For connecting new devices I have separated two ports on my switch into a single dedicated VLAN. So I connect the new devices to one of these ports and patch the Ethernet connection of one PC to the other port, this way they are in their own L2 and can't impact the network.
Another solution is to use a Laptop and connect a new device there first for setup purposes. Just don't connect a device with unknown/conflicting settings to your production network.