The loop is the wire cut into the slab under a parkade door. When it works, nobody notices it. When it fails, the door either won't open for cars leaving or won't close at all. Here is what a parkade loop detector actually does, how it's set up, and what it can and can't be trusted with.
A parkade loop usually has one of two jobs: letting cars out without a remote, or keeping the door from coming down on a car that’s sitting in the opening. The loop is simple hardware, but how it’s wired into the door operator decides what it does. Two parkades with the same loop can behave completely differently.
What a parkade loop detector is
There are two parts:
- The loop: a coil of wire set into or under the pavement. It has no moving parts.
- The detector: a small electronic module, usually in or beside the operator’s control box, that powers the loop and watches for a change when a large metal mass (a vehicle) sits over it. When it sees one, it switches a relay.
Manaras’s accessory catalogue describes it in one line: “Loop detectors are used to detect the presence or passage of a vehicle. To be used in conjunction with an inductive wire loop embedded in the pavement.”
Manaras parts as an example
Manaras’s 2023 catalogue lists a typical set:
| Part | What it is | Published specs |
|---|---|---|
| LOOP035A | Loop detector module | 12-60 VDC or 12-240 VAC supply, dual relay output (NO and NC), loop inductance range 20-2000 µH, -40°C to 82°C, mounts on an 11-pin base |
| LOOP015 | Pre-formed loop, pave-over type | Detection zone about 8′ x 4′, 50′ wire leads |
| LOOP027 | Pre-formed loop, saw-cut type | Detection zone about 8′ x 4′, 50′ wire leads |
| RELAY021 | 11-pin socket base for the module | 10 A, 300 VAC, DIN rail or plate mount |
The same sheet gives the detection height as “1/2 – 2/3 of the shortest side of the surface area covered by the loop”. For a 4′ x 8′ loop that works out to roughly 2 to 2.7 feet above the slab. That’s plenty for a car or van body. It’s why a loop can miss something small and low.
Pave-over vs saw-cut loops
The difference is how the loop goes in:
- Pave-over loops are laid before the surface is poured or paved. They suit new construction or a slab that’s being replaced.
- Saw-cut loops go into a slot cut into an existing slab, then get sealed. That’s the option for an existing slab you don’t want to repave.
LiftMaster’s AELD loop detector manual gives installation details that apply to saw-cut loops generally: 14, 16 or 18 gauge stranded wire, the lead-in “twisted a minimum of 6 turns per foot” from the end of the slot to the detector, and a cut deep enough (typically 2 to 2.5 inches) to keep at least 1 inch of cover over the wire. It also ties the number of wire turns to the loop’s perimeter: 4 turns for a 10-13 ft perimeter, 3 for 14-26 ft, 2 for 27-80 ft and 1 for 81 ft and up.
A 4′ x 8′ loop has a 24 ft perimeter, so the AELD table calls for 3 turns.
What the loop tells the door to do
The detector just closes a contact. The operator decides what that contact means. This is where parkade loop detector set-ups differ.
Free exit (open)
A car drives onto the exit loop and the door opens. No remote needed to leave. Manaras lists loop detectors as an “open only control” option.
Reverse and hold open
Manaras also lists the loop as “a reverse and hold open control for an operator with B2, C2 or timer to close operating mode”. In plain terms: while a car sits on the loop the door stays up, and if the door is closing when a car rolls onto it, it reverses. LiftMaster’s plug-in loop board for its MAXUM DC operators (LPEXPKIT) supports two modes: EXIT, and INTERRUPT, which the manual says “Prevents door from closing on a vehicle in the loop path”. Its SHADOW and AUXILIARY modes are “not supported for DC operators”.
Partial open for cars
LiftMaster operators have a Car Dealer feature. On MAXUM DC, the manual says a Car Dealer input “(typically a treadle switch, loop detector, or motion sensor) will open the door to mid-stop, and TTC will be enabled.” Repeat inputs keep the door at mid-stop and reset the timer. Logic 5.0 has a similar Car Dealer mode, and it needs at least one LiftMaster monitored entrapment protection device installed.
Which mode you want depends on the building. If your door also runs timer-to-close, see our timer-to-close article for how the loop interacts with T and TS modes.
A loop is not a safety device
This is the part that gets missed. A loop sees vehicles. It doesn’t see people, bikes or a child on a scooter, and it can’t see anything above its detection height.
- LiftMaster’s door operator manuals class loop detectors as “auxiliary devices”, meaning any device “that have only dry contacts”, in the same list as treadles, radio controls and pull cords.
- For timer-to-close, those same manuals require a LiftMaster Monitored Entrapment Protection (LMEP) device, such as a monitored photo eye or edge. A loop doesn’t count.
- LiftMaster’s CSL24UL slide gate manual is blunter. Its loop inputs sit under the heading “Access Control Device / NOT TO BE USED AS ENTRAPMENT PROTECTION”.
So a parkade loop detector works alongside the photo eyes and edges. It never replaces them. If someone suggests removing the photo eyes “because the loop does the same thing”, the answer is no. Our UL 325 guide explains the monitored-device rules.
Signs your parkade loop detector is failing
Loop problems show up as door behaviour, which is why they’re often misdiagnosed as operator faults:
- The door won’t close and nothing is in the way. A detector that thinks a car is present keeps holding the door. The AELD manual notes that when the detector sees a loop failure, “it will force a call output” so a broken loop can look like a permanent car.
- Cars sit at the exit and the door doesn’t open. Sensitivity too low, a damaged loop, or a detector that’s lost power.
- The door opens by itself. Sensitivity too high, or two loops interfering. The AELD manual says adjacent loops need at least 5 kHz of frequency separation and different frequency settings.
- Trucks and high vans get missed. The AELD has a “Boost” switch that “will increase the sensitivity to detect high profile vehicles.”
- Problems after slab work. A saw cut crossed by a new crack, a core drill or a resurfacing job is a common cause.
Wet weather adds its own issues with saw-cut loops. Our parkade gate service page covers moisture and loop “saturation”.
Quick checks before you call
- Look at the detector’s LEDs. Most have power and detect indicators. Is it showing “detect” with no car on the loop?
- Check the slab over the loop for fresh cracks, a broken sealant line or exposed wire.
- Note which vehicles are missed (all, or only tall ones) and at what time of day.
Leave the settings alone unless you know the model. Changing frequency or sensitivity on one detector can upset a second loop nearby.
Loop vs photo eye at a parkade door
| Loop detector | Monitored photo eye | |
|---|---|---|
| Detects | Vehicles (metal mass) over the loop | Anything that breaks the beam, including people |
| Counts as entrapment protection | No | Yes, if it’s a device the operator monitors |
| Typical job | Free exit, hold open, reverse for cars | Stop and reverse a closing door |
| Weak spots | Slab damage, cuts, interference | Dirt, misalignment, impacts |
Most parkades need both. The parkade operator selection guide covers how inputs are planned when a new operator goes in, and we diagnose and repair loops as part of our strata parkade door service.
Loop detector questions
What does a loop detector do on a parkade door?
It senses a vehicle over a wire loop set in the pavement and switches a relay. Depending on how it is wired, the operator uses that to open the door for free exit, hold it open, or reverse a closing door while a car is in the opening.
Is a loop detector a safety device?
No. A loop sees vehicles, not people. LiftMaster classes loop detectors as auxiliary devices, and its timer-to-close modes require a monitored entrapment protection device such as a monitored photo eye. Its CSL24UL gate manual labels loop inputs NOT TO BE USED AS ENTRAPMENT PROTECTION.
Why won’t our parkade door close when nothing is there?
One common cause is a loop detector that thinks a car is present. LiftMaster’s AELD manual says that when the detector sees a loop failure it will force a call output, which holds the door open.
What is the difference between a pave-over and a saw-cut loop?
A pave-over loop is laid before the surface is poured or paved. A saw-cut loop goes into a slot cut into an existing slab and is then sealed, so it suits an existing slab.
How big is a typical parkade loop?
Manaras’s pre-formed LOOP015 and LOOP027 loops list a detection zone of about 8 by 4 feet, with a detection height of one half to two thirds of the shortest side of the loop.
Loop or door acting up?
Call (604) 206-5727 or use the contact page. We answer around the clock for commercial door failures across Metro Vancouver.
New commercial clients: 10% off labour on your first service call or repair — mention NEW10 when booking (one per business, not combinable with maintenance-contract pricing, work booked by Dec 31, 2026).
