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DOE Handbook
Electrical Safety
- Requirements for Specific Equipment -
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6.0 REQUIREMENTS FOR SPECIFIC EQUIPMENT
The electrical safety requirements for specific equipment are determined by the following standards:
1. NFPA 70, National Electrical Code (NEC 2002)
2. 29 CFR 1910, Occupational Safety and Health Standards
3. 29 CFR 1926, Safety and Health Regulations for Construction
4. NFPA 70E, Standard for Electrical Safety
in the Workplace
29 CFR 1910 and 1926 frequently reference other safety guidelines for design, operation,
and
maintenance. Such other guidelines comprise ANSI, ASTM, and IEEE specifications and
information derived
from various engineering sources or equipment manufacturer association
standards. However, the key document is
NFPA 70, the NEC; all the other documents are
keyed to it. The NEC reflects wiring and installation
requirements that provide for an installation
that is essentially free from hazard but not necessarily
efficient convenient or adequate for good
service.
6.1 CONVEYING SYSTEMS
Conveying systems are
used to move materials, goods, etc., from one place to another.
Because of their conditions of use, they are
usually classified in service applications as
intermittent duty.
6.1.1 ELECTRICAL DESIGN CRITERIA
Electrical design criteria should be closely coordinated with the architect, structural engineer,
fire
protection engineer, mechanical engineer, and electrical safety engineer to ensure that all
discipline
requirements are coordinated and met.
Factory and field performance tests and control and wiring diagrams
should be specified in the
purchase order or contract because they are not otherwise provided by the factory.
Acceptance
tests conducted by the factory representative, qualified independent inspector, or engineer are
recommended. Tests conducted by UL and Factory Mutual Engineering Corporation (FM) are
also acceptable.
ANSI and CMAA standards should be carefully reviewed to ensure that all applicable safety
requirements are covered in the specifications.
The designer should specify the following requirements:
1. Available system voltage
2. Control voltage
3. The motor is constructed for the specific
application
6-1
4. Motor horsepower, service factor, insulation class, and time ratings are sufficient to meet the
load requirements
5. Working clearances and space requirements
6. Disconnecting means and other NEC
requirements
6.2 CRANES AND HOISTS
The most significant factor in crane and hoist safety, after
structural integrity, is electrical safety.
All the referenced standards support this fact either directly or
indirectly by the amount of
definition and space provided for electrical systems' controls, operations, and
maintenance.
6.2.1 NEC GENERAL REQUIREMENTS
Basic installation and wiring safety requirements for
cranes and hoists are given in NEC Article
6101. Electrical designers and maintenance personnel should
thoroughly understand these
requirements and their intent. Some of the more significant requirements are the
following:
1. Cranes and hoists operated in hazardous (classified) locations shall conform to NEC Article
500.
2. When the crane is operated above readily combustible materials, the resistors must be
located in
a well-ventilated cabinet constructed of noncombustible material and constructed
so that they will not emit flames or molten metal. See the exception (and requirements) that
applies to certain cabinets made of noncombustible materials.
3. Cranes and hoists operating on
electrolytic cell lines have special requirements, as given in
NEC 668.
a. Grounding is not required for
conductive surfaces of cranes and hoists that enter the
working zone of a cell line, and the parts that come in
contact with an energized cell or
attachments shall be insulated from ground.
b. Remote controls that
may introduce hazardous conditions into the cell line working zone
shall employ one or more of the following:
(1) Isolated and ungrounded control circuit in compliance with NEC Section 668.21(a)
(2) Nonconductive rope
operator
(3) Pendant pushbutton with either non-conductive support and surfaces or ungrounded
exposed surfaces.
(4) Radio
1 See Appendix D, Reference Matrix.
6-2
6.2.2 DISCONNECTING MEANS
The disconnecting means provided for cranes and hoists may consist of two
or more lock-opentype
motor circuit switches or circuit breakers. Article 610, Part IV, of the NEC,
"Disconnecting
Means," and the installation and operating plans should be studied carefully to determine the
disconnecting means requirements and locations. The two basic disconnects to consider are:
1. The runway
conductor (conductors run along a crane runway for power or control)
disconnect shall be installed in
accordance with NEC 610.31.
2. The crane and hoist disconnect which shall be provided in the leads from the runway
contact conductors or
other power supply in accordance with NEC 610.32.
Figure 6-1(a). An additional control switch or a remote control switch is required if the second disconnecting
means is not accessible to the operator.
6-3
Figure 6-1(b). Second disconnect not required. A monorail hoist does not require a disconnecting means in the
leads to the hoist machinery if it is controlled from the floor, if it is within view of the power supply
disconnect, and if there is no work platform provided to service the hoist machinery.
6.2.3 GROUNDING
NEC grounding requirements consider the crane or hoist with all its associated equipment,
including electrical equipment, as a single piece of equipment; therefore, all the conductive
component parts
shall be bonded together so that the entire crane or hoist is grounded in
compliance with NEC Article 250, and
NEC Article 610. Metal-to-metal contact is required
between all surfaces including the trolley wheels and bridge. If any such surfaces are painted or
otherwise insulated, a separate bonding conductor is required.
The bonding of all conductive surfaces by
metal-to-metal contact is not to be considered as the
equipment grounding conductor for the electrical
equipment (motors, motor controllers, lighting
fixtures, transformers, etc.)on the crane or hoist. The
equipment ground conductors that are run
with the circuit conductors shall comply with NEC Article 250.
6.2.4 CONTROL
A limit switch is required to prevent the load block from passing the safe upper travel limit
on all
hoisting mechanisms.
Figure 6-1(b). Second disconnect not required. A monorail hoist does not
require a
disconnecting means in the leads to the hoist machinery if it is controlled from the
floor, if it
is within view of the power supply disconnect, and if there is no work
platform provided to service the hoist
machinery.
6-4
6.2.5 CLEARANCES
In the direction of live parts, the working space clearance is 2½ feet, and doors
enclosing live
parts that may require service or maintenance shall open at least 90 degrees or be removable.
6.2.6 OSHA AND NEC REQUIREMENTS
29 CFR 1910.179 and NEC Article 610, Part F, provide additional electrical
requirements
derived from ANSI and other standards. Significant requirements are the following:
1.
Control circuit voltage shall not exceed 600 Vac or dc. Pendant pushbutton voltage shall not
exceed 150 Vac or
300 Vdc.
2. Support shall be provided for pendant multiconductor cables.
3. Electrical systems for cranes and
hoists shall provide failsafe operation. When power fails,
all motors shall be automatically disconnected so
that they will not resume operation when
the power comes back on. Automatic cranes shall not commence motion
automatically when
the power comes on after an outage. Pendant pushbuttons shall be returned to the off
position when pressure is released. When the signal from a remote controller fails, all motion
shall stop.
6.2.7 MAINTENANCE AND OPERATIONS
It is important to have a comprehensive electrical maintenance program for cranes and hoists.
Every electrical part and circuit plays a critical operational safety role and must be checked and
serviced at the frequency and in the manner specified by OSHA, CMAA, ANSI, and the
manufacturer's manual.
Required weekly, monthly, and semiannual tests and required
recordkeeping are contained in ANSI B-30 and CMAA
documents.
The basic references for safe operation and maintenance of cranes and hoists are contained in
sections of 29 CFR 1910 and 1926.
6.2.8 DOCUMENTED MAINTENANCE
Maintenance checklists and schedules
in compliance with OSHA, owner's manuals, and
manufacturer's requirements for the specific equipment shall be
provided as required. Weekly,
monthly, and semiannual inspections shall be conducted, and comments and
condition of the
inspected part shall be documented and certified.
The recommended frequencies of
inspections vary in accordance with application, usage, and
authority. Frequent inspection and periodic
inspection are defined by OSHA as daily to monthly
and 1 to 12 months, respectively. Typical inspection
frequencies for electrical equipment of
cranes and hoists are as follows:
6-5
The inspection records shall provide an ongoing safety assessment of the equipment and be
used to predict repair-part replacement. All inspections shall be dated and initialed by the
inspector.
6.2.9 MECHANICAL ELEVATING AND ROTATING EQUIPMENT
The primary electrical safety concern
is working in proximity to live and unguarded electrical
overhead lines by uninsulated equipment. Unless these
lines are visibly grounded at the point of
work and the owner of the lines indicates that they are deenergized,
barriers or insulating
protective material shall be installed to prevent worker contact with them. The
following
clearances shall be maintained between equipment and electrical overhead lines:
1. Lines 50 kV
or below: 10 ft between the lines and any part of the equipment or load
2. Lines over 50 kV: 10 ft plus 0.4
in. for every 1 kV above 50 kV.
In locations and situations where it is possible that the operator may have
difficulty observing
that these clearances are being maintained, someone shall be designated to monitor the
clearances and provide the operator with timely warning before contact can be made. The use
of cage-type boom
guards, insulating links, or a proximity sensor shall not alter the electrical
safety requirements of 29 CFR
1910.269(p)(4) and 1926.550, even if these devices are
required. (See Figure 6-2.)
6-6
Figure 6-2. A minimum clearance of 10 ft between overhead power lines and equipment is required for 50 kV
and below while a clearance of 10 ft plus 4 in. for every kV above 50 kV is required.
6.3 ELEVATORS AND ESCALATORS
Elevators and escalators are used to move people and elevators are also
used to move
materials. Design, installation, inspection, and maintenance activities require specialized
knowledge for safe operation and use.
6.3.1 CODES AND STANDARDS
A comprehensive electrical safety program for elevators and escalators can be achieved
through the
application of the correct codes and standards. All elevators are required to be
constructed, installed, and
maintained in accordance with ANSI/ASME A17.1. Reference
standards include NFPA 70 (NEC) for the electrical
equipment wiring and NFPA 101 (Life
Safety Code). These standards reflect the interrelated roles of electrical
design, maintenance,
and fire protection in the electrical safety process.
6.3.2 DESIGN SPECIFICATIONS
The electrical designer shall provide for the installation requirements of Article 620 of the NEC
as well as
the ANSI/ASME A17.1 requirements for signaling, automatic fire protection, and
emergency power as required. The
manufacturer shall provide the required fire service key
switches, audible alarm devices, and internal wiring
up to the terminal strips in the elevator
control panel.
6.3.2.1 VOLTAGE AND CURRENT LIMITATIONS
There shall be a 300-V limitation on all operating control and signal circuits and related
equipment, including
door operators. Exceptions are permitted for 25 to 60 Hz ac if the current
OSHA Sections 29 CFR 1910.269
(p)(4), 1926.952 (b)
Figure 6-2. A minimum clearance of 10 ft between overhead power lines and
equipment
is required for 50 kV and below while a clearance of 10 ft plus 4 in. for
every kV above 50 kV is required.
6-7
cannot under any conditions exceed 8 mA, or for dc voltage if the current cannot, under any
circumstances, exceed 30 mA.
6.3.2.2 CONDUCTORS
Hoistway door conductors from the door interlocks to
the hoistway riser shall be flame retardant,
suitable for a temperature of at least 200°C, and Type SF or
equivalent. See NEC Table 400.4
of the NEC for approved types of elevator cables and Note 5 to NEC Table 400.4
concerning
special requirements for traveling control and signal cables. Operating control and signal cable
conductors may be as small as #24 AWG. Traveling cable conductors must be #20 AWG or
larger.
6.3.2.3
DISCONNECTING MEANS
The disconnecting means requirements for elevators and escalators are both specific and
extensive, requiring
careful study of the codes and installation plans during design, acceptance
testing, and routine inspections.
Some of the basic requirements of NEC 620.51 are the
following:
1. There shall be a single means of disconnecting all ungrounded conductors to the main
power supply of each
unit.
2. A single elevator or escalator, with multiple driving machines, shall have one disconnecting
means to disconnect the motors and control valve operating magnets.
3. When there is more than one driving machine in a machine room, the disconnecting means
shall be labeled.
4. The disconnect shall be a fused motor circuit switch or circuit breaker capable of
being
locked open.
5. The disconnect shall not be provided with a means of being operated from a remote
location.
6. A circuit breaker disconnecting means shall not be opened automatically by a fire alarm
system, except as allowed by NEC.
7. The within-sight rule applies to all elevator equipment disconnects.
Specific locations are
given for elevators with or without field control.
8. The disconnecting means
shall be installed in a location that is readily accessible to only
qualified persons.
When power from
more than one source is used for single- or multiple-car installations, a
separate disconnect should be
provided for each source. These disconnects should be in sight
of the equipment supplied, and warning signs
should be placed on or adjacent to the disconnect
to read. For example, "Warning: Parts of the control panel
are not deenergized by this switch."
Lighting circuits for each elevator require a disconnect switch in the
equipment room labeled for
the car it serves and lockable in the open position.
6-8
6.3.2.4 MOTORS
Elevator and escalator motors are considered as intermittent duty. This allows
them to be
protected by the overcurrent protection device supplying the power for the branch circuit, which
is selected by the percentages in NEC Table 430.22 times the full load current of the motors.
For example: What
is the load for a 15-minute rated 40-hp, 460-V, three-phase motor used as a
freight elevator motor?
Step
1: Finding full load current — NEC Table 430.150
40 HP = 52 A
Step 2: Finding demand
factors — NEC Table 430.22 (a)
15 minute rated = 85%
Step 3: Calculating load
52 A x 85% = 44.2A
Answer: Load is 44.2 amps.
6.3.2.5 GROUNDING
All metal
raceways and cables, Types MC, Ml, or AC, shall be bonded to the metal frame of the
car. All elevator equipment
including metal enclosures for electric devices on the car shall be
grounded in accordance with NEC Article
250.
6.3.2.6 OVERSPEED PROTECTION
Overspeed protection for overhauling and under-hauling is
required, as are motor-generator
overspeed requirements that must comply with NEC 430.89, Speed Limitation.
However, these
requirements are a part of the more extensive requirements of ANSI/ASME A17.1 for electrical
safety devices, which require scrutiny by designers, maintenance personnel, and inspectors.
6.3.3 EMERGENCY
POWER
Emergency power requirements are governed by ANSI/ASME A17.1 Rule 211.2, which requires
that the
regenerative power of an overhauling elevator prevent the elevator from attaining the
lesser of the governor
tripping speed or 125 percent of the rated speed. If the elevator power
system cannot absorb this power, a load
shall be provided on the load side of the elevator
power disconnect switch. If an emergency power supply is
designed to operate only one
elevator at a time, the energy absorption means may, if required, be located on
the line side of
the disconnect. Other building loads that may be supplied by the emergency power source may
not be considered as absorbing regenerated energy unless they use the emergency power
source as normal power.
Refer to Article 620, Part X, of the NEC, Overspeed, for the installation
requirements covering these
requirements.
6.3.4 DESIGN
In addition to the NEC, elevator and escalator requirements, there are
numerous electrical
requirements for the facilities designer in ANSI/ASME A17.1 and A17.3. A17.1 is a required
reference for new
elevator and escalator installations and can be used by the designer in
checking submittal drawings from the
manufacturer. ANSI/ASME A17.3 provides the safety
6-9
requirements for existing elevators and escalators and shall be referenced when existing
installations are to be modified or to determine which modifications shall be made to existing
installations and equipment to maintain optimum safety. The following lists typical key electrical
requirements from ANSI/ASME A17.1 that the designer shall control over and above those from
the NEC.
1.
Access to elevator equipment is to be controlled and limited to authorized persons.
2. Elevator equipment cannot share space with other building equipment except when the
elevator equipment is
separated from other equipment, enclosed by a rigid wire fence, and
provided with a lock that is strictly for
that enclosure.
3. Only electrical wiring, including raceways and cables, used directly in connection with
the
elevator, including wiring for (a) signals, (b) communication with the car, (c) lighting, heating,
air
conditioning, and ventilating the car, (d) fire-detecting systems, (e) pit sump pumps, and
(f) heating and
lighting the hoist way may be installed in the hoist way.
4. A minimum lighting level of 108 lux for the
equipment rooms and spaces and 541 lux on the
floor of the pit is required. The basis for the specified
illumination level should be in
accordance with the Illuminating Engineering Society (IES) lighting handbook.
5. A stop switch (emergency stop) is required in each elevator pit at the access door to the pit.
If the pit
exceeds 6 feet 7 inches, a second switch is required adjacent to the ladder. The
two switches will be connected
in series.
6. Car lighting shall consist of a minimum of two lamps to be supplied by a dedicated circuit
with a lock-open disconnect in the equipment room.
7. A 115-V, 20-A receptacle shall be provided in all
equipment spaces and in the pit.
8. A phase-reversal protection shall be provided to ensure that the
elevator motor cannot start
if the phase rotation is in the wrong direction or if there is a failure of any
phase.
9. Capacitors and other devices whose failure could cause unsafe elevator operation are
prohibited; only devices specified by the NEC or the manufacturer may be installed.
6.3.5 FIRE PROTECTION
The electrical designer shall coordinate with the manufacturer the design of the
fire protection
systems that connect to the elevator control panel. The system will be designed to return the
car
to a designated area (normally the first floor or lobby) in the event of smoke or fire in the
equipment
area or near the elevators. In that event, the car returns to a designated area where
passengers can safely
exit the facility. In addition to coordinating car control, the system
provides for the shutdown of the
electrical elevator equipment prior to operation of the sprinklers
and the transmission of the alarm and
provides a means for the firefighters to assume manual
control of the elevator from the designated area. The
requirements for these systems are
detailed in ANSI/ASME A17.1.
6-10
6.3.6 INSPECTIONS AND RECORDS
Elevator inspections and recordkeeping are performed in accordance with
the local authority
having jurisdiction. The ANSI/ASME A17.2 series of inspectors manuals provide a guide for
performing tests and inspections as well as recommended inspection checklists. In addition to
acceptance
inspections and tests, the code requires 1- and 5-year inspections for electric
elevators and 1- and 3-year
inspections for hydraulic elevators.
6.3.6.1 CODES
Elevators are required to be in compliance with the issue of ANSI/ASME A17.1 in force the
date
they were installed. If the local authority has adopted ANSI/ASME A17.3, the code for existing
installations, they shall be in compliance with it, except they shall not be downgraded to it. When
ANSI/ASME
A17.3 is in force, it becomes the minimum standard to which installations shall
adhere, and if existing
installations are upgraded in accordance with ANSI/ASME A17.1, Part
XII, they shall also be in compliance with
the more stringent requirements of A17.3.
6.3.6.2 INSPECTOR QUALIFICATIONS
Inspectors should meet the requirements of ANSI/ASME QEI-1 and be
recognized by the local
enforcing authority. Repair and maintenance personnel should be qualified elevator
mechanics.
6.4 PORTABLE AND VEHICLE-MOUNTED GENERATORS
Using portable and vehicle-mounted generators
to operate electric tools on job sites is permitted
under specific conditions.
However, OSHA inspections
have disclosed a potentially serious hazard resulting from the use
of portable generators. Both OSHA and the
NEC permit the use of two-wire, single-phase
generators of not more than 5,000 W "where the circuit conductors
of the generator are
insulated from the generator frame and all other grounded surfaces." Under these
conditions,
neither the receptacles, cord sets, nor tools need to be protected by GFCIs or an assured
equipment grounding
conductor program. This exception from using GFCIs is granted because
with an insulated (isolated) circuit,
there is no dangerous current flow from the generator-fed
conductors to ground, structural steel, or any other
grounded object. However, the use of GFCI
devices is still recommended.
If the circuit conductors are not isolated, however, the shock hazard would be the same as with
any other electrical source and the exemption does not apply. In wet or high humidity
environments, circuit
conductors may not be suitably isolated and the exception would not
apply.
All portable electric
generators that supply 15-or 20-A, 120-V receptacles and that are in use or
are available for use on construction sites shall meet all the following conditions or be used only
with either GFCIs or an assured equipment grounding conductor program.
1. They must be rated not more than
5 kW.
2. They shall have only a two-wire circuit (i.e., only 120-V output).
6-11
3. They shall have both circuit conductors insulated from the frame and all other grounded
surfaces.
With proper ventilation there are no special requirements for wiring and equipment installed in
battery rooms per NEC 480
Figure 6-3. The ungrounded frame of a generator is acceptable as a grounding electrode if the circuit conductors
are insulated from the frame and all other grounded surfaces.
6.5 BATTERIES
Storage batteries
are considered a live source and appropriate precautions should be taken
when working around them. Information
regarding batteries and battery rooms can be found in
NESC, NFPA 70E Article 240 and 320.
6.5.1
SURROUNDING SPACE
Adequate space should be provided around storage batteries for safe inspection,
maintenance,
testing, and cell replacement. Space shall be left above cells to allow for operation of lifting
equipment when required, for addition of water, and for taking measurements.
6.5.2 LOCATION
Storage
batteries should be located in a protective enclosure or area accessible only to qualified
persons. A
protective enclosure can be a battery room; a control building; or a case, cage, or
fence that shall protect
the contained equipment and minimize the possibility of inadvertent
contact with energized parts.
6.5.3 VENTILATION
The battery storage area shall be ventilated by either a natural or powered ventilation
system to
prevent accumulation of hydrogen. The ventilation system shall limit hydrogen accumulation to
less
than an explosive level.
Figure 6-3. The ungrounded frame of a generator is acceptable as a grounding
electrode
if the circuit conductors are insulated from the frame and all other grounded surfaces.
in NEC
250.6 and 305.6 (a), EX.
6-12
6.5.4 CONDUIT
Because the vapors given off by a storage battery are very corrosive, the wiring shall
withstand
the corrosive action, and special precautions are necessary as to the type of insulation used
and
the protection of all metalwork. It is stated by their respective manufacturers that conduit
made of aluminum
or silicon-bronze is well suited to withstand the corrosive effects of the
vapors in battery rooms. In
contrast, if steel conduit is used, it is recommended that it be zinc-coated
and kept well painted with
asphaltum paint.
6.5.5 BATTERY ROOM
There are no special requirements for the type of fixtures or
other electrical equipment used in
the battery room, with proper ventilation. (See NEC 480 and Figure 6-4)
Figure 6-4. With proper ventilation there are no special requirements for wiring and equipment installed in
battery rooms per NEC 480.
6.5.6 PERSONAL PROTECTIVE EQUIPMENT
PPE capable of protecting
employees from acid splashes shall be used by those working on or
servicing batteries. The minimum acceptable
PPE shall include acid-resistant gloves, aprons,
and chemical-splash goggles. A full-face shield may also be
used; it shall not, however, be worn
in place of goggles. The design and use of PPE for wear when servicing
batteries shall comply
with OSHA requirements. Safety showers and eyewash stations are also required.
6.5.7 TOOLS
Tools used for working on batteries shall be insulated or non-sparking.
Figure 6-4. With
proper ventilation there are no special requirements for wiring and
equipment installed in battery rooms per
NEC 480.
6-13
6.5.8 STORAGE BATTERIES AND BATTERY BANKS
The following subsection covers rechargeable batteries used
as a source of electrical energy.
This category is not limited to batteries of a particular voltage and energy
rating, since the
nature of the associated electrical hazards is similar without regard to battery size; the
severity
of the hazard increases as the battery ratings increase.
6.5.8.1 TYPES OF HAZARDS
Some
of the types of hazards associated with storage batteries and battery banks are listed as
follows:
1.
Accidental grounding of one polarity of a battery bank can create a hazardous voltage
between the ungrounded
polarity and ground.
2. Accidental shorting of the exposed terminals or cables of a battery can result in
severe
electric arcing, causing burns and electric shock to nearby personnel.
3. Hydrogen gas generated
during battery charging can create fire, explosion, and toxicity
hazards.
4. Exposed terminals in a battery bank present electric shock hazards.
5. Batteries, particularly
sealed-cell batteries, can explode if they are shorted or if they are
charged at excessively high rates.
6. Electrolytes can be highly corrosive and can produce severe burns to personnel on contact.
6.5.8.2
DESIGN AND CONSTRUCTION CRITERIA
Reliable design and construction criteria for storage areas for batteries
are as follows:
1. Battery installations shall conform to the requirements in the current edition of the
NEC and
NESC.
2. Battery banks should not be grounded except as required in NEC a ground detector should
be used to indicate an accidental ground.
3. Batteries should be mounted to allow safe and convenient
access for maintenance.
4. Lockable doors should be provided to control access to rooms or enclosures
containing
battery banks.
5. Approved safety showers and eyewash stations should be provided close to
battery banks.
6. Appropriate ventilation for discharges of gas should be provided.
7. In areas where seismic activity is present, the installation should be designed according to
local
standards.
6-14
6.5.8.3 OPERATING CRITERIA
Operating criteria are as follows:
1. Maintain battery bank
connections that are clean and tight to prevent excessive heating
because of contact resistance.
2. Do
not repair battery connections when current is flowing. An accidental opening of the
circuit could result in a
hazardous arcing condition.
3. Clearly post electrical and other hazards of battery banks and emergency
first aid
information near the equipment.
4. Arrange the battery banks so that temperature stratification will not result in over- or undercharging.
Note: The optimum storage temperature for maximum battery life is 77°F ± 2° (25°C ± 1).
6-15
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