I have a two wire system in my house. The electrical code states that it will be replaced with GFCI to allow the 3 pin connector to be used safely. All 10 units work great and I'm learning as I go. Before I started, I had to rent a meter from an electric company. There's no point in getting a shocking surprise. When switched on, all GFCIs work correctly. Cycle power and everything still works without the need for a reboot. The red buttons look cool. Each block has a small green light that glows when they are powered. I will order more soon.