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Services & Separately Derived Systems — Texas Journeyman Practice Questions

12 questions · 11% of the NEC Knowledge exam

Worked questions

1. A building has a concrete-encased electrode and qualifying metal underground water pipe. What is the normal 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

Why C is correct

Electrodes that are present and qualify are generally bonded together as one grounding electrode system. Selecting only one or making downstream neutral bonds can leave conductive systems at different potentials and create objectionable current paths.

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 service equipment, what is the purpose of the main bonding jumper?

  • 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

Why B is correct

The main bonding jumper establishes the service bonding connection and the low-impedance fault-current path. Downstream enclosures normally remain isolated from the neutral, and the jumper does not eliminate the grounding electrode conductor.

4. The calculated service load is within the ampere rating, but available fault current exceeds the service breaker interrupting rating. Is the 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

Why D is correct

Normal load and fault duty are separate checks. Service equipment must safely withstand and interrupt the available fault current; grounding-electrode size or labeling cannot increase a breaker’s tested interrupting capability.

5. At service equipment, where is the grounded service conductor intentionally connected to the equipment grounding and bonding system?

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

Why A is correct

The service bonding connection is made at the service disconnecting means under the service bonding rules. Reconnecting neutral and equipment grounding paths downstream can place objectionable current on metal parts.

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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