Limit Switches Selection Guide

A limit switch is a position switch whose contacts open and close mechanically when a moving part presses its head. Head and contact selection.

What is a limit switch? A limit switch is a position switch whose contacts open and close mechanically when a moving part strikes or presses its head. On machines it is used to detect the end point of an axis, the position of a door or the presence of a part, and to send a signal to the control circuit.

This guide covers what to look at when choosing products in the Limit Switches category.

Actuator head types and where they are used

The same housing and contact block are offered with different heads; the right model is determined by how the moving part reaches the head.

• Plunger: The object presses on the head along its axis. It is used at stopping points with a short stroke and a defined position; models with metal and plastic plungers are available.
• Roller plunger: Thanks to the roller on the end of the plunger, a cam or ramp sliding in from the side pushes the plunger in.
• Roller lever: A short lever with a roller presses the plunger; the cam approaches the lever from the side. In EMAS product names, some of these types appear as single direction.
• Roller lever arm: A cam passing from the side turns the lever on the rotary head. The roller is metal, plastic or rubber; in EMAS product names, the double direction wording appears on these types.
• Adjustable roller lever: The lever length is adjusted to bring the roller to the line where the cam passes; this makes the job easier in setups where the cam position is only fixed during installation.
• Rigid rod: A metal, plastic or fiber rod is fitted in place of the roller.
• Spring rod and coil end: A flexible spring or wire end operates on contact from different directions; it appears as a multi-directional coil end in Gwest data and as a multi-directional spring in ABB data. The pointed and blunt-end types in EMAS product names are also spring rod types.
• Cross-arm crane switches: In the EMAS CSM series there are cross arms on the rotating head; product data includes options with 180° and 360° rotation, 1 forward-1 reverse, 2 forward-2 reverse, and endless rotation.

For models described as single direction or double direction, make the selection according to the direction the cam arrives from and verify it against the manufacturer drawing.

What to check when choosing a limit switch

1. Approach direction and stroke. Determine whether the object arrives at the head along the axis or from the side, whether it passes from one direction or two, and how far it pushes the head. A limit switch is not a mechanical stop; the travel distance the head allows is given in the manufacturer drawing.
2. Housing dimensions. If you are replacing an existing switch, compare the housing dimensions and mounting holes. EN 50047 standardizes the dimensions of position switches at 30 × 55 mm, and EN 50041 at 42.5 × 80 mm. In the product data of ABB LS32 models, the mounting type appears as 30 mm (EN 50047).
3. Contact arrangement. In a 1NO + 1NC model, one contact can be used for stopping or interlocking and the other for indication. 2NO + 2NC models are chosen where two separate circuits need to be informed.
4. Contact action type. In a snap-action contact, the speed of changing position is independent of the head speed; a slow-action contact follows the movement of the head. EN 50047 covers both types. EMAS product names use the wording "ani hareketli" (snap action), and ABB product data uses "snap action".
5. Contact rating. The load of control contacts is given by utilization category: AC-15 is for AC electromagnetic loads (for example, a contactor coil), and DC-13 is for control of DC electromagnets. In ABB and Gwest product data the two values are listed separately, and at a similar voltage the DC-13 current is lower than the AC-15 current; if a DC load will be switched, look at the DC-13 value.
6. Protection rating. ABB and Gwest product data state IP65 and IP66. According to IEC 60529, the first digit 6 indicates dust-tight protection, and the second digit indicates protection against water jets for 5 and against powerful water jets for 6. The Isıso TZ series are cabled models described as waterproof.

Difference from similar switches

• Door switches with a separate actuator that monitor guards and doors, and rope-pull types, are in the safety limit switches category. In a circuit with a safety function, the type and connection of the switch are determined according to the machine's risk assessment and the manufacturer data.
• Small-housing types placed inside devices and mechanisms are under micro and miniature switches.
• Rotary types that determine a stopping point by tracking shaft revolutions through a gear are under rotary limit switches.
• If you need to detect a metal part without contact or avoid mechanical wear, inductive sensors are considered.
• EMAS snap-action and slow-action spare contact blocks are listed in the limit switch accessories and spare parts category.

Brands in this category

• EMAS: limit switches with metal and plastic housings; models starting with codes such as L5, L51, L52, L53, L54 and L61, reset types and CSM series cross-arm crane switches.
• ABB: limit switches with LS32, LS40, LS60 and LS72 codes. According to the product data of LS32 models, P in the code indicates a plastic housing and M a metal housing.
• Isıso: TLS series limit switches with plastic housings and TZ series limit switches with cables.
• Gwest: GLS series limit switches; the product data states a 1NO + 1NC contact arrangement and IP65.

Order notes

• Products are sold by the piece. The manufacturer type code is in the product name (for example L5K13MEM123, LS32M11B11, TLS-103); you can reach the product by typing the code into the search box.
• The same housing has many variants with different heads; before ordering, compare the head type with the product image and the type code.
• For models described as "resetli" (reset type) in EMAS product names and Gwest product data, confirm the operating principle from the manufacturer data.

Limit Switch Actuator Types and Selection Table

Frequently asked questions

What are NO and NC contacts used for in a limit switch?

The NC (normally closed) contact opens when the head is actuated, and the NO (normally open) contact closes. Limits that stop motion are usually wired through the NC contact; this way a broken wire or a loose connection also cuts the circuit and the fault is noticed. The NO contact is mostly used to give position information to a PLC input or a pilot light. The wiring diagram is determined according to the project and manufacturer data.

What does a snap-action limit switch mean?

In a snap-action contact, when the head reaches a certain point, the contact changes position instantly by means of a spring mechanism; the switching speed does not depend on the head speed. In a slow-action contact, the contact follows the movement of the head. EN 50047 covers both contact types for position switches. In the EMAS product names in this category, the type is written as "ani hareketli" (snap action); slow-action spare contact blocks are listed in the accessory category.

Can an inductive sensor be used instead of a limit switch?

It can, if the part to be detected is metal and contact is not wanted; since an inductive sensor has no moving part, there is no mechanical wear. On the other hand, the sensor needs a supply voltage and its output is electronic. A limit switch works without a supply, offers NO and NC dry contacts and can also be actuated by non-metal parts. The choice is made according to the part to be detected and the structure of the control circuit.

Should I choose a metal-housing or a plastic-housing limit switch?

A metal housing is generally preferred for machine-mounted installations exposed to impact and vibration; a plastic housing is light and does not rust. In the ABB LS32 series in this category, according to the product data, metal-housing models have an IP66 protection rating and plastic-housing models IP65. Head types are similar on both housings; the decision is determined by the mechanical stress and environmental conditions at the mounting location.