Electrical receptacle & switch backwiring questions & answers:
Questions & answers about backwiring or back-wiring of electrical receptacles and switches. Is backwiring OK or just easier and faster than using a screw connector? Is back-wiring reliable and safe?
This article series describes types of wire connectors on electrical receptacles and switches, compares their contact area and clamping force differences and offers conclusions about the most-reliable connectors to use. This electrical wiring & receptacle article series explains receptacle types, receptacle grounding, connecting wires to the right receptacle terminal screws, electrical wire size, electrical wire color codes, and special receptacles for un-grounded circuits.
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Is it safe to plug in an ac unit that runs 10 amps , into outlet that is backed wired, i had read that you don't like this method, the outlet is on third floor and is on a 15 amp breaker - Johnny B 5/2/w
Johnny, that's an interesting question and one I'm scared to answer - by online posting one cannot assure the electrical safety of your building.
At BACK-WIRED ELECTRICAL DEVICES, 3 TYPES we illustrate three different types of electrical receptacles that can be wired from their back-side.
Our photo illustrates a spec-grade 20-Amp, 125V rated electrical receptacle that looks as if it is "back-wired" - in fact while a wire can be wrapped around the terminal screws on this device, the screw is intended to be used to tighten a rectangular brass plate against a square metal nut (silver in color) that makes a very strong and positive connection over a good area of wire surface. This receptacle is marked on its back surface as CU Wire Only - copper only. [Click images to see enlarged details.]
That said, I agree that older, spring-type back-wired electrical connections (shown at below left) are not as reliable as connections made under a screw or clamp, as the total contact area between the back-wire spring edge and the wire surface is minimal.
Nevertheless, on a 15-A circuit using 15-A devices such as receptacles, the circuit and its devices are rated and intended to be able to support the 10-amp load you describe, so long as the sum of all of the items plugged into that electrical circuit don't overload it.
Thank you for responding, my town home was built in 1999, not sure if that is considered newer or older, lights do dim though when i use 10 amp vacuum . - Johnny B.
Backwiring electrical receptacles is a permitted installation and might be found in a 1999 home - but as we show above, there are two different approaches, the second of which is a better quality installation and is in our opinion more reliable. See the details just below.
Contractor-grade 15-A spring-type-connector back-wired electrical receptacles (below left) provide a single opening at each of the four terminals (two neutral wires - yellow arrows, and two hot wires - red arrows) on the back of the receptacle.
The white arrows point to the smaller rectangular opening giving access to a press-to-release spring that will allow removal of the wire, but we prefer not to re-use this type of back-wired receptacle. Tightening the screw at the main wire terminal (blue arrow) has nothing to do with the spring-clamp that is securing the back-wired terminal wire.
You can see that this receptacle also includes two binding head screw connectors on each side - silver screws for neutral wire (right side in the photo) and brass-coloured screws for hot or black wire (left side in the photo). I consider these screws a more secure electrical connection than the push-in backwire connectors though of course a bit more labour is involved as well.
Some newer heavy-duty 15-A back-wired electrical receptacles (below-left) do not rely on a simple spring-edge to contact the electrical wire, as we illustrate in our photo below. Rather, when the wire is inserted into any of 4 receiving holes on the back of the receptacle (red arrows) on the line side (black wire) and another 4 receiving openings on the load or neutral side (white wire) of the device.. When the terminal screw is tightened that actually snugs up a clamp that contacts a much larger surface area of the back-wired wire. That's a more secure connection mechanically. On this receptacle, instead on a single back terminal accepting a single wire, there are a pair of back terminal openings at each of the four terminal screws.
The 20-A rated electrical receptacle shown below is a variation on the 15-A pressure-clamp connector discussed just above. This receptacle dispenses with the round holes in the plastic receptacle back and exposes the wire clamps for a more clear view of what's happening. The electrical wire (copper-only according to markings on these device) is inserted between a copper face plate (red arrow) and a thicker silver colored base plate (green arrow). Turning the screw (blue arrow) at any of these four connectors (each of which will accept two wires) pinches the stripped wire-end between these two plates.
A comparison of crude contact areas between the copper wire and the different types of wire connectors is at RECEPTACLE WIRE-TO-CONNECTOR CONTACT AREA SIZES.
Below is a side-view of the tightened connector.
See WIRE-TO-CONNECTOR PERFORMANCE SUMMARY for our conclusions about the most reliable wire connections made at receptacles and switches.
(June 3, 2014) William said:
I am changing a wall plug with a double plug but the wires are too thick to go through the hole of the new device. HOW can I resolve this?
Use the screw terminals not the backward device.
Newer receptacles and switches that permit push-in back-wired connections usually have a small opening that will only accept #14 copper wire. It appears that manufacturers don't want you to use #12 copper nor any aluminum wire in these devices. Aside from other performance issues raised in this article series, we were concerned (speaking for me not manufacturers) that an older device back-wired with #12 copper might later have the #12 wire removed and still later someone may insert a smaller #14 copper wire into the same opening. Because the spring-clip connector was earlier pushed to accommodate the larger #12 wire one would worry that the same spring may no longer apply sufficient clamping force when a smaller #14 wire is inserted.
Furthermore the process of removal of the #12 wire from the spring-clip connector may also have affected its clamping force, either by the pressure on the release portion of the spring or because a gorilla pulled out the older wire by sheer force (not an easy task).
Watch out. What are those large diameter wires? If aluminum you have a bigger safety hazard to address.
See ALUMINUM WIRING HAZARDS & REPAIRS - home
Also see HOW to CONNECT WIRES to a RECEPTACLE or SWITCH for details on how to make the physical connections.
At the end of a circuit, I'm only using 2 of the 4 screws on a conventional plug. What should I do with the 2 unused screws? Should they be screwed all the way in? Or left partially unscrewed? Or does it matter? - Chris Rasko 7/8/12
regarding the un-used screw terminals on an electrical receptacle, you should simply screw them all the way in and leave them alone. Don't remove the screws - it's not necessary, they are deliberately hard to remove completely, and they could be needed in some future wiring change.
Continue reading at BACK-WIRED ELECTRICAL DEVICES - home or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see ELECTRICAL OUTLET, HOW TO ADD & WIRE - home - for general wiring procedures, connections & advice for connecting electrical receptacles.
Or see ELECTRICAL RECEPTACLE CONNECTION DETAILS - where & how to connect black, white, red, green, ground wires.
Or see RECEPTACLE WIRE-TO-CONNECTOR CONTACT AREA SIZES for a discussion of the areas of wire-to-receptacle contacts on electrical receptacles.
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