{"id":972,"date":"2026-07-28T09:00:00","date_gmt":"2026-07-28T01:00:00","guid":{"rendered":"https:\/\/lemaele.com\/blog\/normally-closed-vs-open-microswitch-guide\/"},"modified":"2026-07-24T17:23:38","modified_gmt":"2026-07-24T09:23:38","slug":"normally-closed-vs-open-microswitch-guide","status":"publish","type":"post","link":"https:\/\/lemaele.com\/es\/blog\/normally-closed-vs-open-microswitch-guide\/","title":{"rendered":"Choosing NC or NO Logic for a Microswitch Circuit"},"content":{"rendered":"<div class=\"b2b-article\">\n<p style=\"margin:0 0 16px;line-height:1.7\"><strong>Normally closed and normally open describe the circuit before the actuator moves, and that free state is a design decision.<\/strong> Choose it from what the system must do when a wire breaks or a bracket loosens, not from which terminal is easier to reach.<\/p>\n<figure style=\"margin:26px 0;text-align:center\" class=\"wp-block-image size-large b2b-article-figure\"><img style=\"max-width:640px;width:100%;height:auto;display:block;margin:0 auto;border-radius:8px\" src=\"https:\/\/lemaele.com\/wp-content\/uploads\/2026\/05\/KW7-series-micro-switch.3.webp\" alt=\"LEMA KW7 series micro switch photo for NC and NO logic planning\" loading=\"lazy\" decoding=\"async\" title=\"\"><\/figure>\n<nav class=\"b2b-toc\" style=\"background:#f5f8fa;padding:16px 20px;border-radius:8px;margin:0 0 24px\">\n<h2 style=\"margin:42px 0 14px;scroll-margin-top:96px\">Contenido<\/h2>\n<ul style=\"margin:0 0 18px 1.2em;line-height:1.7\">\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#part-1-what-do-normally-closed-and-normally-open-mean\">Part 1. What do normally closed and normally open mean?<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#part-2-how-does-failure-behavior-drive-the-state-choice\">Part 2. How does failure behavior drive the state choice?<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#part-3-when-is-normally-open-the-right-default\">Part 3. When is normally open the right default?<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#part-4-when-does-normally-closed-earn-its-place\">Part 4. When does normally closed earn its place?<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#part-5-how-should-the-controller-read-each-state\">Part 5. How should the controller read each state?<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#part-6-what-belongs-in-the-rfq-and-fit-boundary\">Part 6. What belongs in the RFQ and Fit Boundary?<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#part-7-how-can-lema-support-a-contact-state-inquiry\">Part 7. How can LEMA support a contact state inquiry?<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#faqs\">Preguntas frecuentes<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"#references\">Referencias<\/a><\/li>\n<\/ul>\n<\/nav>\n<h2 id=\"part-1-what-do-normally-closed-and-normally-open-mean\" style=\"margin:42px 0 14px;scroll-margin-top:96px\">Part 1. What do normally closed and normally open mean?<\/h2>\n<p style=\"margin:0 0 16px;line-height:1.7\">On a changeover microswitch, COM connects to the NC terminal in the free position and transfers to NO at the operating point. The words describe the resting circuit, nothing more.<\/p>\n<table style=\"width:100%;border-collapse:collapse\">\n<thead>\n<tr>\n<th style=\"border:1px solid #d9e1e8;padding:9px 12px;background:#f5f8fa;text-align:left\">Estado<\/th>\n<th style=\"border:1px solid #d9e1e8;padding:9px 12px;background:#f5f8fa;text-align:left\">Free position<\/th>\n<th style=\"border:1px solid #d9e1e8;padding:9px 12px;background:#f5f8fa;text-align:left\">Operated position<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Normally open path<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Circuit open<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Circuit closed<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Normally closed path<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Circuit closed<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Circuit open<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Changeover use<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Both paths available<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">States swap together<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p style=\"margin:0 0 16px;line-height:1.7\">Series documentation in the <a style=\"color:#f27c00;text-decoration:underline\" href=\"https:\/\/lemaele.com\/es\/micro-switch\/\">LEMA Micro Switch product line<\/a> states which arrangements each family offers, so confirm availability before the schematic freezes.<\/p>\n<h2 id=\"part-2-how-does-failure-behavior-drive-the-state-choice\" style=\"margin:42px 0 14px;scroll-margin-top:96px\">Part 2. How does failure behavior drive the state choice?<\/h2>\n<p style=\"margin:0 0 16px;line-height:1.7\">Ask what the controller should believe when the signal disappears. A broken conductor, an unplugged connector, and a failed contact all read the same as an open circuit.<\/p>\n<p style=\"margin:0 0 16px;line-height:1.7\">Wiring the function so that open means stop turns most of those faults into safe stops instead of silent failures. Interlock examples in the <a style=\"color:#f27c00;text-decoration:underline\" href=\"https:\/\/lemaele.com\/es\/blog\/micro-switch-elevator-door-interlock-guide\/\">elevator door interlock guide<\/a> apply exactly this reasoning to door travel.<\/p>\n<h2 id=\"part-3-when-is-normally-open-the-right-default\" style=\"margin:42px 0 14px;scroll-margin-top:96px\">Part 3. When is normally open the right default?<\/h2>\n<p style=\"margin:0 0 16px;line-height:1.7\">Normally open suits event detection without a hazard behind it: counting products on a line, confirming a tray is seated, or lighting an indicator. The circuit stays quiet until something happens, which keeps standby current at zero and logic simple.<\/p>\n<p style=\"margin:0 0 16px;line-height:1.7\">Presence-style detection also tolerates NO wiring when a separate mechanism supervises safety, leaving the microswitch a pure information role.<\/p>\n<h2 id=\"part-4-when-does-normally-closed-earn-its-place\" style=\"margin:42px 0 14px;scroll-margin-top:96px\">Part 4. When does normally closed earn its place?<\/h2>\n<figure style=\"margin:26px 0;text-align:center\" class=\"wp-block-image size-large b2b-article-figure\"><img style=\"max-width:640px;width:100%;height:auto;display:block;margin:0 auto;border-radius:8px\" src=\"https:\/\/lemaele.com\/wp-content\/uploads\/2026\/05\/Contact-Form.4.webp\" alt=\"Micro switch contact form states diagram from LEMA series documentation\" loading=\"lazy\" decoding=\"async\" title=\"\"><\/figure>\n<p style=\"margin:0 0 16px;line-height:1.7\">Normally closed carries the supervision cases. Guard doors, overtravel stops, and permissive chains want a circuit that is intact while conditions are correct, so any interruption removes the permission.<\/p>\n<table style=\"width:100%;border-collapse:collapse\">\n<thead>\n<tr>\n<th style=\"border:1px solid #d9e1e8;padding:9px 12px;background:#f5f8fa;text-align:left\">Scenario<\/th>\n<th style=\"border:1px solid #d9e1e8;padding:9px 12px;background:#f5f8fa;text-align:left\">Preferred path<\/th>\n<th style=\"border:1px solid #d9e1e8;padding:9px 12px;background:#f5f8fa;text-align:left\">Reason<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Guard or cover supervision<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Closed when safe<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Loss of signal removes the run permission<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Product counting<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Open until the event<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">No hazard behind a missed count<\/td>\n<\/tr>\n<tr>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">End-of-travel stop<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Closed until the limit<\/td>\n<td style=\"border:1px solid #d9e1e8;padding:9px 12px\">Wire break reads as the limit reached<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p style=\"margin:0 0 16px;line-height:1.7\">Terminal identification for either choice follows the continuity method in the <a style=\"color:#f27c00;text-decoration:underline\" href=\"https:\/\/lemaele.com\/es\/blog\/how-to-wire-a-micro-switch-oem-guide\/\">terminal wiring review<\/a>.<\/p>\n<h2 id=\"part-5-how-should-the-controller-read-each-state\" style=\"margin:42px 0 14px;scroll-margin-top:96px\">Part 5. How should the controller read each state?<\/h2>\n<p style=\"margin:0 0 16px;line-height:1.7\">Controller configuration completes the decision. The input&#8217;s idle level, debounce time, and alarm logic must match the chosen free state, or the schematic and the firmware will disagree in the field.<\/p>\n<ul style=\"margin:0 0 18px 1.2em;line-height:1.7\">\n<li style=\"margin:0 0 8px\">Write a state table covering free, operated, and fault conditions.<\/li>\n<li style=\"margin:0 0 8px\">Keep signal current inside the model&#8217;s minimum applicable load.<\/li>\n<li style=\"margin:0 0 8px\">Debounce in firmware against snap-action bounce windows.<\/li>\n<li style=\"margin:0 0 8px\">Alarm on impossible state combinations where two switches supervise one motion.<\/li>\n<\/ul>\n<h2 id=\"part-6-what-belongs-in-the-rfq-and-fit-boundary\" style=\"margin:42px 0 14px;scroll-margin-top:96px\">Part 6. What belongs in the RFQ and Fit Boundary?<\/h2>\n<h3 style=\"margin:28px 0 12px\">RFQ input checklist<\/h3>\n<ul style=\"margin:0 0 18px 1.2em;line-height:1.7\">\n<li style=\"margin:0 0 8px\">Schematic with the required free and operated states<\/li>\n<li style=\"margin:0 0 8px\">Failure expectation for each supervised motion<\/li>\n<li style=\"margin:0 0 8px\">Load, voltage, and controller input specification<\/li>\n<li style=\"margin:0 0 8px\">Actuator travel, mounting, and environment notes<\/li>\n<li style=\"margin:0 0 8px\">Volumen y momento de la toma de muestra<\/li>\n<\/ul>\n<h3 style=\"margin:28px 0 12px\">Fit Boundary<\/h3>\n<p style=\"margin:0 0 16px;line-height:1.7\">This guide decides a contact state for control logic. It does not certify a safety category, provide monitored redundancy, or replace the model document&#8217;s contact ratings.<\/p>\n<h2 id=\"part-7-how-can-lema-support-a-contact-state-inquiry\" style=\"margin:42px 0 14px;scroll-margin-top:96px\">Part 7. How can LEMA support a contact state inquiry?<\/h2>\n<figure style=\"margin:26px 0;text-align:center\" class=\"wp-block-image size-large b2b-article-figure\"><img style=\"max-width:640px;width:100%;height:auto;display:block;margin:0 auto;border-radius:8px\" src=\"https:\/\/lemaele.com\/wp-content\/uploads\/2026\/05\/KW7-series-micro-switch.2.webp\" alt=\"LEMA KW7 series micro switch view for a contact state OEM inquiry\" loading=\"lazy\" decoding=\"async\" title=\"\"><\/figure>\n<p style=\"margin:0 0 16px;line-height:1.7\">Changeover families keep both options open until validation. The <a style=\"color:#f27c00;text-decoration:underline\" href=\"https:\/\/lemaele.com\/es\/kw7-series-micro-switch\/\">KW7 series micro switch<\/a> page is a public LEMA route for reviewing contact arrangements against a state table.<\/p>\n<p style=\"margin:0 0 16px;line-height:1.7\"><strong>Recomendaci\u00f3n de producto:<\/strong> submit the state table with the schematic so the review covers logic and load together. Choosing terminals on the bench without that table is how inverted logic ships.<\/p>\n<p style=\"margin:0 0 16px;line-height:1.7\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"https:\/\/lemaele.com\/es\/contact-us\/\">Send an OEM switch RFQ<\/a> with the state table attached.<\/p>\n<h2 id=\"faqs\">Preguntas frecuentes<\/h2>\n<h3>What is the difference between NC and NO on a microswitch?<\/h3>\n<p>NC conducts in the free position and opens when actuated; NO does the opposite. Both usually exist on one changeover contact.<\/p>\n<h3>Why do safety interlocks prefer normally closed wiring?<\/h3>\n<p>A broken wire or failed contact reads as an open circuit, so a closed-when-safe design turns those faults into stops rather than silent failures.<\/p>\n<h3>Can one microswitch provide both NC and NO?<\/h3>\n<p>A changeover type exposes COM, NC, and NO terminals, letting the designer wire either path or both.<\/p>\n<h3>Does the free state change the switch&#8217;s rating?<\/h3>\n<p>No, but each path must still be checked against the model&#8217;s documented load limits, including minimum applicable load for signal circuits.<\/p>\n<h3>How should the controller handle contact bounce?<\/h3>\n<p>Apply input debounce matched to the snap-action bounce window and validate timing on production assemblies.<\/p>\n<h3>What should a contact state RFQ include?<\/h3>\n<p>Include the schematic, state table, failure expectations, loads, actuator travel, environment, volume, and sample timing.<\/p>\n<h2 id=\"references\" style=\"margin:42px 0 14px;scroll-margin-top:96px\">Referencias<\/h2>\n<ul style=\"margin:0 0 18px 1.2em;line-height:1.7\">\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"https:\/\/prod-edam.honeywell.com\/content\/dam\/honeywell-edam\/sps\/siot\/en-us\/products\/switches\/basic-switches\/miniature-basic-switches\/v3-series\/documents\/sps-sst-micro-switch-v3-basic-datasheet.pdf\" target=\"_blank\" rel=\"noopener\">Honeywell V3 basic switch datasheet<\/a><\/li>\n<li style=\"margin:0 0 8px\"><a style=\"color:#f27c00;text-decoration:underline\" href=\"https:\/\/webstore.iec.ch\/en\/publication\/66912\" target=\"_blank\" rel=\"noopener\">Alcance de la publicaci\u00f3n IEC 61058-1<\/a><\/li>\n<\/ul>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>Normally closed and normally open describe the circuit before the actuator moves, and that free state is a design decision. Choose it from what the system must do when a wire breaks or a bracket loosens, not from which terminal is easier to reach. Contents Part 1. What do normally closed and normally open mean? [&hellip;]<\/p>\n","protected":false},"author":6,"featured_media":101,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"class_list":["post-972","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-blog"],"_links":{"self":[{"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/posts\/972","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/comments?post=972"}],"version-history":[{"count":2,"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/posts\/972\/revisions"}],"predecessor-version":[{"id":1057,"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/posts\/972\/revisions\/1057"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/media\/101"}],"wp:attachment":[{"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/media?parent=972"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/categories?post=972"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/lemaele.com\/es\/wp-json\/wp\/v2\/tags?post=972"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}