Under what condition does the Code require the exposed noncurrent-carrying metal parts of fixed equipment to be grounded because of where the equipment is located?
- Where it is within 8 feet vertically or 5 feet horizontally of ground or grounded metal that persons can touch
- BWhere it operates at more than 50 volts to ground, regardless of where in the building it is installed or how it is mounted
Voltage to ground appears in the section, but the threshold is not 50 volts and voltage alone is not the location-based trigger this question asks about.
- CWhere it is installed in a room whose floor is concrete rather than wood or another insulating material
Floor material is a reasonable-sounding proxy for a grounded surface, but the Code states the rule in terms of distance from ground or grounded metal objects.
- DWhere it weighs more than 100 pounds and is fastened permanently to the building structure or its steel
Weight and permanence describe what makes equipment fixed rather than portable. They do not decide whether grounding is required.
Why A is correct
The zone is defined by human reach. Within 8 feet up or 5 feet across, a person standing on or touching grounded metal can also touch the equipment, so a fault that energizes the frame puts full voltage across that person. Grounding the frame gives the fault a path that opens the overcurrent device instead.
What this question is testing
The item tests recall of a dimensional criterion and whether the candidate can distinguish a location-based trigger from voltage-based and construction-based ones in the same section.
On the job
The 8-foot and 5-foot figures decide a lot of everyday questions: whether a metal-cased control panel in a shop needs a grounding conductor, whether a piece of process equipment sitting near structural steel is in the zone, and how far a metal enclosure has to be from a grounded pipe to fall outside it. In practice almost everything in an industrial building lands inside the zone, which is why grounding fixed equipment is close to universal.
Memory technique
Eight feet up, five feet across. Inside that box, ground it.
Exam tip
Grounding requirements for fixed equipment come in a list. Read the whole list before deciding a piece of equipment is exempt.
Where to look it up
Look in the grounding article at the section on equipment fastened in place or connected by permanent wiring methods.