Chapter 6: Grounding and Bonding

Grounding & Bonding is the heaviest single topic on Utah's Journeyman written exam — about 10 questions. It is also where apprentices most often mix up words that sound alike. This chapter slows down on purpose.

You will live in Article 250, with definitions from Article 100 and equipment rules scattered elsewhere. Keep your NEC open while you study.

6.1 The Three Jobs People Confuse

6.1.1 1. System grounding

Connecting a current-carrying conductor (usually the neutral) to earth through a grounding electrode system. Purpose:

• Stabilize voltage to earth during normal operation
• Limit overvoltages from lightning / line surges / unintentional contact with higher voltage lines
• Provide a reference so that a hot-to-earth fault becomes a detectable overcurrent event (together with bonding)

6.1.2 2. Equipment grounding

Providing a low-impedance path from exposed metal parts back to the source so that fault current can flow enough to trip an OCPD quickly. The equipment grounding conductor (EGC) does this job. Earth itself is not a reliable fault-clearing path — dirt is not a conductor you trust for clearing a breaker.

6.1.3 3. Bonding

Electrically connecting metal parts so they are continuous. Bonding jumpers make enclosures, raceways, and piping participate in the fault path or equalize potential. Bonding is about continuity; grounding electrode connections are about earth reference — related, not identical.

6.2 Critical Definitions (Learn Precisely)

Term	Meaning
Grounded conductor	Circuit conductor intentionally grounded (often neutral)
Grounding electrode	Object that establishes connection to earth (rod, pipe, plate, concrete-encased, ground ring, metal water pipe, etc.)
Grounding electrode conductor (GEC)	Connects the grounded system / equipment to the grounding electrode
Equipment grounding conductor (EGC)	Bonds equipment/enclosures to the system grounded conductor / source for fault clearing
Main bonding jumper	Connects grounded conductor to service enclosure / grounding bus at service
System bonding jumper	Similar role for separately derived systems
Supply-side bonding jumper	Bonding on the supply side of the service disconnect / SDS disconnect

If a question says "grounded conductor," it is talking about the neutral (in typical AC systems), not the green wire.

6.3 Why Fault Clearing Needs Metal Continuity

Imagine a hot conductor contacts a metal box. For a breaker to trip, fault current must return to the source. The intended return is the EGC (or metallic raceway acting as EGC) back to the service neutral-ground bond, then to the source.

If the EGC is missing or open:

• The box may remain energized
• Fault current may be too low to trip quickly (especially if someone is relying on earth alone)
• Shock hazard remains until something else fails

Effective ground-fault current path is the phrase to remember: continuous, permanent, low impedance, adequately sized, and capable of carrying fault current safely.

6.4 Service Grounding and Bonding

At the service:

1. The grounded conductor is brought to the service disconnect enclosure.
2. A main bonding jumper bonds the grounded conductor to the metal enclosure / grounding terminal bar.
3. A GEC lands on the grounding electrode system.
4. EGCs and metallic raceways bond to the same grounding terminal system so faults return to the bonded neutral.

You normally bond neutral to ground only once on solidly grounded systems — at the service (or at a separately derived system), not again in subpanels.

6.5 Subpanels and Separately Derived Systems

6.5.1 Subpanel (downstream of service)

Use a 4-wire feeder on 120/240 V single-phase (two hots, neutral, EGC):

• Neutral bar isolated from the can
• Grounding bar bonded to the can
• Neutral and ground not bonded together in the subpanel

6.5.2 Separately derived system (e.g., transformer)

Bond the secondary grounded conductor to the enclosure with a system bonding jumper, connect to a grounding electrode per 250.30, and run EGCs on the secondary side correctly. Utah's practical exam transformer termination task is the hands-on cousin of this theory.

6.6 Grounding Electrodes and the "System"

Article 250 requires a grounding electrode system. Common electrodes:

• Metal underground water pipe (with supplemental electrode rules — water pipe alone is not enough in modern Code)
• Concrete-encased electrode (Ufer) — often excellent when present
• Ground ring
• Rod, pipe, plate electrodes
• Listed electrodes
• Other local metal underground systems as described in the Code

6.6.1 Rod electrodes

If using ground rods, resistance goals and the "two rod" practice appear in Code language: if a single rod does not meet the 25-ohm condition, an additional electrode is required — and in practice many installations drive two rods because measuring 25 ohms is uncommon on residential jobs. Know what the Code actually requires rather than jobsite folklore alone.

6.6.2 GEC sizing

GEC size is based on the size of the service entrance conductors (Table 250.66), with notes for taps, multiple electrodes, and bonding jumpers. You do not size the GEC from the load calculation ampacity directly — you size from the table based on ungrounded service conductor size.

6.6.3 EGC sizing

Equipment grounding conductors are generally sized from the rating of the OCPD ahead of the circuit using Table 250.122, not from Table 250.66. If you upsize ungrounded conductors for voltage drop, you may need to proportionally upsize the EGC — a classic exam trap.

6.7 Bonding Metal Water Piping and Other Systems

Metal water piping and other metal piping systems may require bonding to the electrical system so they cannot remain at a different potential during a fault. Bonding jumpers for piping use sizing rules tied to service conductors / tables in 250. Bonding around water meters and insulating sections matters so the path remains continuous.

Gas piping bonding rules have been clarified over recent Code cycles — read the current 250 requirements rather than assuming old practices.

6.8 Parallel Paths and Objectionable Current

Normal neutral current should not flow on EGCs, cable trays, or water pipes. Objectionable current on grounding paths is why we isolate neutrals in subpanels and avoid multiple neutral-ground bonds. If you feel tingling on a pipe, suspect a wiring error creating parallel neutral paths.

6.9 Isolated Ground Receptacles (Concept)

Some sensitive equipment uses isolated ground receptacles with an insulated EGC run to an isolated ground bus. These are easy to misinstall. Exam: know they still require proper grounding/bonding — "isolated" does not mean ungrounded.

6.10 Temporary Installations and Jobsite Grounding

Construction sites follow Article 590 and OSHA habits: GFCI protection for temporary wiring, proper generator grounding/bonding schemes depending on whether the generator is separately derived, and Assured Equipment Grounding Conductor programs on larger sites.

6.11 GFCI vs Grounding

GFCI can protect people even when an EGC is compromised in some scenarios, but GFCI is not a substitute for required equipment grounding. Do not answer exam questions as if GFCI makes grounding optional.

6.12 High-Yield Article 250 Navigation Tips

When a practice question appears, ask:

1. Are they asking about GEC, EGC, or bonding jumper?
2. Is this service, SDS, or feeder/branch equipment?
3. Which table — 250.66 or 250.122?
4. Is someone trying to use earth as the fault path? (Wrong.)
5. Is a second neutral-ground bond being proposed downstream? (Usually wrong.)

Tab these in your Code book (if tabs are allowed per Prov rules for your sitting):

• 250.4 — general requirements / performance
• 250.24 — service grounding/bonding
• 250.30 — separately derived systems
• 250.52 / 250.53 — electrodes
• 250.66 — GEC sizing
• 250.102 — bonding jumpers
• 250.118 — what may serve as EGC
• 250.122 — EGC sizing

6.13 Worked Mini-Problems

1. EGC sizing. A feeder is protected by a 200 A breaker. What table do you use for the copper EGC size? → 250.122. Look up 200 A row (commonly 6 AWG Cu — verify in your book).

2. Voltage-drop upsize. Same feeder uses 3/0 Cu for ampacity but you upsize to 250 kcmil for voltage drop. What happens to the EGC? → Upsize EGC proportionally per 250.122(B).

3. Subpanel. A garage subpanel has the neutral bar bonded to the enclosure with the green screw installed, and a 3-wire feeder (no EGC). Name two violations. → Neutral-ground bond in subpanel; missing EGC / improper feeder.

4. Water pipe electrode. A metal underground water pipe is present. Are you done with electrodes? → Usually no — Code requires a supplemental electrode with water pipe electrodes.

6.14 Practice Problems

1. True or false: Driving a ground rod at a subpanel allows you to omit the EGC in the feeder if the rod resistance is low.
2. Which conductor normally carries current during everyday operation: grounded conductor or EGC?
3. Main bonding jumper location: service equipment or subpanel?
4. Table for sizing GEC to a ground rod system vs table for sizing conduit EGC for a branch circuit?
5. Why is earth a poor equipment grounding means for clearing breakers?
6. On a 480 V Delta–Wye transformer SDS, where do you establish the secondary system bonding jumper: primary or secondary side?

6.14.1 Answers

1. False — earth cannot replace the EGC fault path.
2. Grounded conductor (neutral) carries normal unbalanced/load current; EGC should not (except during faults).
3. Service equipment (for the premises service).
4. GEC: 250.66 (with rod special maximums/notes); branch EGC: 250.122.
5. Soil resistance is high and variable; fault current may not rise enough to trip an OCPD quickly.
6. Secondary side (separately derived system bonding/grounding rules in 250.30).

6.15 Looking Ahead

With fault paths understood, Chapter 7 turns to what you mount on the wall: boxes, device fill, lighting, receptacles, and general-use equipment rules that fill another large block of exam questions.

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