Tue Mar 12, 2024 9:12 pm
If the device has negative ground, it needs to be completely isolated from common (positive in the case of so-called -48V systems) ground.
They are called -48v but there is not any actually negative voltage involved, as they were born for easyness/convenience in telecommunication installations an backup via a series of 6 or 12 or 24V batteries, it is just the polarity of the ground that is inverted, a low voltage insulated device, like many Mikrotik devices, in a full plastic enclosure, would have no issues with simply inverting the power poles, but the RB5009 has metallic case/parts that are inherently grounded (to the 0 or negative).
There used to be cars (mainly British I believe) that used positive ground, I learned the lesson a lot of years ago attempting to install a "normal", negative ground radio in one of those, the magic smoke came out in no time.