January, 2018
Inspection News and Views from the American Society of Home Inspectors

Is Polarity Really Important?


All home inspectors use small outlet testers to determine whether an electrical outlet is wired correctly. We are checking polarity: Is power at the narrow slot and neutral at the wide slot? We also check for grounding and other potential faults. These small testers are sometimes fooled by unusual wiring problems, but generally, they work pretty well.

When an outlet has reversed polarity, the black wire supplying power is switched with the white neutral wire. This means that power is at the wide slot in the outlet. Even so, any device plugged into the outlet will work. So, what’s the big deal about documenting polarity?

In the old days, before internal transformers powered most electronic equipment, reversed polarity often resulted in a “buzz” in stereo equipment. It could also make clocks run backward…no, just joking.

The Most Common Reversed Polarity Safety Issue

The most common and serious issue with reversed polarity may occur with a simple Edison-base lamp or fixture. You know the kind: the basic screw-in “A” bulb with the little pull chain or twist switch.

When a lamp is powered with reversed polarity, the neutral line, or the line that should be returning power to the electrical system, is providing electricity to the threaded ring around the bulb. The metal around the bulb is electrified at all times. When the lamp is clicked off, the return line is switched and the lamp goes off, but the ring around the bulb stays electrified. You change the bulb with the light off and if you touch the ring around the bulb—ZAP—ouch! 

Miswiring Can Also Cause Problems
Reversed polarity can result from a miswired outlet or a miswired lamp cord. If the plug on the cord has been replaced and was not installed properly, reversed polarity may result. Take a close look at a lamp cord; one wire will have a raised edge or a color marking for the neutral wire.

On really old outlets, the two outlet slots are identical and there is no ground slot.Those non-polarized outlet slots are not very safe, so it’s a good idea to recommend replacing them. In the old days, lamps also lacked plugs that had a wide and narrow blade, so safety involving polarity was just ignored; back then, homeowners were happy to have any type of power. 

Our job as home inspectors is to identify outlet wiring problems—and yes, polarity is important.

Tom Feiza has been a professional home inspector since 1992 and has a degree in engineering. Through HowToOperateYourHome.com, he provides high-quality marketing materials that help professional home inspectors boost their business. Copyright © 2017 by Tom Feiza, Mr. Fix-It, Inc.
Reproduced with permission.