If a device requires 30W, what type of PoE protocol does it likely use?

A device that requires 30W would likely use the 802.3at Power over Ethernet (PoE) protocol, also known as PoE+. This protocol can provide up to 30W of power per port, which aligns perfectly with the device's requirement.

The 802.3at standard is an enhancement over the earlier 802.3af standard, which can only supply up to 15.4W. Given that 30W exceeds the maximum output of the 802.3af standard, it's clear that a device with such a power requirement could not operate effectively with it.

While the 802.3bt standard does provide even more power, up to 60W or even 100W depending on the implementation, the specific requirement of 30W does not necessitate the advanced capabilities of this protocol. Therefore, among the protocols listed, 802.3at is specifically designed to cater to devices with moderate power needs like the one described.