How to strip insulation from electrical wires when wiring a light switch or electrical receptacle.

Here we explain how much insulation to remove and to avoid damaging the electrical wire when preparing wires for connections to receptacles or switches.

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.

How Much Insulation to Strip Off of the Electrical Wire?

If the wire insulation is stripped the perfect amount then after it has been inserted into the clamp or wrapped around the screw you'll see that no wire insulation is under the connector itself, but little or no bare wire is exposed past the edges of the connector.

Above our white wire was stripped correctly - the stripped end was pushed into the clamp until it stopped, and the screw was tightened against bare copper, but just about 1/16" or less of bare copper shows above the screw (photo shown above left).

Our black wire was stripped too much (photo above-right) and some unnecessary bare copper remains exposed after the screw was tightened.

If you going to wrap the electrical wire around the terminal screw on the electrical receptacle (or a light switch terminal) you need to strip back a bit more than 1/2-inch in order to have enough copper to go around the screw leaving no insulation under the screw head when it is tightened.

Our photo (left) shows the strip gauge marked on the edge of our receptacle - those two parallel lines cast into the black plastic housing just below our stripped-back white wire.

Readers of this article should also

see ELECTRICAL CODE BASICS, ELECTRICAL DEFINITIONS.

This website provides information about a variety of electrical hazards in buildings, with articles focused on the inspection, detection, and reporting of electrical hazards and on proper electrical repair methods for unsafe electrical conditions. Critique and content suggestions are invited. Credit is given to content editors and contributors.

Nicks in Stripped Electrical Wires Make a Bad Connection & Risks Broken Wires

Don't damage electrical wires by nicking them: When installing, securing, or stripping insulation from wiring in order to make a connection, the wire and its insulation must not be nicked or damaged, as we show in the sketch at left, courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool company [ carsondunlop.com ]. Why?

Ultimately nicked electrical wires are far more likely to actually break off completely.

The risk of breakage is increased at an electrical receptacle (compared with say a light fixture) because repeated insertion and removal of wall plugs from the receptacle device itself tend to jiggle the device around in its mount, moving the wires connected to it, flexing them, and breaking at nicks.

Nicked electrical wires may also break off when the device is being pushed back into the electrical box.

Finally, where the available free length of an electrical wire inside of an electrical box is already short, you'll be very sorry if you nick the wire end and later break it off, making the remaining wire shorter still.

Ground Wire Stripping & Paper Removal

Typically the ground wire is bare of plastic insulation, but it may be necessary to remove paper around the wire before connecting it. We like to remove all of the paper around the ground wire rather than leave electro-kindling inside the junction box.

In our photo, left, I've pushed the paper off of the ground wire - but have not yet torn it away from the assembly.

If there is more than one feeder wire entering the electrical junction box then all of the grounds are connected together as well as being connected to the ground screw on the receptacle itself. Special crimp-on connectors are used by professionals to join multiple ground wires in the electrical box, but it is also permitted to use a twist-on connector (which takes more space).

If the junction box is plastic, you're done.

If the junction box is metal, a ground wire is also connected to the metal box using an approved grounding screw or clamp device to tie the wire end to the box.

Most metal electrical boxes have a threaded hole intended for use as a connection point for the ground wire connecting screw, as illustrated in our photograph (left).

Details about how to wire up an electrical receptacle are

at ELECTRICAL RECEPTACLE CONNECTION DETAILS - where to connect black, white, red, green, ground wires.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Question: armor around wire through concrete?

I am running a new 15A outlet into the back of a bookcase in a 50 year old house with updated electrical. The wire runs out the back of the retrofit box and down through the concrete foundation into the crawlspace to a wire I plan to splice into. Do I need to put armor around the wire run through the foundation? It goes through open air for about 2 feet and there is no way to secure it to anything.

Thanks!
Tom - 7/19/12

Reply:

You need to look at the type and rating of the electrical wire to determine if it is permitted to bury it in concrete or not.

Question: how do I fix a stripped screw opening in an electrical box?

The little metal tabs to which the electrical outlet screws should mount have holes that have been stripped. Can I just use a sheet metal screw to hold the receptacles in place?

Reply: step by step tips for replacing a stripped electrical receptacle or switch box mounting screw
or screw opening

Julia,

If the problem is the screw itself is stripped, simply purchase a replacement screw or a hand full of them from your electrical supplier. These screws are a standard thread and length, but longer versions are available at any hardware store.

For the case you describe, if the stripped problem is the mounting hole you'll need to either enlarge and tap the hole for the next size larger screw, or purchase a clip-on adapter that slips over the stripped ear through which the original hole passed.

Taking care to move electrical wires out of the way of your drill bit, in a metal electrical box you can drill out the 6/32 screw opening to tap and accept an 8/32 screw.

Watch out: do not just screw a sheet metal screw willy-nilly into any electrical box or component: the pointed tip of the screw can easily penetrate the insulation of an electrical wire in the box, causing a dangerous short circuit.

For photos and step by step details on how to repair stripped electrical outlet mounting screws,

see OUTLET BOX SCREW REPAIR.

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Continue reading  at ELECTRICAL RECEPTACLE TYPES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• ELECTRICAL WIRE STRIPPING TIPS for more deatils about preparing electrical wires for connection to devices.

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STRIPPING ELECTRICAL WIRES at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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