Differences in Protection: Power over Ethernet vs. Power over Data Line (Download)
If you’re designing anything with Power over Ethernet (PoE) or Power over Data Line (PoDL), these systems can be directly tied back to plain old telephone service (POTS) technology.
While multiple innovations have sprung up between POTS and PoE/PoDL systems, POTS was the landline service used for “home phones” from the late 19th to the late 20th century. Since many engineers haven’t thought of POTS for a some time, it pays to take a look back to understand why circuit protection remains a high priority in PoE and PoDL designs.
In a way, POTS could be considered one of the first systems to power devices not using traditional AC mains. For a quick history lesson on POTS, the phone line utilized a pair of conductors, known as the “tip and ring,” that were commonly held at −48 V DC between the two conductors.