I have a receptacle that is the only thing on that circuit. Taking out the one fuse kills the power to both outlets. The house was built late 70's When I opened the receptacle up there are 2 main cables. One is a 2 wire the other a 3. The 2 black wires from each cable are attached to each other with a wire nut but are not attached to anything else. The red wire is attached to one side of the receptacle The white white wires are attached to 1 screw each one the other side of the receptacle . The tab is not broken off and there is no wall switch. How do I hook up my new cable to add an receptacle to this circuit?

What you are describing certainly sounds like a switch loop. Question, are the receptacles hot all the time?

The source (Black) is connected to the switch supply (Black). The Neutral (White) is carried to the switch outlet for use by a specialty device (Motion Detector), and then the power is returned to the receptacle via the Red conductor.

The unbroken tab on the receptacle just means that whatever means controls the return power to the receptacle makes both receptacles on the yoke hot. Sometimes the design of the circuit would call for a double receptacle (two receptacles on one yoke) one would be a constant hot while the other would be controlled by a switch. In that situation, the tab would be broken and you would see a black conductor and a red conductor connected to the receptacles.

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Originally Posted by donf

What you are describing certainly sounds like a switch loop. Question, are the receptacles hot all the time?

The source (Black) is connected to the switch supply (Black). The Neutral (White) is carried to the switch outlet for use by a specialty device (Motion Detector), and then the power is returned to the receptacle via the Red conductor.

The unbroken tab on the receptacle just means that whatever means controls the return power to the receptacle makes both receptacles on the yoke hot. Sometimes the design of the circuit would call for a double receptacle (two receptacles on one yoke) one would be a constant hot while the other would be controlled by a switch. In that situation, the tab would be broken and you would see a black conductor and a red conductor connected to the receptacles.

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Yes both outlets are hot all the time and there is no switch to operate the outlet.

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I have a receptacle that is the only thing on that circuit. Taking out the one fuse kills the power to both outlets.

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Those two statements are logically inconsistent.

Sounds like, at least initially from your description of the wiring, that you have two circuits sharing a neutral.

Agree with Harold, the red and black wire are a typical tell tale. Probably a 14 or 12/3 wire. At the fuse box, are both red and black under the connector? Usually there will be 2 fuses or breakers today. If this is a kitchen, you should have GFCI's but they will not function on a shared neutral.

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Originally Posted by hkstroud

Those two statements are logically inconsistent.

Sounds like, at least initially from your description of the wiring, that you have two circuits sharing a neutral.

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Referring to the outlets on the one receptacle. So can I add a receptacle ?

Although you can extend wiring on a shared neutral, it is not recommended because it unbalances the circuit. Depending on upstream usage and wiring done by a previous installer, the downstream neutral can be hot, please read the following, copied from one of my electrical books.
"In the interest of safety and protection of equipment, all 120 volt branch circuits that extend beyond a distribution panel board should be complete and independent of any other branch circuit. This means that all 120 volt circuits should have dedicated neutrals, and that shared neutrals should not be employed to feed receptacle circuits. In addition, these dedicated neutrals should be identified with the corresponding circuit number, at every splice. In this way, the electrician that comes to alter or extend and existing circuit, is less likely to tap the wrong neutral".

While agree that 3 conductor could easily be associated with a multi-wire circuit I disagree in this instance because:

There would be two breakers associated with the multiwire circuit. There is no suggestion at all that there is a breaker with a red conductor.

What the poster is describing is a two conductor feed from the source, connecting with a 3 conductor cable. To me this is indicative of a switch loop.

Why would any electrician use a 3 conductor cable to share a neutral on the same single circuit breaker?

What you are describing doesn't make sense. Since there is no connected source (that we know of at this time) on the Red conductor? Where is the power coming from? We do know that black is feeding something else on the circuit and that red is receiving power from somewhere else on this circuit.

Despite what I am reading, I don't see why you can't connect to the red and white(and a ground), You must pigtail the white, receptacle terminals cannot be used to complete Neutral.
If a Multi Circuit, it should be on a 2 pole breaker, so it turns off both circuits at once, An open neutral on a multicircuit can provide volatges anywhere from 1 to 239 volts, and cause serious damage.
I would determine what that black wire goes to.
Safely expose wirenut to allow testing to determine which breaker.
Am not for sure if you mean 2 duplex recepticles or 1 Device?
The Neutral on a Multi Circuit carries the difference of the 2 hots(If 1 circuit draws 15 amps, and the other draws 20 amps, The neutrals load would be 5 amps).
Good Luck

IMPORTANT, Power MUST be off on both circuits, especially when dealing with the Neutral.

Here is a simple test.

With the circuit breaker in the OFF position, sepaeate the two black conductors and then cap off the black conductor from the breaker.

If this is a true multi wire circuit, then the receptacle will still becaues it beingf fed by its own breaker.

I the receptacle goes dead, then there is a device that is controlling power to that receotacle.

Is this receptacle near the entry to a room? If it is, look for a wall switch on any outside wall near the room. For example, in the hallway near the entry door.

Something is controlling the feed to the recptacle if that receptacle goes dead with the black conductors separated.

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Originally Posted by donf

Here is a simple test.

With the circuit breaker in the OFF position, sepaeate the two black conductors and then cap off the black conductor from the breaker.

If this is a true multi wire circuit, then the receptacle will still becaues it beingf fed by its own breaker.

I the receptacle goes dead, then there is a device that is controlling power to that receotacle.

Is this receptacle near the entry to a room? If it is, look for a wall switch on any outside wall near the room. For example, in the hallway near the entry door.

something is controlling the feed to the recptacle if that receptacle goes dead with the black conductors separated.

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New information one of the black wires is powering the fridge outlet. I assume this means I have multi branch wiring. Does the fridge receptacle count towards the load on the circuit from the receptacle I want to tap into? I unscrew another fuse to shut power off to the fridge.

OK, so you have a duplex receptical, two outlets on one yoke.

Your wiring indicates that there is something else on the circuit.

That something else could be outlets or lights. Turn off breaker, do a voltage test on both the black and the red wire.

If power is coming in on the 3-wire cable then you have two circuits sharing a neutral.
If power is coming in on the 2-wire cable then logic says that this is a switched outlet. The white of the 3-wire e cable is neutral of course. The black takes power to the switch and beyond. The red of the 3-wire returns power to the outlet from the switch. The tab on the hot side of the outlet is removed if only one half of the outlet is switched and the other half is constant hot.

If can think of no other reason for using 3-wire cable out of an outlet box other than a switched outlet and also a need for power beyond the switch the switch location.

Edit after your latest post.

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New information one of the black wires is powering the fridge outlet.

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I unscrew another fuse to shut power off to the fridge.

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That indicates two circuits sharing a neutral. Power should be coming in on the 3-wire.

Can you add an outlet?

Yes.

Connect the two existing white wires together and add a pigtail. Connect the pigtail to the neutral side of the outlet. Connect the white of cable going to new outlet to neutral side. Connect black of cable going to new outlet to hot side of this outlet.

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Originally Posted by hkstroud

Can you add an outlet?

Yes.

Connect the two existing white wires together and add a pigtail. Connect the pigtail to the neutral side of the outlet. Connect the white of cable going to new outlet to neutral side. Connect black of cable going to new outlet to hot side of this outlet.

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Thank you. One final question I hope. Can I add a gfci receptacle to the new receptacle I want to put in? In other words there would be 3 receptacles and the gfci would be the last one.

Certainly you can, but GFCI receptacles are primarily for use near water, kitchens, bathrooms, basements garages and outdoors.

Depending on the room you may have to install an AFCI receptacle, not a GFCI receptacle.

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Originally Posted by donf

Certainly you can, but GFCI receptacles are primarily for use near water, kitchens, bathrooms, basements garages and outdoors.

Depending on the room you may have to install an AFCI receptacle, not a GFCI receptacle.

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This would be in the bathroom. There was one in there wired to the light with the wire running on top of 2 studs and I almost put a screw through the wire so I got rid of that and just want to run a wire properly. The other receptacle is in the room next the bathroom so just an ordinary receptacle.

Stop right there!

You cannot feed a receptacle in a bathroom with a general use circuit.

NEC allows for a 20 amp circuit to feed multiple bathroom room receptacles, but the circuit is for bathrooms only. You cannot connect to a circuit that supply's any other devices. Only bathroom receptacles.

Present codes require a dedicated 20 amp circuit to a bath. If you have screw in fuses you are certainly not under present or recent codes.

Code does not prohibit additional circuits (or outlets) to bath.

Again, I have to disagree with the previous statement.

Just because a home has a fuse box instead of a breaker box does not correlate to the level of code. This home was built in the 1970s, that correlates to the level of code.

There is no prohibition against the use of a fuse box that I can find in either the 2008 or 2011 editions of the NEC.

So the real question is when did code begin requiring a 20 amp dedicated receptacle branch circuit for a bathroom or bath rooms. Also, would the AHJ allow the use of an extension of a 15 amp general use branch circuit to include the use of a 15 amp branch circuit .

The use of a hair dryer on a 15 amp circuit is risky enough to trip the circuit (overload) so why risk it?

Current code allows the use of 1 dedicated 20 amp branch circuit for one entire bathroom or the use of one dedicated 20 amp branch circuit for receptacles only in more than one bathroom.

Tripping an addition outlet on different circuit would not leave you in the dark.
Better the additional circuit trip, than the Lighting, Leaving you in the dark and dangerous?
Opinion, nothing to do with code?
Would leave the frige alone on the black circuit.