Chains, Ropes, and Slings Test I Source: Questions and answers from the National Safety Council Progress Indicator: Question 5 of 20 5.  There are four approved methods for grounding of metallic frames, casing, and other enclosures of electric equipment receiving power from D.C. power systems with one polarity grounded. Which of the following is NOT specified as permissible? Choices: A solid connection to the mine track A solid connection to the grounded conductor of the system Silicon diode grounding Connection to any existing grounding system