At what voltage must trailing cables without cable reels have grounded metallic shields?

Trailing cables without cable reels must have grounded metallic shields when operating at a voltage of 661 volts. This requirement is based on safety regulations designed to minimize the risk of electric shock and provide effective grounding to neutralize any potential contact with live wires. The grounded metallic shield acts as a protective barrier, helping to ensure that any electrical malfunction does not lead to hazardous situations for workers.

Grounding of these shields becomes crucial at this specific voltage level due to the increased risk associated with higher voltages in mining environments. At lower voltage levels, such as 220 volts or 380 volts, the risks associated with ungrounded cables may not warrant such stringent requirements, while at 1200 volts, there are additional considerations for cable types and constructions that must be taken into account. Thus, 661 volts is established as the threshold where grounded metallic shields become necessary to ensure safety and compliance with mining electrical standards.