To understand the electrical panel, service and service equipment such as over current devices, ground fault protection, and branch circuits are dependent the home inspector, the tools & equipment he utilizes, and his/her understanding electrical systems and how they operate & function.
By testing/analyzing branch circuits at outlets can/may allow a home inspector to determine the condition of that branch circuit and make valuable recommendations.
Analyzing electrical service and equipment.
Common yet defective conditions might be:
1: Open Hot. The "hot" wire (usually/typically black) not actually being hot.
2: Open neutral: The white, usually not so white in older home's, the(neutral) wire, is not connected well somewhere.
3: Open Ground: An open is likely often the case of someone never connected a ground wire to the receptacle, or there was no ground to connect.
4: Poor ground impedance.Grounding the electrical service, the electrical system, is to provide a low impedance path for fault or transient currents into the earth.
5: False grounds.
False ground are common during our electrical surveys. A home owner adding an outlet in a bed room mismanages the wire on the outlet.
6: Missing ground.
Missing ground are suspect in older updated homes.
7: Missing ground fault protection.
In short, missing ground fault protection.
A (GFCI) outlet / receptacle is electronic equipment protection device. It protects the occupants from the effects of ground faults which are dangerous.
The National Electrical Code® (NEC® ) has specific ground fault equipment protection requirements in 215.10, 230.95, 240.13 and 517.17. Ground fault relays (or sensors) are used to sense low magnitude ground faults.
8: Low voltage availability under load.
A bad connection or a broken wire somewhere.
9: High ground-to-neutral voltage.
Mis-wired receptacles. 120V receptacles wired incorrectly...