What marking must be installed at the service disconnect according to Article 230?

The requirement for a permanent marking indicating voltage and phase at the service disconnect is crucial for safety and operational clarity. This marking provides essential information that helps electrical personnel, such as maintenance technicians or emergency responders, quickly understand the characteristics of the electrical system they are working on.

By ensuring that voltage and phase are clearly marked, it minimizes the risk of accidental mishandling or misunderstanding of the electrical system's capabilities and potential hazards. This is particularly important in service disconnects, where understanding the electrical specifications is vital during troubleshooting or maintenance activities.

In contrast to the other options, while dates of installation, the installer’s identification, and service history logs might be useful for record-keeping or administrative purposes, they do not contribute directly to the operational safety of the service disconnect in the same way that voltage and phase markings do. The NEC emphasizes the importance of clear and immediate operational information at points of connection, which is why the permanent marking indicating voltage and phase is mandated.