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National Home Inspector Exam (NHIE) · Home Inspection (All Domains)

National Home Inspector Exam (NHIE): Electrical Systems Concepts

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Overview

This chapter follows electricity from the utility wires to the outlets. It covers the service entrance, the main panel, branch circuits, grounding and bonding, and the special protective devices called GFCIs and AFCIs. Electrical findings are often safety items, so clear reporting matters.

Overhead service wires need enough clearance so people cannot touch them. Under the National Electrical Code they are typically at least 10 feet above finished grade and walkways. At the panel, the inspector checks for proper working space, matching wire and breaker sizes, double-tapped breakers, scorching, and missing covers or knockouts.

Wire size must match the breaker. In common practice, 14-gauge copper is protected at 15 amps, 12-gauge at 20 amps, and 10-gauge at 30 amps. GFCIs protect people from shock in wet areas, while AFCIs reduce fire risk from arcing in living areas. Test them where safe and note any that do not trip.

Key concepts

  • Service drop clearance

    Under the National Electrical Code, overhead service wires are typically at least 10 feet above finished grade, sidewalks, and areas reached only by people on foot. Higher clearances apply over driveways and streets.

    Memory tip10 feet is the minimum over walking areas.

    Source: National Electrical Code (NFPA 70) · as of 2023

  • Panel working space

    Under the National Electrical Code, the space in front of a panel is typically at least 30 inches wide, 36 inches deep, and 6 1/2 feet high, kept clear of storage.

    Memory tipThink 30 wide, 36 deep: room to stand and work safely.

    Source: National Electrical Code (NFPA 70) · as of 2023

  • Wire size and breaker size

    For copper branch wiring the common limits are: 14 AWG on 15 amps, 12 AWG on 20 amps, and 10 AWG on 30 amps. A breaker too large for its wire lets the wire overheat before the breaker trips.

    Memory tipSmaller gauge number = thicker wire = more amps allowed.

    Source: National Electrical Code (NFPA 70) · as of 2023

  • Double tap

    Two wires under one breaker screw that is made for only one. It can loosen and overheat. Some breakers are listed for two wires; most are not.

    Memory tipTwo wires, one screw: report it unless the breaker is labeled for it.

  • GFCI

    A ground-fault circuit interrupter cuts power when current leaks to ground, protecting people from shock. Under the National Electrical Code it is typically required in bathrooms, garages, outdoors, crawlspaces, basements, kitchens, laundry areas, and near sinks.

    Memory tipGFCI = people protection in wet or damp places.

    Source: National Electrical Code (NFPA 70) · as of 2023

  • AFCI

    An arc-fault circuit interrupter detects dangerous sparking in wiring and shuts the circuit off to help prevent fires. Under the National Electrical Code it is typically required for most living-area circuits such as bedrooms, living rooms, and kitchens.

    Memory tipAFCI = fire protection in living spaces.

    Source: National Electrical Code (NFPA 70) · as of 2023

  • Grounding and bonding

    Grounding connects the system to the earth; bonding ties metal parts together so a fault trips the breaker. Neutral and ground wires are joined only at the main service; in subpanels they are kept on separate bars.

    Memory tipNeutrals and grounds together in a subpanel is a defect.

    Source: National Electrical Code (NFPA 70) · as of 2023

Often tested

  • Check that each breaker matches the wire it protects.
  • Report double taps, scorching, open knockouts, and missing panel screws.
  • Test GFCIs where safe; note required locations without protection.
  • Do not confuse GFCI (shock) with AFCI (fire).
  • Panels with known problem histories should be referred to an electrician.

Easy to confuse: GFCI vs. AFCI

ItemGFCIAFCI
Main purposeProtects people from shockHelps prevent fires from arcing
Typical locationsWet and damp areas: baths, kitchens, basements, garages, outdoorsLiving areas: bedrooms, living rooms, kitchens
What it sensesCurrent leaking to groundSparking patterns in the wiring

3 sample questions

Verified practice questions from this unit.

Practice questionReviewedHome Inspection (All Domains) › Electrical Systems★★★★★

Question 1. Under common model codes, which location typically needs GFCI protection for its 125-volt receptacles?

  1. ① Clothes closets
  2. ② Hallway ceiling lights
  3. ③ Bedrooms
  4. ④ Bathrooms
▼ Show answer and explanation▲ Hide answer and explanation

Answer: ④ Bathrooms

Key point: GFCI: bathrooms, kitchens, garages, outdoors, wet areas

GFCI (ground-fault circuit interrupter) protection is required where water and electricity are likely to meet. Common locations include bathrooms, kitchen countertops, garages, outdoors, crawlspaces, unfinished basements, laundry areas, and near sinks.

Wrong choices

  • Bedrooms: Bedrooms commonly need AFCI protection, not GFCI.
  • Hallway ceiling lights: Hallway lighting is not a typical GFCI location.
  • Clothes closets: Closets are not a typical GFCI receptacle location.
Practice questionReviewedHome Inspection (All Domains) › Electrical Systems★★★★★

Question 2. What does a GFCI device mainly protect against?

  1. ① Fires caused by arcing in the wiring
  2. ② Electric shock from current leaking to ground
  3. ③ Power surges from lightning
  4. ④ Overloaded circuits
▼ Show answer and explanation▲ Hide answer and explanation

Answer: ② Electric shock from current leaking to ground

Key point: GFCI protects people from shock

A GFCI compares the current going out on the hot wire with the current coming back on the neutral. If a small amount (about 5 milliamps) is missing, it may be flowing through a person to ground, so the GFCI shuts off power quickly to prevent a serious shock.

Wrong choices

  • Fires caused by arcing in the wiring: That is the job of an AFCI.
  • Power surges from lightning: Surge protectors handle surges.
  • Overloaded circuits: Overloads are handled by breakers and fuses.
Practice questionReviewedHome Inspection (All Domains) › Electrical Systems★★★★★

Question 3. An AFCI device is mainly designed to reduce the risk of:

  1. ① Water heater overheating
  2. ② Shock in wet locations
  3. ③ Fires caused by arcing faults
  4. ④ Low voltage
▼ Show answer and explanation▲ Hide answer and explanation

Answer: ③ Fires caused by arcing faults

Key point: AFCI protects against arcing fires

An AFCI (arc-fault circuit interrupter) senses the electrical pattern of arcing, such as from a damaged cord or loose connection, and shuts off the circuit before a fire can start. AFCIs are commonly required for bedroom and living area circuits.

Wrong choices

  • Shock in wet locations: That is the job of a GFCI.
  • Low voltage: AFCIs do not correct voltage.
  • Water heater overheating: Water heaters have their own high-limit controls.
Practice 5 questions from this unit →