EETC Grounding Systems 5 — Questions and Answers
Question 1: What happens to the neutral-to-ground bond in a subpanel (separate building panel)?
- It must be installed the same as the main panel
- The neutral must be bonded to ground using a smaller bonding jumper
- The neutral must be kept isolated from the grounding conductor (Correct answer)
- A main bonding jumper is always required at subpanels
Correct answer: The neutral must be kept isolated from the grounding conductor
At a subpanel, the neutral (grounded conductor) must remain isolated from the equipment grounding conductor to prevent objectionable current on the EGC.
Question 2: Which type of ground fault protection is required on solidly grounded wye services of 150V to 600V to ground with service disconnects rated 1000A or more?
- GFCI protection
- AFCI protection
- Ground fault protection of equipment (GFPE) (Correct answer)
- Differential relay protection only
Correct answer: Ground fault protection of equipment (GFPE)
NEC 230.95 requires ground fault protection of equipment (GFPE) on solidly grounded wye services where the voltage exceeds 150V to ground and the disconnect is rated 1000A or more.
Question 3: A grounding electrode conductor splice, where permitted, must be made using which method?
- Wire nuts approved for the conductor size
- Irreversible compression connectors or exothermic welding (Correct answer)
- Any listed connector rated for the conductor size
- Mechanical set-screw connectors only
Correct answer: Irreversible compression connectors or exothermic welding
NEC 250.64(C) permits splicing of grounding electrode conductors only by irreversible compression-type connectors or by exothermic welding.
Question 4: What is 'step potential' and why is it dangerous?
- Voltage between the top and bottom of a ladder near energized equipment
- The voltage gradient across the earth's surface that can drive current through a person's legs during a fault (Correct answer)
- The voltage difference between two floors of a building
- The potential required to step up voltage in a transformer
Correct answer: The voltage gradient across the earth's surface that can drive current through a person's legs during a fault
Step potential is the voltage difference between two points on the earth's surface separated by one stride, which can cause current to flow through a person's legs during a ground fault.
Question 5: When a metal water pipe is used as a grounding electrode, interior metal water piping beyond 5 feet from the building entrance must be:
- Bonded to the grounding electrode system (Correct answer)
- Replaced with non-metallic piping
- Used as a supplemental electrode only
- Connected directly to the utility ground
Correct answer: Bonded to the grounding electrode system
NEC 250.104(A) requires that interior metal water piping beyond the 5-foot point of entry be bonded to the service equipment enclosure, grounded conductor, or grounding electrode conductor.
Question 6: What is the function of a system bonding jumper in a separately derived system?
- It connects the grounding electrode to the utility transformer
- It bonds the grounded conductor to the supply-side equipment grounding conductor or enclosure at the source (Correct answer)
- It replaces the main bonding jumper at the service entrance
- It connects two separately derived systems together
Correct answer: It bonds the grounded conductor to the supply-side equipment grounding conductor or enclosure at the source
The system bonding jumper, required by NEC 250.30(A)(1), connects the grounded conductor of a separately derived system to the supply-side EGC or enclosure at the system source.
Question 7: According to NEC 250.119, equipment grounding conductors must be identified by which color when insulated?
- White or gray
- Green, green with yellow stripe, or bare (Correct answer)
- Orange
- Blue
Correct answer: Green, green with yellow stripe, or bare
NEC 250.119 requires insulated equipment grounding conductors to be identified by green insulation, green with one or more yellow stripes, or bare copper.
EETC Grounding Systems 5
What happens to the neutral-to-ground bond in a subpanel (separate building panel)?