In this section: 
Switch terminology ................................................................... 6-1 
 
 
Switch terminology 
The terms Form A, B, or C are used in switch terminology, throughout this manual, and are described 
as follows: 
•  Form A is simply a single-pole normally-open (SPNO) switch (see next figure) A double-pole 
switch normally-open is classified as a 2 Form A. 
•  Form B is similar to Form A except that its contacts are normally-closed (see next figure). A 
double-pole switch normally-closed is classified as a 2 Form B. 
•  Form C (see next figure) is a single-pole double-throw switch. It could also be a multiple switch 
such as a double-pole which would be classified as a 2 Form C. 
Figure 12: Switch terminology 
 
 
Section 6 
Switch terminology