A safety temperature limiter is the last line of defence in heated equipment. The control thermostat regulates temperature minute by minute; the limiter does nothing at all — until the day the control fails, a contact welds shut or a fan stops, and the temperature starts climbing past every safe limit. Then the limiter cuts the power and keeps it cut. Choosing one is not difficult, but the four decisions below — trip temperature, reset type, electrical rating and sensing arrangement — have to be made in the right order.
Start with the trip temperature
The trip point has to clear two fences. It must sit above the highest temperature the equipment legitimately reaches in normal service — including overshoot at full load and hot spots near the element — or the limiter will nuisance-trip and operators will defeat it. And it must sit below the temperature at which oil ignites, insulation degrades or the vessel is damaged. Between those two fences there is usually a comfortable window; pick a point in the upper half of it.
Fixed-point limiters are calibrated at the factory and cannot drift or be tampered with afterwards, which is why most commercial equipment uses them. Our standard fixed points on the AG16-S series are 380 / 400 / 430°C; the TY316-8 trips at 380°C, and the multi-pole AG32-3S and AG32-2S trip at up to 400°C. Where none of the standard points lands in your window, trip points are factory-calibrated to your specification — tell us the equipment’s normal operating range and the cut-out temperature you require.
| Model | Reset | Rating | Trip temperature |
|---|---|---|---|
| AG16-S | Manual reset | 16A / 20A · 110V / 250V | 380 / 400 / 430°C |
| TY316-8 | Manual reset | 16A · 110V / 250V | 380°C |
| WQB | Manual reset | 20A · AC 250V | Factory-set |
| AG32-3S | Manual reset, three-pole | 16A / 32A / 50A · 110V / 250V / 400V | Up to 400°C |
| AG32-2S | Manual reset, double-pole | 16A / 32A / 50A · 110V / 250V / 400V | Up to 400°C |
Technical data is a catalogue reference. Confirm final ratings, dimensions and approvals for the selected model before ordering.
Manual reset is the default — for a reason
Safety standards for commercial heating equipment generally require that an over-temperature event cannot clear itself: if a limiter trips and silently resets, a faulty appliance returns to service with its fault untouched. A manual-reset limiter forces a service check before restart — someone has to open the panel, find out why it tripped, and press the reset. That is why every limiter in the table above is manual-reset. Automatic-reset devices have their place in control duties — within our GAS series, for example, auto-reset versions regulate gas appliances while the manual-reset versions provide the safety function — but a self-resetting device should not be the only over-temperature protection on commercial heating equipment.
Note the mechanical life figure: 6,000 cycles. That is not a weakness. Safety devices are rated for rare trips, not daily switching — a limiter that operates a few times in the equipment’s life has done its job. Never use a limiter as the working control to save the cost of a thermostat.
Match the rating to the load — and the poles to the supply
Size the contacts for the heating load as you would for a control: the AG16-S and WQB cover the 16–20A single-phase range found in most countertop and undercounter equipment. Three-phase equipment needs a limiter that breaks all live conductors together — a single-pole device on a three-phase load can leave the element partly energised. The AG32-3S (three-pole) and AG32-2S (double-pole) exist for exactly that duty, at up to 50A and 400V. Gas-fired equipment is a different case again: the limiter switches a millivolt circuit, not mains power, which is what the GAS series (0.67A · DC 5V, 125–300°C) is built for.
Capillary length and bulb placement
A limiter senses through the same liquid-filled bulb and capillary as a control thermostat, so the bulb can sit in the danger zone while the limiter body stays on the panel. Place the bulb where the temperature rises fastest in a fault — close to the element or in the medium itself — and order the capillary length to suit the real route through the appliance; we configure lengths to order. Routing, bend radii and clamping follow the same rules as for any capillary device, covered in our installation guide. Keep the limiter’s sensing line independent of the control’s: two devices sharing one bulb position can share one blind spot.
Certifications
Limiters are safety components, and approvals matter more here than anywhere else in the appliance. Our thermostats are produced under a TÜV-certified quality system — certificate R50309054 (EN 60730-1 / EN IEC 60730-2-9), verifiable on Certipedia — and models carry the certifications their markets require. Confirm the exact approvals for the model you select, for the market you sell into, before you freeze the design.
FAQ
Do safety limiters replace the control thermostat?
No. A control thermostat regulates day-to-day temperature; a safety limiter is independent backup protection that only operates on a fault. Equipment should have both, sensing independently.
Can the trip temperature be set to my requirement?
Yes — trip points are factory-calibrated to your specification. Tell us the equipment's normal operating range and the required cut-out temperature, and we will confirm the closest standard point or a calibrated setting.
Why is the mechanical life only 6,000 cycles?
Because a limiter is a safety device rated for rare trips, not daily switching. It may operate only a handful of times in the equipment's life; the rating reflects that duty, and a limiter must never be used as the working control.
Manual Reset Safety Limit Thermostats · Capillary Thermostat Installation Guide · How to Choose a Capillary Thermostat