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Plug-In Electrical Testers, continued

Open Neutral

If the neutral is open, a plugged-in tool or appliance should not work. This presents no danger unless the user attempts to work on the tool or appliance while it is still plugged in. Since the hot is still connected, the user could provide a neutral path and get a severe shock. The same applies inside the receptacle — turn off the power at the panel before rewiring.

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If you check the receptacle and the neutral is properly connected, you'll need to trace the wire back toward the panel, looking for a loose connection or a nail that has cut the wire. A loose or partially severed wire can cause a fire. Always leave the power off until you find and fix the problem.

Open Hot

An open hot is immediately obvious: None of the display lights on the tester will light. Turn the circuit off as soon as you've finished making the test; a loose or broken hot can start a fire.

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If there is nothing obviously wrong inside the box, you'll have to look for a loose connection or severed wire somewhere in the circuit.

GFCI Button

Many testers also have a GFCI test button. When the button is pressed, a simulated ground fault is placed on the line. A properly working GFCI will trip (assuming it’s on a grounded circuit). You can also test GFCI-protected receptacles wired downstream from a GFCI receptacle (or circuit breaker). The simulated ground fault at the downstream receptacle should trip the GFCI receptacle.

Although GFCI receptacles will work on two-wire circuits, they can’t be tested with plug-in testers, which work by creating an actual fault to ground. On two-wire circuits you have to use the test button on the GFCI receptacle itself.

Plug-In Tester Limitations

Be aware of what these testers cannot test for:

• False, or “bootleg,” ground: This is where some idiot has jumped the neutral onto the ground connection of the receptacle (see illustration, right). Why? Who knows? It might be an effort to

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fool an inspector into thinking a circuit is grounded when it’s not. This is a very dangerous connection and can be lifethreatening. Assuming something is plugged into that receptacle and turned on, this puts current on the grounding circuit in parallel with the neutral. That means anyone using an appliance anywhere on that branch would be in danger of shock.

• Ground and neutral reversed: This is rare because most people wiring a receptacle know that the ground wire is the bare wire. If it should happen, an appliance plugged into that receptacle will put current flow through the grounding wire instead of the neutral. This can endanger anyone who operates an appliance anywhere on that branch circuit. (It also endangers an electrician who is troubleshooting the circuit.)

• Quality of ground: This is a test to verify that the ground resistance path from the receptacle to the main panel is not only intact but is also a low-resistance path. This can only be done with a more elaborate plug-in tester (see “Advanced Plug-In Tester,” previous page).

• Any combination of defects: If two of the tests share the same indicator light — for example, the open neutral test and the open hot test — you might think there is only an open hot when the neutral is also open. Since the power is off to the receptacle (because of the open hot), there is no way for the tester to light the indicator for the open neutral. The solution is to remedy the open hot, then retest for other faults.

• Check a standard two-prong ungrounded receptacle: For this, you will need a more expensive test device, one with a retractable ground prong.

• Check for voltage drop on the line: Again, this is a job for the professional tester.

Hot and Ground Reversed

An installer would have to be drunk to do this. This could only happen on a circuit with just one receptacle; otherwise, the breaker would immediately trip. Assuming the one receptacle, it's a potentially lethal situation. If an appliance like a clothes washer or electric drill is plugged in, its frame will be hot and will shock anyone that touches it.

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Hot on Neutral with Open Hot

I’ve never encountered this situation and probably never will. It’s basically a reversed polarity situation where the neutral has come loose. Even though the hot is on the neutral side, there is no return path to complete the circuit. Appliances won’t work when plugged into a receptacle wired this way.

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Rex Cauldwellowns Little Mountain Electric in Copper Hill, Va.