What types of systems of 50 to 1000 volts are permitted but not required to be grounded?

The correct answer pertains specifically to systems supplying industrial electric furnaces. In the context of grounding and bonding, Article 250 includes various stipulations regarding the safety and functionality of electrical systems. While grounding is often necessary for various applications to ensure safety and prevent electrical faults, certain systems operating between 50 to 1000 volts—in this case, industrial electric furnaces—are permitted to operate without a grounding system. This flexibility is based on the nature of the equipment and the manner in which it is used in industrial settings.

Industrial electric furnaces typically have specific design attributes and operational protocols that minimize the risk of electrical shock or faults, often rendering grounding less critical compared to other systems. The choice to ground or not can depend on factors such as system function, environment, and the presence of other safety mechanisms. In contrast, other systems listed might be more closely regulated in terms of grounding due to their applications and potential safety hazards, making them less likely to be included in this category.