ERICO Practical Guide to Electrical Grounding - Manual (Page 67)

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500 - 517 of the NEC and installers and designers of
electrical systems should review these articles prior to
designing or installing electrical systems in these types of
locations.
The fifth condition requires exposed noncurrent-carrying
metal parts of fixed equipment to be grounded anytime such
equipment is supplied by metal-clad, metal-sheathed, metal
raceways or any other wiring method which has provisions
for an equipment grounding conductor.
The last condition requires that where fixed equipment
operates with any terminal at over 150 volts to ground, any
exposed noncurrent-carrying parts of such equipment must
be grounded.
These six conditions provide the general guidelines for
grounding exposed metal parts. There are several
exceptions to these guidelines but in general, these
provisions ensure that noncurrent-carrying metal parts are
grounded to protect personnel from the risk of electrical
shock.
General Provisions - Specific Equipment Fastened in
Place. In addition to the general provisions contained in
Section 250-42, the NEC contains provisions under which
exposed noncurrent-carrying metal parts of specific fixed
equipment shall be grounded. Sections 250-43 requires that
these metal parts in the following equipment must be
grounded: switchboard frames and structure, pipe organs,
motor frames, enclosures for motor controllers, elevators
and cranes, garages, theaters and motion picture studios,
electric signs, motion picture projection equipment, power-
limited remote-control, signaling and fire alarm circuits,
lighting fixtures, motor-operated water pumps and metal
well casings. In general, any exposed noncurrent-carrying
metal parts associated with any of the above mentioned
specific equipment shall be grounded. Of course, there are
some exceptions to these general provisions. Designers and
installers of electrical systems who plan to work on these
specific types of equipment should reference the NEC for
specific application guidelines.
General Provisions - Equipment Connected by Cord-
and-Plug. Section 250-45 contains the provisions for
grounding cord-and-plug connected equipment. In general,
four conditions exist under which exposed noncurrent-
carrying metal parts of cord-and-plug connected
equipment, which is likely to become energized, shall be
grounded:
The first condition requires grounding in hazardous
locations. These high-risk locations are covered in Articles
500 - 517 of the NEC and installers and designers of
electrical systems should review these articles prior to
designing or installing electrical systems in these types of
locations.
The second condition covers equipment which operates at
over 150 volts to ground. As with fixed equipment, there are
several exceptions for this provision, such as for motors,
metal frames of electrically heated appliances and listed
equipment which incorporates double insulation systems.
The third requirement applies to cord-and-plug connected
equipment installed in residential occupancies. All of the
following equipment, when installed in residential
occupancies, must be grounded: refrigerators, freezers, air
conditioners, washing machines, dryers, dish-washing
machines, kitchen waste disposers, sump pumps, electrical
aquarium equipment, hand-held motor-operated tools,
stationary and fixed motor-operated tools, light industrial
motor- operated tools, hedge clippers, lawn mowers, snow
blowers, wet scrubbers and portable handlamps. An
exception to Section 250-45 (c) does permit listed tools and
appliances that use a system of double insulation to be
operated ungrounded.
The last requirement applies to cord-and-plug connected
equipment in other than residential occupancies. All of the
following equipment, when installed in other than
residential occupancies, must be grounded: refrigerators,
freezers, air conditioners, clothes-washing, clothes-drying,
dish-washing machines,
electronic computer/data
processing equipment, sump pumps, electrical aquarium
equipment, hand-held motor-operated tools, stationary and
fixed motor-operated tools, light industrial motor-operated
tools, hedge clippers, lawn mowers, snow blowers, wet
scrubbers, cord-and-plug connected appliances used in
damp or wet locations by persons standing on the ground or
in or on metal surfaces such as metal tanks or boilers, tools
used in wet or conductive locations and portable
handlamps.
There are two exceptions from grounding in other than
residential occupancies:
The first permits tools and portable lamps used in wet or
conductive locations to be ungrounded provided the tool or
lamp is supplied through an isolating transformer with an
ungrounded secondary of not over 50-volts.
The second exception permits hand-held, motor-operated
tools, stationary and fixed motor-operated tools, light
industrial motor-operated tools and appliances to be
operated ungrounded provided they are listed and they
Chapter 3: Building Interior Bonding & Grounding
Grounding Book 4/14/99 10/5/99 6:01 PM Page 59 (Black plate)