CSLB C-46 Solar ContractorSafetyHard
An authorized employee is preparing to work on an energized 480V commercial solar inverter that is known to have exposed live parts. According to NFPA 70E, what is the MINIMUM approach distance (MAD) for unqualified persons to this equipment?
- A0 feet (unlimited approach if not touching)
- B10 feet
- C3 feet 6 inches
- D5 feet
Show answer & explanationAnswer & explanation
Correct answer: B. 10 feet
For an unqualified person, NFPA 70E establishes a Limited Approach Boundary. For energized 480V equipment with exposed live parts, the Limited Approach Boundary is generally 10 feet. Unqualified persons should not cross this boundary unless escorted by a qualified person.
Why the other options are wrong
- A. This is incorrect and extremely dangerous; even approaching without touching can lead to arc flash or shock.
- C. 3 feet 6 inches is typically the Restricted Approach Boundary for 480V, applicable to qualified persons only, and much closer than an unqualified person should be.
- D. 5 feet is not a standard boundary for 480V for unqualified persons; it falls between the Limited and Restricted boundaries.
NFPA 70E Limited Approach Boundary (Unqualified)
The Limited Approach Boundary (LAB) is the closest an unqualified person can approach exposed energized electrical conductors or circuit parts. For 50V-750V, it is 10 feet.
- Protects unqualified personnel from arc flash and shock.
- Unqualified persons must not cross the LAB unless escorted.
- LAB varies based on voltage levels.
Memory trick: Ten feet for the 'un-qual', stay far, stay safe, don't fall!