Power over Ethernet in Access Control Projects

Powering access control with PoE, it’s extremely common in nowadays projects. Demand on power requirements however, can generate issues due that it is greater than what typical PoE devices require, such as cameras, phones and access points.

Access control solutions impacts life safety, and because of it, special concern needs to be taken to ensure that mistakes are not made in powering.

This article explains how PoE is useful and how typically can be used and calculated in your projects.

Is PoE useful for my project?
Usually PoE was used to power ACS controllers, however, it is useful in new and retrofits, since it can also bring power to the door locks and other devices, avoiding high voltage devices, which can cost you hundreds of dollars per door.

Two IEEE standards of PoE that are commonly used: 802.3af supports up to 15.4W and is used by most PoE enabled Access Controllers, while 802.3at, or also called 'high' PoE, supports up to 25.5W but used only by a small fraction of security equipment, generally those designed to be used in extreme weather environments. Lastly, ‘af’ devices are compatible with ‘at’ as well.

Even though there are PoE injectors and switches that can provide up to 60W per port, which is useful with controllers that offer pass-thru for powering locks and readers. In this cases, the controller consumes part of the PoE power and allows that low voltage devices to be powered too.

Unlike IP cameras, where a single device draws poer from a PoE source, with access control, controllers supporting PoE are just the first device in a chain, in which they can draw power to several devices. These kind of controllers support up to 4 doors, due to the limitations of PoE power.

How to calculate PoE for your ACS projects
Three main types of devices receive power from the controller - readers, locks and door sensors.

How much power these devices need total is critical in determining whether PoE will be sufficient for each opening:

- Readers: The most common device receiving direct power, most keypad or card readers are specified to operate on steady power sourced only from the controller.

- Locks: Depending on lock types, using controller pass-through power may not be optional. For example, while Strikes may be able to operate off of PoE power budgets, Maglocks typically cannot as they draw significantly more current.

- Door Sensors: In some cases, other sensors may draw power from a PoE supplied controller for door position or even RTE, but this is not commonly needed or used.

In many cases, the total power needed for all these devices will exceed what PoE is able to provide. As a result, totaling up all the individual power requirements and reconciling against the supplied power is critical for every controlled opening.

To calculate, first check what type of PoE the door controller accepts (e.g., 802.3af or 802.3at). Next, verify how much output power max the controller provides to the peripheral devices.

In our first example below, more than enough power is available:

- A door is controlled by a controller that supporting 802.3af PoE, and passing through a max of 650 mA to field devices. To that controller, a prox reader that consumes 75 mA of power and a lock with 240 mA. The total power demanded by the reader and strike is 315 mA from the controller, compared to 650 mA provided, which is more than enough.

However, in this second example, notice how insufficient power is available:

- A door controller supporting 802.3af PoE, and passing through a max of 650 mA to field devices, To that controller, two long distance prox readers (in/out application) drawing a max 230 mA each, and a lock with 510 mA on a continuous duty basis are connected and draw power. The total power demanded by the readers and strike is 970 mA from the controller, exceeding the available power by over 300 mA despite no warning or connection obstacles otherwise.

In a scenario like this, we suggest to use a higher PoE powered device and/or an external power supply unit.

Remind that it is really important to check the specification sheet of the controller and devices to determine if there is power available for them. Also, check if the controller supplies the voltage compatible with the reader and locks.

Another key point is how field power amount varies based on power source type. Typically when using PoE for power, overall available power is less than what is possible with separate low voltage power supplies: Note that the total power available with PoE (9.6W) is 33% less than 12VDC (14.4W) and 66% less than 24VDC (28.8W).

Cost Savings Significant
Using PoE to power doors often save ~$200 - $250 per door, given the elimination of extra cable, power supplies, and labor. For example, one could eliminate:

- 500' of 18/2 Power Cable: $90

- 4A 12/24VDC Power Supply: $50

- Installation Labor for Above: $60 - $100