Choosing the Right Type of Power Transfer

Nov. 1, 2016
The choice of which type of transfer system depends on appearance, requirements to deter tampering and ease of installation.

A representative from a prominent lock company said recently that sales of electronic security products by his company had increased from 10 percent to 40 percent during that last ten years. One important component of an access control system is the transfer of power from door to frame. When installing an electronic access control system, there are many factors to consider in choosing the right type of power transfer for the job.

Power transfer systems are designed to carry electricity from the frame to the door. Many factors affect the final power transfer choice. How often is the door used?  Is this a new or existing door installation?  What is the load on the wires?  Is this a fire-rated door?  Are extra wires required such as for door monitoring? The choice of which type of transfer system depends on appearance, requirements to deter tampering and ease of installation.

For many years the most common type of power transfer was has been the door cord.  It is usually the lowest cost way to transfer power from frame to door.  Door cords can either be jacketed or armored. Jacketed door cords are inexpensive but susceptible to being easily cut.  Armored cables are designed to resist cord cutting attempts but are still vulnerable to attack.  If the door lock system is fail-secure, then cutting the cord will not affect door security but will affect door monitoring.  If the door lock system is fail-safe then a cord cutting attack will allow entrance. In this case some other power transfer system may be suggestable.

Door cords can be installed at any height on the door. When possible, mount the door cord high on the door. This makes the door cord less vulnerable to normal damage both from carts, foot traffic or vandalism.  Door construction also affects height positioning.  Hollow metal doors usually allow the internal wiring to be easily connected to the electronic lock while a non-hollow door will not allow vertical stringing of wires within the door.  In this case door cords may have to be installed at the same height as the lock product. A raceway can then be drilled horizontally along the full door width to carry internal door wiring.  Always temporarily hold the door cord in its final position and move the door to its full open position to determine that cord will have free movement over the entire range from closed to the full-open position. 

Concealed power transfer types provide better protection against vandalism. Concealed power transfer systems may either be a separate component or be part of the pivot or hinge.  Separate component types often require areas to be mortised out on both door and frame.  When the door is fully closed, the vertical cord is concealed in the opening formed by the two mortised areas and completely hidden from outside view.  Separate component concealed power transfer products are usually found in factory-installed door.  Separate concealed transfer systems can be installed on most doors having either butt or offset pivot hinges. Doors using a balanced door hinge system are not designed for separate concealed transfer systems. 

Special pivot or butt hinges can be used to carry concealed electricity.  Wire is passed from one leaf or pivot section to the other. Depending on requirements, butt hinge models with 2 to 10 wires are available.  Door pivots are also available with multiple wires. Electrified door pivots are not designed to be load-bearing and must be installed in intermediate positions on the door (not top mounted). Fire rated doors require electrified pivots must only be made of iron or steel.

An example of a power transfer system is the sliding door on mini-vans. Two probes containing electrical power are located on the door frame. When in a closed position, contacts in the sliding door touch the probes on the frame and power is sent into the door to operate components such as electric windows. Power is lost any time the door is open. 

Assa Abloy has developed a power transfer system called PowerJump.  Electrical transfer boxes are mounted on the door and frame usually just above the existing electrical lock unit.  When the door is in a closed position, electrical current is passed wirelessly between the frame transfer box and the door transfer box. Electrical current from the door transfer box is then hardwired to the access control device.  This system allows the transfer of power from the latch side of the door instead of sending power across the door from the hinge side.

A popular market for locksmiths is the replacement of butt hinges with continuous hinges.  Continuous hinge manufacturers have also developed systems for transferring electrical power from frame to door. Continuous hinge manufacturers usually include wiring within the full continuous hinge. In case of an electrical failure a complete new continuous hinge was often required.  Continuous hinges are now available with a small separate internal electric hinge section. If any future electrical hinge servicing is required, only the small continuous hinge section must be removed.    

Door cord manufacturers have ratings for their internal wiring. Generally an electric hinge will carry a load of up to 30 volts AC or DC at 1 to 4 amps. Check the manufacturer’s specifications when ordering.

 Manufacturers realize the limits of power transfer wiring and are designing there latest products to require less amperage.  Products using latch retraction or delayed egress functions may reach near capacity of electric hinge wiring. It is possible to use pairs of wires to carry current.  This may lessen the possibility of individual wires overheating and causing premature failure.  Always try to include as many extra individual wires as possible in the power transfer in case of future expansion requirements.

Concealed power transfer products only bring power to the hinge edge of the door. Some other system is necessary to run wires from the hinge to the door lock.  The opening to carry wires from hinge to lock inside the door is called a raceway.

Some door manufacturers install raceways at the factory to simplify installations in the field.  Tools are available in order to drill raceways on existing doors in the field.  The tool consists of a long drill bit and a jig to clamp on the door which keeps the drill bit parallel to the surface of the door.

A large percentage of access control products are installed on exterior doors. In most cases the exterior door is fire-rated.  When a fire-rated door is drilled for a raceway the rating of the door is changed.  In order to regain a fire rating, a fire door inspector must recertify the door.  Raceway certification classes and special drill jigs are available so raceway drilling can be done according to building codes.

Locksmiths armed with knowledge of products, codes and applications, can easily select the best product for the job.  Choosing the correct power transfer system for every access control system is an often overlooked requirement for a successful installation.