If you live in an older house without a grounded panel, you're not required by the National Electrical Code to update your ungrounded outlets to grounded ones, but for safety's sake you may want to do this anyway. There's really only one code-compliant way to accomplish this, and that's to install a new, grounded panel and rewire the outlets with cables that include a ground wire. That's a lot of work, and the NEC does allow one workaround -- replace the first outlet in every circuit with a ground fault-interrupting outlet and properly label each three-prong outlet you install.
Before consider the right way to convert ungrounded to grounded outlets, it's important to consider some common strategies and understand why they are not code-compliant:
- Running a ground wire to a nearby water pipe or grounded piece of metal leaves the ground wire exposed and dangerous, and there is no guarantee that the metal to which you attach is actually grounded. In many cases, a high resistance exists that prevents a clear path to ground and leaves the outlet without ground protection.
- Connecting the ground terminal to the neutral one by means of a jumper cable can energize anything you plug into the outlet -- even when it's not on, and you could get a shock. That's because current is running through the ground wire to the equipment casing.
- Running a separate ground wire back to your grounded panel and connecting it to the ground bus seems like a good solution, but it leaves the ground wire exposed and vulnerable to damage. To be compliant, the wire must be contained within the same casing as the hot and neutral wires.
All of these solutions are actually more dangerous than leaving the two-prong outlet as it is, because the three-prong outlet creates the impression of proper grounding when, in fact, that grounding may not exist.
Replacing Outlets with GFIs
GFI outlets monitor the difference between current flowing in the hot and neutral wires and, when a difference of more than 5 milliamps is detected, a breaker trips and power is disconnected. While this is not true grounding, it does provide protection against electrocution, fires and damage to your appliances. A GFI does not protect sensitive electronic equipment that can sustain damage from currents less than 5 milliamps. A GFI should also not be used with a surge protector, because the surge protector uses the ground wire to redirect excess current.
Procedure for Replacing an Outlet
Turn off the breaker controlling the circuit on which you're working. Test the outlet with a non-contact voltage tester to confirm that no voltage is present.
Unscrew the cover plate, then unscrew and remove the outlet from the electrical box. Disconnect the line wires; if they aren't clearly marked, identify the hot wire with black tape. If there is another pair of wires connected to the outlet, disconnect them and identify the hot wire in the same way.
Look on the back of the GFI -- you'll see a label identifying one pair of terminals as "Line" and one as "Load." Connect the line wires to the Line terminals. If you connect the wires to the other pair of terminals, the GFI will still have power, but it won't provide any protection. Connect the load wires to the "Load" terminals, then screw the outlet to the box and replace the cover plate.
Put a label on the cover plate that reads "No Equipment Ground." The NEC requires this label when a GFI is used for this purpose. It's usually supplied in the box in which the outlet came.