{"id":1659,"date":"2026-09-26T14:10:00","date_gmt":"2026-09-26T06:10:00","guid":{"rendered":"https:\/\/lemaele.com\/blog\/limit-switch-ac-dc-contact-rating\/"},"modified":"2026-09-25T11:47:14","modified_gmt":"2026-09-25T03:47:14","slug":"limit-switch-ac-dc-contact-rating","status":"publish","type":"post","link":"https:\/\/lemaele.com\/de\/blog\/limit-switch-ac-dc-contact-rating\/","title":{"rendered":"Limitschalter AC vs DC Kontaktratings: Auswahlhilfe"},"content":{"rendered":"

A limit switch does not have one universal \u201camp rating.\u201d Its permissible load depends on the exact model, voltage, AC or DC supply, load type, switching frequency, and the manufacturer\u2019s test conditions. An AC contact rating cannot be carried over to DC by using the same current or by converting watts. Check the rating printed for the specific contact block and use case before connecting a real load.<\/p>\n

This guide explains how to read AC\/DC contact ratings and gives one LEMA LZ5 example. It is not a blanket approval for every LZ5 configuration: confirm the order code, datasheet revision, terminal form, environment, and actual load with the supplier before design release.<\/p>\n

\"LEMA
Actual LZ5 product reference. The pictured actuator and housing identify the product family, not the electrical limits for every variant.<\/figcaption><\/figure>\n

What a contact rating does\u2014and does not\u2014tell you<\/h2>\n

A rating is a boundary established under specified test conditions, not a promise that any load below the printed amp number will work for the required lifetime. Read the full line: voltage, current, AC or DC, and any load category or power-factor\/time-constant condition. Also check whether the figure describes making current, carrying current, or breaking a load. Those duties are not interchangeable.<\/p>\n

In a machine, a limit switch often senses position and signals a PLC or relay rather than directly carrying motor power. A PLC input is usually a low-energy control load; a contactor coil is inductive; and a motor is an inrush-heavy load. The same switch contact can experience very different stress in each case. If the switch only needs to report position, an appropriately designed control input or an interposing relay may keep the switch away from the power load.<\/p>\n

The LEMA LZ5 sealed limit switch page<\/a> lists an example rating of 10 A at 125\/250 V AC and 0.5 A at 125 V DC for the shown product information. The large difference is a useful reminder: do not read \u201c10 A\u201d as an all-current-type value. Confirm that the selected LZ5 model and contact configuration match the published line before relying on it.<\/p>\n

Why AC and DC ratings can differ<\/h2>\n

When an electromechanical contact opens under load, current may continue briefly through an electrical arc. With AC, the current passes through zero repeatedly, which can help an arc extinguish. DC has no periodic current zero crossing, so an arc may persist until the contacts separate far enough or another suppression mechanism acts. That can increase contact erosion, heating, and the risk of welding. The exact result still depends on voltage, current, gap, contact material, circuit impedance, and load characteristics.<\/p>\n

That is why a switch maker can specify a much lower DC current or voltage than its AC rating. Do not calculate an equivalent DC current from the AC number by matching wattage. A DC inductive load such as a coil can also generate a voltage transient when interrupted; the stored energy depends on the load and circuit. A suppression component may reduce the transient but must be selected so it does not delay release or compromise the required function.<\/p>\n

Switch manufacturers publish separate conditions for different current types and loads because contact capacity is application-dependent. These general selection principles are not LEMA product data. The actual limit for a LEMA part must come from its own specification and the intended application.<\/p>\n

\"LEMA
Check the exact contact diagram before wiring. Contact arrangement and electrical rating are separate checks.<\/figcaption><\/figure>\n

Identify the load category before choosing a switch<\/h2>\n\n\n\n\n\n\n\n\n\n
Load in the machine<\/th>\nWhat to verify<\/th>\nTypical design question<\/th>\n<\/tr>\n<\/thead>\n
PLC or electronic input<\/td>\nInput voltage\/current, leakage or minimum switching load, polarity, and input filtering<\/td>\nWill the contact reliably switch the actual low-level signal?<\/td>\n<\/tr>\n
Relay or contactor coil<\/td>\nCoil AC\/DC type, inrush and steady current, suppression, and contact category<\/td>\nIs the switch rated to break this inductive control load?<\/td>\n<\/tr>\n
Solenoid or valve<\/td>\nCoil voltage, current, release time, transient suppression, and switching cycles<\/td>\nDoes suppression change response time or safety behavior?<\/td>\n<\/tr>\n
Motor or actuator<\/td>\nLocked-rotor or starting current, running current, direction changes, voltage, and duty<\/td>\nShould the limit switch command a relay\/contactor instead of switching the motor?<\/td>\n<\/tr>\n
Lamp or capacitive input<\/td>\nInrush current, power supply input capacitance, and make\/break rating<\/td>\nIs the initial current materially higher than steady current?<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

A resistive rating is not automatically valid for a coil, motor, lamp, or capacitive electronic supply. If the manufacturer gives utilization categories, load curves, electrical-life data, or a specific motor rating, use the value that matches the real duty. If the documentation does not give a matching DC rating, do not infer one from an AC-only entry.<\/p>\n

Read the contact form separately from the rating<\/h2>\n

Contact form tells you how the electrical path changes as the actuator moves. A common SPDT form transfers COM between NC and NO; a multi-pole design can switch more than one circuit. It does not tell you that every pole can break the same voltage simultaneously or that separate supplies may be mixed without conditions. Follow the wiring diagram and the manufacturer\u2019s rules for isolation, pole use, and circuit separation.<\/p>\n

On the LZ5 image, the common, NO, and NC labels identify the contact logic; they do not replace a rating table. Check the terminal designations on the ordered version and confirm the state with a continuity check before wiring. See the limit switch to PLC wiring guide<\/a> for a low-energy input example. For mounting and repeatability, see the separate limit switch positioning guide<\/a>.<\/p>\n

A practical AC\/DC selection workflow<\/h2>\n
    \n
  1. Write down the actual circuit.<\/strong> Record supply type, nominal and maximum voltage, steady current, peak or inrush current, and whether the load is resistive, inductive, motor, lamp, or electronic.<\/li>\n
  2. Describe switching duty.<\/strong> State what the switch makes and breaks, cycle rate, normal and abnormal operation, and required electrical life. A contact that only carries current while closed may still need a robust breaking rating if it opens under load.<\/li>\n
  3. Match the data row exactly.<\/strong> Find the model-specific AC or DC line and the closest load category. Keep voltage and current from the same row; do not combine maxima from different conditions.<\/li>\n
  4. Check the installed circuit.<\/strong> Account for coil suppression, power-supply behavior, cable length, temperature, contamination, and the actual controller or load input.<\/li>\n
  5. Decide whether to switch power directly.<\/strong> If the direct load has high inrush or uncertain interruption behavior, use the limit switch as a control input to a suitably rated relay or contactor, provided that arrangement meets the machine\u2019s functional and safety requirements.<\/li>\n
  6. Validate a representative assembly.<\/strong> Test at the actual voltage, load, switching frequency, and environmental conditions. Inspect contact wear and verify the system\u2019s fault response.<\/li>\n<\/ol>\n

    The IEC 60947-5-1 standard is the relevant product-standard family for many electromechanical control-circuit devices and switching elements. The public IEC catalogue describes its scope; the applicable standard, category, and conformity evidence must be checked for the equipment and jurisdiction. For electrical work, follow the machine\u2019s approved safety procedures and have the design reviewed by a qualified engineer.<\/p>\n

    Common rating mistakes to avoid<\/h2>\n