Exposed live parts of a control assembly operating at 480 volts must be guarded against accidental contact. Which method satisfies that requirement?
- ABrushing a coat of insulating paint over the exposed busbars and terminal connections
Insulating paint is not a recognized guarding method and has never been an acceptable substitute for an enclosure, a barrier, elevation, or restricted access.
- BPosting a warning sign on the door of the room in which the assembly is installed
Warning signs at entrances are separately required where live parts are exposed, but a sign does not guard anything and cannot stand alone as the method.
- CMounting the assembly so its live parts sit at least 4 ft above the finished floor
Elevation is a permitted method only at 8 ft or more above the floor. Four feet leaves live parts squarely within reach of a passerby.
- Locating the assembly in a room or vault accessible only to qualified persons
Why D is correct
Restricting the space to qualified persons is one of the listed guarding methods, and it works because the definition of a qualified person carries both skills and knowledge about the equipment and documented safety training to recognize and reduce the hazards. Anyone who enters that room is therefore assumed to understand what the exposed bus can do.
What this question is testing
This checks that you know guarding is a short closed list of methods rather than a general instruction to be careful. It also tests the 50 volt trigger and the 8 ft elevation figure, plus the role of a qualified person in making restricted access an acceptable method.
On the job
Industrial plants are full of this. Open control assemblies, exposed bus in a switchgear lineup, and older equipment with missing dead fronts all sit in areas where production staff walk. The usual fix is either restoring the enclosure or converting the corner into a restricted electrical room with a locked door and the required entrance signage. The 50 volt threshold catches things people assume are harmless, including many control circuits, and the elevation allowance is high enough that it is rarely the practical answer indoors.
Memory technique
Fifty volts starts it; enclose, restrict, screen, or raise it eight feet.
Exam tip
Remember two numbers here: guarding starts at 50 volts, and elevation only works at 8 ft or more.
Where to look it up
Article 110, the section on guarding of live parts, near the end of the general requirements. Qualified person is defined back in Article 100.