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SEMI S22-1103a © SEMI 2003, 2005 17 11.10.3 Fuse holders a n d fuses sho uld be of a ty pe that is desi gned to be m ounted to a panel or com ponent rail. NOTE 32: So-called ‘inline’ fuse hold ers do not meet this criter…
SEMI S22-1103a © SEMI 2003, 2005 16
b) ground detection lights, a ground-fault circuit-interrupter (GFCI), or a line isolation monitor should be
installed in the output circuit to indicate an isolated conductor ground-fault condition. This will aid in the
detection of ground faults in isolated power systems.
10.3.8 Protection Against Residual Voltages Stored electrical energy should be drained to less than a hazardous
energy level (see §22 for test method).
EXCEPTION: Batteries that produce a hazardous electrical power or hazardous voltage do not need to be
discharged, but other provisions for safe servicing should be made and provided in the system documentation.
11 Protection Against Risk of Electrical Fire
11.1 Measures should be provided in the design of the equipment to protect against the risk of electrical fire as a
result of any reasonably foreseeable single fault due to component failure or abnormal operating conditions.
11.2 The installation documentation should include the necessary data for selecting the facility supply overcurrent
protective device and the facility supply conductors.
11.3 All conductors except protective earthing conductors, protective conductors, and earthed (for example, neutral)
conductors should be protected against overcurrent conditions by protective devices suitably chosen as discussed in
the remainder of this section.
EXCEPTION: The earthed conductor (neutral) may be disconnected by an overcurrent device for valid safety and
design reasons, providing that it is disconnected simultaneously with the unearthed conductors.
11.4 Circuit overcurrent protection devices should not exceed the ampacity of the conductors they protect.
11.5 Circuit overcurrent protection of discrete devices should not exceed 125 percent of the amperage rating of the
device (see §18 for motor protection).
11.6 Circuits that cannot be characterized as serving discrete devices should be provided with overcurrent
protection at 125 percent of maximum nominal load or the next largest standard size of overcurrent device, unless it
can be demonstrated that no risk of electrical fire is present in the event of fault conditions (e.g., power limited).
11.7 All receptacle outlets and connectors as well as the circuits supplying these receptacles should have
overcurrent protection in accordance with their rating.
11.8 Local Lighting Circuits Overcurrent protection for lighting circuits should not exceed 15 amperes.
11.9 Transformers
11.9.1 Transformers that operate at 50/60 Hz, that have a primary rated 600VAC or less, and have no integral
thermal protection should have overcurrent protection in accordance with the applicable row of Table A1-14.
11.9.2 Transformers that operate at 50/60 Hz, that have a primary rated 600VAC or less, and are equipped with
thermal protection provided by the transformer manufacturer that interrupts the primary current in the event of an
overload, should be protected in accordance with Table A1-14 or A1-15.
11.10 Overcurrent Protective Devices
11.10.1
Overcurrent Devices All overcurrent protective devices should be selected and applied with proper
consideration being given to the following:
a) maximum available fault current,
b) interrupting rating of the device,
c) voltage rating,
d) load characteristic,
e) normal operating current, and
f) circuit in-rush characteristics.
11.10.2 Circuit breakers and circuit protectors are preferred over fuses as overcurrent devices because they can be
reset.
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.