Master Electrician Exam (NEC)Special Occupancies, Equipment, and ConditionsHard
A master electrician is installing a new wind electric system for a commercial property. The system includes an inverter that is connected to the normal power supply. The inverter has a continuous output current of 50 amperes. What is the minimum continuous current rating required for the conductors connecting the inverter output to the building's electrical system?
- A80 amperes
- B75 amperes
- C62.5 amperes
- D50 amperes
Show answer & explanationAnswer & explanation
Correct answer: C. 62.5 amperes
According to NEC 694.30(A) and 210.20(A), conductors supplying continuous loads (which inverter output is considered) must have an ampacity not less than 125% of the continuous current rating of the load. Therefore, for a 50-ampere continuous output, the conductors must be rated for at least 50 A * 1.25 = 62.5 A.
Why the other options are wrong
- A. This is significantly higher than the minimum required.
- B. This is higher than the minimum required, but 62.5A is the minimum.
- D. This is the continuous output current, but conductors for continuous loads require a 125% factor.
Wind System Inverter Conductor Sizing
Sizing conductors for the continuous output of a wind electric system inverter, treating it as a continuous load.
- Inverter output is a continuous load.
- Conductor ampacity must be 125% of continuous current.
- Governed by NEC 694.30(A) and 210.20(A).
Memory trick: Wind inverter conductors need 25% extra capacity, like a strong breeze needs extra sail.