SECTION 16460
GROUNDING
PART 1 - GENERAL
1.01
REQUIREMENTS
A.
1.02
SCOPE
A.
1.03
1.04
The general provisions of the Contract, including General and Supplementary
Conditions and General Requirements, apply to the work specified in this
Section.
The work under this Section shall consist of furnishing and installing grounding
systems as shown on the Drawings and herein specified.
QUALITY ASSURANCE
A.
All equipment, materials, and their installation shall conform to the requirements
of the National Electrical Code (NEC), local code requirements, and these
Specifications.
B.
All equipment and material shall be listed by Underwriter's Laboratories, Inc. (UL)
for their intended use and shall bear the UL label.
C.
Equipment shall be constructed in accordance with National Electrical
Manufacturer's Association (NEMA) standards.
DESCRIPTION
A.
The equipment grounding system shall be designed so all building steel, metallic
structures, raceways, enclosures, cabinets, machine frames, junction boxes,
outlet boxes, portable equipment, and all other conductive items in close
proximity with electrical circuits operate continuously at ground potential
providing a low impedance path for possible ground fault currents.
PART 2 - PRODUCTS
2.01
MATERIALS AND COMPONENTS
A.
MAIN GROUNDING SYSTEM:
1.
The ground bus in the main distribution switchboard shall be connected
to at least three (3) copper-clad ground rods, not less than 3/4 inches in
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diameter, ten (10) feet long, and driven full length into the ground outside
in unpaved earth. Where required to meet the requirements of herein
specified tests, extra rods shall be installed at no additional cost to the
Owner. The rods shall be located a minimum of ten (10) feet from each
other, or any other electrode, and shall be loop interconnected with each
other by a minimum No. 4/0 AWG bare copper conductor thermal
welded, using the proper style mold, to each rod below grade.
2.
Provide a minimum No. 4/0 AWG green insulated copper ground
conductor from the main distribution switchboard ground bus to the main
metallic water service entrance (before the first pipe joint inside the
building) and connect to same by means of adequate ground clamps.
Where a dielectric main water fitting is installed, this ground conductor
shall be connected to the street side of the dielectric water fitting. The
conduit shall be bonded to the ground conductor at each end. Furnish
and install with ground clamps, a minimum No. 4/0 AWG jumper around
the water meter.
3.
Provide a secondary building ground bar to serve as part of the building
grounding electrode system in each electric room and other utilitarian
areas of the building where dry-type transformers will be located, and in
each communication room and/or where telecommunications main
distribution frames (MDF) and sub-distribution frames (SDF) will be
located. A ground bar(s) shall also be located at the telephone and
CATV service entrance demarcation point(s). The ground bar(s) shall be
electro-tin plated copper, minimum size of ¼” x 6” x 12” or larger sizes as
shown on the Drawings or required, with 3/8” plastic standoff insulators
bolted to the wall. These ground bars shall be connected with a
continuous No. 4/0 AWG bare copper ground conductor using high
compression two (2) hole lugs. The No. 4/0 AWG ground conductor shall
originate at the main switchboard ground bus and route through the
building corridor ceilings unspliced to each of the ground bars. Provide
“low smoke” type exothermic welds in an accessible ceiling using the
proper style mold. Where impractical to use an exothermic weld due to
space constraints, the Contractor may use an irreversible compression
type connection listed for the purpose but only at locations approved by
the Owner.
4.
(ENGINEER, USE THIS PARAGRAPH FOR AN ALL STEEL FRAMED
BUILDING IN LIEU OF #3 ABOVE.) Provide a secondary building
ground bar to serve as part of the building grounding electrode system in
each electric room and other utilitarian areas of the building where drytype transformers will be located, and in each communication room
and/or where telecommunications main distribution frames (MDF) and
sub-distribution frames (SDF) will be located. A ground bar(s) shall also
be located at the telephone and CATV service entrance demarcation
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point(s). The ground bar(s) shall be electro-tin plated copper, minimum
size of ¼” x 6” x 12” or larger sizes as shown on the Drawings or
required, with 3/8” plastic standoff insulators bolted to the wall. These
ground bars shall be connected with a continuous No. 4/0 AWG bare
copper ground conductor using high compression two (2) hole lugs. The
No. 4/0 AWG ground conductor shall originate at the nearest accessible
building steel beam or column using a “low smoke” type exothermic weld
with the proper style mold. Remove the building steel paint completely
prior to making grounding connections and repaint with proper galvanized
paint when complete.
5.
(ENGINEER, USE THIS PARAGRAPH FOR AN ALL STEEL FRAMED
BUILDING.) Bond the building steel at each building expansion joint with
No. 4/0 AWG bare copper using a “low smoke” type exothermic weld
using the proper style mold at accessible locations. Remove the building
steel paint completely prior to making grounding/bonding connections
and repaint with proper galvanized paint when complete.
6.
New Buildings, Building Additions and Exterior Electrical Equipment
Enclosures:
(ENGINEER TO EDIT PARAGRAPHS BELOW TO SUIT PROJECT)
a.
Buildings with new concrete foundations and/or footings shall be
provided with a minimum No. 4 AWG bare copper ground
conductor from the main distribution switchboard ground bus to
the foundations and/or footings concrete-encased electrode rebar
meeting the requirements of NEC 250.52(A)(3). The conductor
shall be thermal welded to the concrete-encased electrode
(rebar), using the proper style mold. Refer to the detail on the
Drawings. (ENGINEER EDIT OUT THIS PORTION IF NOT
USING) Building additions foundations and/or footings not within a
reasonable distance from the switchboard may have the concreteencased electrode bonded to the buildings secondary building
electrode system ground bar.
b.
Exterior electrical equipment enclosures with new concrete
foundations and/or footings shall be provided with a bare copper
ground conductor from the ground rods (if provided) and/or from
the ground bus of the main panel within the enclosure to the
concrete-encased electrode, meeting the requirements of NEC
250.52(A)(3), as shown on the Drawings. The conductor shall be
thermal welded to the concrete-encased electrode (rebar), using
the proper style mold. The enclosure, if metal, shall be bonded to
the grounded electrode.
c.
(ENGINEER, USE THIS PARAGRAPH FOR A STEEL FRAMED
BUILDING.) Steel frame buildings shall also have the steel
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columns anchor bolt connected to the concrete-encased electrode
(rebar) with a No. 4/0 AWG bare copper ground conductor having
an exothermic weld at both ends, using the proper style molds.
Coordinate the installation of the anchor bolts to the base plate to
scrape away paint/rust prior to the installation of the washer and
nut to the steel columns anchor bolts. Refer to the detail on the
Drawings.
B.
Secondary services shall be grounded on the "line" side in accordance with the
NEC. The neutral disconnecting link, or links, shall be located so that the main
distribution switchboard neutral bus with all interior secondary neutrals can be
isolated from the common ground bus and the service entrance conductors.
C.
The equipment grounding conductors and straps shall be sized in compliance
with the NEC. All equipment grounding conductors shall be provided with green
insulation equivalent to the insulation on the associated phase conductors. The
related feeder and branch circuit grounding conductors shall be connected to the
ground bus with pressure connectors. A feeder serving several panelboards
shall have a continuous grounding conductor which shall be connected to each
related cabinet ground bus.
D.
This Contractor shall furnish and install a separate green insulated equipment
grounding conductor for each single or three-phase feeder and each branch
circuit with a two-pole or three-pole protective device. The required grounding
conductor shall be installed in the same raceway with the related phase and/or
neutral conductors. Where there are parallel feeders installed in more than one
raceway, each raceway shall have a green insulated equipment ground
conductor. Single-phase branch circuits required for 120 and 277 volt lighting,
receptacles, and motors shall consist of phase and neutral conductors installed
in a common metallic raceway, which shall serve as the grounding conductor.
Flexible metallic conduit equipment connections utilized in conjunction with the
above single-phase branch circuits shall be provided with suitable green
insulated grounding conductors connected to grounding terminals at each end of
the flexible conduit.
E.
This Contractor shall furnish and install in the same raceway with the associated
phase and/or neutral conductors, a green colored equipment ground conductor
having the same type insulation and connected as described below:
1.
Where electrical devices, such as heaters, are installed in air ducts,
provide a green insulated equipment ground conductor sized in
accordance with the NEC based on the rating of the overcurrent device
supplying the unit. This conductor shall be bonded to the ground bus in
the associated panelboard.
2.
From the equipment ground bus in panelboards through raceways and
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flexible metallic conduit to ground terminal in a connection box mounted
on three-phase motors, furnish and install a ground conductor sized as
herein specified.
Where the motor has a separate starter and
disconnecting device, the ground conductor shall originate at the ground
bus in the panelboard. Motors shall be bonded to each starter and
disconnecting device enclosure.
PART 3 - EXECUTION
3.01
POWER SYSTEM GROUNDING
A.
This Contractor shall furnish and install green insulated ground conductor(s) in a
raceway to the main ground and domestic metallic water main with ground
clamps designed specifically for that purpose.
B.
Main distribution system: From the ground electrodes, this Contractor shall
furnish and install an insulated ground conductor to the ground bus within the
switchgear, to the neutral of the switchgear, and to all non-current carrying parts.
C.
Secondary building grounding: Furnish and install secondary building ground
bars where indicated and as detailed on the drawings. Connect the ground bars
with No. 4/0 AWG bare copper ground conductors originating from the
(switchgear ground bus) (building steel). Provide green tags on the ground
conductors every fifty (50) feet or less. The tags shall identify the ground
conductor as the building secondary grounding electrode system. Laminate tags
and secure with tie wraps.
D.
Branch circuit grounding: This Contractor shall furnish and install grounding
bushings, ground terminal blocks, and grounding jumpers at distribution centers,
pullboxes, panelboards, and the like.
E.
Bonding jumpers: This Contractor shall furnish and install a green insulated
bonding conductor (size shall correlated with the over-current device protecting
the conductor) attached to grounding bushings on the raceway, to lugs on boxes,
and other enclosures.
F.
Bonding conductors: This Contractor shall furnish and install a bonding
conductor in all flexible conduits connected at each end to a grounding bushing.
G.
Pole mounting luminaire (lighting fixture) grounding: This Contractor shall
furnish and install a ground conductor with green insulation to the lighting
standard (pole). Connect to a corrosion-resistant ground stud or ground clamp
furnished as part of the standard. The ground conductor shall originate and be
run with the branch circuit wiring.
H.
All electrical outlets shall be connected from the device grounding terminal to the
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outlet box with No. 12 AWG green insulated conductor. This Contractor shall
furnish and install a green screw terminal in the outlet box and a continuous
green ground conductor from the green terminal screw to the grounding systems
as indicated on the Drawings.
3.02
COMMUNICATION GROUNDING
A.
3.03
Telephone
1.
This Contractor shall furnish and install one (1) No. 2 AWG green ground
conductor in a ¾ inch raceway from the telephone equipment
demarcation space to the main service ground or building secondary
grounding electrode system.
2.
This Contractor shall furnish and install one (1) No. 2 AWG type green
ground loop between each raceway terminating at the telephone
equipment demarcation backboard by means of a grounding bushing.
B.
Fire detection and alarm systems: This Contractor shall furnish and install one
(1) No. 8 AWG green ground conductor in a 3/4 inch raceway from system
equipment enclosures to the main service ground or building secondary
grounding electrode system.
C.
Ancillary communication systems: Provide additional grounding of other building
systems as described elsewhere in these specifications.
TESTS
A.
The completed grounding system shall be subjected to a ground resistance test
with an earth test megger to ensure that the ground resistance, without chemical
treatment or other artificial means, does not exceed five (5) ohms at the service
entrance equipment’s ground bus. The Contractor shall furnish and install
additional ground rods and conductors from the exterior ground grid to achieve
the required resistance to ground. Testing equipment must be calibrated to the
manufacturer’s requirements. Upon request, the Contractor shall provide
documentation of the testing equipment’s most recent calibration.
B.
(ENGINEER, USE THIS PARAGRAPH FOR AN ALL STEEL FRAMED
BUILDING.) In addition to the above, steel framed buildings shall be subjected
to a ground resistance test with an earth test megger for the adequacy of the
steel framing of the building as a grounding electrode system for five (5) ohms or
less. Testing shall be at all of the secondary building ground bar connection
points. If testing results do not meet the required resistance, the engineer must
be notified.
END OF SECTION
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