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In the world of standard home or office appliances, the default power solution is to plug them into AC power wall outlets, which then enables the device to print, communicate, charge, drill, and display in addition to a number of other use possibilities. In the case of devices that require a wired Ethernet cable for operation, cables are already running to a device. It might, therefore, seem redundant to also plug in an AC power cable, especially considering that power will likely need to be converted to DC—already the basis of what is shooting along via Ethernet as ones and zeros. This situation becomes not only slightly annoying, but also costly when dealing with a remote device that does not necessarily have a readily available power outlet nearby. Which begs the question: Why not obtain energy from the Ethernet cable itself? Such is the promise of Power over Ethernet, commonly referred to as "PoE," which delivers power over the same Ethernet cables that transfer data. As classified by IEEE 802.3, there are three official PoE standards: Alternative A; Alternative B; and, as of September 2018, 4PPoE. Alternative B is perhaps the most straightforward, with power transferred on two twisted pairs, while data flows along the other two. Alternative A, however, shares data and power on the same lines. This is possible because of differential signaling used in wired Ethernet, where ones and zeros are measured by the difference between the two lines, not between the line and ground. This is also the basis for 4PPoE, which, as the name implies, carries power over all four twisted cable pairs. This allows for up to 100 watts of power on a Ponderings About PoE and Protection By Jeremy Cook for Mouser Electronics Power over Ethernet, known as PoE, has found many uses for both data and power transfer to remote devices. As PoE and its uses expand, designers need to consider how to keep both Powered Sourcing Equipment (PSE) and powered devices safe through power fluctuations. | 15 |

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