A liquid-filled transformer has a primary voltage of 12,470 volts and is surrounded by a 6-foot-high fence. The fence height must be extended 1 foot with at least how many strands of barbed wire on top of the fence?

• A. 2
• B. 3
• C. 1
• D. no minimum required

Answer: (B)

The main idea is that barriers around high-voltage equipment include barbed wire on top to deter climbing. When you raise a 6-foot fence by one foot, the added height makes climbing more difficult, and the minimum practical protection at the top is three strands of barbed wire. Three strands provide multiple gripping points and create a stronger obstacle at the top, which is important around a liquid-filled transformer energized at 12,470 volts. Fewer strands wouldn’t give the same deterrent effect, while more strands would be more than typically required for this situation. So the minimum required is three strands.