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SEMI S22-1103a © SEMI 2003, 2005 16 b) ground detectio n lights, a ground-f ault circuit- interrup ter (GFCI), or a line isolation mon itor should be installed in the ou tput circuit to indicate an isolated condu ctor gr…
SEMI S22-1103a © SEMI 2003, 2005 15
10.3 Maintenance and Service Personnel Potential Exposure to Hazards
10.3.1 Energized Electrical Work The equipment should be designed to minimize the need to calibrate, modify,
repair, test, adjust, or maintain equipment while it is energized, and to minimize work that should be performed on
components near exposed hazardous energized circuits. The equipment design should move as many tasks as
practical from Type 4 to Types 1, 2, or 3. Routine Type 4 tasks, excluding troubleshooting, should have specific
written instructions in the maintenance manuals. General safety procedures (e.g., appropriate PPE and barriers) for
troubleshooting, including Type 4 work, should be provided in the maintenance manual.
10.3.2 Protection of Service Personnel Service personnel should not be exposed to inadvertent contact with
hazardous potentials or hazardous energy levels. This may be accomplished by using touch safe terminals or
providing additional barriers over exposed terminals.
10.3.3 Manual Adjustment Equipment requiring manual adjustment should be so designed that adjustment does
not expose personnel to electrical or mechanical hazards.
10.3.4 Access Maintenance and service access should be provided for maintaining and servicing equipment.
10.3.5 Internal Barriers Non-conductive or earthed (grounded) conductive physical barriers or equivalent means
should be provided:
a) where it is necessary to reach over, under or around, or in close proximity to hazards,
b) where dropped objects could cause short circuits or arcing,
c) where failure of liquid fittings from any part of the equipment could result in the introduction of liquids into
electrical parts,
d) where maintenance or service tasks are likely to allow inadvertent contact with un-insulated energized parts
containing either: potentials greater than 30 Volts rms, 42.4 Volts peak, or 60 Volts DC; or power greater than
240 volt-amps in dry locations.
NOTE 29: Removable nonconductive and noncombustible covers are preferred.
10.3.6 Test Points When test points are provided they should satisfy the following:
a) located to provide unobstructed access,
b) marked or identified in the documentation,
c) protected against incidental contact, and
d) provide adequate access for a test probe.
10.3.7 Isolated Power Systems This section applies only to 50-60 Hz AC applications operating at a hazardous
voltage.
NOTE 30: The common purpose for using isolated power systems is to reduce sources of electronic noise by not deliberately
referencing the output circuit conductors to earth (ground).
NOTE 31: Auto transformers do not provide electrical isolation.
10.3.7.1 All accessible conductive components that are likely to become energized under fault conditions should be
effectively bonded to the protective earthing conductor.
EXCEPTION: If the process technology requires conductive parts that are not grounded when they are inaccessible,
but grounded when they are accessible, then the intent of ¶10.3.7.2 is satisfied by ensuring such conductive parts are
grounded when they become accessible.
10.3.7.2 Isolated circuits should meet the following:
a) the transformer or power supply, and any components (devices) connected to their output, should be clearly
labeled adjacent to the isolated circuit(s) or on the enclosure to warn operators and service personnel of the
unearthed condition, and
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.