What marking is required on the insulation of positive conductors that are nonsolidly grounded?

For positive conductors that are nonsolidly grounded, the National Electrical Code (NEC) specifies that the insulation must be marked with the word "POSITIVE" or the symbol "+" in a color other than green. This marking is crucial as it provides clear identification of the conductor's function within the circuit.

Marking the positive conductor distinctly helps ensure that those working on or around the electrical system can easily recognize its purpose, reducing the risk of errors during maintenance or installation. The use of a color other than green is also important, as green is typically reserved for grounding conductors, thereby preventing any confusion between positive conductors and grounding systems.

This requirement emphasizes the importance of proper labeling and identification in electrical installations, ensuring safety and adherence to the NEC guidelines. The other options do not provide the necessary clarity and proper identification as mandated by the code, making option B the appropriate choice.