Electrician's Licensing Practice Exam

According to NEC, how is demand calculated if a branch circuit can handle 20 KW?

1. 75% of the total load

2. 100% of the first 10KW plus 50% of the remainder

3. 10 KW only

4. 50% of the total load

The correct answer is: 100% of the first 10KW plus 50% of the remainder

The correct approach to demand calculation for a branch circuit that can handle 20 KW, as outlined in the National Electrical Code (NEC), involves taking 100% of the first 10 KW and then 50% of the remaining load. This method recognizes that loads do not typically operate at full capacity simultaneously, which allows for a more accurate estimation of the demand on the circuit. In this case, the first 10 KW is fully accounted for since it is understood that these loads will be in use. For the portion above this initial 10 KW, only half is considered because the likelihood of all loads above this threshold operating at peak capacity at the same time is low. Thus, for a 20 KW load, you would calculate 10 KW + (50% of the remaining 10 KW), leading to a demand calculation of 15 KW. This method effectively helps in appropriately sizing circuits and ensuring the safe operation of the electrical system. Other choices do not accurately reflect NEC guidelines for demand calculation, leading to insufficient planning for potential loads when designing and installing electrical systems.