If ventilation for combustion is supplied mechanically, the ventilating system shall be ____ interlocked with the burner.

When ventilation for combustion is supplied mechanically, it is essential for the ventilating system to be interlocked electrically with the burner. This interlocking ensures that the burner only operates when the ventilation system is functioning properly, providing a safe environment by preventing the buildup of hazardous gases that may occur if the burner operates without adequate airflow.

An electrical interlock allows for an automatic shutdown of the burner if the ventilation fails or is turned off, thereby enhancing safety by ensuring that combustion air is available when needed. This is particularly crucial in oil burner systems to avoid potential accidents associated with insufficient ventilation.

Other types of interlocking, such as pneumatic or hydraulic, are not utilized in this context because they do not offer the same level of reliability and safety in monitoring and controlling combustion air supply. Manual interlocks also present risks, as they rely on human intervention which can be overlooked or improperly managed, increasing the chance of unsafe operating conditions. Therefore, the electrical interlocking system is the most appropriate and safest choice for mechanically supplied combustion ventilation.