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SEMI S22-1103a © SEMI 2003, 2005 20 EXCEPTION 2: Assembli es that are not intended t o be used as st and-alone equipment , but rather wi thin an overall integrated system, and which receive their powe r from the end-user…
SEMI S22-1103a © SEMI 2003, 2005 19
12.3.10 Machine parts, other than accessories or attachments, having metal-to-metal bearing surfaces should be
considered as bonded to the protective earthing system. Parts separated by a nonconductive fluid or gas should not
be considered as bonded.
12.3.11 When a part is removed, the continuity of the protective earthing system for the remaining parts should not
be interrupted.
12.3.12 Exclusion of Switching Devices from the Protective Bonding Circuit The protective earthing system
should not incorporate switching or interruption devices.
EXCEPTION: For technologies requiring isolated potentials (i.e. no ground reference) during operation, ground
interrupting devices are acceptable provided the device automatically provides continuity of the protective earthing
system when the related components are accessible and that the device is fault tolerant.
12.3.13 Interruption of the Protective Earthing System Where the continuity of the protective earthing system
can be interrupted by means of connectors (e.g., plug and socket connections), and this could result in increased risk
of electric shock, the following considerations should be satisfied:
a) the protective earthing system should be interrupted only after the energized conductors have been
interrupted, and
b) the continuity of the protective earthing system should be re-established before any energized conductor is
reconnected.
12.4 Bonding Terminations to The Protective Earthing System
12.4.1 The protective conductors should be bonded to a single designated termination (the protective earthing
conductor terminal) that will not be disturbed by any other conductor terminations.
12.4.2 All non-conductive coatings, such as paint or enamel, should be removed from contact surfaces where
protective conductors terminate.
12.4.3 When terminal lugs are used for bonding to the protective earthing system, they should be ring-tongue type,
with lock or star washers. (Refer to ¶17.2(a).)
12.4.4 Terminal lugs used to make connections to the protective earthing system do not need to be insulated.
12.5 Cord and plug connected equipment should pass a leakage current test in accordance with the test described in
§22.
13 Safety Circuits
13.1 General — Transformers or power supplies should be used for supplying safety circuits. Such transformers
should have electrical isolation between the primary and the secondary windings. Safety circuits should be designed
using non-hazardous voltage and power levels consistent with the correct operation of the control circuit.
NOTE 35: See ¶13.3.3 Exception 2 for specific EMO function exception.
13.2 Start Functions
13.2.1 Start functions should operate by energizing the relevant circuit.
13.2.2 Prevention of Unexpected Start-up The engineering design should prevent unexpected start-up.
13.3 Emergency Off
13.3.1 The equipment should have an “emergency off” (EMO) circuit. An EMO actuator (e.g., button), when
activated, should place the equipment into a safe shutdown condition, without generating any additional hazard to
personnel or the facility.
EXCEPTION 1: Cord- and plug-connected single phase equipment, rated no greater than 240 Volts line-to-line/150
Volts line-to-earth and no greater than 2.4 kVA, where the hazards are only electrical in nature, do not need to have
a separate EMO circuit if the main disconnecting means is readily accessible to the operator and maintenance
personnel. This main disconnecting means should be red and labeled indicating its On/Off status.
SEMI S22-1103a © SEMI 2003, 2005 20
EXCEPTION 2: Assemblies that are not intended to be used as stand-alone equipment, but rather within an overall
integrated system, and which receive their power from the end-user system, may not have a separate emergency off
circuit. The assembly’s installation manual should provide clear instructions to the equipment installer to connect
the assembly to the integrated system’s emergency off circuit.
NOTE 36: It is recommended that the emergency off function not reduce the effectiveness of safety devices or of devices with
safety-related functions (e.g., magnetic or braking devices) necessary to bring the equipment to a safe shutdown condition
effectively.
13.3.2 EMO Interfaces External EMO interfaces should be provided where the equipment is likely to be
integrated and is likely to have shared hazards with other assemblies in the end user’s facility. If an external EMO
interface is provided, the supplier should include instructions for connecting to the interface.
13.3.3 EMO Function Activation of the emergency off circuit should de-energize all hazardous voltage and all
power greater than 240 volt-amperes in the equipment beyond the main power enclosure.
EXCEPTION 1: A non-hazardous voltage EMO circuit (typically 24 Volts) may remain energized.
EXCEPTION 2: Safety related devices (e.g., smoke detectors, gas/water leak detectors, pressure measurement
devices, etc.) may remain energized from a non-hazardous power source.
EXCEPTION 3: A computer system or PLC performing data/alarm logging and error recovery functions may
remain energized, provided that the breaker and receptacle supplying the power to the computer system are clearly
labeled as remaining energized after EMO activation.
NOTICE: ¶13.3.4 below will be withdrawn upon July 1, 2006 publication and replaced by the new ¶13.3.4
including: figures and tables as shown in Delayed Revisions §2, however, the EH & S Committee has voted
that implementation of the information is OPTIONAL before the effective date.
13.3.4 EMO Design The design of the EMO circuit should include all the following:
a) the EMO circuit should not include controls that enable it to be defeated or bypassed;
b) the EMO circuit should consist of electro-mechanical components;
c) resetting the EMO switch should not re-energize circuits, equipment, or subassemblies that create a hazard to
personnel or the facility;
d) the EMO circuit should shut down the equipment by de-energizing rather than energizing control components;
and
e) the EMO actuator should be non-lockable and self-latching.
EXCEPTION 1: Solid-state devices and components may be used, provided the system or relevant parts of the
system are evaluated and found suitable for use. The components should be evaluated and found suitable
considering abnormal conditions such as over voltage, under voltage, power supply interruption, transient.
NOTE 37: For equipment intended for use in locations where fire or explosion hazards may exist, it is recommended that a
pneumatic or intrinsically safe EMO circuit be considered.
13.3.5 EMO Identification The EMO identification should include the following:
a) the emergency off actuator should be red and mushroom shaped;
b) a yellow background for the EMO should be provided;
c) all Emergency Off actuators should be clearly labeled as “EMO,” “Emergency Off,” or the equivalent, and
should be clearly legible from the viewing location. The label may appear on the actuator or on the yellow
background; and
d) Emergency Off buttons should be located or guarded to minimize accidental activation.
13.3.6 EMO Location and Size Emergency Off buttons should be readily accessible from operating and regularly
scheduled maintenance locations and appropriately sized to enable activation by the heel of the palm.
13.3.7 No operator or regularly scheduled maintenance location should require more than 3 meters (10 feet) travel
to the EMO button.
SEMI S22-1103a © SEMI 2003, 2005 21
13.4 Operating Modes When a system has more than one operating mode, and operating mode selection can
result in a hazardous condition, mode selection should be restricted to trained service or maintenance personnel.
13.5 Suspension of safeguards should satisfy ¶8.15.
13.6 Safety Controls
13.6.1 Hold-to-run Controls Hold-to-run controls should only be used if a hazard analysis determines that they
are an appropriate and adequate means to mitigate a hazard. When hold-to-run controls are used, they should
necessitate continuous actuation of the control devices to achieve operation.
13.6.2 Two Handed Controls When dual series-connected hand controls are used to isolate the operator from
hazards, the hand controls and/or control circuit should comply with the following:
a) the hand controls should be momentary contact switches with black or green heads. Each hand control should
be protected against unintended operation;
b) each hand control should be arranged by design, construction, and/or separation so that the use of both hands
is needed to start the machine cycle. Preferably, they are mounted at least 610 mm (24 in.) apart at the same
height;
c) two hand controls should be designed so that both hand controls need to be depressed within one second of
each other for the machine to cycle and both hand controls need to be held depressed until the hazard no
longer exists; and
d) the control system should incorporate an anti-repeat feature that limits the machine to one cycle for each
depression of the hand controls. The control system should incorporate an anti-tie-down feature that demands
the release of both hand controls between cycles.
13.6.3 Combined Start and Stop Controls Controls that alternately initiate and stop motion should only be used
when no hazardous condition can arise from their operation.
13.7 Safety Interlock Circuits
13.7.1 Protection against Fault Conditions When a single point failure can result in an unacceptable level of
risk, a safety interlocking circuit or other suitable means should be provided to protect against the consequences of
that single point failure.
13.7.2 Safety interlock Function Safety interlocks should be designed such that the equipment is automatically
brought to a safe condition before personnel can access the point of hazard. Each safety interlock, when activated,
should alert the operator immediately.
EXCEPTION: If a safety interlock triggers the emergency off (EMO) circuit, or otherwise removes power to the
user interface, notification to the operator is not needed.
NOTE 38: An explanation of the cause is preferred upon activation of a safety interlock.
NOTICE: ¶13.7.3 below will be withdrawn upon July 1, 2006 publication and replaced by the new ¶13.7.3
including: figures and tables as shown in Delayed Revisions §1, however, the EH & S Committee has voted
that implementation of the information is OPTIONAL before the effective date.
13.7.3 Safety Interlock Design Electromechanical devices and components are preferred. Solid state devices and
non-programmable solid state components may be used provided that the safety interlock system or relevant parts of
the system are evaluated for suitability for use in accordance with appropriate standard(s). The evaluation for
suitability should take into consideration abnormal conditions such as overvoltage, undervoltage, power supply
interruption, transient overvoltage, ramp voltage, electromagnetic susceptibility, electrostatic discharge, thermal
cycling, humidity, dust, vibration, jarring, or interfacing to a network.
NOTICE: ¶13.7.3.1 below will be withdrawn upon July 1, 2006 publication and replaced by the new ¶13.7.3.1
including: figures and tables as shown in Delayed Revisions §1, however, the EH & S Committee has voted
that implementation of the information is OPTIONAL before the effective date.