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SEMI S22-1103a © SEMI 2003, 2005 18 11.14 Some device loads vary widely depending upon their opera ting conditions and oper ating history (such as ceramic resistive heating elements). The load value s used to select over…
SEMI S22-1103a © SEMI 2003, 2005 17
11.10.3 Fuse holders and fuses should be of a type that is designed to be mounted to a panel or component rail.
NOTE 32: So-called ‘inline’ fuse holders do not meet this criteria.
11.10.4 Panel-mounted fuse holders and fuses should satisfy the following:
a) fuses in screw-type fuse holders should be used as overcurrent protection in only single-phase circuits using a
neutral conductor;
EXCEPTION: Fast-acting fuses in multi-phase circuits may be used where they can enhance safe design.
b) if electric shock due to incidental contact by maintenance or service personnel may occur, a touch-safe fuse
holder should be used;
c) fuse holders that have exposed metal when the cap is removed (non-shockproof fuse holders) should have the
line conductor connected to the end terminal and the load conductor connected to the side terminal; and
d) fuse holders should not move in a way that will loosen electrical connections when a fuse is replaced.
11.10.5 Circuit breakers and circuit protectors should satisfy the following:
a) The circuit breaker or circuit protector should be manually operable and should clear a fault even if the handle
mechanism is held closed;
b) The “ON” and “OFF” position should be clearly marked. The handle should be mounted with the handle up
for the “ON” position;
c) If the circuit breaker is mounted on a vertical surface it should be in a vertical or horizontal orientation only. If
mounted in a vertical orientation, the handle should be up for the “ON” position. If mounted in a horizontal
orientation, the handle should be to the right for the “ON” position. If mounted in two columns, horizontally
oriented, the handles should be toward the center for the “on” position; or clearly marked indicating the “ON”
and “OFF” positions.
d) If the circuit breaker is mounted on a horizontal surface it should be mounted so that the on position is to the
right of the surface or center if there are two columns; or it should have its “ON” and “OFF” position clearly
marked.
e) Overcurrent protection should be provided in all unearthed conductors.
NOTE 33: It is preferred that the supply conductors of the circuit be connected to the top of the circuit breaker or circuit
protector where practical. Circuit breakers and circuit protectors marked with “line” and “load” terminals should be installed in
accordance with the markings.
11.11 Electrolytic Capacitors
11.11.1 Large capacitor venting recommendations: Capacitors that are greater than 25.4 mm (1.0 in.) in diameter or
are capable of storing more than four Joules should be self-vented or protected from rupture by equivalent means. A
capacitor vent should be unobstructed for a minimum of 5.1 mm (0.2 in.). Capacitors mounted horizontally should
have vent holes positioned in the upper half of the enclosure (9, 12, 3 o’clock positions).
11.11.2 Capacitors should have containment provisions within the capacitor itself or be shielded such that vapors or
debris will not become hazardous to personnel.
11.11.3 Capacitor terminals should be insulated or protected from short circuits by tools. Lacquer and sealing
compounds should not be relied upon to provide protection.
11.12 Abnormal Temperatures Under Fault Conditions — Heaters or other circuits which, under any reasonably
foreseeable single fault condition, are capable of causing abnormal temperatures that create a hazardous condition
with an unacceptable level of risk, should be provided with over temperature protection to detect these abnormally
elevated temperatures and interrupt the source of energy driving them. Equivalent means of protection are
acceptable.
11.13 In addition to satisfying the criteria of this document, the criteria of SEMI S3 should be satisfied when
applicable.
SEMI S22-1103a © SEMI 2003, 2005 18
11.14 Some device loads vary widely depending upon their operating conditions and operating history (such as
ceramic resistive heating elements). The load values used to select overcurrent protection devices should account for
the full load range during worst case, normal operating conditions.
12 The Protective Earthing System
12.1 Bonding All accessible non-current carrying conductive components that may become energized under
reasonably foreseeable single fault conditions, and as a result increase the risk of electric shock, should be bonded to
the protective earthing system.
NOTE 34: Non-safety related bonding conductors (e.g., bonding conductors for EMC concerns) are not subject to this section.
12.2 Parts Not Bonded to the Protective Earthing System If non-current carrying conductive parts do not
constitute a hazard under single fault conditions, it is not necessary to bond them to the protective earthing system.
12.3 Protective Earthing System
12.3.1 General The protective earthing system consists of those components that provide electrical continuity
between the protective earthing conductor terminal and non-current carrying frames, enclosures, or components that
are stipulated to be maintained at an earth potential under both normal operating conditions and single fault
conditions in accordance with ¶12.1.
12.3.2 Protective Conductors Copper conductors or structural members with bonding jumpers should be used for
bonding to the protective earthing system.
EXCEPTION: Conductors other than copper that have equivalent ampacity to copper conductor can be used for
protective conductors.
12.3.2.1 When a protective conductor is used in this way, its size should be compatible with the protective
conductor ampacity given in Tables A1-1 through A1-5 that is a function of the ampacity of the current carrying
conductor it is associated with.
12.3.2.2 Bus bars, and/or the equipment frame may be used as protective conductors. When bus bars or the
equipment frame is used, their geometry and material should provide the same ampacity as that stipulated for the
protective conductor in Tables A1-1 through A1-5.
12.3.3 Hinges, slides, and other moving parts of enclosures should not be relied on as part of the protective earthing
system.
EXCEPTION: Hinges are acceptable if the enclosure and its hinges have been identified as suitable for bonding by
an accredited testing laboratory.
12.3.4 Raceways, wireways, and cable trays should not be used as protective conductors, except to effect their own
connection to the protective bonding circuit as may be stipulated by ¶12.1.
12.3.5 It is preferred that a protective conductor be routed with the associated current carrying conductors whenever
possible.
12.3.6 The protective earthing system should not be intentionally used as a current carrying conductor, except as
permitted by ¶9.2.6.
12.3.7 Continuity of the Protective Earthing System The protective earthing system should be permanent,
electrically continuous and capable of carrying any ground fault current likely to be imposed.
See ¶22.3 “Earthing
Continuity and Continuity of the Protective Bonding Circuit” for the appropriate test method.
12.3.8 Connection and bonding points to protective conductors should be designed so that their current carrying
capacity is not impaired by mechanical, chemical, or any other influence that may degrade their current carrying
capacity.
12.3.9 Mounting hardware and cover screws that may be removed for normal servicing should not be used for
terminating the protective conductor to a component or part of the enclosure.
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.