Since shelly output is a relay and schematic is depicted in:
Shelly Plus 1
Shelly Plus 1 is a small form factor smart switch with potential-free contacts, which allows remote control of electric appliances through a mobile phone,…
kb.shelly.cloud
as
[Blockierte Grafik: https://kb.shelly.cloud/__attachments/35094529/Plus-1-internal-schematics.png?inst-v=fba0f242-f9c8-47aa-85fd-3758357f05b6]
Can be connected as follows:
Powered by AC phase voltage, using phase voltage as switch.
Shorting (closing) a DC circuit, being DC from lets say 1V (<0V) to rated DC voltage.
A) FLOATING DC:
B) GROUNDED DC:
I've consulted some diagrams available of the "1" version (about 12 wiring diagram combinations available) but those are not among them.