4 ms·

Kind of curious about this actually. IIRC ethernet cable side is only magnetically coupled to the port/device side via small transformers. So running DC would

Kind of curious about this actually. IIRC ethernet cable side is only magnetically coupled to the port/device side via small transformers. So running DC would probably just melt the cable or transformers but is not really likely to damage the device side (? Not actually sure about this). But in this case it runs mains AC.. so... Do we expect the cable to blow first due to the high current, saving the device, or do would we expect the brief period of AC would cause enough induced current on the device side to also fry that?

ajsnigrutin 4y ago
Depending on the implementation, but most probably it would burn the coils ("transformer") in the port, and probably the whole port module around, since the energies are high enough to burn quite a large chunk of material. Cables are a lot thicker than the electronics inside the port itself, so my bet would be, port goes first, probably fails in a way that disconnects the current, if not, the ethernet cable would probably compete with the circut breaker on who melts first (circut breakers, even if they're marked with (eg.) 20A on them, survive a much higher current for a short time, before they eventually fail, due to some electronics, especially motors and large lightbulbs act almost like a short circut when they're starting up).
xani_ 4y ago
Well ,first off, in POE powered devices it is connected to device, and I'd imagine in many cases (of being cheap) it would be directly coupled to device. > So running DC would probably just melt the cable or transformers but is not really likely to damage the device side (? Not actually sure about this). A step of voltage, whether that's just turning on AC on top of the cycle or just pushing DC thru it would go thru the transformer in form of short spike. So sure, looking at random transformer data they are protected to like 1000Vrms so it wouldn't jump thru isolation, but initial magnetic spike might, and then it is up to any surge protection on the other side to ground that > But in this case it runs mains AC.. so... Do we expect the cable to blow first due to the high current, saving the device, or do would we expect the brief period of AC would cause enough induced current on the device side to also fry that? I'd guess transformer would be the highest resistance/area thing in the chain so it would melt first.

ajsnigrutin 4y ago

Depending on the implementation, but most probably it would burn the coils ("transformer") in the port, and probably the whole port module around, since the energies are high enough to burn quite a large chunk of material. Cables are a lot thicker than the electronics inside the port itself, so my bet would be, port goes first, probably fails in a way that disconnects the current, if not, the ethernet cable would probably compete with the circut breaker on who melts first (circut breakers, even if they're marked with (eg.) 20A on them, survive a much higher current for a short time, before they eventually fail, due to some electronics, especially motors and large lightbulbs act almost like a short circut when they're starting up).

xani_ 4y ago

Well ,first off, in POE powered devices it is connected to device, and I'd imagine in many cases (of being cheap) it would be directly coupled to device. > So running DC would probably just melt the cable or transformers but is not really likely to damage the device side (? Not actually sure about this). A step of voltage, whether that's just turning on AC on top of the cycle or just pushing DC thru it would go thru the transformer in form of short spike. So sure, looking at random transformer data they are protected to like 1000Vrms so it wouldn't jump thru isolation, but initial magnetic spike might, and then it is up to any surge protection on the other side to ground that > But in this case it runs mains AC.. so... Do we expect the cable to blow first due to the high current, saving the device, or do would we expect the brief period of AC would cause enough induced current on the device side to also fry that? I'd guess transformer would be the highest resistance/area thing in the chain so it would melt first.