Understanding a middle of run outlet wiring diagram is essential whenever an outlet sits between two others on the same circuit. Unlike an end-of-run receptacle that has power coming in and stopping there, a middle-of-run outlet has power coming IN from the panel side and continuing OUT to the next device down the line. That means two cables enter the box, and the receptacle has to both serve its own plugs and pass power along. Before you open any box, turn off the breaker and verify it is dead, and if you are not fully confident, hire a licensed electrician. Here is how the connections lay out.
Safety First, Always
This is live electrical work, so the rules are firm:
- Turn off the breaker for the circuit at the panel before touching any wire.
- Verify it is dead with a non-contact voltage tester at the outlet, do not trust the label alone.
- Hire a licensed electrician if you are unsure, if you are adding a circuit, or if local code requires it. Permits often apply.
- Follow your local electrical code, which governs connections, box fill, and protection like GFCI or AFCI where required.
This article explains the connections conceptually. It is not a substitute for training or a permit.
What “Middle of Run” Means
Picture a circuit as a chain of outlets. Power leaves the breaker, reaches the first outlet, then continues to the second, the third, and so on. Any outlet that is not the last one in that chain is a middle-of-run device. The defining feature is that it has two cables in the box:
- The incoming (line) cable brings power from the panel side.
- The outgoing (load) cable carries power onward to the next outlet.
An end-of-run outlet, by contrast, has only one cable. Recognizing two cables in the box is your clue that you are dealing with a middle-of-run setup.
The Conductors in Each Cable
A standard cable for this work has three conductors:
- Hot (black): The energized conductor.
- Neutral (white): The return conductor.
- Ground (bare copper or green): The safety ground.
Because there are two cables, the box contains two black wires, two white wires, and two ground wires. The whole task is connecting them so power both serves the outlet and continues to the next device.
How the Connections Lay Out
A standard receptacle has terminal screws on both sides plus a ground screw, which makes the two-cable connection straightforward. A typical duplex receptacle has:
- Two brass (hot) screws on one side, joined by a small metal tab.
- Two silver (neutral) screws on the other side, joined by a tab.
- One green ground screw.
For a middle-of-run outlet, there are two common, code-acceptable methods.
Method 1: Use Both Screws on Each Side
Because each side has two screws connected by a tab, you can land one cable on each screw:
- Connect the incoming black (hot) to one brass screw and the outgoing black (hot) to the other brass screw. The tab between them passes power through.
- Connect the incoming white (neutral) to one silver screw and the outgoing white (neutral) to the other silver screw.
- Connect both ground wires together with the outlet’s ground; typically the two grounds and a short pigtail are joined, and the pigtail goes to the green ground screw.
This is the classic approach: the receptacle itself carries the current through to the next device via its internal tabs.
Method 2: Pigtail the Connections
Many electricians prefer pigtailing, which keeps power flowing downstream even if the receptacle is removed and avoids running all the circuit current through the device:
- Join the two black wires (incoming and outgoing) together with a short black pigtail using a wire connector, then run the pigtail to one brass screw.
- Join the two white wires together with a white pigtail, then run that pigtail to one silver screw.
- Join the two ground wires together with a green or bare pigtail, then run that pigtail to the green ground screw.
With pigtailing, the splices carry the through-current and the outlet just taps off the pigtails. This is often the more robust method.
A Note on the Ground
The ground always connects to the green ground screw on the receptacle. With two cables, the two bare or green grounds are joined, usually with a pigtail to the green screw, so the safety ground is continuous both to the outlet and on to the next device. Never leave a ground disconnected; it is the safety path that protects against shock.
Common Mistakes to Avoid
- Reversing hot and neutral, black goes to brass, white to silver. Swapping them creates a reversed-polarity hazard.
- Breaking the wrong tab, the tabs stay intact for a standard pass-through outlet; you only break the hot tab when intentionally splitting the receptacle (a different setup).
- Loose connections, backstabbed or under-tightened wires can overheat. Make screw terminals snug.
- Skipping the ground, always continue the ground to both the outlet and the next box.
- Overfilling the box, two cables plus a device must respect box-fill limits.
Telling Line From Load in the Box
With two cables present, you may want to know which one is the incoming power (the line) and which feeds onward (the load). The safe way to identify them is with the power on only briefly and using a non-contact voltage tester or a proper multimeter, work that should be left to someone experienced or a licensed electrician, since it involves a live circuit. For a simple pass-through middle-of-run outlet, the distinction often does not change the connections, because both blacks go to brass and both whites to silver. It matters when a switch, GFCI, or split receptacle is involved, which is another reason to bring in a professional for anything beyond a straightforward replacement.
When GFCI or AFCI Protection Applies
Code increasingly requires GFCI protection in areas like kitchens, bathrooms, garages, and outdoors, and AFCI protection in many living spaces. A middle-of-run location can complicate this, because a GFCI receptacle has dedicated LINE and LOAD terminals, and wiring it incorrectly in the middle of a run can leave downstream outlets unprotected or non-functional. If your circuit needs GFCI or AFCI protection, identifying line versus load correctly becomes critical, and getting it wrong defeats the safety device. This is firmly a situation where consulting or hiring a licensed electrician is the right call rather than guessing.
The Bottom Line
A middle of run outlet wiring diagram simply shows two cables, power in and power out, landing on a receptacle so it both serves its plugs and feeds the next device. Connect the hots to the brass screws and the neutrals to the silver screws, either using both screws per side or pigtailing the splices, and always tie the grounds together to the green screw. Because this is live circuit work, kill the breaker, test that it is dead, follow local code, and call a licensed electrician for new circuits or anytime you are unsure. Wired correctly, the outlet works safely and power continues cleanly down the line.
