Recommended Grounding Practices for Single-Polarity D-C Structures AIEE Committee Report

Recommendations for grounding metal structures surrounding single-polarity d-c circuits are different from those for surrounding ungrounded d-c or a-c systems. For more than 50 years, it has been common practice to insulate the surrounding structures of d-c apparatus (300 volts and over) where one polarity is grounded and switching is done only on the opposite polarity. When the electric system is ungrounded, 2-pole circuit breakers are used and the surrounding structures are grounded as explained in AIEE Report no. 953.1 Case histories show that danger to personnel results from high currents rather than high voltage. Applications in the mining, heavy industrial (steel mill for example), railway, and electrochemical fields are separately discussed and recommendations drawn for the maximum safety to personnel and equipment.