GDI JDMG-LG Jackshaft Operator
The JDMG-LG is GDI’s sprocket-to-sprocket jackshaft operator for commercial and medium-duty industrial doors, rated at 3,200 open and close cycles per day and UL 325 compliant.
Medium duty is the honest description and the reason to read the cycle number before specifying. A door that opens a few dozen times a day is well inside this unit’s rating. A dock door on a busy shipping floor cycling hundreds of times a shift is a JHMG-VC or HAML-RBH conversation instead — undersizing the operator is the single most common cause of premature commercial operator failure we see.
Specifications
| Specification | Value |
|---|---|
| Drive type | Jackshaft (sprocket to sprocket) |
| Duty rating | 3,200 open/close cycles per day |
| Standard enclosure | 16″ × 16″ × 6″, NEMA 1 |
| Standard part number | JDMG-LG-2030-NLF0000408-1000 |
| Input power | 115 / 208 / 230 / 460 / 575 VAC, 1Ø or 3Ø, 50/60 Hz |
| Auxiliary power | 24 VDC 1.5 A · 24 VAC 1 A |
| Listing | UL/ULC listed · UL 325 compliant |
GDI lists three models in the JDMG-LG range; the part number above is the standard NEMA 1 build from the published sheet. We confirm the exact configuration against your opening before ordering.
Hoist and brake options
GDI’s sheet lists three accessories on this operator that are worth deciding on up front, because they change the unit you order:
- Hoist — allows manual operation of the gear motor, with a floor-level
release, water tight.
- Hoist with brake — manual operation of the gear motor with a brake, again
floor-level release and water tight.
- Brake — brake on the gear motor, floor-level release, water tight.
The floor-level release is the part that matters during a power failure: staff can move the door from ground level without a ladder or a lift.
Sprocket-to-sprocket, in plain terms
The operator drives a sprocket that is chained to a second sprocket on the door’s torsion shaft. It is a forgiving arrangement on a retrofit because the operator does not have to sit exactly on the shaft centreline — the chain takes up the offset. It also means the drive chain is a wear item worth checking on a maintenance visit, along with sprocket alignment.
Where the JDMG-LG fits against the rest of the line
Use the cycle ratings as the first filter, then the drive type:
- JDMG-LG — 3,200 cycles/day, medium-duty jackshaft.
- SGWD — up to 4,000 cycles/day, slide gates to 8,500 lb.
- HAML-RBH — 5,000 cycles/day, direct drive hollow shaft.
- GLWD — up to 8,000 cycles/day, barrier lift gates.
- JHMG-VC — 10,000 cycles/day, heavy-duty horizontal and jackshaft.
Common JDMG-LG faults and what they usually mean
The door stops halfway and the operator hums but won’t run. On a JDMG-LG, that usually means the drive chain has stretched or jumped a tooth on the driven sprocket. Because this unit mounts off the shaft centreline, the chain takes all the torque. If the chain tension wasn’t checked at the last PM, the slack lets the chain ride up on the sprocket under load. You’ll hear a rhythmic click-click-click when it tries to start.
The operator runs for a few cycles then locks out on thermal overload. This unit is rated for 3,200 cycles per day. If the facility added a shift or the door is cycling on a loop sensor, you’re past the duty rating. The motor windings heat faster than the NEMA 1 enclosure can shed it. No fan, no heatsink — just the sheet metal box. The reset button on the board clears the fault, but it will trip again by lunch.
Floor-level hoist release won’t engage. The cable runs through the NEMA 1 enclosure wall. If the grommet dried out or the cable kinked where it exits the box, the release lever at floor level pulls slack but the pin inside the gearmotor doesn’t retract. You’ll find the cable sheath crushed against the enclosure knockout.
Limit switches drift after a power bump. The JDMG-LG uses mechanical cams on the output shaft. A hard stop or chain shock loads the cam shaft and shifts the cam position. The door then opens six inches short or slams the floor.
Specifying a JDMG-LG correctly
Confirm the door cycle count before you quote. This operator is medium duty: 3,200 cycles per day maximum. If the door runs 400 cycles per shift on two shifts, you’re at the ceiling. Three shifts or a high-traffic loading dock needs the heavy-duty JDMG-HG. Undersizing burns the motor in six months.
Measure the torsion shaft centreline height and the wall offset. The JDMG-LG drives a sprocket on the door shaft via roller chain. The operator body does not need to sit on the shaft centreline, but the chain run must be straight. If the wall mounting point forces a chain angle greater than 15 degrees off parallel, the side load eats sprockets. You need clearance for the 16 x 16 x 6 inch NEMA 1 enclosure plus chain guard access.
Pick the release option at order time. Three factory configurations exist: hoist only (manual gearmotor operation, floor-level release, watertight); hoist with brake; or brake only (floor-level release, watertight). You cannot add the brake or change the release type in the field — the gearmotor casting and control board wiring are model-specific. Part number JDMG-LG-2030-NLF0000408-1000 is the base hoist unit; the suffix changes for brake variants.
Verify supply voltage at the disconnect. The control board accepts 120/208/240 V single-phase or 208/240/480/600 V three-phase, but the transformer tap must be set before power-up. If the site has 600 V three-phase and the board is tapped for 240 V, the board fails on first energization.
Confirm the door shaft diameter and keyway. The driven sprocket bore must match. GDI does not ship adapter bushings — wrong bore means a return and a week of downtime.
What every GDI operator shares
- One operator, every common voltage. A single GDI unit connects to 115, 208, 230, 460 or 575 VAC, single or three phase, 50/60 Hz. You are not ordering a voltage-specific part number, which matters when a building’s service turns out to be different from what the drawings said.
- Sealed, maintenance-free GearMotor. Sealed stainless-steel bearings, no belts, no mechanical limit switches, no hydraulic cylinders to service.
- Electronically set open and close limits. Nothing mechanical to drift out of adjustment after a few thousand cycles.
- Soft start and soft stop, with open and close speeds set independently and adjustable on site.
- Battery backup capability as an add-on, so the door or gate still runs through an outage or a brownout.
- 24 VDC 1.5 A and 24 VAC 1 A available for external devices — loop detectors, photo eyes, card readers.
- UL/ULC listed, with field-upgradable Opto-Block, NEMA 4 photo-eye UL-325 packages, and a thermostat-controlled heater (115–575 VAC) orderable at any time.
Download the GDI spec sheet
The manufacturer sheet for this operator is hosted here so you can send it straight to a consultant, an electrician or a property manager without hunting for it:
Authorized GDI dealer in Metro Vancouver
CCGDS is an authorized GDI dealer. That matters for two practical reasons on a commercial site. First, we order the operator as the correct configuration the first time — enclosure rating, shaft size, arm length, accessories — instead of discovering a mismatch on install day. Second, when a unit needs parts years later, we are working from the same spec sheet the factory published rather than guessing at a substitute.
Specifications on this page are taken from GDI’s published sheet for this model. GDI states it reserves the right to modify contents without prior notification, so we confirm the current configuration with the factory at order time.
Installation, service and repair across the Lower Mainland
We install, service and repair GDI operators in Richmond, Vancouver, Burnaby, Surrey, Delta, New Westminster, Coquitlam, Langley and North Vancouver. Typical work on this family of units includes commissioning and limit setup on a new install, diagnosing a control-panel or input fault, replacing worn drive components on the door or gate side, and adding accessories such as photo eyes, loop detectors or battery backup to an operator already in service.
Call (604) 206-5727 to talk through an application, get a unit specified for your opening, or book service on an operator you already have.