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PEC: grounding and bonding: board exam questions with solutions

On the RME exam under Philippine Electrical Code, Parts 1 and 2. Try each question before you open its solution.

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Grounding, bonding and lightning protection · Grounding, bonding and surge protection: the two jobs of earth: the same circuits on a live bench, with meters you can move.

Questions

1. How does the PEC define bonding (bonded)?

  1. Permanently joining metallic parts to form an electrically conductive path
  2. Connecting a circuit conductor to the earth through a resistor
  3. Insulating metal enclosures from the circuit conductors
  4. Connecting the neutral to every subpanel enclosure
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Answer: A. Permanently joining metallic parts to form an electrically conductive path

Bonding is the permanent joining of metallic parts to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any current likely to be imposed.

Reference: PEC 2017 Part 1, Art. 1.1 (Definitions: Bonding)

2. An insulated equipment grounding conductor must have an outer finish of which color?

  1. White or gray
  2. Green, or green with one or more yellow stripes
  3. Black
  4. Orange
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Answer: B. Green, or green with one or more yellow stripes

Insulated equipment grounding conductors are identified by a continuous green outer finish, or green with yellow stripes. Bare conductors are also permitted.

Reference: PEC 2017 Part 1, Art. 2.50, Part 2.50.6 (Equipment Grounding Conductors)

3. How is an insulated grounded conductor (the neutral of a grounded system) identified?

  1. Green
  2. Green with yellow stripes
  3. White or gray
  4. Red
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Answer: C. White or gray

The grounded conductor is identified by a continuous white or gray outer finish (or, for larger conductors, other permitted white or gray markings).

Reference: PEC 2017 Part 1, Art. 2.0 (Use and Identification of Grounded Conductors)

4. A subpanel in another room is fed from the main service panel by a 4-wire feeder (two ungrounded, neutral, and EGC). How should the neutral and equipment grounding conductors be terminated at the subpanel?

  1. Neutral and EGCs on the same bar bonded to the enclosure
  2. Neutral bonded to the enclosure and EGC left unconnected
  3. Both connected to a new ground rod only
  4. Neutral on an isolated neutral bar; EGCs on a grounding bar bonded to the enclosure
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Answer: D. Neutral on an isolated neutral bar; EGCs on a grounding bar bonded to the enclosure

The grounded conductor is bonded to the equipment grounding system only at the service (main bonding jumper). Re-bonding downstream puts normal neutral current on enclosures and EGCs.

Reference: PEC 2017 Part 1, Art. 2.50 (Grounding and Bonding)

5. What is the purpose of the effective ground-fault current path required by the PEC?

  1. To carry fault current back to the source with low impedance so the overcurrent device operates quickly
  2. To use the earth as the main return path for fault current
  3. To carry the normal neutral current of the circuit
  4. To limit fault current to a few milliamperes
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Answer: A. To carry fault current back to the source with low impedance so the overcurrent device operates quickly

Equipment must be bonded to form a low-impedance path capable of carrying the maximum ground-fault current back to the source so the OCPD opens. The earth is not an effective ground-fault current path.

Reference: PEC 2017 Part 1, Art. 2.50, Part 2.50.1 (General requirements for grounding and bonding)

6. A single ground rod is driven as the grounding electrode and measures 40 Ω to earth. What does the PEC require?

  1. Nothing more; any single rod is acceptable
  2. It must be supplemented by an additional electrode
  3. The rod must be replaced with a longer one
  4. The service must be ungrounded instead
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Answer: B. It must be supplemented by an additional electrode

A single rod, pipe or plate electrode must be supplemented by an additional electrode unless it has a resistance to earth of 25 Ω or less. 40 Ω exceeds that limit.

Reference: PEC 2017 Part 1, Art. 2.50, Part 2.50.3 (Grounding Electrode System)

7. What is the conductor that connects the system grounded conductor or the equipment to the grounding electrode called?

  1. Equipment grounding conductor
  2. Main bonding jumper
  3. Grounding electrode conductor
  4. Grounded conductor
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Answer: C. Grounding electrode conductor

The grounding electrode conductor connects the grounding electrode(s) to the equipment grounding conductor, to the grounded conductor, or to both.

Reference: PEC 2017 Part 1, Art. 1.1 (Definitions: Grounding Electrode Conductor)

8. A 230 V circuit protected by a 20 A breaker has no equipment grounding conductor; its metal enclosure is connected only to a local ground rod of 25 Ω. The utility system ground is 5 Ω. If the line touches the enclosure, about how much fault current flows, and what happens?

  1. About 46 A; the breaker trips instantly
  2. About 0 A; the rod drains all voltage safely
  3. About 9.2 A; the breaker trips within a cycle
  4. About 7.7 A; the breaker does not trip and the enclosure stays energized
Show the answer and solution

Answer: D. About 7.7 A; the breaker does not trip and the enclosure stays energized

I = 230/(25 + 5) = 7.67 A, far below 20 A, so the breaker never trips and the enclosure rises to about 192 V. This is why the earth cannot serve as the effective ground-fault current path.

Reference: PEC 2017 Part 1, Art. 2.50 (Grounding and Bonding: effective ground-fault current path)

Other topics in the same subjects

PEC Part 1: general requirements · PEC: wiring methods and materials · PEC: branch circuits, ampacity and protection · PEC: special occupancies and equipment

An independent, free reviewer: not affiliated with the PRC or the Boards. Subject weights and passing rules are from the PRC examination programs and the laws (RA 9292, RA 7920); check the current PRC program before you file. Code questions follow the Philippine Electrical Code 2017 Part 1; check them against your own copy of the Code.