[Clive] draws out a schematic, which is deceptively simple. The two LEDs are an older style of green LED, ... (FS140) whole house surge protector installed. Report comment. Reply.

Surge protectors expand your outlet capacity and keep devices safe from power surges. Here's how they work, and when to use one.

A good surge protector will have a certification logo from UL, ETL, or another Nationally Recognized Testing Laboratory (NRTL), usually on the back side. Sarah Witman/NYT Wirecutter.