Power Over Ethernet (PoE)

As the name implies, some devices can provide power to other devices over an ethernet connection. Typically, the power is supplied by a PoE-capable switch, or by a dedicated single-port power supply called a PoE injector.

Suppliers and Consumers

A PoE device which supplies power to other devices is technically called a "PSE" or Power Sourcing Equipment.

A PoE device which consumes power from a PSE is technically called a "PD" or Powered Device.

Some devices (typically switches) can do both. For example, a small 8-port switch may be a PD capabale of receiving its power from a high-powered PSE, and can then serve as a PSE itself by passing on some of that power to other downstream PDs.

Interpreting Specifications

When choosing a network switch to supply PoE, there are two primary variables to consider:

• Maximum power required from any single port

• Maximum power required in total from all ports

Maximum Power per Port

There are several PoE standards that were developed over time as power requirements changed. (Wikipedia)

Different versions are in common use today, and you may see references to the following:

• PoE: 802.3af - approx. 15W max per port
• PoE+: 802.3at - approx. 30W max per port
• PoE++: 802.3bt - approx. 60W max per port

The PoE standards provide a method for PSEs and PDs to negotiate an appropriate supply of power over their link, which creates a plug-and-play experience for users and avoids damage to equipment.

WARNING

There are also older versions of PoE which were developed in proprietary contexts before standardization, as well as static-supply PoE injectors which do not negotiate power levels and can therefor damage some devices.

Maximum Power Overall

Switch specification sheets will tell you the "power budget" of a PoE-capable switch. This is the total amount of power the switch can output (don't confuse this with the amount of power the switch will consume, which will be a bit higher).

TIP: Fan Noise

If you are concerned about fan noise in a quiet show environment, be aware that switches with higher power budgets often have larger power supplies, higher heat dissipation, and therefore louder fans. A higher power budget is not always better.

Example

Model: Cisco SG350-28MP

Specification	Notes
PoE Type: 24 ports support PoE+	Of the 24 ports which are PoE-capable (GE1-GE24), any given port can provide up to 30W.
Power Budget: 382W	The total power consumption of connected PDs cannot exceed 382W.

Choosing Equipment

EXAMPLE: Intercom Tech Table Distro

Powered devices:

Model	Qty	Power Consumption
HRM-4X	10	14W
HKB-2X	4	14W
HXII-BP	1	4W
Total	14	200W

Switch candidates:

Model	PoE Ports	Type	Power Budget	Result
Cisco SG350-10P	8 ❌	PoE+ ✅	62W ❌	❌ Not enough ports
Cisco SG350-28P	24 ✅	PoE+ ✅	195W ❌	❌ Not enough power
Cisco SG350-28MP	24 ✅	PoE+ ✅	382W ✅	✅ Meets requirements