National Home Inspector Exam (NHIE) Electrical Systems Summary

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.

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.

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.

Most breaker terminals are made to clamp one wire. When two wires are put under one, one of them may be loose, which can cause overheating and arcing. Inspectors report double taps unless the breaker is listed for two conductors.

Wrong choices

• Two breakers fitted on one bus stab, like a tandem breaker: Listed tandem breakers are allowed in panels designed for them.
• Two electrical panels in one house: Having a subpanel is not a double tap.
• Two ground rods for the service: Two ground rods are common and not a defect.

Breakers protect the wire. Common sizes for copper branch circuits are: 14-gauge on a 15-amp breaker, 12-gauge on a 20-amp breaker, and 10-gauge on a 30-amp breaker. A breaker that is too large lets the wire overheat before it trips.

Wrong choices

• 20 amps: 20 amps is typical for 12-gauge copper.
• 30 amps: 30 amps is typical for 10-gauge copper.
• 40 amps: This is far too large and the wire could overheat.

Solid aluminum wire expands and contracts more than copper and oxidizes at connections. Over time, terminals can loosen, overheat, and start fires. Inspectors report it and recommend evaluation by a licensed electrician familiar with approved repair methods.

Wrong choices

• It carries more current than copper of the same size: Aluminum carries less current than the same size copper.
• It cannot be used on any 240-volt circuits: Stranded aluminum is still widely used for larger 240-volt feeders.
• It attracts lightning: Wire metal type does not attract lightning.

12-gauge copper branch wiring is typically protected at 20 amps. A 30-amp breaker allows more current than the wire can safely carry, so the wire can overheat and start a fire before the breaker trips. This should be corrected by an electrician.

Wrong choices

• The breaker is too small and will trip too often: The breaker is too large, not too small.
• No issue, because 12-gauge is rated for 30 amps: 12-gauge copper is typically limited to 20 amps.
• It causes reverse polarity: Breaker size has nothing to do with polarity.

Receptacles are made so the narrow slot is hot and the wider slot is neutral. When the wires are swapped, devices like lamps may have live parts even when switched off, which is a shock hazard. A plug-in tester shows this condition.

Wrong choices

• The ground wire is missing: A missing ground is called an open ground.
• The receptacle is installed upside down: Mounting direction is not polarity.
• The breaker is turned off: No power is not reverse polarity.

Wire splices must be inside a box with a cover. Open boxes leave live connections exposed to touch and damage and let sparks escape. Inspectors report missing covers and splices outside of boxes.

Wrong choices

• A breaker labeled in the panel directory: Labeling is a good practice.
• A covered junction box that is accessible: Covered, accessible boxes are correct.
• A GFCI receptacle in a bathroom: This is correct protection.

Knob-and-tube wiring runs separate hot and neutral wires on ceramic supports. It has no ground wire, its insulation may be brittle, and it was designed to shed heat to open air, so burying it in insulation can be risky. Many insurers also have concerns. Inspectors recommend evaluation by an electrician.

Wrong choices

• Is the newest type of wiring: Knob-and-tube is very old, used roughly before the 1940s.
• Uses plastic-jacketed cable: It uses single wires on ceramic knobs and tubes.
• Is always GFCI protected: It is not automatically GFCI protected.