Q
Grounding vs. bonding -- the core distinction
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A
Grounding connects a system/equipment to earth; bonding joins metal parts together to form a continuous, low-impedance path for fault current. Bonding is what actually clears a fault -- earth itself is a poor conductor.
NEC Art. 100
Q
Grounding electrode system -- required electrodes
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A
All electrodes present at a premises (metal water pipe, concrete-encased electrode, ground ring, rod/pipe/plate electrodes, etc.) must be bonded together to form one grounding electrode system.
NEC 250.50
Q
Concrete-encased electrode (Ufer ground) specs
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A
At least 20 ft of 1/2 in.+ rebar or 4 AWG+ bare copper conductor, encased in at least 2 in. of concrete, near the bottom of a footing/foundation in direct contact with earth.
NEC 250.52(A)(3)
Q
Equipment grounding conductor (EGC) sizing basis
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A
Sized from Table 250.122, based on the rating of the circuit's overcurrent device -- a completely different table/basis than the GEC.
NEC 250.122
Q
Why the neutral-ground bond exists only at the service
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A
A second neutral-ground bond downstream (e.g. at a subpanel) creates a parallel path for neutral current, which can flow over grounding conductors, metal piping, and equipment enclosures -- a serious shock/fire hazard.
NEC 250.24(A)(5), 250.142
Q
Separately derived system -- definition
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A
A premises wiring system whose power source (transformer, generator, etc.) has no direct electrical connection to the supply conductors of another system -- requires its own grounding electrode connection and bonding jumper.
NEC Art. 100, 250.30
Q
Bonding of metal water piping systems
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A
Interior metal water piping that could become energized must be bonded, typically via the service equipment or grounding electrode system, using a bonding jumper sized per Table 250.66.
NEC 250.104(A)
Q
Bonding of other metal piping systems (gas, etc.)
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A
Metal gas piping likely to become energized must be bonded -- often satisfied by the EGC of the circuit supplying equipment likely to energize it, per the equipment grounding conductor sizing rules.
NEC 250.104(B)
Q
Ground ring electrode specs
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A
A bare copper conductor not smaller than 2 AWG, at least 20 ft long, encircling the building/structure, buried at least 30 in. deep.
NEC 250.52(A)(4)
Q
Equipment grounding conductor types permitted
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A
Includes copper/aluminum conductors (bare or insulated), rigid/intermediate metal conduit, EMT, listed flexible metal conduit under specific conditions, cable armor, and other recognized methods in 250.118.
NEC 250.118
Q
Grounding electrode conductor -- can it be spliced?
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A
Generally must be installed in one continuous length without a splice or joint, with narrow exceptions (e.g. irreversible compression connectors, exothermic welding, or busbars).
NEC 250.64(C)
Q
Metal underground water pipe as an electrode
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A
Qualifies if in direct contact with earth for 10 ft or more, but can never be the sole grounding electrode -- must always be supplemented by another electrode.
NEC 250.52(A)(1), 250.53(D)(2)
Q
Bonding jumper on the supply side of service equipment
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A
Called a "supply-side bonding jumper" (not "equipment bonding jumper") when it connects the grounded conductor to the metal enclosure on the line side of service disconnects.
NEC Art. 100, 250.92
Q
Effective ground-fault current path -- required property
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A
Must be permanent, electrically continuous and conductive, and have the capacity to safely carry the maximum ground-fault current likely to be imposed on it.
NEC 250.4(A)(5)