[{"data":1,"prerenderedAt":-1},["ShallowReactive",2],{"doc-seo-655291-105":3,"detail-sidebar-cat-0-en-105":80,"doc-detail-655291-en":130},{"code":4,"msg":5,"data":6},0,"ok",{"site_id":7,"language":8,"slug":9,"title":10,"keywords":11,"description":12,"schema_data":13,"social_meta":73,"head_meta":75,"extra_data":77,"updated_unix":79},105,"en","chapter-2-ladder-basics-understanding-electrical-ladder-drawings","Chapter 2 - Ladder Basics - Understanding Electrical Ladder Drawings","","Chapter 2 introduces ladder diagram fundamentals before PLC discussion, separating electrical schematics into power and control portions and emphasizing how control analysis drives understanding. It explains symbol usage, compares common American and European symbol sets, and describes device states labeled normally open (NO) and normally closed (NC). The chapter then outlines ladder diagram components such as power bars, current flow through switches, relay coils, and neutral rails, including how ladder rungs complete circuits to energize coils and how STOP/START placement affects current paths.",{"@graph":14,"@context":72},[15,34,55],{"@type":16,"itemListElement":17},"BreadcrumbList",[18,23,27,31],{"item":19,"name":20,"@type":21,"position":22},"https://docshare.wps.com","Home","ListItem",1,{"item":24,"name":25,"@type":21,"position":26},"https://docshare.wps.com/document/","Document",2,{"item":28,"name":29,"@type":21,"position":30},"https://docshare.wps.com/document/technology/","Technology",3,{"item":32,"name":10,"@type":21,"position":33},"https://docshare.wps.com/document/chapter-2-ladder-basics-understanding-electrical-ladder-drawings/655291/",4,{"url":32,"name":10,"@type":35,"image":36,"author":41,"headline":10,"publisher":44,"fileFormat":47,"inLanguage":8,"description":12,"dateModified":48,"datePublished":49,"encodingFormat":47,"isAccessibleForFree":50,"interactionStatistic":51},"DigitalDocument",{"url":37,"@type":38,"width":39,"height":40},"https://docshare.wps.com/thumbnails/chapter-2-ladder-basics-understanding-electrical-ladder-drawings/655291.png","ImageObject",300,407,{"name":42,"@type":43},"Kyle","Person",{"url":19,"name":45,"@type":46},"DocShare","Organization","application/pdf","2026-10-30","2026-10-25",true,{"@type":52,"interactionType":53,"userInteractionCount":33},"InteractionCounter",{"@type":54},"ViewAction",{"@type":56,"mainEntity":57},"FAQPage",[58,64,68],{"name":59,"@type":60,"acceptedAnswer":61},"Why must the ladder diagram be understood before discussing a PLC?","Question",{"text":62,"@type":63},"PLC learning depends on understanding the devices the PLC was designed to replace, and that replacement system is the ladder diagram.","Answer",{"name":65,"@type":60,"acceptedAnswer":66},"What is the difference between the power portion and the control portion of a ladder diagram?",{"text":67,"@type":63},"The power portion focuses on power flow to a motor or device, while the control portion focuses on controlling that device; the control portion is emphasized for analysis.",{"name":69,"@type":60,"acceptedAnswer":70},"How do normally open (NO) and normally closed (NC) states affect circuit behavior?",{"text":71,"@type":63},"Normally open devices read OL on a resistance check, while normally closed devices read 0.0. The ladder diagram does not label these states, so the reader must recognize the symbol and consider gravity and spring exceptions.","https://schema.org",{"og:url":32,"og:type":74,"og:title":10,"og:site_name":45,"og:description":12},"article",{"robots":76,"canonical":32},"index,follow",{"doc_id":78,"site_id":7},655291,1793030585,{"code":4,"msg":81,"data":82},"success",[83,87,91,95,100,104,109,114,119,122,126],{"id":22,"doc_module":4,"doc_module_name":25,"category_name":84,"show_sort_weight":85,"slug":86},"Story & Novel",90,"story-novel",{"id":26,"doc_module":4,"doc_module_name":25,"category_name":88,"show_sort_weight":89,"slug":90},"Literature",80,"literature",{"id":33,"doc_module":4,"doc_module_name":25,"category_name":92,"show_sort_weight":93,"slug":94},"Exam",70,"exam",{"id":96,"doc_module":4,"doc_module_name":25,"category_name":97,"show_sort_weight":98,"slug":99},5,"Comic",60,"comic",{"id":101,"doc_module":4,"doc_module_name":25,"category_name":29,"show_sort_weight":102,"slug":103},6,50,"technology",{"id":105,"doc_module":4,"doc_module_name":25,"category_name":106,"show_sort_weight":107,"slug":108},7,"Healthcare",40,"healthcare",{"id":110,"doc_module":4,"doc_module_name":25,"category_name":111,"show_sort_weight":112,"slug":113},8,"Research & Report",30,"research-report",{"id":115,"doc_module":4,"doc_module_name":25,"category_name":116,"show_sort_weight":117,"slug":118},9,"Religion & Spirituality",20,"religion-spirituality",{"id":117,"doc_module":4,"doc_module_name":25,"category_name":120,"show_sort_weight":117,"slug":121},"World Cup","world-cup",{"id":123,"doc_module":4,"doc_module_name":25,"category_name":124,"show_sort_weight":123,"slug":125},10,"Lifestyle","lifestyle",{"id":127,"doc_module":4,"doc_module_name":25,"category_name":128,"show_sort_weight":96,"slug":129},19,"General","general",{"code":4,"msg":81,"data":131},{"doc_id":78,"user_id":132,"nickname":42,"user_avatar":133,"doc_module":4,"category_id":101,"category_name":29,"doc_title":10,"doc_description":12,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":33,"is_deleted":4,"is_public":22,"is_downloadable":22,"audit_status":22,"page_count":139,"language":140,"language_code":8,"site_id":7,"html_lang":8,"table_of_contents":141,"faqs":142,"seo_title":143,"seo_description":12,"update_tm":144,"read_time":145},3985741905716,"https://ap-avatar.wpscdn.com/davatar_994ba38a5ba835b3df7d355c54d3ed8d","Chapter 2 Ladder Basics  \nUnderstanding Electrical Ladder Drawings  \nBefore discussing or understanding the Programmable Logic Controller, we must first understand the devices the PLC was invented to replace. That was the ladder diagram. The ladder diagram or electrical schematic or elementary diagram can be divided into two distinct portions. The first is the power portion and the second is the control. Showing flow of power toa motor or other device in a factory environment is the primary focus of the power portion. Showing control of that motor is the focus of the control portion. While power flow is important, the focus is to dissect the control portion. Items such as fuses and disconnect devices may appear in both power and control circuits. The use of symbols is important for both power and control. The types of symbols vary and are somewhat arbitrary based on where you are located and, in some cases, the company you work for. This is contrary to the symbols used in the PLC which must be fixed or uniform. The use of symbols is a descriptive description of the device being used. A list of some symbols and the function of the device is given below:  \n\n|  SPST\u003Cbr>|  |  |  |  |  |  |  SPDT |  |  |  |\n| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |\n|  DPST |  |  |  |  |  |  |  |   DPDT |  |  |\n| |  |  |  |  |  | Spring\u003Cbr>return | Spring  return |  |  |  |\n| |  | Pushbutton\u003Cbr>make |  |  |  |  | |  | Pushbutton\u003Cbr>break |  |\n| |  | Pushbutton\u003Cbr>2-circuit |  |  |  |  | | Selector\u003Cbr>switch |  |  |\n| |  |  | Shorting\u003Cbr>selector |  |  |  | |  | Proximity\u003Cbr>limit switch |  |\n| |  |  |  |  | Time delay\u003Cbr>make |  | |  | Time delay\u003Cbr>break |  |\n| |  |  | Safety\u003Cbr>interlock |  |  |  |     Flow  actuated |  |  |  |\n| |  |  | Liquid level\u003Cbr>actuated |  |  |  |     Pressure  activated |  |  |  |\n|     Temperature  activated |  |  |  |  |  |  | |  |  | Inertia\u003Cbr>switch |\n| | |  | Relay\u003Cbr>contact\u003Cbr>NO |  |  |  | |  |  | Relay\u003Cbr>coil |\n| |  |  |  | Relay\u003Cbr>contact\u003Cbr>NC |  |  | | Pilot\u003Cbr>light |  |  |\n\nFig. 2-1a Examples of American Symbols used in Electrical Diagrams  \n| |  |  | Make\u003Cbr>contact | |  |  |  | Break\u003Cbr>contact |\n| --- | --- | --- | --- | --- | --- | --- | --- | --- |\n|  |  |  | Two way\u003Cbr>contact | |  | Passing\u003Cbr>make-contact |  |  |\n| |  |  | Spring\u003Cbr>return |  | Stay put |  |  |  |\n|  |  |  | Limit\u003Cbr>switch | |  | Circuit\u003Cbr>breaker |  |  |\n| |  | Time delay\u003Cbr>make |  | |  |  | Time delay\u003Cbr>break |  |\n| | Liquid level\u003Cbr>actuated |  |  | |  | Gas flow\u003Cbr>actuated |  |  |\n| | Temperature\u003Cbr>switch |  |  |  |  | Fuse |  |  |\n\nFig. 2-1b Examples of European Symbols used in Electrical Diagrams  \nSome of the symbols are used in examples on the following pages. Many devices follow the pattern of how the device actually works. For example, notice how the foot switch resembles an actual foot switch or how a flow or sail switch resembles a sail on a sailboat. Also, note that different combinations of open and closed contacts can be furnished on the same device to give multiple combinations of functions to the control circuit either through hard-wired circuits or to the PLC and then through its logic to the appropriate output.  \nMany times, the input devices are said to be either normally open (NO) or normally closed (NC) . The normally open or closed status refers to the shelf state of the device. If a device is normally open, a resistance check of the device with a digital multi-meter will give a reading of OL. If the device is normally closed, a resistance check will give a reading of 0.0.  \nThe normally open and normally closed state of the devices is not labeled on the ladder drawing. Rather, the reader must recognize the symbol. A helpful hint in trying to determine whether the contacts are open or closed is to think of them in terms of gravity. If gravity is acting on the device, its normal state is as shown in the drawing. An exception to this concept is found in devices that contain spr","cbCaigB6yKNZFm7D","https://ap.wps.com/l/cbCaigB6yKNZFm7D","pdf",1727329,46,"English","# Chapter 2 Ladder Basics\n## Understanding Electrical Ladder Drawings\n## Components of the Ladder Diagram\n## Ladder Rungs, Power Rails, and Device Placement","[{\"question\":\"Why must the ladder diagram be understood before discussing a PLC?\",\"answer\":\"PLC learning depends on understanding the devices the PLC was designed to replace, and that replacement system is the ladder diagram.\"},{\"question\":\"What is the difference between the power portion and the control portion of a ladder diagram?\",\"answer\":\"The power portion focuses on power flow to a motor or device, while the control portion focuses on controlling that device; the control portion is emphasized for analysis.\"},{\"question\":\"How do normally open (NO) and normally closed (NC) states affect circuit behavior?\",\"answer\":\"Normally open devices read OL on a resistance check, while normally closed devices read 0.0. The ladder diagram does not label these states, so the reader must recognize the symbol and consider gravity and spring exceptions.\"}]","Chapter 2 - Ladder Basics - Understanding Electrical Ladder Drawings | PDF",1792960615,116]