Grounding an Old Receptacle

A properly grounded system ties each device, appliance, and fixture back to the service panel with a separate grounding conductor (the bare copper or green insulated copper wire). It’s unrealistic to attempt this with an old electrical system unless you’re replacing it (in which case, the grounding would be part of replacing the system). You also could install a GFCI in place of an existing, two-wire receptacle. The National Electrical Code allows an ungrounded, two-wire receptacle to be replaced with a GFCI. A GFCI can even protect any receptacles downstream (away from the panel or power source). A GFCI used in this manner will only protect you from ground faults; it will not act as a ground for any equipment plugged into the receptacle(s). As a rule, it’s best for GFCIs to protect only a single box, not multiple receptacles. If you try to use one GFCI to cover multiple receptacles, you might experience nuisance tripping due to the greater sensitivity to current fluctuations. A GFCI installed to replace a twowire receptacle should be marked “No Equipment Ground.” A GFCI must be wired according to stamped terminals on the back of the receptacle. They will be marked “Load” and “Line” as well as “Hot” and “White.” The hot wire (which runs from the panel or fuse box) is the line conductor; anything going off to another load or receptacle is the load conductor. How do you know which is which? You’ll need your voltage tester.
With the power off and the old receptacle removed, separate all the wires in the box so they’re not in contact with each other (or with the box if it’s metal). Turn the power back on, and put one end of your probe on one hot wire and one on the neutral that is paired with the hot you are testing. If the bulb doesn’t light up, try the other black wire and neutral. The one that lights up the tester’s bulb is the line conductor. It’s the one receiving power from the current you switched back on at the service panel or fuse box. Connect this to the “Line,” “Hot” side of the GFCI. It is very important that the line side hot and neutral conductors or wires be connected to the “Line” side of the GFCI; otherwise, the GFCI will trip or will not work at all. If the line and loads are reversed, the GFCI will still have power if it is tripped, producing a hazardous situation.
As an alternative to installing a GFCI to replace an ungrounded receptacle, it is permissible to install a grounding conductor to an ungrounded circuit by using an individual No.12 insulated green copper conductor to connect each receptacle being grounded to the closest cold-water pipe. The grounding conductor will then have to be secured to the pipe using an approved clamping device. It also can be run directly back to the panel and installed in the grounding/ neutral bar.

Installing a New Receptacle

Receptacles are a little more straightforward than three- and four-way switches. With a single duplex receptacle, you’re dealing with one or two cables coming into the box. An end-of-the-run receptacle will have one cable, and a middle-of-the-run will have two. The receptacle has two sets of terminal screws, silver for the neutral wires and brass for the hot.
After shutting off the power and testing the terminal screws, remove the outlet by loosening the screws attaching it to the box. Remove the hot and neutral wires, noting their position on the outlet (hot upper, hot lower, neutral upper, neutral lower) by marking the position on an attached piece of masking tape. Reconnect to the new receptacle in the same locations, and gently push the wires back into the box while reattaching the new receptacle. Turn on the power at the service panel or fuse box and test.

Two-Wire Grounding

Do the following to test a two-slot receptacle: Place one probe in the hot slot and the other end on the screw securing the cover plate. The screw must be clean as well as paint and grease free.

• If the receptacle is grounded, the tester’s bulb will light up.
• Put the probe in the neutral slot if the tester does not light up in the hot slot. If it lights, the receptacle is grounded, but the neutral and hot wires have been reversed and are attached to the wrong terminals. If the bulb doesn’t glow at all, the receptacle isn’t grounded.
• To be absolutely sure that the receptacle is grounded (if your test indicates that it is), turn the power off and remove the cover plate. Check to see if an actual grounding conductor is present.

Test for Grounding

You can test a grounded, three-slot receptacle for grounding (remember, the power is on) by placing one probe of your tester in the short slot and one in the hole for a plug’s grounding pin. The short slot is for the hot wire. The bulb should glow to indicate that the receptacle is grounded. If it doesn’t, keep one probe in the grounding hole and place the other one in the longer, neutral slot. In this position, if the bulb glows, it shows that the receptacle is grounded, but the black and white wires have been reversed (they’re attached to the wrong terminal screws) and should be corrected. If the bulb doesn’t glow in either case, the receptacle isn’t grounded. A three-slot receptacle that isn’t grounded is misleading and dangerous to a user. It might indicate that only the individual receptacle is incorrectly wired or that it was inadvertently used to replace an ungrounded receptacle. Either way, you want to know so you can correct the problem.

Check and Check Again

Receptacles, like switches and fixtures, need to be checked with a voltage tester before you do any work on them. The test is similar for both grounded and ungrounded receptacles, except you’ll be testing for grounding as well with the former. A grounding test can only be done with the power on.
With the power off, insert both ends of your voltage tester into the slots of the receptacle. The light in the tester should not go on. If it does, the power has not been turned off, or the wrong circuit was shut off. Even if the tester bulb does not light up, you can’t be sure that the current is off. The receptacle might be damaged but still receiving a current. Remove the cover plate and carefully pull the receptacle out. Place one probe on the brass terminal, which should be connected to the black or hot wire. Place the other probe on the silver or neutral terminal. You must touch both terminals to complete the circuit. The bulb shouldn’t glow if the power has been shut off.

Disreputable Receptacles

Receptacles are pretty long-lasting, but old ones eventually can give out when the clips no longer hold a plug snuggly. There also are drawbacks to some old receptacles if they’re neither polarized nor grounded. Receptacle bodies also get broken if furniture or toy trucks somehow bang into them. (This happens at gyms all the time, only barbells do the damage.)
You want your receptacles and their cover plates to be intact. Broken or missing sections can set up you and yours for a shock or worse. When replacing an old receptacle, you can’t simply pop a new, grounded receptacle into an existing two-slot outlet. It doesn’t work that way, although there is a trick you can do with a GFCI that will give you some protection, but it will not ground any equipment plugged into the receptacle. A GFCI does not give grounding protection unless a grounding conductor already is present.

Old Wire, New Switch

It can be difficult working with the deteriorated knob-and-tube wire ends inside a box. You might have to snip off the end, and the remaining wire can be a little too short to easily connect to a new switch or receptacle. In this case, you can pigtail a short, new piece of wire to the existing wire and connect the pigtail to the terminal screw on the device. This also will bring the wires into compliance with the NEC, which calls for six inches of workable wire length inside a box. The following diagram shows this type of pigtail.