As locksmiths, the services we provide are normally focused on locks, lock related hardware and keys. We specify the necessary products, we will key and customize, and then install.
Locksmiths are beginning to become more aware of the door in respect to adjusting closers and replacing hinges with continuous hinges if the door sags/drags. However, there is much more that we need to consider we go out to a job. We need to be aware of the composition of the door, if the opening we will be working on is rated, as well as making sure the existing lock hardware meets standards. We must know what can and cannot be installed depending upon the location and if the opening is rated.
For this overview article, we will focus on butt hinges, pivots and continuous hinges, covering their composition and electrification for fire rated and non-fire rated openings.
A standard three-foot wide by seven-foot tall, 1-3/4-inch thick door will usually have three butt hinges. A seven-foot door is 84 inches tall. A general rule is one butt hinge for every 30 inches for up to a 36-inch wide conventional door. Butt hinges are rated for traffic, door weight and width. Butt hinges are available in a variety of configurations.
The basic parts of a butt hinge are the two leaves and the pin. One leaf is attached to the frame. The other leaf is attached to the door and permits it to swing. The rounded portions of the butt hinge that interconnect using the pin are the barrels. Each rounded portion of the barrel is a knuckle. Standard butt hinges have either three or five knuckles. The knuckles of the two leaves are offset from each other and mesh together. A hinge pin is inserted into the two sets of knuckles to combine the leaves, making the hinge a single swinging unit. Depending upon the butt hinge, there can be decorative tips (acorn, ball, steeple), ball bearings and a removable or non-removable pin (NRP). A removable pin permits the hinge to be disassembled.
Butt hinges can be manufactured of different base materials having a variety of finishes. The base material is the metal used to construction the hinge but it may have a different finish. Butt hinges can be manufactured of aluminum, brass, bronze, steel, stainless steel, etc. A steel hinge is susceptible to corrosion and basically designed for interior applications. For exterior or hazardous applications, brass or stainless steel butt hinges are usually recommended.
For fire rated or labeled opening applications, only butt hinges manufactured of and to the standard hinge weight as specified in ANSI 156.1 and NFPA 80 meet the requirements. All of the butt hinges installed onto the fire rated openings, over 20 minutes, must be steel or stainless steel.
In 1991, the National Fire Protection Association (NFPA) released their revised NFPA 80, Standard for Doors, Windows and Other Opening Protectives (the 2007 edition has been re-named “Standard for Doors, Frames and Other Opening Protectives”), requiring annual fire door inspections.
The 1991 Edition, for the first time, called out not only what could be done to doors and frames (such as prepping them), but also made it clear that if something was not explicitly allowed, it was disallowed. Final decisions are still in the jurisdiction of the local Authority Having Jurisdiction (AHJ).
There are very specific allowances for the size, diameter and location of holes that can be placed into doors (such as the maximum of one-inch diameter). Since there was no mention of modifying a fire labeled opening or a hinge, pivot, etc., in the NFPA 80, these procedures are not allowed. Some doors and frames for fire listed and rated openings come factory prepared for electrified hinges and lock hardware. Most of the newer frames come with holes in the hinge back plate already stamped out for a center wire hinge position.
When discussing hinges, only power transfer butt hinges bearing the UL Mark (“F” in a circle) stamped into one leaf, or the recognized mark of a Nationally Recognized Testing and Listing Agency acceptable to the AHJ, should be considered to be listed for fire door applications.
The leaves of a butt hinge can be mounted into the edge of the door or frame or onto the face of the door or frame. Depending upon the mounting configuration, the butt hinge is either a full mortise, half mortise, full surface or half surface. A full mortise butt hinge has both leaves mortised into the edge of the door and the frame. A half mortise butt hinge has the door leaf mortised into the door edge and the frame leaf surface mounted onto the face of the frame. A half surface butt hinge has the door leaf surface mounted onto the door face and the frame leaf mortised into the frame. A full surface butt hinge has both leaves surface mounted onto the face of the door and the frame.
Butt hinges have been modified to provide power transfer to the locking mechanism. Early power transfer hinges were equipped with minimal gauge wires to accommodate the required minimal openings. In the 1990s, the first high amperage power transfer hinge was introduced. This hinge had two 20 gauge wires for inrush power and four smaller 30 gauge wires for controls and switches.
Important: Power transfer hinges should be installed in the center hinge location.
Power transfer hinges are designed for low voltage, 48 volts maximum. The amperage rating of the twenty gauge wires is 16 Amps inrush for 200 milliseconds and up to 3.5 Amps continuous operation. This is sufficient to operate a large solenoid powered exit device latch retraction mechanism.
What made the first high amperage power transfer hinge unique was the use of Plenum rated Teflon jacketed silver plated, stranded copper wires. The Teflon coating is significantly thinner than standard insulation enabling the use of larger gauge wires (thicker). Teflon jacketed wiring is non-flammable, suitable for harsh environments.