overvoltage, reversal of current, excessive currents,
may set off a chain reaction of successively acting
and so on.
relays, which then perform various functions.
Control relays are also classified as open,
Control relays can also be used in so-called
semisealed, or sealed. Figure 2-21 illustrates the
lockout action to prevent certain functions from
various types of relays used today. Relays E, G, and
occuring at the improper time. In some equipment,
H are examples of open relays. The mechanical motion
control relays are used to sense undervoltage and
Figure 2-21.--Relay enclosures.