Skip to main content

What It Takes to Power an Access Control Door

By Ron Broussard

TL;DR — Powering an access control door starts with the exact hardware and whether it operates fail-safe or fail-secure. From there, calculate the current draw of every device on the supply, account for voltage drop over the wire run, size any required battery backup, and determine whether the opening requires a life-safety release. Use the manufacturer’s published electrical requirements for the exact hardware rather than sizing from a generic lock rating.

The panel, reader, and credentials may be the obvious parts of an access control quote. The power side is easier to underestimate, and problems there can show up on install day when the lock chatters, the supply runs hot, or the inspector starts asking how the opening releases.

Getting the power side right means looking at the whole opening: lock function, current draw, supply capacity, wire distance, battery backup, and any required life-safety interface. Those decisions need to work together before the parts leave the counter.

Fail-Safe or Fail-Secure Sets the Power Budget

One of the first things to establish is how the locking hardware behaves when power is removed.

A fail-safe lock unlocks when power is removed. An electromagnetic lock, or maglock, works this way by design: power creates the magnetic bond that secures the door, so removing power releases it. There is no fail-secure maglock.

A fail-secure lock remains locked from the secure side when power is removed. Many electric strikes can be configured or ordered as either fail-safe or fail-secure, so don’t assume the operating mode based on the hardware category alone.

That distinction matters when you’re calculating power, but the actual current draw still needs to come from the manufacturer’s data for the exact device. A maglock that must remain energized to stay locked creates a continuous load. Other electrified hardware may have different operating characteristics, voltage options, and current requirements.

Pay particular attention to the duty rating on electric strikes. Some models are rated for continuous DC operation while others have restrictions depending on voltage or power type. For example, some HES electric strike models are rated for continuous duty on DC but intermittent duty on AC. If the application requires the strike to remain energized, confirm that the exact model and configuration are rated for it.

The rule for the quote is simple: don’t size power from “fail-safe” or “fail-secure” alone. Identify the exact hardware, operating voltage, current draw, and duty rating first.

What Draws Power on a Single Door

The lock gets most of the attention, but it may not be the only device drawing power at the opening. Before sizing the supply, identify every powered device and which source is feeding it.

  • The lock. Start with the manufacturer’s published current draw for the exact model and operating voltage. The same device may have different current requirements at 12V and 24V, and its operating mode can affect whether that load is continuous or momentary.
  • The reader. Readers typically draw power continuously, but they may be powered by the access control panel rather than the same supply feeding the lock. Confirm where that load belongs before adding it to the calculation.
  • Request-to-exit devices. Don’t assume every REX device has the same power requirement. A motion-based REX or other powered device adds load, while other request-to-exit arrangements may work differently. Use the published requirements for the device being specified.
  • Door position switches. A typical door position switch may simply provide a contact back to the access control system rather than operating as a separately powered load. Check the specific device instead of automatically adding current for every door contact.
  • The controller and other modules. If the controller, relay modules, or other electronics share the power supply being sized, their loads belong in the calculation too.
  • Additional powered hardware. Door operators, delayed-egress hardware, annunciators, sounders, and other devices can add load to the opening. If they’re part of the system, identify their power requirements rather than assuming the existing supply has room for them.

Once you have the hardware list, separate continuous loads from loads that occur only during activation or another specific operating condition. Then consider the maximum load the supply may have to support at one time. On a multi-door system, that means thinking about what happens when multiple devices operate simultaneously, not just what one door draws under normal conditions.

Sizing the Supply Without Running It at the Limit

Once you know what is drawing power, add up the loads that will be connected to the supply. Use the manufacturer’s published current draw for each device at the voltage you plan to use, and account for the maximum combination of devices that may operate at the same time.

Don’t choose a supply simply because its nameplate output matches your calculated load. Check the manufacturer’s published loading requirements and leave appropriate capacity for the application. If the system may expand later, planned future devices should be part of that conversation too.

On a multi-door system, simultaneous operation matters. A supply may normally carry mostly steady loads but still need to support several locks or other powered devices operating at once. Some equipment may also have startup or activation current that differs from its normal operating draw, so check the manufacturer’s specifications rather than relying on the steady-state current alone.

Two practical habits make this easier:

  • Build the calculation before the order. List each powered device, its operating voltage, published current draw, and whether the load is continuous or occurs during operation. For a multi-door system, identify which devices may operate simultaneously.
  • Check the supply against the complete load. Confirm that its rated output and manufacturer requirements support the calculated load and application. If future expansion is already planned, account for it now instead of assuming unused capacity will be available later.

Finally, the right amperage doesn’t automatically make it the right power supply. Confirm that the supply and any associated power-distribution equipment are listed and suitable for the access control application being designed. If the system also performs a life-safety function or interfaces with the fire alarm system, those requirements need to be evaluated separately for the specific opening and jurisdiction.

Voltage Drop Is a Wire Problem

A lock can work correctly at the power supply and still have problems at the door if too much voltage is lost along the wire run.

Voltage drop increases with current, conductor resistance, and distance. That means longer runs and higher-current devices may require larger conductors to keep the voltage reaching the lock within the manufacturer’s operating range. Before selecting wire, check the device’s published voltage and current requirements and calculate the drop over the actual run.

Where the hardware supports both 12V and 24V operation, 24V can be useful on longer runs. For a device designed to provide comparable operation at either voltage, the 24V configuration will typically draw less current. Lower current means less voltage drop through the same conductor over the same distance. The exact current draw still needs to come from the manufacturer’s data for that device.

Increasing conductor size is another way to reduce voltage drop because a larger conductor has less resistance. Which approach makes sense depends on the hardware, run length, available voltage, current draw, and manufacturer’s requirements.

The mistake to avoid is selecting lock wire by habit. The actual device, wire run, and applicable installation requirements should determine the conductor. If the run is long or the current draw is high, calculate the expected voltage at the device before the wire is pulled.

Check the Life-Safety Interface Before You Order

Electrified locking hardware can introduce requirements that go beyond access control. Depending on the type of locking arrangement, the opening may need to unlock upon loss of power, activation of a fire alarm or detection system, operation of a sprinkler system, use of a manual release device, or another event required by the applicable code.

That’s why the fire alarm and egress requirements need to be identified before the power supply and locking hardware are ordered, not worked out after installation.

For example, model-code provisions for certain sensor-release electrically locked egress doors require the lock to release upon loss of power and upon activation of specified fire-protection systems. They also include requirements for independent manual release and listed locking-system equipment. Other locking arrangements, including delayed-egress systems and door-hardware-release systems, have their own requirements.

Three questions should be answered before the order:

  • What type of electrically locked opening is being designed? A maglock alone doesn’t tell you which egress provisions apply. How the door releases and how occupants exit matter.
  • What systems have to release the lock? Determine whether the opening must respond to the fire alarm, sprinkler or detection system, loss of power, manual release device, door hardware, or some combination required by the applicable code.
  • Does the specified equipment meet the requirements for that application? Confirm the required listings and interface method for the locking hardware, power supply, and other equipment being used.

The applicable code and the authority having jurisdiction (AHJ) ultimately determine what the opening requires. Getting that answer during design keeps the necessary interface equipment on the quote instead of discovering it during inspection.

Running the Battery Calculation

Battery backup should be sized from the actual system load and the required backup duration, not simply from the size of the enclosure or the battery that normally ships with a power supply.

Start by identifying every device that will be supported by the battery and its current draw in the operating conditions that apply. Then determine how long the system is required to operate on standby power. Depending on the application, the calculation may also need to account for a period of higher current draw during an alarm or other active condition.

Hardware that must remain energized to stay locked can have a major effect on that calculation because it creates a continuous load on the battery. Fail-secure hardware operates differently, but its actual contribution still needs to come from the manufacturer’s published specifications rather than an assumption based only on lock function.

Battery capacity also isn’t something to calculate from nameplate amp-hours alone. Follow the power-supply and battery manufacturer’s requirements for factors such as battery capacity, charging capability, operating temperature, and any required reserve or derating. The batteries selected also have to physically fit the enclosure and be compatible with the charging system.

A practical battery-sizing process is:

  • List everything supported by the battery and its published current draw.
  • Determine the required standby and any applicable active or alarm duration for the system.
  • Calculate the required capacity using the equipment manufacturer’s instructions and the requirements that apply to the project.
  • Confirm the power supply can charge and support the selected batteries and that they fit the specified enclosure.
  • Keep the calculation with the job documentation so the assumptions behind the battery size are available later.

The required backup duration isn’t universal. It can depend on the system, application, adopted code, project specifications, and AHJ. Confirm the requirement for the specific project before selecting the batteries.

What Gets Left Off the Door Quote

Some parts that can get overlooked aren’t the reader, controller, or lock. They’re the pieces that connect the access control system to the actual opening.

Before the order goes out, check whether the door needs:

  • Power transfer to the door leaf. If powered hardware is mounted in the moving door, the design needs an appropriate way to get power from the frame to the door, such as an electrified hinge or other listed power-transfer device.
  • Power distribution. On multi-door systems, confirm how power will be distributed and protected at each output rather than assuming every device can simply land on the same supply terminals.
  • The transformer and enclosure. Confirm what’s included with the selected power supply and what has to be ordered separately.
  • Battery backup. If backup power is required, order the battery capacity established by the system calculation rather than defaulting to whatever battery was used on the last job.
  • Life-safety interface components. If the locking arrangement requires an interface with a fire alarm, detection, sprinkler, manual release, or other system, make sure the necessary components are accounted for in the design and quote.
  • Lock power cable. Select the conductor based on the actual device load, voltage, run length, and applicable installation requirements rather than simply ordering the same gauge used on every door.

None of these parts is particularly unusual. They’re easy to miss because they often sit between the access control panel and the door hardware itself. Checking the complete opening before the order goes out can prevent a small missing component from holding up the installation.

What to Ask Your Distributor

The power side of an access control door is where a counter conversation can catch a missing part before it becomes an install-day problem. Bring the hardware list, the operating voltage, and the approximate wire runs so the conversation is about the complete opening rather than one component at a time.

Ask your SDS franchise:

  • Can you help me check the power requirements against this hardware list? Bring the exact lock, reader, controller, and other powered devices being specified so the published voltage and current requirements can be checked together.
  • What else does this opening need? Depending on the design, that may include power distribution, battery backup, power-transfer hardware, interface components, an enclosure, or additional cable.
  • What’s available for this job now? Knowing what’s stocked locally can help identify available options before the installation is scheduled around equipment that isn’t available.
  • Can you get the manufacturer involved if we need to confirm something? For questions about current draw, duty rating, power-supply compatibility, listings, or a specific hardware configuration, the manufacturer’s published documentation and technical support should be the final reference.

SDS distributes products across access control, power, wire and cable, fire, intrusion, video, AV, networking, and tools. That makes it possible to look at more of the opening in one place instead of treating the lock, power supply, cable, and related components as separate purchases.

SDS franchise teams are trained on the product lines they distribute and can help contractors identify relevant manufacturer documentation and related components for the hardware they’re ordering. The system design, installation, code compliance, and licensing responsibilities remain with the contractor and the applicable project team.

Frequently Asked Questions

How do I size a power supply for an access control door?

Identify every powered device connected to the supply and use the manufacturer’s published current draw at the voltage being used. Account for continuous loads as well as the maximum combination of devices that may operate at the same time. Then confirm that the selected power supply’s rated output and manufacturer requirements support the complete calculated load and application.

What is the difference between fail-safe and fail-secure for power draw?

A fail-safe lock unlocks when power is removed, while a fail-secure lock remains locked from the secure side when power is removed. That difference can significantly affect the power calculation, especially with hardware such as maglocks that must remain energized to stay locked. The actual current draw and duty cycle should always come from the manufacturer’s specifications for the exact device.

Can an electric strike be used as a fail-safe lock?

Some electric strikes can be configured or ordered for fail-safe operation, but the specific model must be rated for the way it will be powered. Check the manufacturer’s published fail-safe/fail-secure configuration, voltage, current draw, and duty rating before specifying the strike.

Should I run access control locks at 12V or 24V?

It depends on the hardware and the installation. Where a device supports both, its 24V configuration will typically have a lower published current draw, which can help reduce voltage drop over longer wire runs. Compare the manufacturer’s electrical specifications and calculate voltage drop using the actual run length and conductor rather than choosing 12V or 24V by habit.

Does a maglock have to release on a fire alarm?

Not every maglock installation follows the same release requirements. The answer depends on the locking arrangement, applicable code, occupancy, fire-protection systems, and authority having jurisdiction. Certain electrically locked egress-door arrangements are required to release upon activation of specified fire alarm, detection, or sprinkler systems, while other arrangements have different requirements. Confirm the required release methods for the specific opening before selecting the lock, power supply, and interface equipment.

How do I calculate battery backup for an access control system?

Start with every device that will be supported by the battery and its published current draw. Determine the required standby duration and any applicable active or alarm duration, then calculate the required battery capacity according to the equipment manufacturer’s instructions and project requirements. Also confirm that the power supply can properly charge the selected batteries and that they fit the enclosure.

What parts should I check before ordering an access control door?

Common items worth checking for include power-transfer hardware when power must reach the door leaf, power distribution, the correct enclosure or transformer, battery backup where required, life-safety interface components where applicable, and lock power cable sized for the actual device and wire run. The exact list depends on the opening and hardware being installed. Your local SDS franchise can help check the complete opening against the hardware being specified.

About the Author

Ron Broussard is Chief Executive Officer of Security Data Supply and has more than 30 years of experience in the security industry. He has held executive leadership roles across distribution and manufacturing, giving him a broad perspective on the challenges contractors, integrators, and distributors face every day. At Security Data Supply, he guides the company’s franchise network, vendor relationships, and long-term growth strategy.

Methodology

This article combines Security Data Supply’s experience supporting security, fire, and low-voltage contractors with published technical guidance for access control hardware and power systems. Electrical characteristics such as operating voltage, current draw, duty rating, and power requirements should always be verified against the manufacturer’s documentation for the exact equipment being specified.

Life-safety and egress requirements vary by locking arrangement, adopted code, occupancy, project, and jurisdiction. This article describes general considerations rather than providing a code interpretation or system design. Contractors should confirm the requirements for a specific opening with the applicable manufacturer’s documentation, project specifications, adopted codes, and authority having jurisdiction.

Sources and Further Reading