The short answer is yes, it's best if they're installed onto the same electrical circuit. When installing a powerline adapter, it's important to make sure the two adapters are plugged into outlets on the same circuit. This will allow them to connect and share data between each other more effectively. When installing a pair of adapters, both should ideally go into outlets that are part of one arrangement or group (for example: two groups in different rooms with no intervening wall switches). However, this isn't essential as long as each contains an always-on outlet and you avoid daisy chaining them by plugging only one device at first so that any switch can activate either unit. If your home network requires more than 2 adapters for full coverage then additional units may work better when plugged directly into mains sockets rather than via extension cables - which will limit their speed due to line attenuation