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Services & Separately Derived Systems — Texas Journeyman Practice Questions

12 questions · 11% of the NEC Knowledge exam

Worked questions

1. A new building has both a qualifying concrete-encased electrode and qualifying metal underground water pipe, with both electrode connections accessible before concealment. Under the general grounding-electrode-system rule in 2026 NEC 250.50, what is the required treatment?

  • AUse only the concrete electrode and cut the water-pipe bond
  • BUse only the water pipe and isolate the concrete electrode
  • Bond both into the grounding electrode system
  • DBond each electrode to a different downstream neutral

Where to look it up

https://www.nctcog.org/getContentAsset/662260f2-2502-4ea3-b6fb-794bdd432cc1/dfc3d011-8f63-43f6-9ed8-4b444333a1d0/RCCC-PPT_2026_04-28_External.pdf?language=en-US

Why C is correct

C, bond both into one grounding electrode system. Both qualifying electrodes are present; choosing only one does not satisfy the rule. Bonding each to a different downstream neutral is not an alternative to forming that electrode system. This question concerns accessible electrodes in new construction, not the treatment of inaccessible concrete reinforcement in an existing building. Source: NCTCOG, April 28, 2026 Regional Codes Coordinating Committee presentation, PDF page 27, unchanged first paragraph of 250.50: https://www.nctcog.org/getContentAsset/662260f2-2502-4ea3-b6fb-794bdd432cc1/dfc3d011-8f63-43f6-9ed8-4b444333a1d0/RCCC-PPT_2026_04-28_External.pdf?language=en-US . The separately underlined North Texas proposal about an electrode covered before inspection is not applied here.

2. A transformer secondary is a separately derived system. Where must its grounding and bonding arrangement be established?

  • At the source or permitted first disconnect
  • BBy bonding neutral to ground at every downstream panel
  • COnly at the primary service disconnect
  • DNowhere if the primary has an equipment ground

Why A is correct

A separately derived secondary needs its own system bonding and grounding connection at a location permitted by the applicable rule. Repeated downstream bonds create parallel neutral paths, while primary grounding does not establish the secondary reference.

3. At the service disconnect of a solidly grounded 120/240-volt, single-phase dwelling service, what is the purpose of the main bonding jumper under the 2026 NEC?

  • AIt replaces the grounding electrode conductor
  • It bonds the service neutral to grounding components
  • CIt isolates the service enclosure from ground
  • DIt carries normal neutral current to every downstream enclosure

Where to look it up

https://fasttraxsystem.com/grounding-vs-bonding/ ; https://www.dli.mn.gov/sites/default/files/pdf/eli_inspection_checklist-2026NEC.pdf

Why B is correct

B. The main bonding jumper connects the grounded service conductor (neutral) to the service enclosure and equipment grounding path. That connection helps complete the effective path for a line-to-metal fault back to the source so the protective device can operate. It does not replace the grounding electrode conductor, isolate the service enclosure, or make downstream enclosures normal neutral-current paths. This is the service bond, not a separately derived system bond. Sources: Paul Abernathy, Grounding vs Bonding in the 2026 NEC, sections on the main bonding jumper, service bonding and downstream neutral bonds: https://fasttraxsystem.com/grounding-vs-bonding/ ; Minnesota DLI, 2026 NEC residential inspection checklist, page 8, items 066 and 067: https://www.dli.mn.gov/sites/default/files/pdf/eli_inspection_checklist-2026NEC.pdf

4. Under 2026 NEC 110.9 and 110.10, a fully rated service installation has a calculated load within the service breaker’s ampere rating, but the available fault current at its line terminals exceeds its interrupting rating at the circuit voltage. No series-rated combination is used. Is this installation acceptable?

  • AYes; load current is the only rating that matters
  • BYes; a larger grounding electrode fixes the interrupting rating
  • CYes; adding a warning label increases breaker capacity
  • No; adequate fault-current ratings are required

Where to look it up

https://www.mikeholt.com/newsletters.php?action=display&letterID=3022

Why D is correct

No. The breaker’s interrupting rating must cover the available fault current at its line terminals at the circuit voltage; an adequate load-current rating does not satisfy that separate requirement. Equipment short-circuit ratings must also be adequate. A larger grounding electrode or a warning label cannot raise those ratings. This question specifies a fully rated installation and does not evaluate a series-rated combination. Source: Mike Holt, General Requirements, based on the 2026 NEC, Ratings (110.9 and 110.10). https://www.mikeholt.com/newsletters.php?action=display&letterID=3022

5. A solidly grounded 120/240-volt, single-phase dwelling service has its main service disconnect in one enclosure. Under the 2026 NEC, where does the main bonding jumper connect the service neutral to the enclosure and equipment grounding system?

  • At the service disconnecting means as permitted
  • BAt each receptacle grounding terminal
  • CAt the farthest branch-circuit outlet
  • DAt every downstream panelboard

Where to look it up

https://fasttraxsystem.com/grounding-vs-bonding/ ; https://www.dli.mn.gov/sites/default/files/pdf/eli_inspection_checklist-2026NEC.pdf

Why A is correct

A. The service bond is at the service disconnecting means in this installation. The main bonding jumper connects the service neutral, enclosure and equipment grounding path there. It is not repeated at receptacles, the farthest branch outlet, or every downstream panel. Downstream feeder panels keep the neutral isolated from the enclosure and equipment grounding conductors so ordinary neutral current does not divide onto those metal paths. The question concerns this service bonding point, not every permitted grounding electrode conductor connection location or a separately derived source. Sources: Paul Abernathy, Grounding vs Bonding in the 2026 NEC, sections on the main bonding jumper, service bonding and downstream neutral bonds: https://fasttraxsystem.com/grounding-vs-bonding/ ; Minnesota DLI, 2026 NEC residential inspection checklist, page 8, items 066 and 067: https://www.dli.mn.gov/sites/default/files/pdf/eli_inspection_checklist-2026NEC.pdf

6. Field documentation shows available fault current greater than the service equipment short-circuit rating. What is required before energizing?

  • AReplace only the panel directory
  • Increase equipment rating or reduce fault current by an approved design
  • CAdd warning tape to the service raceway
  • DIncrease the normal-load ampacity label

Why B is correct

Equipment must be suitable for the available fault current. Labels do not provide withstand capability; the design must use adequately rated equipment or an engineered, permitted method that limits the fault exposure.

5 more in the bank

Answers and explanations for these are in the app.

  • A building has several service disconnects scattered through separate rooms without a permitted arrangement. What should be evaluated?
  • Service conductors enter a building and run a long distance before reaching the service disconnect. What is the central code concern?
  • A building has several permitted service disconnects. What arrangement is generally required?
  • A new one-family dwelling service is being installed. What protection must be provided for the dwelling electrical system?
  • Where must the required emergency disconnect for a new one-family dwelling be located?

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