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Ethernet with PoE

The Compute Blade features a Gigabit Ethernet port that supports IEEE 802.3at (PoE+) and 802.3af (PoE).

Power Consumption

Power consumption will vary based on load, accessories connected, the power requirements of any devices installed in the M.2 slot, whether or not the CM4 is overlocked, etc.

A compute blade with a CM4 overlocked to 2GHz and a normal NVMe SSD consumes ~7W under load. Normal operation may range from 3W to 17W.

A cluster of 40 blades running CI/CD tasks in a production environment consumes 260-280W, with 20 blades @ 1.8GHz and 20 blades overclocked to 2GHz.


The cost to run a blade will depend on the power consumption considerations noted above and your local utility provider’s rates. Some providers will vary the cost of electricity over the course of a day (peak vs. non-peak), which can further complicate the equation.

You can use an energy cost calculator to figure out kWh per day, month, or year, then mulitply that by your local utility provider’s rates to determine the total cost to run a blade.


If a blade consumes 10W and runs 24 hours a day, that’s 0.24 kWh/d. A fully-populated 19” rack mount shelf with 20 blades would consume 4.8 kWh/d.

  • USD: At $0.20 per kWh, a blade would cost $0.048/d, or $0.96/d for a full shelf.
  • EUR: At €0.19 per kWh, a blade would cost €0.046/d, or €0.82/d for a full shelf.

PoE Modules

Different Compute Blade revisions use different PoE modules. See the table below.

VersionPoE ModuleVoltsWatts (Peak)PoE SupportClassification
RC2Silvertel Ag53055V20W (22W)IEEE 802.3af, 802.3atType 2, Class 4 1
v1.0Silvertel Ag54055V25.5W (30W)IEEE 802.3af, 802.3at, 802.3btType 2, Class 4 2

1 “The Ag5300 classification is fixed at Class 4, this means that an IEEE802.3at Type 1 or an IEEE802.3af PSE will default to Class 0. However an IEEE802.3at or IEEE802.3bt PSE will recognise the Class 4 as a Type 2 PD.” (source)

2 “The Ag5400 is a fixed Type 2 - Class 4 PD requesting 30W of power from a compliant IEEE802.3 Type 2 or greater PSE by displaying the correct class pulses shown in Table 3 below. If the Ag5400 is connected to a Type 1 PSE, the PSE will not recognise the Class 4 request from the Ag5400 and default to a Class 3 power level device and supply 15.4W.” (source)

PoE Standards

This is not meant to be an exhaustive reference. For detailed information, see Power over Ethernet.

StandardCommon NameTypePDMax. PSE
IEEE 802.3afPoE112.95W15.4W
IEEE 802.3atPoE+225.5W30.0W
IEEE 802.3btPoE++, 4PPoE351W60W
IEEE 802.3btPoE++, 4PPoE471.3W100W

Use Cat5 cabling or better. Cat3 can be used in certain low-power situations, but most should not find themselves in a situation where Cat3 is needed.

Switch Recommendation

A switch that supports IEEE 802.3at (PoE+) is recommended. However, IEEE 802.3af (PoE) is sufficient for a blade with a CM4 @ 1.8GHz and a standard NVMe SSD. Future M.2 modules (Coral, RAID, etc.) will require more power; 802.3af may not be adequate.


  • PoE standard(s) supported.
  • PoE budget.1
  • Port count.
  • Port speed.
  • Form factor.

1 Note the switch’s PSU, switch power consumption, and power available to PoE. Switches are not always capable of providing full power to all available switch ports. For example, a switch with a 500W PSU, with 50W switch power consumption, has a 450W PoE budget. That allows 26.25W per port for a 24-port switch, but only 9.375W for a 48-port switch.

Switches In Use

A list of switches that Compute Blade users have successfully used to connect and power Compute Blades. For reference only.

SwitchPart No.PortsPoE
Ubiquiti Switch Pro 24 PoEUSW-PRO-24-POE24x 1GbE RJ45, 2x 1/10GbE SFP+16x PoE+, 8x PoE++
HP 5120-48G-POE+JG237A48x 1GbE RJ45, 4x SFP, 2x Expansion48x PoE+
Zyxel GS1200-5HP v2GS1200-5HPV2-EU0101F5x 1GbE RJ454x PoE+