaller wires allowed for a 100% rated breaker. It seems like this article should be setting minimum sizes on the breakers instead of minimum sizes on the conductors.
Final question: Do the unit loads in table 220.3(A) already have the 1.25 factor built in, or do I need to multiply lighting loads taken from this table by 1.25?
Thanks: Steve
210.19 (2002 NEC) makes it clear that a branch circuit has to be sized for 1.25 times the continuous load. Since a branch circuit is sized per the breaker, the breaker has to be 1.25 times the continuous load.
215.3 makes the same case for feeders. The overcurrent device shall not be less than 1.25 times the continuous load.
230.42(1) states the minimum size for service entrance conductors. Basically, 1.25 times the continuous load unless the breaker is 100% rated. For a 100% rated breaker, the conductors can be sized at 100% of the continuous load.
Question: Why doesn't 230.42 require the breaker to be sized for 1.25 times the continuous load? Also, why are smaller wires allowed for a 100% rated breaker. It seems like this article should be setting minimum sizes on the breakers instead of minimum sizes on the conductors.
Final question: Do the unit loads in table 220.3(A) already have the 1.25 factor built in, or do I need to multiply lighting loads taken from this table by 1.25?
Thanks: Steve