Power-over-Ethernet (PoE) is a means of distributing power to Ethernet devices over the Ethernet cable using either data or spare pairs. PoE eliminates the need for power supplies at the Ethernet device. Common applications of PoE are security cameras, IP Phones and wireless access points (WAP). The host or mid-span equipment that supplies power is the power source equipment (PSE). The load at the Ethernet connector is the powered device (PD). PoE protocol between PSE and PD controlling power to the load is specified by IEEE 802.3bt standard. Transformers are used at Ethernet host ports, mid-spans and hubs, to interface data to the cable. A DC voltage can be applied to the center tap of the transformer with no effect on the data signals. As in any power transmission line, a relatively high voltage (approximately 50 V) is used to keep currents low and minimize the effects of IR drops in the line to preserve power delivery to the load. Standard 2-Pair PoE delivers approximately 13 W to a type 1 PD, and 25.5 W to a type 2 PD, whereas standard 4-Pair PoE are capable of delivering approximately 51 W to a type 3 PD and 71 W to a type 4 PD.