The frames of all portable motors over a certain voltage must be guarded or grounded. What is the voltage?

• A. 100 volts
• B. 120 volts
• C. 150 volts
• D. 220 volts

Answer: (C)

Keep the frame safe by making sure it can’t be touched if something goes wrong. The frame of a portable motor is metal and can become energized if insulation fails or a wire gets damaged. When the voltage to ground reaches a level where a shock would be dangerous, the frame must be either guarded (enclosed so you can’t touch it) or grounded (tied to earth to provide a fault path). The threshold used here is 150 volts, so frames above that level require guarding or grounding. At voltages below that, this particular protection rule doesn’t apply, and the focus would be on general grounding practices and safe enclosure.