Electrifying Door-Mounted Locks, Contacts and Switches With Power Transfer Devices

Power transfer devices (PTDs) provide an enclosed carrier to transfer low voltage wiring from the jamb into a swinging door in order to power a locking mechanism, control or switch mounted on the swinging door.

There are many different ways to provide low voltage power to door-mounted lock mechanisms, contacts and switches. The choices depend upon the application, level of security required and the power/functionality of the application.

Power transfer devices come in three basic styles:

1. Invisible: An electric hinge or pivot where no evidence of the wiring can be seen

2. Concealed: Concealed Door Loop and power transfer products, visible only when the door is open.

3. Visible conduit: Door Loops/Armored Door Cords, which are surface mounted onto the jamb and the face of the door. A flexible metal conduit carries the wiring and is always visible.

Invisible and concealed power transfer devices are vandal resistant when the door is closed.

A power transfer device can provide 12 to 24 volts or higher to power mortise locks, cylindrical locks trim, latch pullback devices, Request-to-Exit (REX) and door or latch monitoring.

Power transfer devices can be used on both fire rated openings and non-fire rated openings. If the opening is fire rated, the power transfer device must be rated, having the listing agency’s mark. For example, a Underwriters Laboratories fire rated electric butt hinge has the UL-F stamped into a leaf.

Electric Hinges

For the purpose of this article, I will use the term "Electric Hinges" to describe butt hinges that have been modified to accommodate wiring in order to transfer low energy to a locking mechanism, control or switch mounted into the door.

Three- or five-knuckle butt hinges can be used for electrification. The butt hinge used is normally the same ball bearing equipped hinge used to secure the door to the jamb. A ball bearing butt hinge modified to accommodate wiring has had one or more approximate 2mm holes drilled through each leaf into the central knuckles to accommodate the wires. For five-knuckle butt hinges, the wiring goes through the leaf into the center knuckle and departs through the knuckle above or below with the same number of holes drilled through the second leaf. To secure the two leafs without damaging the wiring, two short pins are installed one from each end. The space between the two pins permits the wires to run between the two adjacent knuckles. The process is similar for three-knuckle hinges; however, the spacings are offset because of the fewer and larger knuckles.

Holes are drilled into the exterior face of each leaf through which the wires are run. Depending upon the manufacturer, modifier or the type of ball bearing butt hinge, the entry hole location can vary. Most standard five-knuckle ball bearing butt hinges have the holes between the two middle mounting  screw holes in each leaf. Depending upon the company that electrifies the hinge, the access holes for the wiring may or may not be center located within the leafs.

For three-knuckle butt hinges and five-knuckle heavy duty ball bearing butt hinges, the wire holes are offset rather than centered because of design limitations. As a result, the butt hinges may be handed. Before ordering, check to be certain this design of electrified hinge can be used in the specific application.

The electric hinge should be installed as the center hinge on a door equipped with an odd number of butt hinges. On a four-butt hinge door, the electric hinge should be the second from the top. It must never be used at the top or bottom as modifying the butt hinge for wiring results in the hinge no longer meeting the manufacturer’s load bearing specifications.

If the electric hinge is being used on a fire rated opening, the hinge must have a fire listing for the electrification. This requires the hinge be retested as the modified hinge has two short pins, since a fire rated hinge is required to have a single pin.

Most fire rated jambs and hollow metal doors have a pre-drilled center hole to accommodate an electric hinge. If there is no predrilled hole, one must be drilled so the wires will not be crimped when installed.

The approximate 2mm diameter hole drilled through the edge of the standard butt hinge can accommodate one 18 or 20 AWG wire or up to four 28 AWG wires. Electric latch retraction applications can require two 18 or 20 AWG wires that can provide up to 3.5 or 5 Amps @ 24VDC (16 amp in-rush). Most low power operations including controls, REX and latch bolt monitoring can be powered using two or more 26 or 28 AWG wires. Standard wire configurations for electric hinges are two to 12 wires. Note: Electrified butt hinge leaves must not be separated as separation can result in breaking the wires.

Electric hinges can be ordered with two to 12 wires to accommodate the application. There are no set standards for the wire gauge or quantity in electric hinges.

Some wire configurations for electric hinges are:

Electric Latch Retraction:

2 Wire (18 or 20 AWG)

Low power applications:

4/6 Wire (26 AWG)

8/10/12 Wire (28 AWG)

Electric Latch Retraction and controls/switches:

4 - 12 Wire (2 wires @ 18 AWG + 2-10 wires 28 AWG)

If fewer wires are need than the amount provided, splicing two or more similar gauge wires together can provide additional amperage. However, never overload the wires. Do not connect a 28 AWG wire to a 20AWG wire or a 24 AWG wire to an 18 AWG wire. The current that would try to go through the smaller gauge wire could cause the insulation to melt, resulting in a short or possible fire.

Hinges from some companies can be ordered with different wire lengths. For example, an electric hinge to be used with a latch pullback device requires a shorter wire run than an electric hinge used with an electrified mortise or cylindrical lock.

Important: When installing an electric hinge into a wood door when there is going to be a splice at the edge of the door, make sure there is an opening about 1-1/2" deep and ¾" diameter to accommodate the excess wire and any connectors.

Electric hinges should be ordered to match the other hinges on the door. An electric hinge can be ordered with door position monitoring, custom connectors or varying length wire runs.

Electric Continuous Hinges

Continuous hinges provide a more stable mechanism for high traffic openings or those that have larger and heavier or specific application swinging doors. Continuous hinges are available in aluminum, steel and stainless steel, in either geared or pin and barrel configurations. They can be order as concealed, half surface, full surface, swing clear, wide throw and safety hinge.

Electrified continuous hinges come in one-piece or multiple section styles. For example, the Select Hinges Removable Electrical Aluminum Gear Hinge has three sections. The electrified hinge section can be removed from the door and jamb without having to remove the entire continuous hinge. The Select Hinge Accessible Electrical Aluminum Gear Hinge is a one-piece hinge that allows the electrified hinge portion to be accessed without having to remove the entire continuous hinge.

Depending upon the application and/or the manufacturer, the electrified continuous hinge may be handed.

Electric Pivots

Just like butt and continuous hinges, intermediate offset pivots, center hung top pivots and the pocket pivots are available electrified. Intermediate ¾" and 1-1/2" offset pivots and center hung top pivots are not load bearing; they keep the door in position.

Electrified pivots are available with up to 12 wires. Electrified door and jamb pivot leaves must not be separated as separation can result in breaking the wires.

The ¾" intermediate offset pivots have a brass, bronze or metal base. These handed intermediate pivots are available with different gauge and numbers of wires. For example, the Marray TEF10C Electric ¾ Offset Stainless Steel Pivot with 10 wires is listed for three-hour fire rated openings. Brass or bronze base materials are not suited for fire doors with ratings in excess of 20 minutes.

Electric pocket pivots are non-handed full mortise that are UL listed for fire doors on 3 hour "A" label, and 20 minute wood doors. Eight 28 AWG wires are normally supplied as standard.

Concealed Door Loop

The tamper resistant Concealed Door Loop (CDSL) is designed to slide into the cavity within the door and/or jamb when the door is closed, concealing the conduit. As the door is opened, the armored conduit extends between the door and jamb. The CDL conduit is long enough to support up to a 180-degree door swing.

The Command Access patented Concealed Door Loop makes uses of custom stainless steel, .268" inner diameter flexible armored conduit that can be installed directly into the door edge and jamb, or into most configurations of continuous hinges and butt hinges. Because the CDL is limited only by its inner diameter of more than one-quarter inch, it has the capability to accommodate larger gauged wires. This large opening will accommodate more than eight 18 AWG wires, more than sufficient to power a locking mechanism, controls and switches. In addition, electronic cabling (CAT5, etc.) can be run through the Concealed Door Loop.

For doors equipped with 3/4” offset pivots, Command Access has longer CDL that is fixed at the door and extends into the jamb cavity. Like the standard Concealed Door Loop, the ¾" offset pivot version can be installed anywhere along the door edge and the jamb.

In a CDL-equipped opening, as the door opens, the custom ¼" diameter flexible armored conduit is pulled from door side into the opening. As the door is closed, the CDL slides into the frame completely concealing itself. The Concealed Door Loop for ¾" offset pivots can be installed into entrances whose door swing is up to 105 degrees.

Door Loops/Armored Door Cords

Surface-mounted door loop/armored door cord is the simplest, most economical and most vulnerable solution for transferring low voltage power from the jamb into the door. A door loop is comprised of two connectors and a flexible metal conduit (usually between 12" and 36"). One end of the door loop is mounted onto the jamb. The other end is mounted onto the face of the door. The length of the conduit depends upon the type of hinge and the desired degree of opening. The conduit can be cut using a hack saw to the desired length.

The diameter of the flexible conduit can vary with most having an approximate 5mm inner diameter. Most door cords will accommodate up to twelve 28 AWG. Unlike electric hinges, door loops do not come with pre-installed wire.

The main variation for a door loop is the method of attaching the conduit to the door and jamb. Some models are secured using screws and some use the "screwless" design. The "screwless" door loops do not require any screws to attach them to the door and frame as they snap into place.

Power Transfer

Power Transfers are designed to provide low voltage power or pneumatic latch retraction from the jamb into the hinge side of the door edge. A Power Transfer is normally installed between the upper two butt hinges. When the door is closed, the Power Transfer is a concealed, tamper resistant method to provide power to a door-mounted lock mechanism, control and/or switch.

The Von Duprin Electric Power Transfer (EPT) has two stamped steel housings with an extendable rigid conduit mechanism that must be mortised in the door edge and the jamb. The Von Duprin EPT is UL Listed as a Fire Door Accessory and can be used on doors that have up to a 3 hour fire rating. For fire rated openings, the jamb and door cut-outs must be manufactured by the door company.

Note: Von Duprin offers the Pneumatic Control PNT-1 functions with pneumatic latch retraction exit devices. The PNT-1 is dimensionally identical to Von Duprin EPT models.

Some companies offer electric power transfers that have only one housing and a flexible spring steel conduit. An example is the Securitron Square-Cut Electrical Power Transfer (SEPT). The SEPT is mounted into the hinged edge of the door and the connector is attached to the jamb. As the door closes, the flexible spring steel conduit with the connector and spring steel conduit enters into the housing. The SEPT conduit has a ¼" inner diameter.

Most Electric Power Transfers have a larger diameter conduit, which can accommodate varying sizes and numbers of wires. Unlike most electric butt hinges, Electric Power Transfers can be rewired or come without wire. The larger inner diameter and the ability to upgrade the wiring for different applications including communications cabling (i.e. CAT5) make the EPT a more flexible product.

When installing an EPT, consider the size of the butt hinges, which determines the swing of the door. As the hinge size increases, the swing of the door decreases. Butt hinges up to five inches have up to 180-degree swing, 5-1/2" butt hinges have up to 130-degree swing and 6" butt hinges have up to 110-degree swing. Most Electrical Power Transfers are not for use with balanced doors or center hung pivots. Some power transfer devices will operate with no greater offset than ¾" offset pivots and some swing clear hinges. Note: Functionality and door swing may vary by EPT manufacturer and models.

Important: Electrical power transfers cannot be retrofit into fire rated openings.

Inductive Coupling Power Transfer

The newest power transfer device is the Securitron PowerJump. The Inductive Coupling Power Transfer (ICPT) provides low voltage power across the gap between the jamb and the door edge, wirelessly and contact free.

Inductive Coupling Power Transfer occurs when fluctuating current flows within a coil, creating changing magnetic fields. This power can be induced to jump onto a second coil having the exact same frequency, providing contactless low voltage transfer of power. The PowerJump range is approximately 3/16" between the frame side unit (frame unit) face and the door edge unit (door unit) face.

The PowerJump ICPT mechanism provides up to 500mA@12VDC or 250mA @24VDC at the door. It can support up to a 500 millisecond inrush of up to 1.5 Amps. The voltage output is field-selectable and set at the door unit.

The PowerJump receiver can be mounted into the top, bottom or sides of a door with the transmitter installed the jamb, header or floor within 3/16". The PowerJump was designed for Fail Secure devices.

For More Information

The following is a partial list of power transfer device manufacturers and their web sites. For more information, contact your local locksmith distributor or:

ABH: www.abhmfg.com

ACSI: www.acsi-inc.com

Command Access: www.commandaccess.com

Hager: www.hagerco.com

Ives:  www.ives.ingersollrand.com

Markar:  www.markar.com

Marray:  www.marray.com

McKinney: www.mckinneyhinge.com

Pemko: www.pemko.com

Rixson: www.rixson.com

SDC: www.sdcsecurity.com

Securitron: www.securitron.com

Select Hinges: select-hinges.com

Von Duprin: www.vonduprin.com