The Power Transfer Problem Every Electrified Opening Creates
When an electrified lock, electric latch retraction exit device, or access-controlled trim is mounted in the door, current must travel from the fixed frame to the moving door leaf. That gap -- typically three to five millimeters at the hinge edge -- is where many electrified hardware projects run into trouble. This article is for commercial contractors, facility managers, and hardware specifiers who need to match the right power transfer method to the opening, not just default to an electric hinge because it is familiar.
What Is an Electric Power Transfer (EPT)?
An electric power transfer (EPT) is a device that carries low-voltage conductors across the hinge-line gap between a door and its frame as the door swings. The term is used broadly to describe the product category, but EPT also refers to a specific mortised device distinct from electric hinges and door cords. Understanding the three main approaches -- and their real-world limitations -- is the first step toward specifying the right solution.
The Three Main Power Transfer Approaches
1. Door Cord (Armored Loop)
A door cord is the simplest and most economical option. It consists of a flexible armored stainless steel cable -- with plastic end fittings -- that loops externally from the frame edge to the door face, spanning the gap without any routing into the frame or door.
- Available in standard and extended lengths (for example, 18-inch and 36-inch versions)
- Visible from the pull side, but quick to install and easy to retrofit on existing construction
- Handles virtually any wire gauge or conductor count your lock or device requires
- Best where budget is the primary constraint or aesthetics are not critical -- industrial maintenance replacements, storage rooms, utility corridors
- Not appropriate where door appearance or vandal resistance is a priority
McKinney offers door cord products (TSB-C series) under this approach, and they are among the most field-serviceable options available.
2. Mortised EPT Device
A mortised EPT installs into routed pockets in both the frame edge and the door edge. Spring-loaded pins or wiping contacts bridge the gap as the door swings. This is the approach most people mean when they say "EPT" on a schedule.
- Clean, professional appearance -- nearly invisible from either door face
- Handles significantly more conductors than a standard electric hinge
- Standard EPT and long EPT (EPTL) versions accommodate different wire counts; ElectroLynx EPT versions (EL-EPT, EL-EPTL) can carry up to 12 wires
- Compatible with most doors hung on butt hinges, continuous hinges, or offset pivots
- Does not work on center-pivot doors -- on a center pivot installation the pivot itself is the only viable transfer point, and a mortised EPT cannot be positioned there
- Requires accurate routing in both door and frame; coordinate with door fabricator on new construction
Securitron, McKinney, and Pemko all offer mortised EPT products in this family. Specifying the ElectroLynx version gives you the added benefit that wires can be replaced without pulling the entire device -- a meaningful maintenance advantage in schools and healthcare facilities where long service life matters.
3. Electric Hinge (Through-Wire)
An electric hinge replaces one standard butt hinge in the leaf set. Conductors run through the barrel, making the transfer invisible from outside the opening. Electric hinges come in several sub-types:
- Electric contact (exposed): Visible contacts on the knuckle; easy to service
- Air/electric power transfer: Transfers power and, in some configurations, pneumatic lines
- Through-wire with monitor: Combines wire transfer with door position monitoring in one hinge
- Monitor only: No power transfer; door position signal only
Electric hinges are listed only for low-voltage applications -- 50 volts or under. Most manufacturers rate them at roughly 3.5 amps continuous duty and 16 amps intermittent. The critical field limitation: electric hinge conductors are typically 22 or 24 AWG. That wire gauge is not adequate for electric latch retraction (ELR) exit devices, which can draw 1.5 to 3 amps at peak. Running an ELR on a standard electric hinge risks voltage drop, nuisance trips, and premature device failure.
Hager and McKinney both offer electric hinge lines preferred at DoorwaysPlus for their stability and serviceability. Always confirm the amperage rating and wire gauge against your device's actual current draw before specifying.
Matching the Method to the Opening: A Quick Decision Guide
Wire Count and Current Draw First
Before picking a transfer method, add up every conductor your electrified device needs:
- Basic electric lock or strike: 2 conductors
- Add door position monitoring: 2 more (4 total)
- Add request-to-exit (REX): 2 more (6 total)
- Add alarm or status monitoring: 2 more (8 total)
- ELR exit device: higher current -- likely rules out standard electric hinge; use mortised EPT or door cord
Always specify at least two spare conductors beyond current requirements.
Application Context
- Schools and healthcare: Mortised EPT with ElectroLynx-style replaceable wiring is ideal -- serviceability over the life of the building saves budget and downtime.
- Retail and office: Electric hinge where aesthetics matter and current draw is modest (electric mortise lock with monitor and REX only).
- Industrial and maintenance replacements: Door cord is fastest to install and easiest to troubleshoot.
- Center-pivot doors: Electric hinge or pivot-mounted transfer only -- EPT devices cannot function here.
- Fire-rated openings: Verify that any electrically modified hinge or EPT device carries the appropriate listing for the fire door assembly. Confirm with the AHJ and NFPA 80 requirements before specifying.
Coordinate Early -- or Pay for It Later
Power transfer method is not a field decision. It affects door and frame fabrication (routing for mortised EPT), conduit stub-out location, and wire schedule at the panel. On new construction, the hardware schedule should call out the transfer method alongside the electrified device so the door fabricator preps the opening correctly. On retrofit, confirm whether the existing door and frame can accommodate routing before ordering a mortised EPT -- if they cannot, a door cord or electric hinge may be the only practical path.
DoorwaysPlus carries EPT devices, door cords, and electric hinges from preferred lines including McKinney, Hager, and Pemko. If you are working through a wire schedule or need help matching a transfer device to an electrified exit device or mortise lock, our team can help you get the specification right the first time. Contact DoorwaysPlus or browse our electrified hardware section online.