{"id":2417,"date":"2026-06-23T08:30:42","date_gmt":"2026-06-23T08:30:42","guid":{"rendered":"https:\/\/electrical.lazyhungryminds.com\/?p=2417"},"modified":"2026-06-23T08:30:46","modified_gmt":"2026-06-23T08:30:46","slug":"understanding-the-plc-bsc-120uc-21-21-h-relay-base-1012014-features-wiring-and-applications","status":"publish","type":"post","link":"https:\/\/electrical.lazyhungryminds.com\/index.php\/2026\/06\/23\/understanding-the-plc-bsc-120uc-21-21-h-relay-base-1012014-features-wiring-and-applications\/","title":{"rendered":"Understanding the PLC-BSC-120UC\/21-21\/H Relay Base (1012014): Features, Wiring, and Applications"},"content":{"rendered":"\n<p>The <strong>PLC-BSC-120UC\/21-21\/H (1012014)<\/strong> is a <strong>14 mm DIN rail-mounted relay base<\/strong> that accepts compatible plug-in electromechanical relays or solid-state relays. It is supplied <strong>without the relay itself<\/strong>, allowing users to select the appropriate relay based on their application requirements. The base is designed for <strong>120 V AC\/DC control circuits<\/strong> and includes built-in circuitry such as an LED status indicator and bridge rectifier.<\/p>\n\n\n<div class=\"wp-block-image\">\n<figure class=\"aligncenter size-full is-resized\"><img decoding=\"async\" width=\"531\" height=\"466\" src=\"https:\/\/electrical.lazyhungryminds.com\/wp-content\/uploads\/2026\/06\/image-2.png\" alt=\"\" class=\"wp-image-2418\" style=\"width:538px;height:auto\" srcset=\"https:\/\/electrical.lazyhungryminds.com\/wp-content\/uploads\/2026\/06\/image-2.png 531w, https:\/\/electrical.lazyhungryminds.com\/wp-content\/uploads\/2026\/06\/image-2-300x263.png 300w\" sizes=\"(max-width: 531px) 100vw, 531px\" \/><\/figure><\/div>\n\n\n<h2 class=\"wp-block-heading\">Key Features<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Compact 14 mm Design<\/h3>\n\n\n\n<p>The narrow 14 mm width allows more relay interfaces to be installed inside electrical panels while minimizing DIN rail space.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">DIN Rail Mounting<\/h3>\n\n\n\n<p>The relay base snaps onto a standard <strong>NS 35\/7.5 DIN rail<\/strong>, making installation quick and straightforward.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Screw Terminal Connections<\/h3>\n\n\n\n<p>Field wiring is completed using reliable screw terminals, supporting conductor sizes from <strong>0.14 mm\u00b2 to 2.5 mm\u00b2 (AWG 26\u201314)<\/strong>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Dual Changeover Contacts<\/h3>\n\n\n\n<p>The base supports relays with <strong>2 changeover (DPDT) contacts<\/strong>, allowing one relay to control multiple circuits or perform changeover switching.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">LED Status Indicator<\/h3>\n\n\n\n<p>An integrated LED provides visual confirmation when the relay coil is energized, making troubleshooting easier.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Universal Control Voltage<\/h3>\n\n\n\n<p>Designed for <strong>120 V AC\/DC<\/strong> control voltage, the base includes an internal bridge rectifier that enables operation with either AC or DC control signals.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Understanding A1 and A2 (Relay Coil Terminals)<\/h2>\n\n\n\n<p><strong>A1<\/strong> and <strong>A2<\/strong> are the <strong>relay coil terminals<\/strong>.<\/p>\n\n\n\n<p>When the rated control voltage (120 V AC\/DC for this relay base) is applied across these terminals, the relay coil energizes and changes the state of the relay contacts. The PLC-BSC-120UC\/21-21\/H base includes an LED indicator and an internal bridge rectifier, allowing it to accept either AC or DC control voltage of the specified rating.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Example<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>120 V AC\/DC Supply<br><br>L\/+  \u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500 A1<br>                  \u2502<br>               Relay Coil<br>                  \u2502<br>N\/-  \u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500 A2<\/code><\/pre>\n\n\n\n<p>When voltage is applied between <strong>A1<\/strong> and <strong>A2<\/strong>:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The relay coil energizes.<\/li>\n\n\n\n<li>The LED turns ON.<\/li>\n\n\n\n<li>The relay contacts change position.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">Understanding 11, 12, and 14 (Relay Contact Terminals)<\/h2>\n\n\n\n<p>These terminals belong to one <strong>changeover (SPDT\/Form C)<\/strong> contact.<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><thead><tr><th>Terminal<\/th><th>Function<\/th><th>Normal Condition<\/th><\/tr><\/thead><tbody><tr><td><strong>11<\/strong><\/td><td>Common (COM)<\/td><td>Connected to either 12 or 14<\/td><\/tr><tr><td><strong>12<\/strong><\/td><td>Normally Closed (NC)<\/td><td>Connected to 11 when the coil is OFF<\/td><\/tr><tr><td><strong>14<\/strong><\/td><td>Normally Open (NO)<\/td><td>Connected to 11 when the coil is ON<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h3 class=\"wp-block-heading\">Relay De-energized (Coil OFF)<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>      12 (NC)<br>        \u2502<br>11 -----\u25cf<br>        \u2502<br>      14 (NO)<br><br>Connection:<br>11 \u2194 12<br>11 \u2715 14<\/code><\/pre>\n\n\n\n<p>Current flows from <strong>11<\/strong> to <strong>12<\/strong>, while <strong>14<\/strong> remains open.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h3 class=\"wp-block-heading\">Relay Energized (Coil ON)<\/h3>\n\n\n\n<pre class=\"wp-block-code\"><code>      12 (NC)<br><br>11 -----\u25cf<br>        \u2502<br>      14 (NO)<br><br>Connection:<br>11 \u2715 12<br>11 \u2194 14<\/code><\/pre>\n\n\n\n<p>Current now flows from <strong>11<\/strong> to <strong>14<\/strong>, while the connection to <strong>12<\/strong> opens.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Common Applications<\/h2>\n\n\n\n<p>The PLC-BSC-120UC\/21-21\/H relay base is commonly used in:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>PLC output interfacing<\/li>\n\n\n\n<li>DCS control panels<\/li>\n\n\n\n<li>Motor control centers (MCCs)<\/li>\n\n\n\n<li>Pump control systems<\/li>\n\n\n\n<li>HVAC automation<\/li>\n\n\n\n<li>Water and wastewater treatment plants<\/li>\n\n\n\n<li>Packaging machines<\/li>\n\n\n\n<li>Conveyor systems<\/li>\n\n\n\n<li>Industrial process automation<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>The PLC-BSC-120UC\/21-21\/H (1012014) is a 14 mm DIN rail-mounted relay base that accepts compatible plug-in electromechanical relays or solid-state relays. It is supplied without the relay itself, allowing users to select the appropriate relay based on their application requirements. The&#8230; <a class=\"more-link\" href=\"https:\/\/electrical.lazyhungryminds.com\/index.php\/2026\/06\/23\/understanding-the-plc-bsc-120uc-21-21-h-relay-base-1012014-features-wiring-and-applications\/\">Continue Reading &rarr;<\/a><\/p>\n","protected":false},"author":3,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"rank_math_lock_modified_date":false,"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[6,29],"tags":[],"class_list":["post-2417","post","type-post","status-publish","format-standard","hentry","category-electrical","category-control-systems"],"jetpack_featured_media_url":"","jetpack_likes_enabled":true,"jetpack_sharing_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/posts\/2417","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/users\/3"}],"replies":[{"embeddable":true,"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/comments?post=2417"}],"version-history":[{"count":1,"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/posts\/2417\/revisions"}],"predecessor-version":[{"id":2419,"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/posts\/2417\/revisions\/2419"}],"wp:attachment":[{"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/media?parent=2417"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/categories?post=2417"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/electrical.lazyhungryminds.com\/index.php\/wp-json\/wp\/v2\/tags?post=2417"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}