Rockwell Automation 1770 Industrial Automation Wiring and Grounding Guidelines - Manual (Page 19)

Industrial Automation Wiring and Grounding Guidelines 19
Publication 1770-4.1 – February 1998
Unintentional turn-on of outputs as the power source is connected or
disconnected, even if momentary, can result in injury to personnel as
well as damage to equipment. The danger is greater with
fast-response actuators. You can help minimize the probability of
unintentional momentary turn-on of ac and dc circuits by following
each of these guidelines according to your specific application:
•
follow the surge-suppression guidelines in this publication
•
follow the bonding and grounding guidelines in this publication
•
do not unnecessarily disconnect the power source from output
circuits
•
where possible, turn off all outputs before using CRM contacts to
interrupt the output circuit power source
•
hold off all outputs anytime the CRM contacts are open to be
certain that they are off as power is reconnected
Even if unintentional momentary turn-on does occur, the effects can
be minimized if:
•
actuators have a home position, i.e. defined by a spring return
•
for latching actuators, in the ladder logic, use non-retentive
energize (OTE) instructions with hold-in (seal-in) paths to
maintain the established position until power turn-off and leave
outputs off initially at power turn-on
•
each input or other load device connected to an output has an
input-filter time constant no lower than necessary for the
application
After designing and installing your system following these
guidelines to minimize unintentional momentary turn-on and any
effects thereof, test the system by de-energizing and the
re-energizing the CRM relay (Figures 7 and 8).
For additional information regarding wiring and grounding
guidelines, refer to:
•
Publication Index (Allen-Bradley publication SD499) — this
lists all current Automation Group publications.
•
Application Considerations for Solid-State Controls
(Allen-Bradley publication SGI-1.1) — this is an aid to the user
of solid-state controls who has considerable familiarity with
relay-type controls but may have limited electronic experience
and knowledge.
Avoiding Unintentional
Momentary Turn-on of
Outputs
Related Publications