The Cisco Catalyst 4500 Series external AC power shelf must be used in conjunction with the 1400 WDC power supply. In addition to providing power for the chassis, fans, and non-PoE line cards, the 1400 WDC power supply contains a power entry module (PEM). The PEM is used to pass-through additional power to the chassis backplane-power demanded by the PoE line cards. The chassis power trace used for PoE is independent from the one used by the supervisor engine(s), fan tray, and backplane components. The 1400 WDC power supply can accept up to 7500 WDC for data and PoE applications. Up to 1400W can be dedicated for data (supervisor[s], fan tray, etc.), while the remaining power is passed through via the PEM and is used for PoE.