If you work in industrial automation, machine design, or heavy-duty appliances, sooner or later you’ll encounter the Honeywell BZ-2RQ18M-A2. This roller plunger limit switch is part of Honeywell’s long-standing MICRO SWITCH™ BZ series, known for robust construction, high current ratings, and reliable, repeatable snap-action performance in demanding environments. In this guide, we’ll break down what the Honeywell BZ-2RQ18M-A2 actually is, how it works, its detailed technical specifications, and how to install, specify, and apply it correctly in real-world systems.
What is the Honeywell BZ-2RQ18M-A2 Roller Plunger Limit Switch?
At its core, the Honeywell BZ-2RQ18M-A2 is a heavy-duty basic limit switch with a high-overtravel roller plunger actuator and a single-pole double-throw (SPDT) contact arrangement. That means one common contact can switch between a normally open (NO) and a normally closed (NC) terminal, allowing you to use the switch for either “make-on-actuation” or “break-on-actuation” functions in your circuit.
Unlike light-duty microswitches, the Honeywell BZ-2RQ18M-A2 is rated for 15 A at common AC voltages such as 125, 250, and 480 VAC, and also 15 A at 28 VDC for low-voltage DC applications. Above those DC levels, current is derated according to UL limits, making this switch suitable for both power and control circuits. The roller plunger is panel-mounted through a threaded bushing, and the roller tip is meant to ride on a cam or sliding mechanism to sense position, travel limits, or interlock status in machinery and equipment.
Because the Honeywell BZ-2RQ18M-A2 belongs to the MICRO SWITCH™ BZ family, it inherits a long track record in industrial equipment, appliances, and even aerospace derivatives, where similar mechanical and electrical construction has been field-proven over millions of cycles in harsh operating conditions.
Key Technical Specifications of the Honeywell BZ-2RQ18M-A2
For engineers and specifiers, the Honeywell BZ-2RQ18M-A2 is easiest to understand through its key parameters: actuator type, contact configuration, electrical ratings, mechanical life, operating forces, environmental ratings, and physical dimensions.
Actuator and Form Factor
The Honeywell BZ-2RQ18M-A2 is built around a high-overtravel roller plunger:
- Actuator type: Spring-loaded plunger with a roller mounted parallel to the plunger axis.
- Roller use: Designed to ride on a cam or moving surface, allowing smooth actuation as the cam ramps up.
- High overtravel: The plunger and roller assembly are designed to tolerate additional travel after the contacts trip, preventing mechanical damage from minor misalignment or over-travel of the mechanism.
The base housing follows the standard Honeywell large basic MICRO SWITCH™ form factor, approximately 50.8 mm × 17.8 mm × 25.4 mm (2.0″ × 0.7″ × 1.0″). The Honeywell BZ-2RQ18M-A2 also includes through-holes on the housing for alternative chassis mounting, with 1.00″ (25.4 mm) spacing for #6 screws, offering flexibility in mechanical design.
Contact Arrangement and Material
Inside the Honeywell BZ-2RQ18M-A2, the switch mechanism provides:
- Contact type: SPDT (1 Form C) – common, NO, and NC terminals.
- Contact material: Silver alloy, optimized for power switching with good conductivity and resistance to oxidation at higher currents.
This configuration allows you to design circuits where a single Honeywell BZ-2RQ18M-A2 can provide both “on” and “off” feedback signals, such as energizing one relay while de-energizing another, or switching from a “run” circuit to a “stop” circuit at a defined travel limit.
Electrical Ratings
The electrical performance of the Honeywell BZ-2RQ18M-A2 is one of the reasons it is widely used in industrial equipment:
- AC ratings: Up to 15 A at 125, 250, or 480 VAC.
- DC ratings: 15 A at 28 VDC, with derated current at higher DC voltages in line with UL practice (e.g., fractions of an ampere at 125–250 VDC).
These ratings make the Honeywell BZ-2RQ18M-A2 suitable for directly switching relays, contactors, solenoids, small motors, or heaters, provided you respect the load category and inrush characteristics.
Mechanical and Electrical Life
Honeywell’s MICRO SWITCH™ BZ series, including the Honeywell BZ-2RQ18M-A2, is known for high durability:
- Mechanical life: Minimum 10 million operations under normal conditions; in low-load or signal-level use, the same mechanism has been tested to as many as 20 million cycles in some configurations.
- Electrical life: Typically on the order of 100,000 switching cycles at the full 15 A load, depending on load type (resistive vs inductive).
This balance of mechanical robustness and electrical endurance means the Honeywell BZ-2RQ18M-A2 can operate for years in production machinery where cycle counts are high and downtime is costly.
Forces and Travel
Because the Honeywell BZ-2RQ18M-A2 is often used on cams and mechanical linkages, force and travel data are critical:
- Operating force (OF): Roughly 2.5–3.63 N (250–370 gf), with a typical value near 3.6 N to trip the mechanism.
- Release force (RF): At least 1.1 N (110 gf), ensuring a clear reset when the load on the plunger is removed.
- Pretravel (PT): Very small, roughly 0.38 mm (0.015") before actuation.
- Overtravel (OT): Generous, ≥3.56 mm (0.140") beyond the operating point.
- Differential travel (DT): Extremely small, typically 0.01–0.05 mm, which gives the Honeywell BZ-2RQ18M-A2 its sharp, precise snap action and repeatable switching point.
Environmental Ratings and Materials
The Honeywell BZ-2RQ18M-A2 is designed for a wide range of environments:
- Operating temperature: -55 °C to +85 °C (-67 °F to +185 °F).
- Housing: High-strength phenolic thermoset and engineering plastics (e.g., PBT) for electrical insulation and mechanical strength.
- Actuator hardware: Metal roller and threaded bushing for durability and secure panel mounting.
- Ingress protection: Typically around IP40 (unsealed plunger), suitable for clean or moderately protected enclosures.
Other variants in the series offer higher temperature ratings and sealed constructions, but the standard Honeywell BZ-2RQ18M-A2 is ideal for general industrial and appliance environments where it isn’t directly exposed to heavy dust, oil spray, or washdown.
Inside the Snap-Action Mechanism: How the Honeywell BZ-2RQ18M-A2 Works
Understanding how the Honeywell BZ-2RQ18M-A2 functions internally helps you design cams, stops, and linkages that use the switch correctly and safely. At the heart of the device is a pre-loaded spring and contact system that “snaps” between states when the plunger passes a critical point.
As the roller plunger of the Honeywell BZ-2RQ18M-A2 is depressed by a cam, force is transmitted through the plunger to a spring-powered mechanism. Initially, the contacts remain in their normal state (e.g., COM-NC closed, COM-NO open). Once pretravel is consumed and the plunger reaches the operating point, internal geometry causes a rapid transfer of spring energy. The movable contact arm flips to its opposite position, closing COM-NO and opening COM-NC in a very short movement, minimizing contact bounce and arc duration.
One key advantage of the Honeywell BZ-2RQ18M-A2 is its extremely small differential travel. This means the plunger only has to move a tiny additional distance before the contacts reset on the way back. For designers, this yields a tightly repeatable switching point — perfect for position detection, repeatable homing, or accurate travel limits in high-precision systems.
The “M” suffix in the Honeywell BZ-2RQ18M-A2 part number indicates high overtravel capability. After the contacts switch, the roller plunger can continue to travel further without damage, thanks to a collapsible or deflecting mechanism that absorbs extra motion. However, this high-overtravel behavior is directional: the roller is intended to be driven from one side; if the cam approaches from the wrong side, the roller may collapse instead of actuating the switch. This makes proper orientation essential when installing the Honeywell BZ-2RQ18M-A2.
Compliance, Certifications, and Quality Assurance
In regulated industries, having a limit switch like the Honeywell BZ-2RQ18M-A2 backed by recognized approvals simplifies design validation and safety documentation. The BZ series carries several global certifications and compliance statements, which typically apply to the Honeywell BZ-2RQ18M-A2 configuration as well.
Safety Certifications
The Honeywell BZ-2RQ18M-A2 is associated with:
- UL and CSA recognition: The BZ/BA/BM family is recognized by UL and certified by CSA as special-use snap switches under UL 1054 and related standards. This confirms that the Honeywell BZ-2RQ18M-A2 meets stringent requirements for electrical spacing, flammability, and temperature rise.
- ENEC / IEC compliance: ENEC approval indicates conformity to IEC 61058-1 and related European standards, allowing use in equipment bearing the CE mark in EU markets.
These markings usually appear on the switch housing alongside the electrical ratings for the Honeywell BZ-2RQ18M-A2, giving visual confirmation that the device is built and inspected under audited quality systems.
Environmental and Material Compliance
On the environmental side, the Honeywell BZ-2RQ18M-A2 typically complies with:
- RoHS directive: No restricted hazardous substances above allowable thresholds.
- REACH: Conformance to European regulations regarding chemicals and substances in industrial products.
Honeywell also provides certificates of conformance that can be attached to your project documentation, helping you demonstrate that assemblies using the Honeywell BZ-2RQ18M-A2 meet internal and external environmental requirements.
Military and High-Reliability Heritage
Although the standard Honeywell BZ-2RQ18M-A2 itself is a commercial part number, closely related models in the same family are qualified to MIL-PRF-8805 (formerly MIL-S-8805), with dozens of listings on the Qualified Products List (QPL). The core mechanical design, contact system, and housing concept are similar, which means the Honeywell BZ-2RQ18M-A2 benefits from a long legacy of aerospace and defense use where reliability is non-negotiable.
Alternative Models Related to the Honeywell BZ-2RQ18M-A2
Even though the Honeywell BZ-2RQ18M-A2 is a very versatile choice, you may encounter situations where a different actuator, environmental rating, or contact configuration is better. Honeywell offers several related models that share the same basic design and dimensions but tweak specific parameters.
Different Actuator Styles
If the main requirement is a different mechanical interface, you can look at alternate actuator designs instead of the standard Honeywell BZ-2RQ18M-A2 roller plunger:
- Cross-roller plunger (e.g., BZ-2RQ181-A2): The roller is oriented 90° to the long axis of the switch, ideal for side actuation where the cam moves perpendicular to the switch body. High-overtravel versions like BZ-2RQ181M and sealed variants such as BZ-2RQ181M-A2RS are available.
- Pin plunger (e.g., BZ-2RQ1-A2): A panel-mount pin plunger without a roller for direct end-of-travel sensing. This can be used when mechanical contact is simple and rolling friction isn’t needed.
In many cases, footprint and contact ratings remain similar, making it possible to substitute a Honeywell BZ-2RQ18M-A2 with these alternatives if the actuator style better matches your cam or linkage.
Sealed and Harsh-Environment Variants
When dust, splash, or light washdown is expected, an unsealed Honeywell BZ-2RQ18M-A2 may not offer enough protection. In that case, Honeywell provides:
- Sealed “RS” variants (e.g., BZ-2RQ18M-A2RS), which add an internal seal boot and protective cover. These options provide roughly IP64-class environmental sealing, protecting the plunger and terminals from dust and splashing water.
You can also protect the standard Honeywell BZ-2RQ18M-A2 by installing it inside a sealed enclosure or using terminal covers, but when direct environmental exposure cannot be avoided, a sealed model is usually the better long-term choice.
Low-Current Gold-Contact Versions
For very low-energy circuits, such as PLC inputs or instrumentation where currents may be in the milliamp or microamp range, a silver-contact Honeywell BZ-2RQ18M-A2 may not be ideal. Oxide films on silver contacts can cause unreliable switching at low currents. Honeywell therefore offers gold-plated contact variants (with “-72” suffix) like BZ-2RQ1872-A2, which use a gold alloy contact system optimized for low currents (typically up to about 1 A).
Although these variants may not carry the full 15 A rating of the Honeywell BZ-2RQ18M-A2, they are far better suited to logic and signal applications, especially where switching loads are tiny but reliability is critical.
Higher Current Series
If your design requirements exceed the 15 A rating of the Honeywell BZ-2RQ18M-A2, look at these related families:
- BA series: Typically rated around 20 A.
- BM series: Around 22 A current ratings.
- BE series: Up to 25 A, often used under UL 508 for motor control and similar heavy loads.
These higher-current switches share similar mechanical layouts but use different contact and spring systems. When moving from a Honeywell BZ-2RQ18M-A2 to a BA, BM, or BE equivalent, always confirm contact ratings, terminal types, and temperature limits in the datasheet.
Accessories and Mounting Options for the Honeywell BZ-2RQ18M-A2
A dedicated range of accessories helps you integrate the Honeywell BZ-2RQ18M-A2 into panels and enclosures safely and conveniently.
Panel-Mount Hardware
The roller plunger of the Honeywell BZ-2RQ18M-A2 is fitted into a threaded bushing designed for panel mounting:
- Thread size: Approximately 15/32″ (around 12 mm) diameter, matching common panel hardware dimensions.
- Supplied hardware: Typically includes two hex nuts (and sometimes a lock washer), enabling you to clamp the bushing securely to a panel or bracket.
- Recommended torque: Around 0.5–0.7 N·m (4–6 in·lb) to avoid damaging the housing or distorting the switch.
This allows you to mount the Honeywell BZ-2RQ18M-A2 directly through a panel located near your moving cam or striker.
Terminal Covers
For electrical safety and cleanliness, Honeywell offers a snap-on terminal cover that shields the screw terminals of the Honeywell BZ-2RQ18M-A2:
- Prevents accidental finger contact with live terminals.
- Reduces the risk of conductive debris bridging connections.
- Provides knock-out openings so wires can exit at convenient angles.
Using a cover is recommended wherever the Honeywell BZ-2RQ18M-A2 is installed in accessible control panels or areas where maintenance workers might reach near the switch.
Seal Boots and Special Options
Certain basic switch models offer seal boots or pre-assembled environmental seals. For a roller-plunger part like the Honeywell BZ-2RQ18M-A2, it’s usually more practical to choose a factory-sealed variant than to retrofit a boot, because the geometry of the roller makes field sealing complex. When you need extra protection, plan upfront to use a sealed Honeywell BZ-2RQ18M-A2 derivative or enclose the switch in a suitable housing.
Installation and Setup Best Practices
Correct installation of the Honeywell BZ-2RQ18M-A2 ensures long life, accurate switching points, and safe operation. Let’s walk through panel mounting, surface mounting, wiring, and adjustment.
Panel-Mount Installation
To use the threaded bushing on the Honeywell BZ-2RQ18M-A2:
- Drill the panel hole to the bushing’s clearance size (around 12 mm/15⁄32″).
- Insert the bushing through the panel from the front or back, aligning the roller with the approach path of your cam.
- Secure with nuts: Use one nut on each side of the panel (or two nuts on the same side as a jam pair), tightening to the recommended 4–6 in·lb.
- Check thread engagement: Ensure enough threads are engaged to hold the Honeywell BZ-2RQ18M-A2 firmly without bottoming out the nut.
Proper panel mounting prevents vibration slippage and ensures your cam meets the roller at the right point in its travel.
Surface or Chassis Mounting
Alternatively, you can mount the Honeywell BZ-2RQ18M-A2 using the two housing flange holes:
- Hole spacing: 1.00″ (25.4 mm) center to center.
- Screw size: #6 machine screws (≈3.5 mm).
- Torque: About 3 in·lb maximum to avoid warping or cracking the phenolic base.
Spacers or stand-offs can be used to position the switch so the plunger aligns precisely with the machine element.
Orientation and Cam Design
The roller plunger mechanism in the Honeywell BZ-2RQ18M-A2 is directional. To get consistent actuation:
- Mount the switch so that the cam contacts the roller from the intended side, causing the plunger to depress rather than collapse.
- Use a cam slope of ≤30° relative to the roller, which allows smooth engagement and minimizes shock.
- Ensure the cam surface is smooth; rough surfaces increase wear on the roller and shorten the life of the Honeywell BZ-2RQ18M-A2.
The goal is to have the cam pass through the switch’s operating point with enough overtravel to guarantee actuation, but not so much that you consistently bottom out the plunger.
Wiring and Electrical Setup
The Honeywell BZ-2RQ18M-A2 uses screw terminals with captive cup washers for COM, NO, and NC:
- Isolate power before wiring.
- Terminate wires using crimp lugs or fork terminals, or wrap stripped wires around the screw under the cup washer.
- Tighten each terminal screw to roughly 3–4 in·lb, enough to secure the wire but not so much as to strip the threads or crack the base.
- Verify you have used the correct pair of terminals (COM-NO or COM-NC) according to whether the circuit should close or open when the Honeywell BZ-2RQ18M-A2 actuates.
After wiring, install the optional terminal cover and route the wires through its knock-outs for strain relief and protection.
Final Adjustment and Testing
Once the Honeywell BZ-2RQ18M-A2 is mounted and wired:
- Manually move your machine part or cam through its travel while observing the roller and listening for the switch “click”.
- Verify that the switch trips at the intended position and that overtravel stays within a comfortable range (using the built-in ~3.6 mm OT as a guideline).
- Use a multimeter or test circuit to confirm that the correct contact (COM-NO or COM-NC) changes state at the expected point.
Tuning the mechanical position of the Honeywell BZ-2RQ18M-A2 and the cam profile at this stage greatly improves system reliability and reduces later maintenance.
Typical Applications of the Honeywell BZ-2RQ18M-A2 in Industry
The Honeywell BZ-2RQ18M-A2 is one of those components that quietly shows up in many different types of equipment. Its combination of roller plunger actuation, 15 A rating, and long life makes it a flexible design choice.
Industrial Machinery and Automation
In factories and plants, the Honeywell BZ-2RQ18M-A2 is widely used as an end-of-travel or position limit switch on:
- Conveyor systems and diverters
- Packaging and filling machines
- Presses and forming machines
- Machine tools and CNC equipment
Here, the roller of the Honeywell BZ-2RQ18M-A2 rides on cams connected to moving parts. When the part reaches a limit, the switch trips, sending a signal to stop motion, reverse a motor, or trigger another sequence. Because it can directly handle 15 A at typical mains voltages, it can often switch smaller loads directly, or act as an input to relays or PLCs.
Home Appliances and HVAC
In appliances and heating systems, the Honeywell BZ-2RQ18M-A2 serves as a durable, precise position sensor:
- Door-closed detection in dryers or washers
- Limit sensing in garage door openers
- Safety interlocks in water heaters, boilers, or furnaces
The broad temperature range and mechanical endurance of the Honeywell BZ-2RQ18M-A2 make it ideal for repetitive on/off cycles found in domestic and light commercial equipment.
Safety Interlocks and Emergency Systems
In safety-critical systems, the Honeywell BZ-2RQ18M-A2 can form part of interlocks and emergency stop bars:
- Detecting when guards or doors are fully closed before enabling hazardous motion
- Sensing that an emergency stop bar has been pressed along the edge of a conveyor or machine
- Providing redundant limit feedback in hoists or automated storage systems
The precise snap-action and robust contact design of the Honeywell BZ-2RQ18M-A2 make it well suited to these roles, particularly when combined with safety relays and monitored circuits.
Door, Gate, and Access Control
In access control and door hardware, the Honeywell BZ-2RQ18M-A2 can:
- Sense fully open or closed positions of doors, gates, and hatches
- Control power to solenoid locks or magnetic latches based on door position
- Provide feedback to alarm panels or building automation systems
Because the Honeywell BZ-2RQ18M-A2 can switch modest inductive loads, it is often wired close to door actuators or as part of an interlock network tying together sensors, locks, and indicators.
Mobile, Automotive, and Off-Highway Equipment
In off-highway vehicles, agricultural machines, and material handling equipment, the Honeywell BZ-2RQ18M-A2 takes on rugged roles such as:
- Detecting pedal or lever positions
- Sensing when a lift mast reaches its lowest or highest point on forklifts
- Acting as a limit on hydraulically driven implements
Vibration resistance, long life, and a roller plunger design make the Honeywell BZ-2RQ18M-A2 a robust choice in mobile environments where straightforward, mechanical limit sensing is needed.
Instrumentation, Timing, and Aerospace Heritage
In timing devices, counters, and indexing tables, the Honeywell BZ-2RQ18M-A2 serves as the “end-of-cycle” switch. A cam driven by a motor or gear train actuates the roller at precisely defined positions, allowing circuits to count cycles or trigger events.
In aerospace and defense, MIL-qualified versions of this basic design are used for critical limit sensing — from landing gear indicators to valve position feedback. Even if your particular Honeywell BZ-2RQ18M-A2 is not a MIL part, its shared lineage means the mechanical and electrical principles are proven in some of the most demanding contexts.
Design Tips: Selecting and Integrating the Honeywell BZ-2RQ18M-A2
When integrating the Honeywell BZ-2RQ18M-A2 into your own design, several practical considerations will help you avoid problems and make the most of the switch’s capabilities.
Confirm the Load and Duty Cycle
First, check that your load is compatible with the Honeywell BZ-2RQ18M-A2 ratings:
- For resistive AC loads (heaters, lamps), the 15 A rating is straightforward, but inrush currents must still be considered.
- For inductive loads (motors, solenoids), add appropriate suppression (RC snubbers, MOVs, or flyback diodes) and keep an eye on contact wear over time.
- For low-current logic loads, re-evaluate whether a gold-contact variant might be better than the standard silver-contact Honeywell BZ-2RQ18M-A2.
Matching the switch to the load extends service life and keeps your system reliable.
Plan Mechanical Overtravel and Tolerance
The high-overtravel design of the Honeywell BZ-2RQ18M-A2 is forgiving, but not limitless. In the mechanical layout:
- Ensure the cam begins to engage the roller some distance before the desired trip point.
- Allow a modest overtravel margin after the switch trips — enough to guarantee actuation under worst-case tolerances, but not so much that you routinely bottom out the plunger.
- Use the small differential travel of the Honeywell BZ-2RQ18M-A2 to your advantage by designing tight, repeatable trip positions.
This attention to detail pays off in consistent operation and longer switch life.
Consider Environment and Protection
If the Honeywell BZ-2RQ18M-A2 will be in a clean control panel, the standard unsealed model is usually sufficient. But if you expect:
- Dust or fine particles (e.g., wood, flour, or metal dust)
- Oil mist or light splashing
- Occasional washdown or humidity swings
then consider placing the Honeywell BZ-2RQ18M-A2 inside a sealed enclosure, using a sealed companion variant, or adding terminal covers and gaskets as needed. Environmental protection is often cheaper than troubleshooting intermittent faults caused by contamination later on.
Document Settings and Part Numbers
Finally, when you standardize on the Honeywell BZ-2RQ18M-A2, document:
- Full part number (including any suffixes or sealed versions).
- Mounting orientation and cam geometry.
- Terminal usage (e.g., COM-NC used for safety chain, COM-NO used for indicator lamp).
This makes replacement and troubleshooting far easier for future technicians and helps ensure that the correct Honeywell BZ-2RQ18M-A2 is always used in the right location.
Related Product Collections for Honeywell BZ-2RQ18M-A2
If you’re working with the Honeywell BZ-2RQ18M-A2, chances are you’ll need complementary devices for control panels, automation projects, and maintenance work. These curated collections from Industrial Electrical Warehouse can help you build a complete solution around your chosen limit switch.
- Honeywell Collection ➜ – Explore a focused range of Honeywell products, including the Honeywell BZ-2RQ18M-A2 and other Honeywell sensors, switches, and control components that integrate easily into industrial and commercial systems.
- Limit Switches ➜ – Browse a broader selection of industrial limit switches with different actuator styles, ratings, and form factors to match your specific machine design or retrofit requirements.
- Push Buttons & Switches ➜ – Complete your control panel with compatible push buttons, selector switches, and auxiliary switches that work alongside the Honeywell BZ-2RQ18M-A2 for reliable operator and machine interface.
Conclusion: Is the Honeywell BZ-2RQ18M-A2 Right for Your Project?
The Honeywell BZ-2RQ18M-A2 roller plunger limit switch brings together a proven MICRO SWITCH™ mechanical platform, a strong 15 A contact rating, high-overtravel roller plunger actuation, and global approvals that support use in industrial, commercial, and appliance applications. From conveyors and packaging lines to HVAC units and mobile equipment, it offers reliable position sensing and limit protection with long service life and precise, repeatable switching.
If you’re designing or maintaining machinery that needs a robust, panel-mountable limit switch with a roller plunger, the Honeywell BZ-2RQ18M-A2 is a strong candidate to put on your shortlist. To see how it fits into your system – whether in terms of dimensions, electrical ratings, or available sealed and gold-contact variants – take a moment to review the detailed specifications and options on the product page for the Honeywell BZ-2RQ18M-A2 where you source your components. That quick check can help you confirm compatibility, streamline purchasing, and ensure your next project benefits from a switch that’s built to perform for millions of operations.