Under which condition can a non-metallic conduit be used for grounding purposes?

The use of non-metallic conduit for grounding purposes is acceptable when insulated grounding conductors are used. This is because non-metallic conduit itself does not have conductive properties, so it cannot act as an effective ground. However, when insulated grounding conductors are utilized within such conduit, those conductors can provide a safe path to ground, ensuring that any fault current can be properly directed away from users and equipment.

This scenario demonstrates the importance of maintaining proper grounding practices in electrical installations. Insulated conductors ensure safety even in non-conductive pathways, as they minimize the risk of short circuits and protect against electrical hazards.

The other options imply practices that either do not adhere to safety standards or misinterpret the role of grounding in electrical systems. For example, using non-metallic conduit with metallic fittings or for system voltages over 600 volts may lead to confusion about grounding effectiveness, while connecting two metal boxes does not inherently provide a grounding solution unless it adheres to specific installation methods and codes. Thus, it is essential to use insulated grounding conductors in conjunction with non-metallic conduit to effectively achieve grounding.