How Many Wires Can You Connect To An Outlet?
In new homes, if you open up your outlet, you will usually see two wires. One entering and providing power to the outlet, the other exiting and providing power to outlets downstream. There may sometimes be a third wire to ground the outlet, or to provide power to a downstream line in another direction.
Per NEC (National Electrical Code) standards, you can use no more than one wire per screw. Never connect more than one wire under a single screw terminal as it could cause arching wires or a loose hot wire as the wires heat and cool. This will eventually start a fire and other safety hazards.
If you are working on a receptacle that is in the middle of a circuit, there are two cables within the outlet box. One cable is where the power is coming from the source, entering the box from one side. The other cable is exiting the box through the other side, continuing the route from the source to the downstream locations. If the circuit is heading in another direction, such as up or down, there may also be a third cable to continue this path.
When it comes to wiring the receptacle to the incoming and outgoing power cables, you usually have two options, using a pigtail and direct wiring.
Using a Pigtail to Connect Wires
The first option is that you connect the receptacle to the circuit wires using pigtails. Pigtails are short lengths of conductor that are added to a junction in order to connect a device. Switches and receptacles can be connected this way, as the circuit would not be interrupted if the device failed or was removed.
The pigtails will tap into the circuit wires that are passing through the box. Using pigtails will make it so that the electrical load will flow to both the receptacle and the other receptacles on the circuit downstream, without being dependent on moving through the receptacles connecting tab.
Direct Wiring Your Outlet
The second option is to direct-wire the circuit through the receptacle. This is where you will take the entry cable and attach it to one pair of hot and neutral screw terminals on the receptacle. You then attach the exit cable to the other set of screws, creating a passthrough.
Using this method, the circuit will flow through the receptacle at all times, using the connecting tabs and establishing a continuous circuit path. The issue with this is if the receptacle fails, any receptacles on the downstream will also stop working. If you want to replace the receptacle later, you will need to undo this wiring as well.
When you have two cables in an outlet, one is the incoming power line and the other is the outgoing load cable. The load cables function is to give any other receptacles that are connected downstream, access to the circuit.
Color Coordinated Screws and Wires
If you are using a standard 120-volt receptacle, you will see three different types of screw terminals. There is a brass-colored, a silver-colored, and a green-colored screw terminal. These are color coded to make it easy to know which wires to connect to which, as they each serve different functions.
Brass-Colored Screw, Black Hot Wire
The brass-colored screw is for black wires, which are the ‘hot’ wires. This is the line that carries electricity from the breaker panel into the receptacle. Make sure to use extra caution when handling these, as this is where all the electrical load is and should be considered live at all times.
Silver-Colored Screw, White Neutral Wire
The silver-colored screw is for white wires, which are the neutral wires. These connect to the electrical panel’s neutral bus bar. Once power leaves the electrical panel through the hot wire it will return to the service panel using the neutral wire. This will return the current to the electric utility grid. These still carry a current, usually an unbalanced load, so you must also handle these with caution.
Green-Colored Screen, Green Grounding Wire
The green-colored screw is where you will connect the bare copper grounding wires. These will run to the ground bus bar in an electrical panel, in order to provide a path to ground. When you give electricity a means to return to the ground, via the electric panel, this is known as grounding.
Grounding is a safe way to discharge excess energy. It protects your appliances, your home, and everyone else from surges of electricity. If your system is grounded, then all excess energy will go to the earth, and not somewhere unsafe.
Other Types of Colored Wires
In old homes, the wires within your walls may not follow these color-coded variants. Hotwires may also have red insulation on the wire jacket, neutral wires may be gray, and there are also other colored wires. Generally speaking, if your home was built in the last 40 years, they will follow the black, white, green, color scheme. For older homes, you may find an assortment of colors and stripes, so it’s best to use a wire tester to be sure.
Why There Are So Many Wires
Circuits are usually in a string of junction boxes that are daisy-chained together. This is why you may have more wires in your box than are connected to the outlet. Daisy-chaining means that the hot and neutral wire is only coming from one wire and then being sent to the other wire. This helps cut back on how much wire is needed within your house. Nearby outlets will be connected to each other instead of connected to the circuit breaker. This saves the electrician from having to run long lengths of wire through the house.
Only one wire will be connected to the circuit breaker and containing hot/neutral power. The other wires are meant to pass on the power to the next outlet or ground the connection. If you have more wires than you have screws, you will want to use a pigtail.
Box Size, Wire Limits, and Box Fill
Knowing how many wires you can connect to an outbox is very important if you are doing your own home electrical work. You will need to follow the National Electrical Code (NEC) for any wiring that you do to make sure it is safe.
The NEC limits the amount of electrical wires that you can have inside an electrical box, for safety reasons. Too many it can cause electrical shorts and overheating, due to the tightly-packed wires. The amount that you can have inside is referred to as a ‘Box Fill’. You will also need to consider cable clamps, outlets, switches, and other items that go inside the box.
Different Boxes Allow a Different Number of Wires
The box manufacturer will let you know how many wires can be put inside the box. Generally, if there are screws then you can use one wire per screw. The same goes for holes, with one hole being good for one wire. For quick wiring, it used to be that 12- and 14-gauge wires were allowed, though now only 14 gauge wires can be used.
The box size is the ultimate determining factor in how many wires you can use. Each box volume has a fixed allowance of wire usage. There are rules that you need to follow to figure out the minimum box volume to hold a certain number of wires, devices, and clamps.
Can You Run Two Wires Through the Same Hole?
You should only be passing one wire through each hole. This is to prevent them from being too crammed together. As electricity runs through the wiring, it heats up and cools down, expanding and contracting. If you have too many wires going through a hole, it can create a dangerous situation. When wiring heats up and expands, it can cut into the box and damage the wire, or cause friction burns.
How Many Receptacles Can Be on A 20 Amp Circuit?
The rule of thumb is that each receptacle has a 1.5amp max draw, so you can safely put 10 receptacles on a 20 Amp circuit. Since electrical outlets don’t draw power until you plug something in, you could use more than this. But for safety’s sake, it is best to not chance overloading your circuit.
Sean Jarvis is an interior decorator, writer, and expert handyman. Well versed in everything home improvement, he is a savant at manipulating words and spaces and upgrading everything around him. Sean specializes in writing concise guides about appliance repair and installation, home and lifestyle, and other residential projects.
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