How do I install a GFCI receptacle with two hot wires and common neutral?

Question

In my kitchen, I want to replace a regular 120V receptacle with a GFCI-protected receptacle. The instructions describe what to do with a regular 2-wire + ground feed, with and without daisy chaining to other receptacles, but not how to do it with a 3-wire + ground feed. Please describe how I should connect the new receptacle.

Here's a diagram of how the non-GFCI receptacle is currently wired, in my best 6-year-old artistry:

I think it's connected this way so that each receptacle in the kitchen has their two sockets supplied by different breakers. At the service panel the circuit is controlled by a joined pair of 15A breakers. I assume the white and black are separate 15A lines and the red is a common neutral (?).

Here are the instructions for connecting in a 2-wire scenario.

How do I connect this? Or should I consult an electrician?

EDIT

From The complete guide to home wiring

Answer 1

The first problem is that you may be using the wrong cable and breakers. NEC calls for 2 20Amp small appliance circuits in the kitchen, to accomplish this you'll need to switch to 20Amp breakers and #12 wire.

The next problem. You'll have to pull new wire anyway, if you want to hook up GFCI receptacles. GFCI receptacles will not work properly with a shared neutral, you'll end up with nuisance tripping with a shared neutral. GFCI receptacles work by monitoring the balance between hot and neutral, so if the neutral is shared the GFCI will not work properly.

To wire up the kitchen properly, you'll have to pull 2 new 12/2 cables from the breaker to the kitchen (all #14 wire on that circuit will have to be replaced). Then install 2 20Amp breakers, to supply the kitchen. You'll install the GFCI's as the first receptacle on each circuit, which will protect all downstream receptacles.

After a little more research:

I've found a few sources that say you can share a neutral between 2 GFCI receptacles. The catch is you'll have to pigtail the neutral to the receptacles, not use the neutral from the load side of the first GFCI to feed the second.

So you may be able to do something like this...

But not like this...

You'll then be able to use the load side of each receptacle to feed other devices, like this.

Answer 2

Most of what Gregmac has said is correct, however I have to correct a couple of small items. It is totally acceptable and often done to use a three wire circuit (black/red hot, white neutral & bare ground) like you have to "alternate" kitchen receptacles, thus giving you two circuits. It is not a code requirement to split the top and bottom of the recpts, however it is fine to do that, but it complicates the GFI functions. Splitting the top and bottom would require two GFI's upstream, one feeding each of the legs. More common would be two single pole GFI breakers in the panel.

With that said, your situation is different. I bet you will find that the the black feeds every other recpt, and likewise the red does the same thing with alternate recpts. Once you confirm that, simply install a GFI on the first powered recpt of each string (color). As a matter of fact, this is the most common way kitchens are wired and meets NEC.

Answer 3

Dont over complicate this. It is very simple problem. Just leave the red wire alone. No one here knows for sure what it is used for but it doesnt matter. Every electrician/homeowners wire things a little different. It could be right or wrong but if everything works dont worry about it.

Without using the red wire you can use the diagram you provided. The only thing to figure out is what wires is the hot feed. The easiest way to find this out is to turn off the breaker and disconnect one set of black and wire wires. Then put a separate wire nut on each and turn the breaker back on. if the outlet still works then the wires connected are hot. If not then obviously the wires you took off and capped are. Now you have to decide if you want the rest of the outlets on this series to be protected by the GFI and connect your load wires up accordingly. It will be label on the back of the gfi which load connection point is protected.

Answer 4

Pigtail the neutral and the hot. This is the correct way to install any receptacle, GFCI or not.