Journeyman Electrician Grounding and Bonding Review: Core Definitions
System Grounding vs. Equipment Grounding
Understanding the distinction between system grounding vs equipment grounding is fundamental to scoring well on the Journeyman exam. System grounding involves the intentional connection of a circuit conductor—typically the neutral—to the earth. This practice limits the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines. It also stabilizes the voltage to earth during normal operation. For example, in a 120/240V single-phase system, the center tap of the transformer is grounded to ensure that neither hot leg exceeds 120V relative to the ground.
Equipment grounding, conversely, focuses on connecting the non-current-carrying metal parts of the electrical system (such as motor frames, conduit, and panel enclosures) to the system grounded conductor, the grounding electrode conductor, or both. The primary goal here is safety under fault conditions. If a hot wire touches a metal junction box, the equipment grounding conductor provides a low-impedance path back to the source, triggering the overcurrent protective device (OCPD). Without this path, the metal box would remain energized at line voltage, creating a lethal shock hazard for anyone who touches it. On the exam, remember that system grounding protects the system, while equipment grounding protects the personnel.
The Purpose of Bonding and the Fault Current Path
Bonding is the act of physically connecting metal components to ensure electrical continuity and the capacity to conduct safely any current likely to be imposed. For an electrical system to be safe, it must establish an ground fault path and effective grounding mechanism. This path must be permanent, continuous, and possess low impedance. High impedance in a fault path is a leading cause of fire and electrical shock because it prevents the circuit breaker from "seeing" the fault. If the resistance is too high, the current flow will not reach the trip threshold of the breaker, leaving the fault active.
In exam scenarios, you will often be asked to identify the Effective Ground-Fault Current Path. This is an intentionally constructed, low-impedance electrically conductive path designed to carry current under ground-fault conditions from the point of a fault on a wiring system to the electrical supply source. It facilitates the operation of the OCPD or ground-fault detectors. Bonding jumpers are the tools used to bridge gaps in this path, such as around concentric knockouts that are not fully removed or across expansion joints in conduit runs. Failure to maintain this path is a direct violation of NEC 250.4(A)(5).
Key NEC Definitions from Article 250 Part I
A solid NEC Article 250 study guide must begin with the definitions found in Part I and Article 100. Candidates must distinguish between the Grounded Conductor (the neutral) and the Grounding Conductor (the safety ground). The Grounded Conductor is a system or circuit conductor that is intentionally grounded; it carries current during normal operation. The Grounding Electrode Conductor (GEC) is the conductor used to connect the system grounded conductor or the equipment to a grounding electrode or to a point on the grounding electrode system.
Other critical terms include the Main Bonding Jumper, which provides the connection between the grounded circuit conductor and the equipment grounding conductor at the service. You should also be familiar with the Intersystem Bonding Termination, a device that allows for the connection of communications systems (like phone or cable lines) to the electrical grounding system. On the exam, terminology is often used to trick students; for instance, the term "grounded" refers to the earth, while "bonded" refers to the connection of parts. Pay close attention to these nuances when reading question stems to avoid selecting the wrong sizing table.
System Grounding: Connecting to the Earth
Grounding Electrode System and Its Components
NEC 250.50 requires all grounding electrodes present at each building or structure to be bonded together to form the grounding electrode system. The exam frequently tests the hierarchy and requirements of these electrodes. The Metal Underground Water Pipe (in direct contact with the earth for 10 feet or more) was historically the primary electrode, but it must be supplemented by an additional electrode, such as a rod, pipe, or plate.
One of the most effective components is the Concrete-Encased Electrode, often referred to as a Ufer Ground. This consists of at least 20 feet of 1/2-inch bare copper or reinforcing steel (rebar) located near the bottom of a concrete foundation or footing that is in direct contact with the earth. Other electrodes include ground rings (at least 20 feet of #2 AWG bare copper), rod and pipe electrodes (must be at least 8 feet long), and plate electrodes (must expose at least 2 square feet of surface to exterior soil). If a rod electrode does not have a resistance to earth of 25 ohms or less, NEC 250.53(A)(2) requires it to be augmented by one additional electrode. Note that for exam purposes, if you add a second rod, you do not need to meet the 25-ohm requirement; the second rod satisfies the code regardless of the final resistance.
Sizing the Grounding Electrode Conductor (GEC)
Grounding electrode conductor sizing is a high-probability exam topic. The GEC is sized based on the cross-sectional area of the largest ungrounded service-entrance conductor or equivalent area for parallel conductors. This calculation is performed using NEC Table 250.66. For example, if a service uses 3/0 AWG copper conductors, the table indicates that a #4 AWG copper GEC is required. If the service uses 500 kcmil copper, the GEC must be 1/0 AWG copper.
There are important exceptions to Table 250.66 that often appear in multiple-choice questions. If the GEC connects to a rod, pipe, or plate electrode, that portion of the conductor is not required to be larger than #6 AWG copper. If it connects to a concrete-encased electrode, it is not required to be larger than #4 AWG copper. Even if the service conductors are 2000 kcmil, the lead to a ground rod never needs to exceed #6 copper. Understanding these "ceiling" sizes is essential for efficiency during the exam, as it prevents you from over-calculating and choosing an unnecessarily large (and incorrect) conductor size.
Installation and Connection Methods for Electrodes
The installation of the GEC and its connection to electrodes must follow strict physical protection rules. According to NEC 250.64, a #4 AWG or larger GEC must be protected if exposed to severe physical damage. A #6 AWG GEC is permitted to run along the surface of the building if it is securely fastened and not subject to physical damage; otherwise, it must be in a raceway (conduit). Any GEC smaller than #6 AWG must be protected by a raceway or cable armor.
Connections must be made using Exothermic Welding, listed lugs, listed pressure connectors, or listed clamps. A critical rule for the exam involves the connection to the water pipe: the GEC must be connected within the first 5 feet of where the pipe enters the building. This ensures that the electrical path is not interrupted by the removal of a water meter or the installation of plastic piping sections later. Furthermore, if you are using a metal raceway to protect a GEC, the raceway must be bonded at both ends to the GEC to prevent the "choke effect," where the high-impedance raceway acts as an inductor during a high-frequency surge, effectively blocking the path to ground.
Equipment Grounding and Effective Fault Paths
Sizing Equipment Grounding Conductors (EGC)
Unlike the GEC, which is sized by the supply conductors, sizing equipment grounding conductors (EGC) is determined by the rating or setting of the overcurrent protective device (fuse or breaker) protecting the circuit. This is handled via NEC Table 250.122. For a 20-ampere circuit, a #12 AWG copper EGC is required. For a 100-ampere circuit, a #8 AWG copper EGC is required.
Exam questions often add a layer of complexity regarding the adjustment of conductor sizes. If ungrounded conductors are increased in size for any reason (such as voltage drop), the EGC must be increased proportionately in circular mil area. For example, if you increase 12 AWG wire to 10 AWG to combat voltage drop on a 20-amp circuit, you must also increase the EGC from 12 AWG to 10 AWG. However, if multiple circuits are installed in a single raceway, only one EGC is required, but it must be sized according to the largest overcurrent device protecting any of the conductors in that raceway. This "largest-device" rule is a frequent point of assessment on the Journeyman exam.
Proper EGC Connection and Splice Methods
The integrity of the EGC depends on the quality of its connections. NEC 250.148 mandates that when circuit conductors are spliced or terminated within a box, all EGCs associated with those conductors must be spliced together or connected to the box. This ensures that removing a device, such as a receptacle, does not break the continuity of the grounding system for downstream loads.
Connection to a metal box must be made using a Grounding Screw (identified by a green color and a hexagonal head) or a listed grounding device. Solder is never permitted as the sole means of connection for grounding conductors because it can melt under high-fault-current heat, breaking the path before the breaker trips. In the case of Isolated Grounding Receptacles, the EGC is insulated and runs directly from the receptacle's grounding terminal to the service or derived system grounding terminal, bypassing the local metal box to reduce electromagnetic interference (noise) for sensitive electronic equipment. On the exam, remember that the metal box still needs to be grounded by a conventional EGC or the raceway system, even if an IG receptacle is used.
Identifying and Fixing Common Grounding Errors
A common error tested on the exam is the "objectionable current" created by multiple connections between the grounded conductor (neutral) and the grounding system. Per NEC 250.24(A)(5), a grounding connection shall not be made to any grounded circuit conductor on the load side of the service disconnecting means, except as permitted for separately derived systems. If the neutral and ground are bonded at a subpanel, current will split between the neutral and the metal raceways/EGCs, creating a dangerous condition where metal enclosures carry normal load current.
Another frequent error involves the use of improper materials. For instance, using a standard drywall screw to attach a grounding lug to a box is a violation; the screw must be a machine screw with at least two threads engaged or a secured nut. Also, ensure you recognize when a raceway is permitted as an EGC. Electrical Metallic Tubing (EMT) and Rigid Metal Conduit (RMC) are generally permitted as EGCs if installed with listed fittings, but in certain high-vibration or healthcare environments, a separate wire-type EGC is often required by code or specification. Identifying these nuances is key to passing the practical application sections of the exam.
Bonding Services, Feeders, and Separately Derived Systems
Main Bonding Jumper and System Bonding Jumper Rules
The connection between the grounded conductor and the equipment grounding conductor at the service is the most critical link in the fault current path. This is the Main Bonding Jumper (MBJ). Its purpose is to ensure that any fault current returning on the EGC can jump over to the service neutral, which then carries the current back to the utility transformer to complete the circuit and trip the breaker. Without the MBJ, the ground-fault current would have no path back to the source, and the breaker would not trip.
Bonding jumper requirements exam questions often focus on sizing. The MBJ is sized using NEC Table 250.102(C)(1), which is based on the size of the largest service-entrance conductor. This is the same table used for sizing the Supply-Side Bonding Jumper. For a Separately Derived System, such as a transformer with no direct electrical connection to the service conductors, a System Bonding Jumper is required. This jumper performs the same function as the MBJ but is located at the source of the derived system (the transformer) or the first disconnecting means. You must know where to locate these jumpers and how to apply the 12.5% rule for very large conductors (over 1100 kcmil copper) where Table 250.102(C)(1) reaches its limit.
Bonding at Service Equipment and Disconnecting Means
Bonding at the service is more stringent than at subpanels because of the high available fault current. NEC 250.92 requires that all non-current-carrying metal enclosures for service conductors be bonded together. This includes the service raceways, cable trays, and the service disconnect enclosure. Standard locknuts are not considered sufficient for bonding at the service. Instead, you must use Bonding Bushings with jumpers or other listed means, such as threaded hubs.
If you have a service with multiple disconnects in separate enclosures, the bonding must be maintained across all of them. The exam may ask about the Supply-Side Bonding Jumper, which is the conductor installed on the supply side of a service or between a transformer and its first overcurrent device. This conductor must be sized according to Table 250.102(C)(1) because it is not yet protected by a branch-circuit or feeder OCPD. It must be rugged enough to carry the full, unrestricted fault current available from the utility or transformer.
Transformers and generators are classified as separately derived systems if the neutral is not solidly connected to the service neutral (often via a 4-pole transfer switch for generators). For a transformer, the System Bonding Jumper must connect the neutral (X0 terminal) to the transformer case and the grounding electrode conductor. This connection can be made at the transformer itself or at the first system disconnecting means, but not both.
For generators, the exam often asks whether the generator is a separately derived system. If the transfer switch switches the neutral conductor, it is a separately derived system, and a system bonding jumper must be installed at the generator. If the neutral is solid (not switched), the generator is not a separately derived system, and the neutral must not be bonded to the generator frame; instead, it relies on the service's main bonding jumper. Misapplying these rules is a common "trick" on the Journeyman exam, as it leads to parallel paths for neutral current.
Grounding and Bonding for Specific Equipment
Grounding Requirements for Ranges, Dryers, and Appliances
Historical code allowed the use of the grounded (neutral) conductor to ground the frames of electric ranges and clothes dryers. However, in modern installations (since the 1996 NEC), this is generally prohibited for new construction. NEC 250.140 requires these appliances to be grounded via an equipment grounding conductor. A 4-wire cord and receptacle (two hots, a neutral, and a ground) are now the standard.
On the exam, you may see questions regarding "existing installations" where a 3-wire cord is used. This is only permitted if the grounded conductor is at least #10 AWG copper and is insulated (unless it is part of Type SE cable and originates at the service). For other appliances, metal frames must be grounded if they are within 8 feet vertically or 5 feet horizontally of ground or grounded objects and are subject to contact by persons. This ensures that a failure in the appliance insulation does not energize the external housing.
All metal raceways, cable armor, and enclosures must be bonded to ensure they do not become energized. For circuits over 250 volts to ground (such as 277/480V systems), the bonding requirements are stricter. NEC 250.97 requires that for these higher-voltage systems, the electrical continuity of metal raceways containing any conductor other than service conductors must be ensured by one of several methods, such as the use of bonding jumpers or threaded hubs.
Standard locknuts (one inside and one outside) are often not sufficient for bonding 277V or 480V circuits where "ringed" knockouts (eccentric or concentric) are used, unless the box is listed for such bonding. If the knockouts are not listed for bonding, a Bonding Jumper must be used around the knockout. This is a critical safety measure because the higher voltage increases the risk of arcing at loose connections during a fault. In the exam, assume that any raceway entering a box with concentric knockouts at 480V requires a bonding jumper.
Special Rules for Hazardous Locations and Healthcare Facilities
In Hazardous (Classified) Locations, the bonding requirements are the most stringent. NEC 250.100 states that regardless of the voltage, the electrical continuity of non-current-carrying metal parts must be ensured by the methods specified for service equipment (250.92). This means you cannot rely on standard locknuts; you must use bonding bushings or threaded connections to prevent any spark that could ignite an explosive atmosphere.
In Healthcare Facilities (NEC 517), specifically in "patient care spaces," the code requires "redundant grounding." This means that the equipment must be grounded by both a metal raceway system (or cable armor) that qualifies as an EGC AND an insulated copper EGC installed within the raceway. This redundancy ensures that even if a conduit fitting vibrates loose, the insulated copper wire maintains the ground path, protecting sensitive patients and medical equipment from leakage current. The exam frequently tests this double-grounding requirement.
Ground-Fault Circuit Interrupter (GFCI) and Arc-Fault (AFCI) Principles
How GFCIs Utilize Grounding Principles for Safety
A Ground-Fault Circuit Interrupter (GFCI) does not actually measure the current in the grounding conductor. Instead, it uses a differential current transformer to monitor the balance between the hot and neutral conductors. If the current going out on the hot wire does not match the current returning on the neutral (within 4 to 6 milliamperes), the device assumes the missing current is leaking to ground—potentially through a person—and trips the circuit.
While a GFCI does not require a ground wire to operate (it will still trip if a person provides the path to ground), the NEC requires that if a GFCI is used to replace a non-grounding type receptacle where no ground exists, the receptacle must be marked "No Equipment Ground." On the exam, remember that GFCIs are designed for personnel protection, whereas circuit breakers are designed for equipment and conductor protection. The GFCI is the final line of defense in the effective grounding strategy.
AFCI Protection and Its Relationship to Circuit Integrity
Arc-Fault Circuit Interrupters (AFCI) are designed to detect unintended electrical arcs, which are a leading cause of house fires. While GFCIs look for leakage to ground, AFCIs look for the specific "signature" of an arc—a high-frequency wave pattern that indicates electricity is jumping through the air between damaged conductors or loose connections.
There are two main types of arcs: series arcs (occurring along a single wire, such as a frayed cord) and parallel arcs (occurring between two different wires or a wire and ground). While an AFCI is not a grounding device per se, its ability to detect "arc-to-ground" faults complements the grounding system. If a hot conductor arcs to a grounded metal box, the AFCI may trip before the current reaches the level needed to trip a standard thermal-magnetic breaker. For the Journeyman exam, distinguish between the two: GFCIs prevent shocks; AFCIs prevent fires.
NEC Mandated Locations for GFCI and AFCI Protection
The NEC is constantly expanding the list of required locations for these devices. GFCI protection is generally required in "wet" or "moist" areas, including bathrooms, kitchens (all receptacles serving countertop surfaces), crawl spaces, unfinished basements, and outdoor locations. A common exam question involves the 10-foot rule for swimming pools or the requirements for commercial kitchens (where all 125V through 250V receptacles 50A or less require GFCI).
AFCI protection (NEC 210.12) is required for most 120V, single-phase, 15A and 20A branch circuits in residential "dwelling unit" rooms, including kitchens, family rooms, dining rooms, bedrooms, and even hallways. Note the exceptions: AFCIs are generally not required in bathrooms or garages, where GFCIs are the priority. Understanding the specific room-by-room requirements is a staple of the Journeyman exam's "Code search" questions.
Applying Grounding and Bonding Rules in Exam Scenarios
Step-by-Step Problem Solving for GEC/EGC Sizing
When faced with a sizing question, the first step is to identify if the question is asking for the GEC (use Table 250.66) or the EGC (use Table 250.122).
- For a GEC: Find the size of the service-entrance conductors. If parallel, add their areas together. Look up the size in Table 250.66. Check for exceptions (e.g., is it a rod or Ufer?).
- For an EGC: Find the size of the fuse or breaker. Look up the size in Table 250.122. If the ungrounded conductors were upsized for voltage drop, calculate the ratio of the increase and apply it to the EGC's circular mil area.
For example, if a 400A service uses two 3/0 copper conductors in parallel per phase, the total area is 167,800 x 2 = 335,600 circular mils. This falls into the "Over 250 through 500" kcmil category in Table 250.66, requiring a #1/0 copper GEC. Mastering these steps ensures accuracy under the time pressure of the exam.
Interpreting Diagrams Showing Grounding Connections
Exam diagrams often depict a service entrance with various bonding jumpers and electrodes. You must be able to identify the Main Bonding Jumper, the Grounded Conductor, and the Grounding Electrode Conductor. Watch for "illegal" connections, such as a neutral-to-ground bond in a subpanel or a GEC connected to a gas pipe (which is prohibited as a grounding electrode per NEC 250.52(B)).
Pay attention to the symbols used for "ground" and "bonded." If a diagram shows a transformer, verify that the system bonding jumper is on the correct side of the first disconnect. If the diagram shows a metal raceway, ensure there is a bonding jumper around any "reduced" knockouts if the voltage is 480V. Visualizing the flow of fault current—from the fault, through the metal enclosure, through the EGC, across the MBJ, and back to the transformer—will help you spot errors in any given diagram.
Code References for Common Grounding and Bonding Questions
Efficiency in using the NEC index is vital. Most grounding and bonding questions will be found in Article 250, but you should also know where to find related rules.
- 250.66: Sizing GEC
- 250.122: Sizing EGC
- 250.102: Sizing Bonding Jumpers
- 250.52: Types of Electrodes
- 250.146: Receptacle Grounding
- 250.148: Continuity of EGCs in boxes
When a question asks about "bonding of piping systems," look at 250.104. For "grounding of separately derived systems," look at 250.30. Being able to flip directly to these sections will save valuable minutes. Always read the "Informing Note" or "Exception" following a rule, as the exam often tests the exception rather than the general rule. This Journeyman Electrician grounding and bonding review serves as your roadmap, but your success depends on your ability to verify these rules within the text of the Code during the test.