Residential Wiring Fundamentals: Grounding and Bonding for Safe Fault Clearing

Grounding vs. Bonding: What Each One Does

Grounding connects parts of the electrical system to the earth (via electrodes). In a home, grounding is mainly about stabilizing voltage to earth and handling surges (like lightning or utility transients). It is not intended to clear most everyday faults by itself.

Bonding connects metal parts together (and to the system grounded conductor at the correct location) so that if a hot conductor faults to metal, the fault current has a low-impedance path back to the source. Bonding is what makes breakers trip quickly during common faults.

A useful way to remember it: bonding is for fault clearing; grounding is for reference and surge control. They work together, but they are not interchangeable.

(1) Purpose of the Equipment Grounding Conductor (EGC)

Low-impedance fault path = fast breaker operation

The equipment grounding conductor (EGC) (bare/green wire, metal raceway, or approved metal sheath) ties non-current-carrying metal parts (boxes, appliance frames, yokes) back to the source so that a line-to-case fault produces a large fault current. A large fault current causes the breaker to trip quickly.

If the fault path is high impedance (loose connection, missing EGC, corroded bond), the fault current may be too small to trip the breaker. The metal can remain energized, creating shock risk and overheating risk.

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What “back to the source” really means

For a breaker to trip, current must return to the transformer/source through a complete loop. In a typical fault to a metal box, the loop is:

• Hot conductor faults to metal box
• Metal box is bonded to EGC
• EGC returns to the service equipment where neutral and grounding are bonded (main bonding jumper)
• Neutral returns to the transformer

The earth is not a reliable fault-return conductor for clearing typical branch-circuit faults. The EGC/bonding path is.

Step-by-step: verifying a low-impedance path (practical checks)

• Power off the circuit at the breaker and verify de-energized.
• Inspect that the EGC is present in the cable/raceway and is terminated under the correct terminal/screw (not loose, not under insulation).
• Confirm metal boxes are bonded (see bonding methods below).
• Look for loose wirenuts, paint under bonding points, or missing bonding bushings/locknuts where required.
• If you have an approved continuity tester/meter and are qualified to use it, check continuity from the metal box/yoke to the panel’s grounding bar (with power off). Continuity alone doesn’t prove low impedance, but an open reading is a clear problem.

(2) Bonding Concepts That Prevent Shock and Fire

Bonding metal boxes and raceways

Any metal that could become energized must be bonded so it cannot “float” at a dangerous voltage. Common bonding points include:

• Metal device boxes
• Metal conduit/raceway systems
• Metal cable armor/sheath (when listed as an EGC)
• Metal enclosures of equipment (furnace, range, dishwasher, etc.)

Bonding is typically done by connecting the EGC to the box with a green bonding screw or a listed bonding clip, and by ensuring the device yoke is bonded (either through the mounting method or a grounding pigtail).

Bonding the service neutral where required (and only where required)

In most residential systems, the neutral (grounded conductor) is bonded to the equipment grounding system at the service disconnect/main service equipment using the main bonding jumper. This single connection is intentional: it establishes a reference to ground and provides the return path for fault current from EGCs to the source.

Downstream of the service disconnect (in subpanels and branch circuits), neutrals and grounds must be isolated from each other. Neutrals land on an insulated neutral bar; EGCs land on a grounding bar bonded to the enclosure.

Avoiding improper neutral-ground connections downstream

Improper neutral-to-ground connections in subpanels or devices create parallel return paths. That can put normal neutral current onto metal parts (conduit, boxes, appliance frames), causing:

• Shock risk from touch voltage on metal parts
• Nuisance tripping of GFCIs
• Overheating of unintended current paths (like a loose locknut or corroded conduit joint)
• Confusing troubleshooting symptoms (intermittent voltage on grounds)

Common mistake: installing the green bonding screw or bonding strap in a subpanel, tying neutral to the metal can. Another common mistake is tying neutral and ground together in a receptacle box to “fix” an open ground (bootleg ground), which is unsafe and misleading.

(3) Grounding Electrode System (GES) Overview

What the grounding electrode system is (and isn’t)

The grounding electrode system (GES) is the set of electrodes connected to the service grounding electrode conductor (GEC): ground rods, concrete-encased electrodes (UFER), metal underground water pipe (when present and qualifying), and other electrodes. The GES helps with:

• Stabilizing system voltage to earth
• Dissipating lightning and surge energy
• Reducing voltage gradients around the building during certain events

It is not intended to be the primary fault-clearing path for branch-circuit faults; that job belongs to the EGC/bonding network back to the source.

Ground rods (conceptual and practical notes)

Ground rods are common electrodes. Key practical considerations:

• They must be connected with an appropriately sized grounding electrode conductor and listed clamps.
• Connections must be protected from physical damage and corrosion.
• Multiple rods may be required depending on local rules and measured resistance requirements (where applicable).

UFER / concrete-encased (footing) electrodes (conceptual)

A concrete-encased electrode (often called a UFER) uses reinforcing steel or a conductor encased in concrete in contact with earth. It typically provides a very effective connection to earth because of the large contact area and the moisture-retaining properties of concrete.

Metal water pipe bonding

If a metal underground water pipe qualifies as an electrode, it must be connected into the GES. Separately, interior metal water piping is typically bonded to ensure it cannot become energized and to maintain continuity across sections that might be interrupted by repairs.

Continuity considerations: water meters, filters, softeners, dielectric unions, and sections of plastic pipe can break electrical continuity. Where continuity could be interrupted, a listed bonding jumper is used to maintain bonding around the nonconductive section.

Step-by-step: checking bonding continuity across plumbing interruptions (visual method)

• Locate the bonding connection to the metal water piping (often near where the pipe enters the building).
• Identify any nonmetallic sections or devices (meter, filter, softener, dielectric union).
• Look for a bonding jumper that connects metal-to-metal around the interruption.
• Confirm clamps are listed for the purpose and tight on clean metal (not on paint or corrosion).

(4) Practical Device-Level Grounding and Bonding

Green screws and grounding pigtails

In a metal box, the EGC should be bonded to the box with a green grounding screw (or listed clip) and typically continued to the device with a pigtail. This ensures the box remains grounded even if the device is removed.

EGC from cable ----+---- pigtail to device green screw/yoke
                  |
                  +---- pigtail to metal box (green screw)

Step-by-step: bonding a metal box and receptacle (typical method)

• Turn power off and verify.
• Join all EGCs in the box with a wirenut (or listed connector) and add two pigtails if needed: one to the box, one to the device.
• Attach the box pigtail to the threaded grounding hole using a green grounding screw (tight, metal-to-metal contact).
• Attach the device pigtail to the receptacle’s green ground screw.
• Fold conductors neatly to avoid loosening connections when installing the device.

Self-grounding receptacles

Self-grounding receptacles have a spring clip or feature that bonds the yoke to a properly grounded metal box through the mounting screws. They can reduce the need for a separate grounding pigtail to the device when the metal box is reliably grounded and the receptacle is listed as self-grounding.

Practical cautions:

• If the box grounding is questionable (loose conduit fitting, painted surfaces, old cable armor issues), use a grounding pigtail rather than relying on self-grounding.
• Self-grounding does not fix an open EGC upstream.

Bonding jumpers for continuity

Bonding jumpers are short conductors used to ensure metal parts remain electrically continuous when a fitting or device might not provide a reliable bond. Examples include:

• Bonding around a water meter or filter
• Bonding around flexible metal conduit sections where required
• Bonding bushings/jumpers on certain service raceways

Use only listed parts and methods appropriate to the installation.

(5) Troubleshooting Patterns and What Testers Indicate

Basic plug-in receptacle testers can quickly indicate common wiring faults. They are screening tools: they do not prove that the grounding path is low impedance, and they can be fooled by certain miswirings (especially bootleg grounds). Use them to identify patterns, then verify by inspection and proper testing methods.

Open ground

What it is: the receptacle ground is not connected to the equipment grounding system (missing EGC, broken ground wire, loose ground connection, unbonded metal box).

Common causes:

• Ground wire not connected to device/box
• Broken ground pigtail or loose wirenut
• Nonmetallic box with no EGC present
• Old two-wire cable with no grounding conductor

Typical tester indication: “Open Ground” (pattern varies by tester brand).

Step-by-step: isolate the likely location

• Test multiple receptacles on the circuit to find the first location where ground disappears.
• De-energize and open the first failed receptacle and the last good one; inspect ground splices and terminations.
• In metal boxes, confirm the box is bonded (ground screw/clip) and that the device ground is connected.

Bootleg ground (false ground)

What it is: someone ties the receptacle ground terminal to the neutral terminal (or neutral conductor) in the receptacle box to make a tester show “grounded.” This is unsafe because it can put neutral current on metal parts and can energize the grounding system if the neutral opens upstream.

Why it’s dangerous:

• If the neutral opens, the “ground” can rise to line voltage through loads.
• Metal boxes and appliance frames can become energized.
• It defeats the purpose of separating neutral and ground downstream of the service.

Typical tester indication: often shows “Correct” even though it is wrong. Some advanced testers can flag it, but many basic ones cannot.

Practical clue: a three-prong receptacle installed on an ungrounded two-wire cable, especially in older areas, is a red flag. Visual inspection may reveal a jumper between neutral and ground screws.

Reversed polarity

What it is: hot and neutral are swapped on the receptacle. The receptacle may still power loads, but the screw shell of lamps and internal parts of some appliances can be energized in unexpected ways.

Typical tester indication: “Hot/Neutral Reversed.”

Step-by-step: correction approach

• De-energize and verify.
• Confirm the hot conductor is on the brass-colored terminal and neutral on the silver-colored terminal (for typical receptacles).
• Check for miswired feed-through connections if multiple cables are in the box.

Open neutral (often confused with other faults)

What it is: the neutral conductor is broken/loose. Loads may not work, or you may see strange voltage readings due to backfeed through connected loads.

Typical tester indication: many testers show “Open Neutral.” Some conditions can also produce confusing patterns depending on what is plugged in.

Practical approach: look for loose neutral splices, backstabbed connections that have failed, or a loose neutral termination at an upstream device.

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