Yes, it is common for inspectors to question the use of aluminum mechanical set-screw type connectors to extend main service conductors, especially in a situation where copper conductors are already present. Here are a few reasons why: Safety concerns

Aluminum and copper have different thermal expansion rates, which can lead to loose connections over time. Loose connections can create a fire hazard.

Code requirements

In some areas, code requirements prohibit the use of aluminum mechanical set-screw type connectors for main service conductors.

Electrical performance: Copper is a better conductor of electricity than aluminum, so using aluminum connectors can reduce the efficiency of the electrical system.While the inspector may have ultimately passed your installation, it is important to note that this does not mean that it is the best or safest practice. It is always recommended to use the appropriate materials and methods for electrical installations, especially when dealing with main service conductors.In your case, the inspector may have passed the installation because: He/she was aware of the cost constraints of the homeowner and did not want to burden them with unnecessary expenses. He/she believed that the aluminum connectors were properly installed and would not pose a safety hazard. He/she may not have been familiar with the specific code requirements in your area regarding the use of aluminum connectors.It is important to communicate openly with the inspector and address any concerns they may have. By explaining your reasons for using the aluminum connectors and providing evidence of their proper installation, you can help the inspector make an informed decision. Flag for review