Glen wants to know if ransomware can happen if you unplug your backup from the network. Leo says not until he plugs it back in. But it's less likely with a home-based system than say, a commercial network. So clean up the infected computer before reconnecting the backup, otherwise, it could infect it. A lot of ransomware also has time-released capability. It may not infect right away. So if Glen has backup unplugged from the network, he should keep it that way until he's wiped the hard drive and removed the ransomware.
Leo also recommends little ejector bays for the drive. Once he's done the backup, he can eject the hard drive and keep it disconnected. Just in case.
This is also why cloud backup can come in handy. Cloud backup services like iDrive (Sponsor) will also do snapshots of a hard drive, so he can always go back in time should it happen.
From the chatroom, he can set the computer up with a physical dongle like YubiKey that would require authentication before ransomware can escalate and bypass security. It's a physical connection. It would take some jiggering to get it right, but it would certainly make it harder.