What should not penetrate the metal housing for fuel gas appliance connectors?

Unprotected copper tubing should not penetrate the metal housing for fuel gas appliance connectors because it can pose a safety risk. The metal housing is designed to provide a secure and reliable connection while protecting the gas line from potential hazards such as leaks or physical damage. When unprotected copper tubing penetrates the housing, it may be subject to corrosion, wear, or other environmental factors that could weaken it over time, leading to potential gas leaks.

In contrast, materials like stainless steel connectors are designed for durability and compatibility with gas appliances, providing a safe and secure method of connection. Copper tubing can be safe when properly protected and treated, but unprotected copper is susceptible to failure in the harsh conditions that might surround gas appliance installations. Thus, maintaining the integrity of the metal housing and the connectors is vital to ensuring safe operation.