Finding an open ground.
An open ground refers to a break or "opening" in the ground wire circuit. The ground wire (technically called the equipment ground( is the bare copper or green wire you see in most outlets. It corresponds with the rounded slot in a receptacle and the round prong on a three-prong plug. The ground wire circuit is supposed to form a continuous path back to the main electrical panel and then literally to the earth.
But if there's a bad connection in the ground wire system or a broken or missing wire, the grounding circuit is "open." Electrical current can;'t flow through it, and the safety system won't work.
Here's the rub: You won't notice that the grounding circuit isn't working in normal day-to-day living. It won't interfere with the toaster, the TV or a table lamp. But you could get a dangerous shock if it's not there. (See "How Does an Equipment Ground Work?" for more details.)
In this article we'll show you how to find and correct this common problem.
HOW TO FIND AN OPEN GROUND
The best way to detect an open ground is with a receptacle tester ($7 to $20 at most hardware stores and home centers). See July/Aug. '97, p. 70, for more details about these testers. Simply plug it into the receptacle and the combination of lights indicates whether the equipment ground is working. Exception: The tester won't detect an open ground when the ground terminal on the receptacle is directly wired to the neutral terminal. Pros frequently report finding this wiring error. If you find it once, it may occur in other places in your home. The only way to find out is to shut off the power to the receptacles and pull them out one by one.
HOW TO TRACE AND FIX THE PROBLEM
If the tester indicates an open ground, turn off the power to the circuit at the main panel (the tester light will go out), and remove the receptacle. Check for loose or disconnected ground wires. While the problem occurs most often at the receptacle that shows the problem, the bad connection could be elsewhere in the system. Don't hesitate to call in an electrician to tract it down.
In reality, open grounds are most common in older homes where many folks replaced the old two-slot receptacles with the modern three-slot types. Old receptacles had only two slots, because pre-1958 homes rarely had ground wires. But to conveniently handle the wave of new three-prong plugs, many owners of old homes upgrade their receptacles to the three-slot type. But they didn't bother to upgrade the old electrical system to include an equipment ground. In this situation your tester will indicate an open ground, and you won't find a ground wire when you pull out the receptacle.
In this case, you have three good options:
1. GFCI solution. Install a GFCI ($8). A GFCI (ground-fault circuit-interrupter) delivers even better shock protection than the equipment ground. And it operates dependably without the equipment ground. On the downside, they're expensive. And they are not meant to substitute for proper grounding (Option 3) of appliances that are required to be grounded by the National Electrical Code or the appliance manufacturer, such as refrigerators, air conditioners, laundry equipment and sump pumps.
2. Ungrounded receptacle solution. Install an old-style, two-slot receptacle. It's occasionally a nuisance for three-prong plugs, but if you're only plugging in lamps, radios and other devices that only have two-prong plugs, it's all you need.
3. New cable solution. Run a new cable that has a ground wire from a junction box that already contains a ground or from the main panel. For information about running new cables, see July/Aug. '96, p. 63. This option can turn into a big job; you might have to break through a wall or ceiling to get the new cable in. However, it's the only good solution if you intend to plug in a computer or other device that contains a microprocessor. These devices require a ground wire to operate well.
OPEN GROUND IN STEEL GROUNDING SYSTEMS
Open grounds frequently occur in electrical systems where the wiring is run in steel conduit or armored cable, since the steel itself can be part of the grounding path. In these systems, an open ground is usually caused by a loose connection. Loose connections are often difficult to trace, because the walls and ceilings hide most of the system. But the breaks usually occur where vibrations have loosened a screw or loosened a clamp. Check the connections at the electrical box that shows the open ground first.
If the bad connection isn't at the box, check any expose rigid conduit elsewhere, like in a basement. Steel conduit always looks like a tempting clothes rack, and the added weight often loosens connectors at the junction boxes.
Still baffled? Call in a pro to trace the problem.
A receptacle tester will help you sniff out this common wiring hazard.
Usually there's a simple, safe fix.
1 Tester shows open ground
Simply plug the tester into the receptacle and the combination of lights indicates whether the equipment ground is working. You can test all the receptacles in your home in about 15 minutes. (Don't forget the one behind the bookcase!)
2 GFCI solution when no ground is present
Install a GFCI when an equipment ground isn't present. Be sure to connect the power supply wires to the "line" terminals. (The "load" terminals are covered by a warning label.) You might have to install a new, larger box if the old one isn't large enough. Label the GFCI "NO EQUIPMENT GROUND" as required by code. Medical equipment and devices containing microprocessors might not work if plugged into it.
3 Ungrounded receptacle solution when no ground is present
Install an old-style, two-slot receptacle ($1.50) This is the easiest, least expensive solution, but isn't suitable if you want to insert three-prong plugs.
4 Reconnect armored cable when metal acts as ground
Pull armored cable back up into the clamp, if it has fallen out. The ground path runs through the steel. You can usually give a stubborn cable an additional lift by sliding a screwdriver between the box and wall and prying upward. In some cases, you might have to break into the wall.
Retighten the clamp with a screwdriver. make sure the screw that clamps the copper equipment ground to the metal box is tight as well.
6 Reconnect loose conduit when metal acts as ground
Reconnect loose conduit by screwing the clamping nut back on. Tighten the nut by tapping one edge with a hammer and screwdriver.
How does an equipment ground work?
The grounding system is an interconnected network of wires and/or metal that's designed to siphon off electrical leaks from hot and neutral wires that have accidentally broken loose, worn through their insulation, or were connected wrong. These bare copper or green wires are technically called the "equipment" grounds to keep them distinct from the neutral (white) wires, which are also grounded at the main panel.
The equipment ground picks up the stray current and conducts it back to the main panel, eventually causing a circuit breaker to trip or a fuse to burn out. The shutdown alerts you to an electrical problem, with in your electrical system itself or in a plugged-in device.
Most homes built before 1958 didn't have this safety feature,and this situation is shown in Photos 1 through 3.
Although it's tempting, don't use those three-prong to two-prong adapters. In effect, they usually bypass the ground wire safety system and increase the chance of receiving a lethal shock. Electrical devices and extension cords whose plugs have the third, round prong broken off are equally risky.
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|Title Annotation:||common wiring hazard; includes related article on how an equipment ground works|
|Publication:||The Family Handyman|
|Date:||Sep 1, 1997|
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