Reversed polarity electrical receptacles:
Definition of reversed polarity at an electrical receptacle, its causes, cures, and dangers. What happens if you reverse the hot and neutral wires at an electrical receptacle? We also explain the difference between reversed polarity and reversed LINE - LOAD connections in a building electrical circuit.
This article series describes how to choose, locate, and wire an electrical receptacle in a home. Electrical receptacles (also called electrical outlets or "plugs" or "sockets") are simple devices that are easy to install, but there are details to get right if you want to be safe.
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Carson Dunlop Associates' sketch points out that the white wire, i.e. the neutral wire, will be connected through the receptacle's internal parts to the wide slot on the receptacle face in order to assure that the neutral wire side of an appliance being plugged-in there is properly connected.
One of our buddies argues "what the heck, it's "alternating current" - the energy is flowing rapidly back and forth at 60 cycles per second on the wires - why would direction or polarity make any difference whatsoever?"
A non-technical answer might be "Why do you think wall plugs and electrical receptacles are 'polarized' or designed with a wide plug blade slot and a narrow plug blade slot (and on many devices a ground connector too) so that the plug will only go into the receptacle one way?" Given that there is extra cost and trouble involved, surely that's not for "no reason"!
Which Wall Plug Blades Connect to Which Receptacle Slots?
Notice that the neutral blade on a wall plug (sketch at left) is the wider blade, plugs into the wider slot in the electrical receptacle, and is intended to connect electrically to the neutral wire inside the receptacle.
The more narrow wall plug blade on a polarized plug is the "hot" blade and is intended to connect electrically to the hot or live terminal in the electrical receptacle.
What Happens When Polarity is Reversed at a Receptacle?
Most electrical appliances and devices are designed so that their "on-off" switch interrupts electrical power at the point of entry into the appliance or device circuitry or components. If you switch the hot and neutral wires that may not quite be the case, and parts of the device will remain energized or potentially energized even when the electrical device switch is OFF. No electrical current may flow, but it could flow if someone touches the wrong part of the device, or damage may be caused in other circumstances as well, as we describe next.
Watch out: Reversed polarity on an electrical outlet is dangerous. If you accidentally reverse these wires the device you plug in to the receptacle may "work" but it is unsafe and risks a short circuit, shock, or fire.
Even a simple light or floor lamp is less safe with polarity reversed
While some devices such as an incandescent electric light may appear to work properly and safely regardless of which way the lamp's plug is inserted into the wall outlet, virtually all modern electrical appliances, even lamps, use polarized plugs. In the case of an electric light, the device will "work" properly in either position.
When a lamp or light fixture is connected with proper polarity, the hot wire connects to a contact at the bottom inside center of the bulb socket or screw-in base, and the neutral wire is connected to the shell that contacts the sides of the bulb when it is inserted and screwed into the socket.
But if the lamp is plugged in with its polarity reversed the metal "shell" into which the bulb screws is energized or "hot". Because this component is much easier to touch when changing a light bulb than is the connector in the internal center of the bulb base, a shock hazard is present.
Some appliances and electronic devices may be damaged if polarity is reversed
Some appliances and some electronic equipment may be damaged if left connected to a reversed-polarity electrical circuit.
We disassembled a coffee maker that had burned-up and found that the appliance had been damaged by being left connected to its receptacle with polarity reversed. The presence of live voltage at the "wrong end" of a circuit or circuit board may cause some devices on the board to remain energized even when the device has been "switched off". A result can be overheating or electrical shock hazards.
Common Causes of Reversed Electrical Polarity on 120V Circuits, Devices, Appliances in Buildings
Is Reversing Line/Load Connections the Same as Reversed Polarity?
You can reverse LINE and LOAD connections on daisy-chained devices (like the GFCI receptacle shown at left) and the circuit will appear to work properly. However the circuit may not be safe or fully protected.
Line and load electrical wire connections are important to get right on certain electrical devices such as GFCIs and AFCIs. Our photograph (left) illustrates the line and load markings on the back of a GFCI electrical receptacle.
Looking at the side or back of the molded case of this and other electrical devices such as AFCIs, you will see that one pair of terminals will be marked "line" and the other "load".
The Line terminals (green arrows in photo at left) on an electrical receptacle are for the incoming hot wire - the terminal marked LINE is connected to the incoming power source or the "hot" wire (typically black or red in insulation color) that connects to the brass colored screw (marked "Black" or "Noir) at the lower left " in our photo.
And the incoming neutral (white) wire from the electrical panel connects to the "Line" and "White" or "Blanc" terminal marked at the lower right in our photo
The Load terminals (red arrows near the top of our photo at left) on an electrical receptacle are for the outgoing wires. These wires feed electrical receptacles that are located "downstream"(farther from the electrical panel) from the device. The outgoing hot or black wire (red arrow, above left in our photo) connects to the terminal marked "Load" or "Charge" and "Black" or "Noir". The outgoing white, neutral wire, connects to the terminal marked "Load" or "Charge" and "White" or "Blanc" in our photograph.
Readers of this article should also
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The illustration at left shows the typical wiring of an electrical outlet or "receptacle", courtesy of Carson Dunlop Associates.
Watch out: Electrical components in a building can easily cause an electrical shock, burn, or even death.
Even when a hot line switch is off, one terminal on the switch is still connected to the power source.
Before doing any work on the switch, the power source must be turned off by setting a circuit breaker to OFF or removing a fuse.
Continue reading at ROUTING, Securing & Protecting Electrical Wires or select a topic from the More Reading links shown below.
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Frequently Asked Questions (FAQs)
Question: When wiring an electrical receptacle, what do I do with the red wire? Can I ground it?
I have a 3 wire (Black, White, Red and ground) feeding a outlet and I want to add another receptacle to run further down the line. The line out is 14/2. What do I do with the Hot Red wire? Can i attach it to the ground. - Rick
After capping off the red wire, can I extend the line to the next plug by following the diagram above and adding the black and white wires to the respective second screw connections?
You see, the wiring has already been installed by the builders and they left the boxes without receptacles so all I have to do is connect them to the. I don't know why the extra red wire is there. It was done over a year ago. I want to finish the connections. It runs 14/3 and then 14/2. That's why I have the extra red.
Question: what do I do with a third white wire attached to the side of the old receptacle when I'm moving them
I have changed several receptacles in my 1994 home, but this time when removing the receptacle from the wall I see a third white wire attached to the side of the old receptacle. Can you explain to me what this third neutral wire is? - DW 6/12/12
DW, it is just too dangerous to claim to know what wiring connections someone has made in a building that is unseen and untested.
It would be common for an additional white wire connected to an electrical receptacle to be carrying the neutral line to another receptacle downstream. In other words the incoming neutral is connected to one terminal and the outgoing neutral is connected to a second screw that is electrically common with the first.
Check for a second hot wire also present in the same box.
Question: I've lost electrical power to the whole room after testing power at the light switch
I've lost elec to the whole room.
I tested the wiring at the light switch.
If I turn the switch off I get elec to the switch,If I turn it on I get no elec.to the switch. I've lost electricity to the whole room - Dave
Dave, your wiring or perhaps the switch itself is unsafe; sounds as if it's shorted. Leave the circuit off until the wiring has been traced, lest you start a fire or zap someone.
Question: are receptacles wired after a GFI receptacle OK?
Are receptacles wired after GFI receptacles OK? - Denny 11/25/12
Watch out: When wiring a GFCI the incoming leads are connected to the LINE terminals and the downstream receptacles are connected to the LOAD terminals marked on the back of the receptacle. If the devices is not wired correctly it is unsafe and does not provide the intended safety protection from ground faults.
Question: 3 plugs on one of my walls went out
Ok from everything I can tell I'm having trouble with trouble with 3 plugs on my outer wall has went out. I've did the common thing checked my breakers they are fine. Must not I have 2 switches in this room one on each wall but they do nothing I feel somehow those switches are connected to those 3 plugs. I've pulled the covers off each plug and noticed the wires are secured. I've flipped the switches in many combos with something plugged in and they still don't work at all. What can I do to fix it. I wanna avoid calling a electrician if possible. - Josh DeBerry 12/11/12
Start by checking fuses or circuit breakers. If there is no tripped breaker or blown fuse, I suspect a damaged receptacle, wire, or wire connector. Your electrician will track down the location of the fault. But if you know which receptacles were all wired on a given circuit, and with power on at the electrical panel, using a receptacle tester you can check to see if any of the devices on the circuit have power.
\Since receptacles are most often wired in a daisy-chain or series circuit, the last one that has power tells you that the problem is between that receptacle and the next one in the chain.
Questions & answers or comments about how to install and wire electrical outlets or receptacles in buildings.
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