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

Choices include electric butt hinges, electric continuous hinges, electric pivots, door loops, armored door cords and Inductive Coupling 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, an 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.

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