In many Power over Ethernet (POE) setups the transmission voltage is 48V or slightly more. While higher voltage has obvious efficiency advantages, how safe it is? Is there any risk of electrocution when accidentally exposed, in particular to children? Such wirings lack the protection that is used for 120/230V, and frankly the difference between 48V and 120V doesn't seem to be that significant.
Answer
frankly the difference between 48V and 120V doesn't seem to be that significant.
120V is 2.4 times higher than 48V - hardly what I would call 'not that significant'. 120VAC is even worse, for two reasons:-
120VAC has a peak voltage of 170V, 3.5 times higher than 48VDC.
The 'electric shock' feeling occurs on every peak of the AC waveform, whereas with DC it mostly occurs on initial contact.
It only takes about 30mA of 60Hz AC current through the heart to cause fibrillation, compared to 300-500mA of DC current. The 'let go' current (above which you cannot let go of a grasped conductor) is 4 times higher for DC than AC. So that means you need 4-17 times more DC voltage to get a fatal shock.
Combine 2.4 times higher voltage with 4-17 times higher susceptibility, and 120VAC is approximately 10-40 times more deadly than 48VDC.
But is 48VDC safe in an Ethernet cable? Provided you don't strip off the insulation and poke the bare wires into your flesh, the chances of getting a fatal electric shock from it are negligible. I know from personal experience because I was a telephone exchange technician for 15 years, and regularly worked on live equipment with exposed contacts. The biggest DC shock I ever got was a light tingle when grasping a 50V bus bar (90VAC ringing was a different story...).
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