What are the differences between the 1 and 1PM Shelly relay products?
The main differences are:
- the PM can measure power usage
- the PM relay is NOT isolated from the line voltage.
On the surface, these devices seem very similar, and you may ask – why not just buy a PM product for all my use cases. The reason is that sometimes you want to use a relay to control a low voltage load (for example my garage door opener), and in this case it is best to get the non-PM version with an isolated relay.
It is also a little confusing why there are L and L1 terminals on the PM products – these terminal are simply connected internally and are provided for convenience and may reduce the need for splicing wires.
The following drawing is helpful in understanding on the PM is wired:
