I’ve checked with Ubiquiti and they said
“All the passive injectors in all switches sense their current draw and will disconnect power if it exceeds a certain value, so they don’t burn up an improperly connected cable or device.”
They go on to say “802.3af and 803.3at POE+ compliant devices can be powered with passive power - I do this all the time. Including bt (PoE ++) units from the passive 50V injectors. They work just fine.”
My understanding is Ubiquiti’s passive POE ports are mode B and use pins 4,5 7 and 8 whether 24v or 48V and are powered constantly when switched on through their GUI. In contrast, active POE or POE+ ports autosense using the industry standard methods to decide when and if to provide PoE or not.
They finally say “No 802.3af/at/bt PDs I am familiar with are incapable of working with a UBNT passive PoE source - they all just work. And they will be modeB unless it’s one of the oddball 4 pair units, which look like 802.3bt power (unless they are 24V, obviously).”
Based on this I think its safe to use 48v passive POE power on my HA Yellow. Only one way to find out!