What type of protective device is required for instrument transformers used on the supply side of service disconnecting means?

The requirement for overcurrent protection for instrument transformers used on the supply side of service disconnecting means is primarily based on safety and operational integrity. Instrument transformers, such as current transformers and potential transformers, are crucial for monitoring and controlling electrical systems. These devices step down high current and voltage levels to manageable values for metering and relay purposes.

Overcurrent protection is essential to guard against potential damage caused by excessive current flow. This can happen due to faults, overloads, or failures within the electrical network. By incorporating overcurrent protection, any fault condition can be quickly detected and isolated, preventing damage to the instrument transformers as well as enhancing overall system reliability.

In contrast, the other options do not specifically address the safety requirements for instrument transformers on the supply side. Surge suppressors protect against voltage spikes, grounding cables are aimed at providing a safe path for fault currents, and voltage regulators serve to ensure stable output voltage rather than protecting from excessive current. Thus, the requirement for overcurrent protection is a fundamental consideration that aligns with NEC guidelines and best practices in electrical safety.