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Grounding and bonding

20 original questions. The keyed answer, the article to open, and a short explanation are on the page. Confirm the section in your NEC 2026 book. These items are a sample. The rest of this topic stays in the practice app.

All free sections·Study notes·20-question practice test

1 · Grounding and bonding · NEC Knowledge
The only electrode proposed for a service is a metal underground water pipe, and the grounding electrode conductor was sized from a photo of an old table. What two mistakes are in that plan?
1. A. A metal water-pipe electrode has to be supplemented by another electrode, and the grounding electrode conductor is sized from the service-conductor table in the book, not from a photo of an old edition.Keyed answer
2. B. A water pipe may be the only electrode, and any conductor 14 AWG or larger is a legal grounding electrode conductor.
3. C. The grounding electrode conductor is sized from the largest motor horsepower.
4. D. A supplemental electrode is required only when a ground ring is used.
Article 250 requires a metal underground water-pipe electrode to be supplemented, and it sizes the grounding electrode conductor from the service conductors. An old photo is not that table. Confirm both rules in NEC 2026 before you connect the pipe and call the electrode system done.
Open NEC 2026 250.66
2 · Grounding and bonding · NEC Knowledge
A subpanel is supplied by a feeder that already includes an equipment grounding conductor. Where is the neutral-to-ground bond normally made?
1. A. In the subpanel and again at the service
2. B. At the service equipment, with the grounded conductor kept off the subpanel enclosureKeyed answer
3. C. Only at the last receptacle on the longest branch circuit
4. D. Nowhere. The grounded conductor is never bonded to an enclosure.
The bond that ties the grounded conductor to the equipment grounding path is made at the service. A downstream panel supplied with an equipment grounding conductor keeps the grounded conductor isolated so normal current stays on the neutral. Confirm the main bonding jumper and the subpanel separation in NEC 2026 Article 250. Separate buildings have more rules in that article.
Open NEC 2026 Article 250
3 · Grounding and bonding · NEC Knowledge
A bonding jumper is installed around a water meter. What is that jumper there to do?
1. A. Keep a metal path around the meter when the meter is pulled outKeyed answer
2. B. Carry the normal neutral current of the dwelling
3. C. Replace the service disconnect
4. D. Raise the resistance of the water-pipe electrode
The meter can be removed, and the jumper keeps the piping on both sides connected for bonding. It is not the neutral and it is not a disconnect. Article 250 covers bonding of metal piping and jumpers around equipment that can be taken out. Confirm the section in NEC 2026.
Open NEC 2026 Article 250
4 · Grounding and bonding · NEC Knowledge
A feeder is pulled in EMT. Two set-screw couplings are loose, and one section is interrupted by a short length of PVC with no equipment grounding conductor in the pipe. The helper says the raceway is the equipment grounding path. What fails?
1. A. A metal raceway is an equipment grounding path only when that metal path is continuous. Loose couplings and a PVC gap break it, so a wire-type equipment grounding conductor has to be in the run.Keyed answer
2. B. EMT is never permitted to be an equipment grounding path, even with listed fittings made up tight.
3. C. PVC is a better equipment grounding path than EMT.
4. D. Bond the neutral at both ends of the feeder and omit the equipment grounding conductor.
Article 250 allows a metal raceway to serve as the equipment grounding path when the raceway and its fittings actually form that path. A loose coupling or a plastic insert breaks it. Confirm when a wire-type equipment grounding conductor is required in NEC 2026.
Open NEC 2026 Article 250
5 · Grounding and bonding · NEC Knowledge
The only electrode proposed for a service is a metal underground water pipe. What does Article 250 say about relying on that pipe alone?
1. A. Article 250 requires a supplement. A metal water pipe is not the only electrode.Keyed answer
2. B. The pipe is bonded only if the plumber asks for it.
3. C. The pipe replaces the main bonding jumper.
4. D. A metal water pipe is the only electrode a dwelling is allowed to use.
A metal underground water pipe that qualifies as an electrode is supplemented by another electrode. Article 250 is where that requirement is written. Confirm the supplement in NEC 2026 before you land the grounding electrode conductor on the pipe and stop.
Open NEC 2026 Article 250
6 · Grounding and bonding · NEC Knowledge
This drill says metal gas piping is bonded, and it is not used as a grounding electrode. What does that rule stop you from doing?
1. A. Bonding the gas piping to the electrical system.
2. B. Installing a ground rod at the service.
3. C. Landing the grounding electrode conductor on the gas pipe and calling the pipe the electrode.Keyed answer
4. D. Keeping the equipment grounding conductor with the circuit conductors.
Bonding gas piping puts it at the same potential as the electrical system. Using it as the grounding electrode is a different act, and Article 250 does not treat the gas pipe as that electrode. Confirm both the bond and the electrode list in NEC 2026.
Open NEC 2026 Article 250
7 · Grounding and bonding · NEC Knowledge
The equipment grounding conductor is run with the circuit conductors instead of taking a separate path around the building. Why does Article 250 want it in the same raceway or cable?
1. A. So the fault path stays with the circuit and the impedance stays low enough to open the device.Keyed answer
2. B. So the equipment grounding conductor can be routed outdoors around the building to save wire.
3. C. So the grounding electrode can carry the normal load current.
4. D. So the neutral can be smaller than the ungrounded conductors on every circuit.
A fault path that follows the circuit stays short, and the magnetic field of the outgoing and returning fault current cancels. A long separate path can leave the impedance too high to open the breaker. Confirm the run-with-the-circuit rule in NEC 2026 Article 250.
Open NEC 2026 Article 250
8 · Grounding and bonding · NEC Knowledge
The footing steel and the building steel are tied together in a way that qualifies the structural metal as a grounding electrode. The helper says steel is only structural and leaves it out of the grounding electrode system. What else is that steel?
1. A. A grounding electrode that is present, so it is bonded into the electrode system with the others.Keyed answer
2. B. A permitted grounded conductor for ordinary branch circuits.
3. C. An equipment grounding conductor for a remote building, with no other conductor required.
4. D. A substitute for the service disconnect.
Article 250 treats qualifying structural metal as a grounding electrode. If it is present, it is bonded into the grounding electrode system. Calling it structural only does not remove it. Confirm the electrode list in NEC 2026.
Open NEC 2026 Article 250
9 · Grounding and bonding · NEC Knowledge
An aluminum grounding electrode conductor is planned to leave the soil at a rod and run bare against the masonry into the building. The helper says aluminum is fine anywhere copper is fine. What limit do you check?
1. A. Aluminum grounding electrode conductors are not left in contact with the earth or with masonry. The last length out of the soil needs a different plan.Keyed answer
2. B. Aluminum is required for every grounding electrode conductor.
3. C. Masonry contact is a problem only for copper.
4. D. The limit applies only to conductors smaller than 14 AWG.
Article 250 restricts aluminum grounding electrode conductors where they would contact earth or masonry, or where corrosion is a problem. The run against the foundation fails that limit even if the ampacity would otherwise be fine. Confirm the conductor material rule in NEC 2026.
Open NEC 2026 250.64
10 · Grounding and bonding · NEC Knowledge
A ground ring, a ground rod, and a qualifying metal water pipe are all present at a service. What does Article 250 tell you to do with them?
1. A. Connect each electrode to a different branch circuit.
2. B. Use only the rod and leave the others unconnected.
3. C. Isolate the water pipe from the service enclosure on purpose.
4. D. Bond them into one grounding electrode system.Keyed answer
The electrodes that are present are bonded together so they act as one grounding electrode system. Leaving a qualifying electrode unconnected skips that system. Confirm the bonding requirement in NEC 2026 Article 250.
Open NEC 2026 Article 250
11 · Grounding and bonding · NEC Knowledge
Which statement matches how Article 250 points you at the two different sizing jobs?
1. A. The main bonding jumper follows the service-conductor size. The equipment grounding conductor follows the overcurrent device.Keyed answer
2. B. Both are always 14 AWG copper, with no table.
3. C. The equipment grounding conductor is sized from the service conductor, and the main bonding jumper follows the smallest branch breaker.
4. D. Both are sized from the lighting load in volt-amperes only.
The main bonding jumper is associated with the size of the service conductors. The equipment grounding conductor is associated with the rating of the overcurrent device ahead of it. Both tables are in Article 250. Confirm them in NEC 2026 rather than using one table for both jobs.
Open NEC 2026 Article 250
12 · Grounding and bonding · NEC Knowledge
A transformer creates a separately derived system. Where is the system bonding connection normally made?
1. A. The bond is made at the transformer and again at every subpanel.
2. B. A separately derived system is never bonded.
3. C. The bond is made only at the farthest receptacle.
4. D. The grounded conductor of the derived system is bonded at the transformer or at the first disconnect, not at both.Keyed answer
The system bonding jumper goes in at the source or at the first disconnecting means, and Article 250 does not want that bond repeated downstream. Confirm the single location in NEC 2026 Article 250. Transformer protection itself is Article 450.
Open NEC 2026 Article 250
13 · Grounding and bonding · NEC Knowledge
A feeder to a detached garage is two hots and a neutral. The helper bonds the neutral to the garage can, drives a rod, runs no equipment grounding conductor, and calls the garage a second service. What is the garage actually missing?
1. A. Nothing. A rod turns every outbuilding feeder into a service, and three wires are the service.
2. B. A switched neutral, because the garage must open the grounded conductor.
3. C. A second utility drop, because a feeder to a garage is prohibited.
4. D. An equipment grounding conductor run with the feeder, and an isolated neutral. The rod does not make the feeder a service and does not replace the fault path.Keyed answer
Article 250 keeps the neutral isolated at a feeder-supplied building and requires the equipment grounding conductor back to the service. The electrode is not that conductor. Confirm the separate-building rules in NEC 2026.
Open NEC 2026 Article 250
14 · Grounding and bonding · NEC Knowledge
A concrete-encased electrode is available, and the footing steel stub is still reachable. The helper drives a ground rod and says a rod is the modern replacement, so the stub can be ignored. What electrode did he leave out?
1. A. No electrode. A rod is always the only electrode the article accepts.
2. B. The concrete-encased electrode. When it is present and available, a rod does not take its place.Keyed answer
3. C. The gas pipe, which must replace footing steel.
4. D. The stub, because concrete-encased steel is used only when no rod can be driven.
Article 250 includes a concrete-encased electrode that is present and available. Driving a rod and walking past the stub skips that electrode. Confirm the electrode rules in NEC 2026.
Open NEC 2026 Article 250
15 · Grounding and bonding · Calculations
This drill sizes a copper main bonding jumper from the largest ungrounded service conductor: 2 AWG uses an 8 AWG jumper, 1/0 uses 6 AWG, 3/0 uses 4 AWG, and 250 kcmil uses 2 AWG. The service conductor is 3/0 copper. What jumper do you select?
1. A. 4 AWGKeyed answer
2. B. 6 AWG
3. C. 2 AWG
4. D. 8 AWG
The 3/0 row in the stem calls for a 4 AWG jumper. A larger service conductor would move you down the list to a larger jumper. Confirm the real main-bonding-jumper table in NEC 2026 Article 250. The rows above are a drill, not a copy of the table.
Open NEC 2026 Article 250
16 · Grounding and bonding · Calculations
This drill prints its own copper equipment-grounding-conductor sizes: 20 A uses 12 AWG, 40 A uses 10 AWG, 70 A uses 8 AWG, and 150 A uses 6 AWG. The breaker is 70 A. What size do you select?
1. A. 10 AWG
2. B. 8 AWGKeyed answer
3. C. 6 AWG
4. D. 12 AWG
The 70 A row in this drill calls for 8 AWG copper. On exam day you use the equipment grounding conductor table in Article 250, not this shortened list. The list is printed here so the lookup can be practiced.
Open NEC 2026 Article 250
17 · Grounding and bonding · Calculations
This drill sizes a copper grounding electrode conductor from the largest ungrounded service conductor: 1 AWG uses 6 AWG, 2/0 uses 4 AWG, 4/0 uses 2 AWG, and 300 kcmil uses 1/0. The service conductor is 4/0 copper. What grounding electrode conductor do you select?
1. A. 2 AWGKeyed answer
2. B. 6 AWG
3. C. 1/0 AWG
4. D. 4 AWG
The 4/0 row in the stem calls for a 2 AWG copper grounding electrode conductor. A larger service conductor would move you to a larger grounding electrode conductor. Confirm the real table in NEC 2026 Article 250. The rows above are a drill.
Open NEC 2026 Article 250
18 · Grounding and bonding · Calculations
A fault on a 120 V circuit returns on an equipment grounding path of 0.25 ohm. Other impedance is ignored. Using I = V / R, about how much current flows?
1. A. 30 A
2. B. 240 A
3. C. 480 AKeyed answer
4. D. 120 A
120 / 0.25 = 480 A. That is the current available to open the overcurrent device in this estimate. Article 250 is the equipment grounding path. The stem leaves out source impedance so the division stays on the numbers you were given.
Open NEC 2026 Article 250
19 · Grounding and bonding · Calculations
A 200 A feeder has two conductors per phase, and all of them are in the same raceway. This drill says one equipment grounding conductor, sized for the full 200 A device, is enough when the parallels share a raceway. The drill size is 6 AWG copper. How many 6 AWG equipment grounding conductors go in that raceway?
1. A. 4
2. B. 1Keyed answer
3. C. 3
4. D. 2
One raceway means one equipment grounding conductor under this drill, even though each phase has two conductors. A separate raceway for each parallel set would change the count. Article 250 covers the equipment grounding conductor for the circuit. The count comes from the single raceway in the stem.
Open NEC 2026 Article 250
20 · Grounding and bonding · Calculations
A fault at a water-heater fault returns through three equipment-grounding sections in series: 0.4 ohm, 0.2 ohm, and 0.2 ohm. Other impedance is ignored. Using I = V / R with V = 240, what fault current flows?
1. A. 600 A
2. B. 400 A
3. C. 300 AKeyed answer
4. D. 192 A
The sections add: 0.4 + 0.2 + 0.2 = 0.8 ohm. 240 / 0.8 = 300 A. Using only the first section gives 600 A. The equipment grounding path has to be low enough for the overcurrent device to open. Article 250 is that path.
Open NEC 2026 Article 250

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