Do you trust your receptacle tester?

[Greg Fretwell]

There was an interesting article in IAEI news this month about new ideas and marketing them but the thing that grabbed my attention was a couple ways a receptacle could have a fatal wiring flaw and still test OK or marginally OK with the typical tester.
One is a 2 wire system with a bootleg ground and reverese polarity . The box and any attached 3 wire equipment would be 120v above ground but the 3 light tester would be happy.
Number 2 is a 2 wire system with the ground pin pigtailed to an ungrounded box (or simply connected via the yoke) and a ground fault. The tester would simply show reverse polarity.

You can see how this could actually happen in one house.
The guy gets the reverse polarity in #2, he switches wires in #2 (that feeds #1 and now both test normal. He traded #2 fatal condition for #1.

[gbeaumont]

Hi Greg,

which one

Regards

Gerry

[Greg Fretwell]

All of them will be tricked by these problems unless you use the adapter and a known good ground. That is the "idea" this guy is trying to develop, a tester that finds this problem.

[Paul W. Abernathy]

Greg,

Is this part of the article you are speaking of...

In this case, however, the white wire was now energized at 120 V and thus the jumper wire energized all of the following at 120 V: the grounding terminals, the device mounting yoke, the wallplate screws, and all metal in contact. The black wire and terminal became the grounded circuit conductor and were connected to ground at the service.

The electrician tested the installation with a listed outlet circuit tester of the three-lamp type, and it indicated a correct installation. A plumber plugged a three-wire trouble light with metal lamp guard into the GFCI receptacle, crawled under the house to do plumbing, and was electrocuted by contact with the metal lamp guard.
It should be noted that the GFCI was doing its job. The GFCI function was being bypassed by the jumper.

As I investigated the accident, I was initially surprised that the outlet circuit tester showed that all was okay. As we look at the conditions and the construction of all of these three-wire circuit testers, we see that all listed, three-lamp outlet circuit testers would have shown that all was okay.

All of these testers have an indicating light between the hot and the grounded circuit conductor blades, that we will call light 1, a light between hot and the equipment grounding blades, that we will call light 2, and a light between the grounded circuit conductor and the equipment grounding blades, that we will call light 3 (see figures 1 and 2).

It doesn’t take a combination of a two-wire circuit, reversed polarity, and a jumper, intentional or unintentional, to cause serious unsafe signals from these testers. Let’s assume that a house has only two-wire circuits, correctly wired, black-to-black, and white-to-white. Section 406.3(D)(3) of NEC-2005 permits all the two-wire receptacles in the house to be replaced by three-wire receptacles, when protected by GFCIs and properly marked.

There are lots of scenarios, and I’m sure our inspectors can give us some others. At the Eastern Section meeting this year, I learned of a beaut. It seems that a small New England town with many nice decades-old Victorian homes built before equipment grounding conductors were required has most of its homes with two-wire branch circuits having reversed polarity.

The white wire is energized at 120 V and the black wire is the grounded circuit conductor! It turns out that the authority having jurisdiction (AHJ) way back then believed that the color white was more appropriate as the hot conductor and black was better as the grounded circuit conductor!