Ladder Diagram Locators

Ladder Rung Locators


Take a look at the lower portion of this wiring diagram and locate the relay coils “IFR” and “CI” on lines 52 and 57. In the detail shown in red letters, note that there are small numbers along the right-hand side of the diagram as well. These numbers designate the line location of relay contacts. The number 33 in the right-hand margin tells you the line location of the contacts associated with relay coil “IFR.” Look at line 33 in the ladder rungs above,and you will find the “IFR” contacts.

Likewise, the numbers 7,11, and 39 in the right-hand margin of refer you to the lines where the contacts associated with relay coil “CI” can be found. Note that the 39 is underlined. An underlined number signifies a normally closed contact (and, conversely, a number that is not underlined signifies a normally open contact). Accordingly, you will find that the “CI” contacts located on line 39 above are shown as normally closed, and that the “CI” contacts on lines 7 and 11 in above are shown as normally open.

EXCERPT FROM ELECTRICITY FOR HVACR TECHNICIANS available from the online store at RSES (Refrigeration Service Engineers Society) The HVACR Training Authority.

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