Effective February 2013 Technical Data TD04703002E Supersedes December 2006 Cam selection for pushbutton selectors Contents Introduction Description Page Selector switches in their varied forms (two-position, three-position, four-position, and Cam selection ............................ 2 Roto-Push) are a big factor contributing to the Summary ................................ 3 great flexibility of control that a well-rounded line Roto-Push.............................. 4 of pushbuttons can achieve. Contact block selection................... 5 But because selector switches can be made to perform in such complex and varied ways, Three-position selector switch.............. 6 selection and application can be difficult. This is Four-position selector switch............... 7 only because a well thought-out approach is not Three-position Roto-Push switch............ 8 readily apparent. Glossary of terms....................... 10 This document provides a time-proven systematic approach that will work in all cases. Many complex selector switch control schemes have been solved using the methods outlined here. Even if you work with it only occasionally, we ensure that you will be able to easily work out the most complex schemes. Cam and contact block selection is better understood if you: Work with each incoming and outgoing wire (each circuit) separately Recognize that the terms NO and NC only identify the type of contact by its mode before mounting it to the operator. The X-O chart shows how that contact will act after assembly to the operator with the selected cam shape Each cam has two separate lobes, each of which operates one of the two plungers on the contact block independently of each other. Those are identified as position A (top) and position B (bottom). The position designations give direction in selecting and mounting the contact blocksTechnical Data TD04703002E Cam selection for Effective February 2013 pushbutton selectors So, the secret of success is a careful, step-by-step analysis of the Cam selection several elements that make up a complete operating scheme, taking The cam you select determines the operation of all the contact one circuit at a time. Operating schemes that may seem complex at blocks mounted to the operator. It is selected on the basis that it first can be broken down into a series of single circuits that are easy provides the simplest circuitry for the desired X-O diagram. For to analyze. this selection, we publish a chart in our catalog, and other literature, As an exercise, select a switch for one of the most common showing all X-O combinations. For the purpose of this discussion, applications found in motor control, which is the HAND-OFF-AUTO the applicable portion of the chart is shown in Table 1. selector switch. In this circuit, one incoming line is distributed to For a complete chart, see Page 6 and Page 7. two other outgoing circuits by the switch. These two circuits can each be looked at individually. Table 1. Selected Portion of Chart The first step is to construct on paper, or in your mind, a simple Cam 2 Cam 3 elementary diagram of the switching scheme as follows: X-o HAND pattern Outgoing Circuit Incoming Line OFF Outgoing Circuit AUTO Combination top Bottom top Bottom number position a position B position a position B a 1 X O O From this, you can construct an X-O diagram that describes when the contacts are to be closed (X) or open (O) in the various positions of the switch. The X-O for the hand circuits looks 4 O O X like this: HAND OFF AUTO a Top and bottom circuits are series connected. X0 0 To make the cam selection, make a simple worksheet such as: In this circuit, you want a contact closed on the left (hand) but none Cam 2 Cam 3 in the center or the right. XO O ANO BNC ANO BNC For the automatic (AUTO) circuit, the X-O diagram would look OO X BNO BNO like this: It becomes immediately obvious that Cam 3 is the better choice HAND OFF AUTO for two reasons: (1) the series combination can be avoided, making 00 X it simpler to wire, (2) only two contacts are required, which is less expensive than the three contacts required by Cam 2. Putting them together, the complete X-O diagram is: XO O OO X Once the X-O diagram has been generated, the next step is to select the cam and the contact block or blocks needed to perform the desired X-O functions. The selection table listed in Eatons Electrical Sector Solutions, Volume 7, CA08100008E, lists the various types (shapes) of cams by number to choose from and type of contact and position to achieve the function outlined in the X-O diagram. 2 eaton C orporatIon www.eaton.com