Commercial overhead door and dock leveler installation field guide

What overhead door and dock work actually is

A commercial overhead door is a powered or manual door that lifts overhead to clear an opening freight moves through, counterbalanced by a spring system so the operator or a person is not lifting the door's full dead weight. A loading dock is the set of equipment at the building face that bridges a parked trailer to the floor: the door, the leveler, the seal or shelter, the bumpers, and the vehicle restraint that holds the trailer in place.

The work splits into two jobs that share a wall. The door side is the panel or curtain, the springs, the tracks, the operator, and its safeties. The dock side is the leveler in the pit, the seal that closes the weather gap, the bumpers that take the truck's impact, and the restraint that keeps the trailer from leaving while a forklift is inside it.

Both jobs look like steel and bolts. The danger in each is invisible until it lets go. On the door it is the energy stored in the spring. At the dock it is the trailer that moves when nobody is watching it. Get those two right and most of the rest is fit and finish.

The two things on this job that kill people

Two parts on a commercial door and dock carry the real hazard, and both kill or maim when they fail. The first is the counterbalance spring on the door. It holds the energy of the door's weight under tension, and a spring or cable that lets go during adjustment whips with enough force to break bone, take an eye, or worse. This is why winding and servicing springs is trained-tech-only work, not a task for a maintenance generalist with a wrench.

The second is the trailer at the dock. A trailer that creeps away under forklift traffic, or pulls off before loading is done, opens a gap the forklift drops into. The operator and anyone nearby gets hurt or killed. The device that stops it is the vehicle restraint that physically locks the trailer to the dock. It is the most important piece of safety equipment at the opening.

Treat everything in this guide as general field practice, not a substitute for training or the governing documents. The manufacturer's instructions for the specific door, spring, operator, leveler, and restraint control the work. ANSI and DASMA cover doors, UL 325 covers operators, and OSHA covers the dock and the workplace. When this guide and one of those part ways, the document wins.

The door types and where each one goes

Commercial overhead doors fall into a few families, and the type drives the spring system, the headroom, and the operator. Sectional doors ride up and back on horizontal tracks. Rolling steel doors coil around a barrel above the opening. High-speed doors trade insulation and mass for cycle speed. Fire-rated rolling doors add a closing system that drops the door on an alarm. Pick by the use, the cycle count, and what the opening can give you for headroom.

The table below is a starting point. The manufacturer's submittal for the actual door governs the spring rating, the cycle life, and the clearances.

The counterbalance springs: torsion and extension

The counterbalance spring is what makes a heavy door movable. It stores the energy of the door's weight when the door is down, then gives that energy back to help lift it. Two systems do the job. A torsion spring sits on a shaft above the opening, and cables on drums at each end wind the spring as the door closes. Extension springs run along the horizontal tracks on each side and stretch as the door comes down.

Torsion is the system on most commercial doors because it controls the door more smoothly and lasts more cycles. Extension is common on lighter and older doors. The danger is the same in both: a spring under tension is a loaded weapon. A torsion spring on a fully closed door holds enough torque to break a wrist or skull if a winding cone slips. An extension spring under stretch snaps like a whip when it fails.

Spring rating is matched to the door weight, and it is not a guess. The manufacturer sizes the spring to the door, and the cycle life, commonly 10,000 to 25,000 cycles on a standard spring with high-cycle springs rated far higher, is part of that spec. Confirm the spring rating and the cycle class against the door submittal. Never adjust, wind, or replace a spring untrained. That work belongs to a trained door technician with the right tools, and there is no safe shortcut around it.

Torsion spring

Spring on a shaft above the door, wound by drums and cables; stores energy by twisting

Extension spring

Spring along each horizontal track that stores energy by stretching as the door closes

Counterbalance

The spring system that offsets the door's weight so the door can be lifted with little force

Cycle life

The number of open-close cycles a spring is rated for before replacement; high-cycle springs last longer

Spring safety is not optional, and it is not for amateurs

Read this twice. Servicing a door spring is the part of this trade that sends people to the hospital, and almost every serious injury comes from someone untrained loosening a spring that is still holding tension. If you have not been trained to wind springs, you do not touch them. Call a trained door technician. This is the single firmest rule on the door side of the work.

Torsion springs are adjusted with winding bars, steel bars sized to the winding cone, never a screwdriver or a piece of rebar. The technician seats both bars, holds the load, loosens the setscrews only with a bar fully seated and braced, and lets the spring down or winds it up under control, one quarter turn at a time. The cone holds all that stored torque on two setscrews. Loosen them with a bar that is not seated and the spring unwinds through your hands.

Extension springs need their own containment. A safety cable runs through the center of each extension spring, anchored at both ends, so that when the spring breaks the cable catches the pieces instead of letting them fly across the bay. A door with extension springs and no safety cables is a missing safety device, and it gets corrected before the door goes back in service. The same goes for the door's lift cables: a frayed or rusted cable is a failure waiting for a load, and it gets replaced, not nursed.

A balanced door floats; an unbalanced door is dangerous

Balance is the spring tension matched to the door weight so the door holds position anywhere in its travel. Disconnect a balanced door from the operator, lift it halfway by hand, and it stays there. It does not slam down or shoot up. That float is the test, and it is the foundation of a safe install.

An unbalanced door is dangerous in two directions. Spring too weak and the door is heavy: it drops if the cable or operator lets go, and the operator strains, overheats, and wears out early carrying weight the spring should be holding. Spring too strong and the door wants to fly up, which fights the operator's down force and can defeat the very reversing the door depends on. Either way you are running the operator against the door instead of with it.

Balance is also where operator life is won or lost. A door that is out of balance burns through operators and the operator's safeties have to work harder to control a door fighting them. Set the balance with the door disconnected and the spring tuned, then connect the operator to a door that already moves freely. Spring winding is trained-tech-only, so the balance step belongs to the same trained technician, not to whoever hangs the operator.

Tracks, rollers, cables, and the running gear

The running gear is everything the door rides on and hangs from: the vertical and horizontal tracks, the rollers, the hinges, the drums, and the lift cables. It does quiet work until it is out of alignment, and then it shows up as a door that binds, racks, or jumps the track.

Tracks have to be plumb on the verticals and level and parallel across the horizontals, set to the manufacturer's spacing and back-hang. Rollers should turn freely and sit in the track without slop. Hinges on a sectional door carry the panel loads and the roller stems, so a bent hinge or a worn stem walks the door out of square. On a coiling door the curtain and the barrel do the same job the panels and tracks do on a sectional, and the bracket plates and the barrel bearings carry the load.

Lift cables and drums are part of the spring system and carry the same warning. The cables wind onto the drums in matched grooves, and the drum has to be the right size for the door height or the cable spools wrong and the door racks. Cables get inspected at every service. A strand starting to break, a flat spot, or rust at the bottom bracket where water sits means the cable is on its way out. Replace cables in pairs and only with the spring tension safely managed, which again is trained-tech work.

The operator: type, mounting, and power

The operator is the motor and gearbox that opens and closes a powered door, plus the controls and the safeties. The two common commercial types are the jackshaft, which mounts on the wall at the end of the torsion shaft and drives the shaft directly, and the trolley, which rides a rail above the door and pushes a sectional door open and closed. Rolling steel and high-headroom openings usually take a jackshaft; standard sectional doors take either.

The operator does not fix a bad door. It moves a door the springs have already balanced. Hang the operator after the door runs free by hand, set the open and close limits and the force settings to the manufacturer's procedure, and confirm the door reverses on an obstruction before anyone uses it. An operator forced to drag a heavy, unbalanced door is an operator that fails early and a safety system working at its margin.

Power and controls are electrical work, and they are sized and run like any motor circuit: a dedicated circuit, a disconnect within sight, and the conductors and overcurrent device per the nameplate. Our device-wiring guide covers terminating the line side, the disconnect, and the control wiring at the operator. Voltage drop matters on long runs to a remote dock, since an operator that browns out at the far end of a feeder runs hot and trips. Pull the operator's power and control conductors to the manufacturer's wiring diagram, and keep the low-voltage safety wiring separated from the line voltage.

What is UL 325 and why does the door have to reverse?

UL 325 is the safety standard for powered door operators, and its core requirement is entrapment protection: a powered door has to keep from trapping a person or object under it. For commercial operators the standard calls for two independent means of entrapment protection, and the operator has to monitor its external safety device or fall back to constant-pressure operation. This is the most important code point on the operator side, and it is not negotiable.

The first means is usually inherent force sensing built into the operator. If the door meets resistance on the way down, the operator senses the load and stops or reverses. The second is an external device: photo-eyes that beam across the opening near the floor and reverse the door when the beam is broken, or a safety edge along the door's bottom that reverses on contact. Since the 2016 edition took effect, commercial operators carrying the UL label have to monitor those external devices, and if the monitored device is missing or faulted, the operator drops to constant-pressure-to-close, meaning someone has to hold the button and watch the door the whole way down.

Test the reversal, do not assume it. Lay a solid object in the opening, run the door closed, and confirm it reverses on contact or on the photo-eye. Break the photo-eye beam with the door closing and confirm it reverses. A door that does not reverse is a door that is not safe to leave on automatic, full stop. Set and verify entrapment protection to the operator manufacturer's instructions and the UL 325 requirements for the operator's usage class.

Fire-rated rolling doors and the drop test

A fire-rated rolling door is a coiling door in a rated wall that closes automatically in a fire to keep the opening from spreading flame and smoke. It is held open in normal use and released by a closing system: a melted fusible link in the simplest version, or an alarm-initiated release tied to the fire panel. When the link melts or the alarm drops the door, a governor controls the speed so the curtain comes down at a controlled rate rather than free-falling.

The life-safety check on these doors is the drop test, and NFPA 80 governs it. The door is tested at install and then at least annually: released so it closes from the alarm or the fusible-link point, watched for full closure, and then reset. The accepted closing speed sits in a band, commonly cited as roughly 6 to 24 in/sec average, fast enough to close in time but not so fast it injures someone. The test is run twice, once to confirm the door closes fully and once to confirm the closing device was properly reset.

Fusible links carry a load limit, often around 40 lb of pull, so the number of links and the closing-system design are part of the listing, not a field improvisation. A fire door drop test is documented work for a trained door professional. Treat the NFPA 80 schedule and the door manufacturer's instructions as the authority, confirm the rating matches the wall, and never paint or coat a fusible link, since that changes when it releases.

The dock leveler that bridges the truck-to-dock gap

A dock leveler is the steel plate that bridges the height difference and the gap between the dock floor and the trailer bed so a forklift can drive across. It hinges at the back and ranges up and down to meet the bed, with a lip that extends onto the trailer. Without it, the gap and the height mismatch make loading slow and unsafe.

Three drive types cover most installs. A mechanical leveler is spring-loaded and released with a pull chain, then walked down onto the trailer. A hydraulic leveler runs on a power unit and a push button, holds capacity well, and needs less routine adjustment. An air-powered leveler raises on an inflating bag and a button. Pick by duty cycle, capacity, and budget. Capacity requests commonly run 25,000 to 35,000 lb, with higher ratings available for heavy work, and the rated capacity has to match the loaded forklift plus the load, not just the freight.

Pit-style levelers drop into a formed pit at the dock edge. Where a pit is not practical, an edge-of-dock leveler bolts to the dock face for smaller height differences and lighter duty. Set the leveler to the manufacturer's install instructions for the pit dimensions, the anchoring, and the working range, and confirm it ranges through its full travel and holds the lip on the trailer before it goes into service.

What is a vehicle restraint and why is it the top dock device?

A vehicle restraint is the device that physically locks a parked trailer to the dock so it cannot move while a forklift is loading it. It is the most important safety device at a loading dock, because the failure it prevents kills people. A trailer that creeps away under forklift traffic, or that pulls off before loading is finished, opens a gap, and a forklift driving across that gap drops into it. Trailer creep and early departure are the named hazards, and the restraint is the answer to both.

Two designs dominate. A hook-style restraint rises and captures the trailer's rear impact guard, the steel bar across the back of the trailer also called the RIG or ICC bar, and holds it until the restraint is released. A wheel-based restraint raises a barrier in front of a rear wheel. Both beat a manual wheel chock, which slips on ice or grease, gets knocked loose, walks out under repeated impact, or gets pulled before loading is done. OSHA requires trailers to be secured during loading and unloading, and names both chocks and restraints.

Tie the restraint into the dock's communication so the equipment enforces the sequence: the restraint engages, the inside light turns green to tell the forklift operator it is safe to enter, and the driver's outside light turns red so the truck does not pull away. The best installs interlock the restraint with the leveler or the door so the dock cannot be used until the trailer is locked. Install and set the restraint to the manufacturer's instructions and the dock's OSHA safety program, and never let the light system become the only thing holding the sequence together. The physical lock is the safety. The lights communicate it.

Dock seals and shelters

A dock seal or shelter closes the weather gap between the trailer and the building so conditioned air stays in and rain, dust, and pests stay out. The difference between the two is how they make the seal. A dock seal is a set of foam pads on the head and both sides that the trailer compresses against when it backs in, sealing tight on three sides. A shelter is a fabric or framed enclosure with flexible curtains or a head curtain that drapes around the trailer, which suits a wider range of trailer sizes.

Pick by trailer mix and door size. Foam seals work well where trailers are a consistent size and the seal can take the compression. Shelters handle mixed fleets and larger openings where a rigid foam pad would not fit every trailer. On freezer and climate-controlled docks the seal is doing energy work every hour, and a torn or compressed-out seal leaks money and ices the opening.

Set the seal or shelter to the door and the dock-bumper projection. The bumpers set how far the trailer stops from the wall, and the seal has to make contact at that standoff without being crushed flat on every hit. A seal mounted as if the trailer parks against the wall gets destroyed by the first few trucks. Follow the manufacturer's projection and mounting dimensions for the bumper depth you actually have.

Dock bumpers

Dock bumpers are the rubber or laminated blocks bolted to the dock face that take the impact of the trailer backing in. They protect the building wall and the trailer, and they set the standoff that the leveler lip and the dock seal are designed around. They are cheap, they wear out, and a worn bumper is a real hazard, not a cosmetic one.

When a bumper is crushed, sheared, or missing, the trailer parks too close, the leveler can foul the trailer or run short of travel, and the impact starts hitting the building structure and the leveler frame instead of the rubber. Worn bumpers are one of the most common dock deficiencies, and they get replaced before they are gone, not after. Match the replacement to the projection the leveler and seal were set for, because changing bumper depth shifts where every trailer stops.

Confirm the bumper height covers the range of trailer bed heights you actually see, including a low or high bed and an air-ride trailer that settles. A bumper the trailer rides over or under is a bumper doing nothing.

Dock lights and the communication system

Dock lights and the communication lights are two different jobs that often share a panel. Dock lights are the swing-arm or LED lights that put work light inside a dark trailer so the forklift operator can see the load. The communication system is the red-and-green light pair that tells the forklift operator and the truck driver when it is safe to load and when it is safe to pull out.

The communication lights earn their place by being tied to the restraint. When the restraint locks the trailer, the inside light goes green and the outside light goes red, telling the forklift it is clear to enter and telling the driver to stay put. When the restraint releases, the lights flip. Wire the lights so they follow the restraint state, not so they can be switched independently, because a green light that does not mean the trailer is locked is worse than no light at all.

This is electrical work that ties the dock devices together, and on docks with access control or a building management interface it overlaps with door integration. The communication light wiring, the restraint interlock, and the operator controls are device wiring at heart. The point of the whole package is one sequence: the trailer is locked, the light says so, and the dock cannot be used until it is true.

The dock leveler pit

A pit-style leveler lives in a formed concrete pit at the dock edge, and the pit decides whether the leveler ever works right. The pit has to be the manufacturer's dimensions for the leveler model, square, level, and at the correct depth, with the embedded angles and anchors set where the leveler frame lands. A pit poured to the wrong dimensions or out of level means a leveler that binds or never seats, and there is no field adjustment that fixes a bad pit.

Drainage is the detail people miss. Water runs off the dock and the trailer into the pit, and a pit with no drainage rusts the leveler frame and the structure from the bottom up. Slope and drain the pit per the design, and keep the curb angles and rebar set as the structural drawings call out so the leveler frame is anchored into sound concrete, not the edge of a crumbling slab.

Coordinate the pour with the leveler submittal before the concrete trucks show up. The embeds, the depth, the rebar, and the drainage are cheap to get right in the forms and expensive to chase after the pour. Set the pit to the structural drawings and the leveler manufacturer's pit detail, and confirm the dimensions in the forms, not after the concrete sets.

The door opening: headroom, backroom, and the jambs

The opening drives which door fits and how it installs. Three dimensions decide it: the clear opening width and height, the headroom above the opening for the spring, shaft, and curl, and the backroom behind the opening for the horizontal tracks on a sectional door. Measure all three before you order, because a door that does not fit the headroom is a door that has to be re-engineered for a low-headroom track or changed to a coiling door.

Coiling doors win where headroom is tight because the curtain coils into a small barrel above the opening instead of running back on tracks. Sectional doors need both headroom for the spring and backroom for the panels to ride flat. High-lift and vertical-lift track configurations exist for special cases, and each has its own headroom math from the manufacturer.

The jambs and the structure above the opening have to carry the load. The spring system, on a torsion door, hangs off the header and the spring anchor, which means real structural load lands on the wall above the opening. Confirm the jamb material and the header can take the door and operator loads, and follow the manufacturer's rough-opening and structural requirements. Measure the rough opening as built, not as drawn, since the framed opening rarely matches the plan to the inch.

The install sequence

The install order matters because each step depends on the last being right. The short version: confirm the opening and structure, set and plumb the tracks, hang the door or curtain, install and wind the springs, set the balance, then add the operator and its safeties. Spring winding and balance are trained-tech-only steps inside that sequence.

Set the tracks plumb and level first, because a door hung on racked tracks never runs right no matter what you do later. Hang the panels or the curtain and confirm the door moves freely by hand through its travel with the springs still slack. Then the trained technician winds the springs to the door's spring chart, sets the balance so the door floats, and only then is the door ready for an operator. Hang the operator, set the limits and force, and connect the entrapment protection.

Finish with the proof. Run the door through full open and close cycles, confirm it reverses on an obstruction and on the photo-eye, and confirm the manual release works so the door can be operated if power is lost. On the dock side, set the leveler, seal, bumpers, and restraint, then run the leveler through its range and test the restraint on an actual trailer or the manufacturer's test fixture before anyone loads through the opening.

• Confirm clear opening, headroom, backroom, and that the structure carries the door and operator loads.
• Set vertical tracks plumb and horizontal tracks level and parallel to the manufacturer's spacing.
• Hang the door or curtain and confirm it moves freely by hand with the springs slack.
• Have a trained technician wind the springs to the spring chart and set the balance so the door floats.
• Install the operator, set open and close limits and force per the manufacturer, and confirm the manual release.
• Connect and test the entrapment protection so the door reverses on an obstruction and on the photo-eye, per UL 325.
• Set the leveler in the pit, the seal, the bumpers, and the vehicle restraint to their install instructions.
• Test the leveler through its full range and the restraint on a trailer before the dock goes into service.

Integration with access control and building systems

A commercial overhead door often has to talk to the rest of the building: an access-control reader that releases the door, a card or fob that opens a secured bay, a building management system that logs the door state, or an alarm interface that closes a fire door. The integration is where the door stops being a standalone machine and becomes part of the security and life-safety picture.

Keep the safety hierarchy straight when you integrate. Free egress and fire-alarm release outrank any access-control or security function, exactly as they do on a swing door. A fire-rated rolling door has to close on the alarm regardless of what the access system is doing, and a powered door's entrapment protection has to work no matter how the open command was given. Our access-control guide covers the reader, the controller, fail-safe versus fail-secure, and the egress and fire-alarm interface that the door integration has to respect.

On the wiring side, the open-close interface, the dock restraint interlock, and the communication lights are low-voltage control wiring run to the manufacturer's diagrams and kept separated from the line-voltage operator power. Coordinate the interface points early so the door controller, the access controller, and the BMS agree on which device commands the door and which one just reports its state.

Maintenance and the preventive schedule

Doors and docks fail on a schedule you can predict, so the maintenance is about catching wear before it becomes a failure under load. Springs and cables have a cycle life, and a high-cycle door in a busy distribution center burns through a standard spring fast. Track the cycles where the operator counts them, and plan spring and cable replacement against the cycle rating instead of waiting for the break, because the break is the dangerous moment you are trying to avoid.

On the door, the recurring items are the springs and cables, the rollers and hinges, the track alignment, the operator's limits and force, and the entrapment-protection test. Lubricate and inspect to the manufacturer's interval. On the dock, the leveler gets its hydraulics or springs and its lip checked, the seal and bumpers get inspected for wear, and the restraint gets tested and serviced so it actually locks when called on. A restraint that has rusted or seized is a restraint that will not save anyone.

Spring and cable work inside this schedule is still trained-tech-only. A maintenance contract that has a generalist greasing rollers is fine; one that has the same person adjusting a torsion spring is a contract writing a check on someone's safety. Keep the spring, cable, and balance work with a trained door technician, and document every service so the cycle history and the last spring change are on the record.

Testing the safety devices so they actually work

Every safety device on a door and dock is only worth what its last test proved. The three tests that matter most are the operator reversal under UL 325, the vehicle restraint on a real trailer, and the fire-door drop test under NFPA 80. Run them at install and on the manufacturer's and code interval, and write down the result.

For the operator, place an obstruction and confirm the door reverses on contact, then break the photo-eye and confirm it reverses on the beam. For the restraint, confirm it engages the trailer's rear impact guard or wheel and holds, and that the communication lights follow the lock state. For the fire door, run the NFPA 80 drop test: release the door, confirm it closes fully at the controlled speed, then reset it and confirm the closing device reset, which is why the drop test is run twice.

The blunt part: a safety device that has not been tested is a device you are guessing about. A door that does not reverse, a restraint that does not lock, and a fire door that hangs up on the way down are all failures that hide until the day they matter. Prove each one works, on a schedule, and the test result is the only thing that lets you say the dock is safe.

What to document

The record is what tells the next technician what is installed, when the spring was last changed, and whether the safeties passed their last test. On a door and dock that means the door type and model, the spring rating and cycle class, the operator model and its safety configuration, the leveler and restraint models, and the dates and results of every safety test. Capture it on the device, not on a clipboard that gets lost, so the cycle history and the last drop test travel with the opening.

Tie the records to a field tool so the door, the spring, the operator test, the leveler, the restraint, and the PM history live in one place per opening. FieldOS keeps that per-door history, the photos, and the safety-test dates together, so a manager can see at a glance which doors are due for a drop test and which restraints passed their last check.

Common mistakes

• Servicing a door spring untrained, which is how the worst injuries on this trade happen.
• Running a powered door with no working entrapment protection, so it does not reverse on an obstruction.
• Leaving a dock with no vehicle restraint, or relying on a wheel chock that slips, so the trailer creeps.
• Hanging the operator on an unbalanced door, which burns the operator and undermines the reversing.
• Leaving worn lift cables or fatigued springs in service past their cycle life instead of replacing them.
• Never drop-testing a fire-rated rolling door, so nobody knows it will close in a fire.
• Mounting the dock seal or leveler to the wrong bumper projection, so the seal or lip is wrong on every trailer.

Standards and references

The governing documents split by part of the system. For the doors themselves, ANSI and DASMA cover the construction, performance, and the inspection and testing practices, including the DASMA technical data sheets on rolling-door drop testing and the door types. For powered operators, UL 325 sets the entrapment-protection requirements, and ASTM F2200 is the companion standard often referenced for gate and door construction. Treat these as the framework and the specific door, spring, and operator manufacturer's instructions as the controlling detail.

For the dock and the workplace, OSHA governs. Trailers have to be secured during loading and unloading, with the powered-industrial-truck rules at 29 CFR 1910.178 covering chocks and restraints, and the general dock and walking-working-surface rules covering the fall and struck-by hazards at the edge. Confirm the citations against the current OSHA text, since section references and interpretations get updated.

For fire-rated doors, NFPA 80 is the standard for the installation, the drop test, and the annual inspection, and the adopted fire code and the AHJ control which edition applies. Three things carry the most weight on this work and are worth repeating: door springs store lethal energy and are trained-tech-only, the operator has to reverse under UL 325 with the door balanced, and a vehicle restraint that stops trailer creep is the top dock hazard control. Hedge the springs, the operator, and the restraint to the manufacturer, ANSI/DASMA, UL 325, NFPA 80, and OSHA, and verify the editions the jurisdiction has adopted.

Units and terms

Door and dock work uses a handful of terms that mean specific things, and getting them straight keeps a submittal and a service ticket readable across the door side and the dock side.

Cycle counts measure spring and door life as open-close cycles. Leveler capacity is in pounds and has to cover the loaded forklift plus the freight, not the freight alone. Door speeds on high-speed doors are given in inches per second. Fire-door closing speed under NFPA 80 sits in an inches-per-second band. These are the numbers that travel between the manufacturer's spec, the submittal, and the field, so read which one a document means before you act on it.

Overhead door

A door that lifts overhead to clear an opening, counterbalanced by a spring so it can be lifted without its full weight

Torsion vs extension spring

Torsion winds on a shaft above the door; extension stretches along the side tracks; both store the door's weight as energy

Door balance

Spring tension matched to door weight so a disconnected door floats and holds position anywhere in its travel

UL 325 entrapment protection

The requirement that a powered door sense an obstruction and reverse, using two independent monitored means

Dock leveler

A hinged steel plate in a pit or on the dock face that bridges the gap and height difference to the trailer bed

Vehicle restraint

A device that locks a trailer to the dock by its rear impact guard or wheel to stop creep and early departure

Dock seal / shelter

Foam pads or a fabric enclosure that close the weather gap between the trailer and the building

Fire door / fusible link

A rated rolling door released to close on an alarm or by a heat-melted link, drop-tested per NFPA 80

Related tools

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