E-Stop Safety Module
– Models ES-UA-5A and ES-VA-5A
E-Stop Switch Requirements
As shown in Figures 4, 5, and 6, the E-stop switch must provide contacts which are
closed when the switch is in the “armed” position. Once activated, the E-stop switch must
open its contacts and be returned to the closed-contact position only by a deliberate
action (such as twisting, pulling, or unlocking). The switch should be a “positive-opening
type,” as described by IEC 60947-5-1. A mechanical force applied to such a button (or
switch) is transmitted directly to the contacts, forcing them open. This ensures that the
switch contacts will open whenever the switch is activated.
NFPA 79 specifies the following additional Emergency Stop Actuator requirements:
• Emergency Stop push buttons shall be located at each operator control station and at
other operating stations where emergency shutdown shall be required.
• Stop and Emergency Stop push buttons shall be continuously operable from all control
and operating stations where located.
• Actuators of Emergency Stop devices shall be colored RED. The background
immediately around the device actuator shall be colored YELLOW. The actuator of a
push-button-operated device shall be of the palm or mushroom-head type.
• The Emergency Stop actuator shall be a self-latching type.
NOTE: Some applications may have additional requirements. The user must refer to all
relevant regulations.
When a 1-channel E-stop is used, the user must guard against failure modes that
can result in an unsafe condition, for example the failure of the contact to a short
circuit condition. A switch with positive opening operation should be used to reduce
the possibility of a failure of the switch to open. A short circuit failure results in loss of
switching function. This can occur from a short across the switch contacts, a short across
the wires connected to the switch somewhere between the switch and the
E-Stop Safety Module, or a short to a secondary source of power. To reduce these
possibilities, physically separate the wires from each other and from other sources of
power (e.g., in separate wireways or conduit).
According to the definition of European standard EN 954-1, a 1-channel E-stop should
generally be used in applications where Safety Category 2 or less (1 or B) has been
determined via a risk-assessment procedure.
Two-channel E-stops, with positive open switches, are designed to issue a stop
command even in the event of a single failure of this type and provide a high level of
safety.
If the Module is configured for 2-channel E-stop, the immediate normally open output
contacts (13-14, 23-24, 33-34, and 43-44), will open as soon as at least one of the two
E-stop contacts opens. Although simultaneity is not required, the E-stop contacts must
both be open at the same time and then both be closed, to reset the output contacts.
If not, the unit will go into a lockout condition that results in the outputs opening and
requiring a reset after the fault has been corrected.
WARNING . . .
1-Channel Input
If a 1-channel E-stop
button is used, a single fault (such as a
short across the single contact or to a
secondary source of power) can lead to
the complete loss of safety.
A 1-channel E-stop should be used
only in applications where such a fault
can be excluded, or the resulting loss
of safety cannot result in serious injury
or death (Safety Category 2, 1 or B; see
page 3).
If a 1-channel E-stop is used, separate
the wires from each other and from
other sources of power, by routing
them through separate wireways or
conduit in order to increase the reliability.
WARNING . . .
Multiple
E-Stop Switches
Whenever two or more E-stop
switches are connected to the same E-
Stop Safety Module, the contacts of both
switches must be connected together in
series. This series combination is then
wired to the respective Safety Module input.
Never connect the contacts of multiple
E-stop
switches in parallel to the E-Stop Safety
Module inputs; this defeats the switch
contact monitoring ability of the Safety
Module, and creates an unsafe condition
which could result in serious injury or
death.
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