On Networks PL500P User Manual - Manual (Page 12)

Getting Started
12
Powerline PL500 Series Adapter
 To set the encryption key for more Powerline adapters:
1. Plug in the next Powerline adapter.
It cannot communicate with the first and second Powerline adapters yet because it is
using a different encryption key.
2. On the first Powerline adapter, press the Security button.
3. Within two minutes, press the Security button on the Powerline adapter that you are setting
up.
The Powerline adapters detect each other and synchronize using the random encryption
key.
Now, all three Powerline adapters use the same random encryption key to communicate.