Johnson Controls CK721-A User Manual

Figure 3-36: Field Installed Metal Oxide Varistor
A full line of varistor components is available
from Harris Semiconductor (now
Littelfuse Corp.).
The ZA family of components covers the complete operating range of
Cardkey Strike and Output relays in a radial leaded component suitable for
field wiring applications. Failure to provide these protection devices will
limit the contact life of the relay resulting in failed operation.
CK721-A Installation and Operation S300 Expansion Enclosures
24-10349-8 Rev. B 3-53
This document contains confidential and proprietary information of Johnson Controls, Inc.
© 2012 Johnson Controls, Inc.
Output Wiring
To insure proper operation and extend the contact life of mechanical relay outputs
(SIO8 Outputs and IO8 Outputs), the contacts should be protected by an external
protection circuit. This protection circuit is application- specific as configured in the
field. Johnson Controls would advise, at a minimum, a Metal Oxide Varistor (MOV)
at the rated voltage relative to the application across the power source and power
load interrupted by the mechanical relay.
+

+

+V
V
+V
V
CNC
NO
Output Relay
Source
Power
Load
Power
Field Installed
Metal Oxide Varistor
Field Installed
Metal Oxide Varistor
IMPORTANT

Johnson Controls CK721-A Specifications

General

Brand	Johnson Controls
Model	CK721-A
Category	Controller
Language	English