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SEMI S22-1103a © SEMI 2003, 2005 15 10.3 Mainte nance and Service Personnel P o tential Exposure to Hazards 10.3.1 Energized Electrical Work The equipm ent should be designed t o minim ize the need to calibrat e, modi …
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NOTE 24: A mechanical interlock is preferable to an electrical interlock.
9.4 Cord and Plug Connections used as Facility Connection
9.4.1 When a cord and plug connection is intended to be used as a main disconnecting means, it should either be
capable of being under the exclusive supervision of the person carrying out the work, or be provided with a means
for lockout (see discussion of conductors and cables in §16).
9.4.2 If a supply cord is provided with the system, the cord, as well as the installation instructions, should comply
with applicable local codes where it will be installed, or the equipment should have provisions for hard wiring using
a raceway.
9.4.3 If there are provisions for hard wiring, a cord and plug should not be used as a main disconnecting means.
9.4.4 If the cord and plug is used for the main disconnecting means the equipment should also have an on-off
control.
NOTE 25: Uses preferred for cord and plug connection to the facility include:
a) equipment with an attachment plug and powered from a receptacle outlet to connect movable equipment to facilitate
frequent interchange, and
b) the fastening means and mechanical connections of the equipment are designed to permit removal for maintenance or
service.
NOTE 26: Materials are restricted by ¶16.3.1.
10 Protection Against Electric Shock
10.1 General The electrical equipment should provide protection to persons against electric shock under normal
operating conditions and under any reasonably foreseeable single fault condition.
10.2 Protection Against Electric Shock During Normal Operation
10.2.1 Where operator access to a hazardous voltage is controlled through the use of a grounded conductive or non-
conductive enclosure, that enclosure should either:
1) require a tool to open and be labeled with the hazard against which it protects personnel, or
2) be interlocked.
Reference Jointed Finger Probe Access Test. Reference IEC61010-1 Annex B for the test finger.
NOTE 27: IEC 60529 “Degrees of Protection Provided by Enclosures” may be used as a reference.
10.2.2 Spacing between uninsulated energized parts and conductive enclosures should be maintained in compliance
with Appendix 1 Tables A1-12 and A1-13 or determined to be adequate by dielectric testing in accordance with §22.
10.2.3 Energized parts protected by insulation should be completely covered with insulation that can be removed
only by destruction. Such insulation should be capable of withstanding the mechanical, chemical, electrical, and
thermal stresses to which it may be subjected under normal operation.
10.2.4 Protection Against Electric Shock Hazards Resulting from Fault Conditions — Use of measures to prevent
the occurrence of a hazardous touch voltage may include one or more of the following:
a) Double or reinforced insulation may be used to prevent a hazardous touch voltage through contact with
exposed conductive parts that results from the failure of basic insulation of the energized parts of that circuit,
b) Electrical separation (clearance and creepage) may be used to prevent a hazardous touch voltage through
contact with exposed conductive parts that results from the failure of basic insulation of the energized parts of
that circuit,
c) Automatic disconnection of the supply of any circuit affected by the occurrence of an insulation failure that
results in a ground fault may be used to prevent contact with a hazardous voltage.
NOTE 28: See definition of GFCI.
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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
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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.