Transfer Switch

A transfer switch is an electrical device that safely switches a home’s power source between the utility grid and a backup source — such as a solar battery system or generator. It prevents the two power sources from being connected simultaneously, which could cause dangerous backfeeding to the grid.

In solar-plus-storage installations, the transfer switch is a critical safety component. When the grid goes down, the transfer switch disconnects the home from the utility and connects it to the battery/solar system. When grid power is restored, it switches back. There are two types: manual transfer switches require someone to physically flip the switch, while automatic transfer switches (ATS) detect the outage and switch over within milliseconds, often before you even notice the power was out. Most modern home battery systems (Tesla Powerwall, Enphase, etc.) include an integrated automatic transfer switch or equivalent gateway device. For whole-home backup systems, the transfer switch is installed at the main service panel. For critical-loads-only backup, it is installed between the main panel and the critical loads subpanel. Transfer switches must be rated for the amperage they handle and installed by a licensed electrician to meet NEC requirements.