I'm trying to install an exterior outlet to an interior outlet for power. I took the interior outlet out of its box and noticed 4 wires (excluding the ground) attached to the outlet. 2 of the white wires attached to the neutral side and 2 attached to the hot side. All wires were attached into push holes and not the sides screws.

The top 2 wires I assume are the line wires and the bottom 2 the load wires. My question is once I run the exterior outlet wires to the interior outlet, where do the wires attach and how, by pigtailing? And, where do I pigtail to? The side screws to the interior outlet are still free from any wiring.

  • 1
    Please attach a picture. – Kris Apr 18 '17 at 13:43

The question I would have is the box large enough to have 7 conductors and a device for wire fill calculations. I would turn the power off remove the wires from the back stabs and connect the 2 existing blacks with the new black and a short pig tail to the inside outlet. once that is done I would do the same to the Hot side making sure to keep the polarity correct to the outlet. Tie the ground for the new outlet to the existing grounds. With that done install a GFCI outlet outside with a "in use" or extra duty cover and it would be fine. Make sure to use the same gauge wire to the new outlet (you can use larger but that affects the box fill calculations. With 14 awg wire 18 cu inch box would be needed (if plastic no clamps +2 if it has clamps) for 12 awg wire 20.25 cu inch box would be needed if no clamps (+2.25 for clamps).


The only way to determine which wires are the line and which the load is to disconnect one of the hot wires. If that disconnected one is hot with the breaker on, then it is the line. The receptacle will then be unpowered. If the other is the hot, then the receptacle will still be powered and the disconnected wire will not be hot. The neutral paired with a given hot will be ascertainable as being in the same cable sheath.

The back wiring connections in the holes can be of two types. The old cheap and inferior receptacles made a spring loaded connection when the conductor was pushed into the back hole. The side screw had no effect on this connection. This is considered an inferior connection and should not be used even for copper wires. It was prohibited for aluminum conductors. I hope you have copper.

The other type of back wiring (which I have heard about but not seen myself) uses the side screws to clamp the wires in the back wiring holes. Duplex receptacles with this feature are more expensive (~>$5.00) and are considered desirable. I believe in this type one can attach wires by looping around the screw in addition to inserting into the back holes. If I understand correctly, this type allows more branching without the use of wire nutted pigtails, but one of the experts on this site should confirm this.

If feeding an exterior receptacle is allowed by code, you could use a GFCI receptacle in the exterior box.

  • Your note about the back wire clamps is correct. I recently purchased one (Leviton calls them their "Industrial" receptacles). Instead of holes to push wire into (backstab), you provide clamp force with the side wiring screw. You should be able to both back and side wire them. – Hari Ganti Apr 18 '17 at 20:25
  • I thought back and side were only good for back or side or a max of 4 wires on the hot or neutral. My apprentice wanted to use both so I called Leviton and talked to there support person after quite a while on hold wile double checking the rep said there was no indications that they could not be used with up to 6 wires. I regularly use these and they outlast every other outlet on the market. Not only Leviton, but Hubble and other brands. Why would you care about line and load on a daisy chain. Hook up the existing wires and run to the GFCI outlet unless you want to go inside to reset the GFCI. – Ed Beal Apr 18 '17 at 22:18

First step is to check with a qualified electrician to see if this even allowed under your local building code.

In many jurisdictions it is not permitted to have interior and exterior fixtures on the same circuit. There are also often requirements to use a GFCI protected circuit (or at the very least, a GFCI protected outlet), especially if the exterior receptacle is in an exposed location.

TL;DR - this is potentially unsafe, get qualified help.

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    Good information, but not an answer. – isherwood Apr 18 '17 at 19:55
  • I seriously want to see a cite for "it is not permitted to have interior and exterior fixtures on the same circuit"...I've never even heard of such a requirement or seen it in the NEC... – ThreePhaseEel Apr 18 '17 at 23:08
  • @ThreePhaseEel I'm in Canada - local codes may differ from US codes/NEC? See one example here - "19) Outdoor receptacles must be installed on a spearate circuit and more than one can be on the same circuit. Outdoor receptacles must be arc fault and ground fault protected and require wet location covers marked for “Extra Duty.”" lethbridge.ca/Doing-Business/Planning-Development/… – Duodenalsalmons Apr 19 '17 at 21:03
  • @isherwood fair point - should have made this a comment really. Also specific to where OP lives? – Duodenalsalmons Apr 19 '17 at 21:06

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