Wire connectors are electrical fasteners that are essential to help you join (splice) electrical conductors together so that you can connect house wiring to outlet receptacles, switches, and lighting fixtures. Using a wire connector to make such a splice is easy. Even those of us who aren’t electricians can do it. On the other hand, if you get it wrong, it’s possible you can create a short because the wires worked loose or the connector cracked in half, exposing live electrical components to their surroundings. In the worst case, you can start an electrical fire—with catastrophic results. The circuit breaker or fuse may or may not offer protection from a melt down caused by an improperly applied wire connector.

To help you on the path to make a safe, tight, and electrically sound splice, we’ve done several things. Below, we show some reliable electrical connectors; all of them are listed by Underwriters Laboratories (UL) or a similar listing agency. Simply stated, don’t use any connector that lacks this. Second, we have provided links to wire-stripping tools (since you need to strip wire without damaging it before you apply the connector that will make the splice). These are tools that we’ve used and can vouch for.

Aside from relying on our own experience (for example, where we have worked on volunteer construction projects under the supervision of a licensed electrician), we’ve also interviewed David Shapiro, a licensed electrician, electrical inspector, and expert who has spent countless hours as member of various electrical code advisory groups. Having practiced the electrical trade for the last 40 years, he’s made thousands of electrical splices and investigated nearly as many failed splices in old homes. His book on old house wiring and upgrading old house wiring are considered by many to be industry classics and the definitive works on these subjects.

More From Popular Mechanics
preview for Popular Mechanics All Sections

The Types of Wire Connectors

wire connectors

The Tools for the Job

The Splicing Process

Using a twist-on wire connector comes down to three basic steps: strip the wires (conductors), line them up, and twist on the connector.

wire connections

And within those steps, Shapiro suggests some additional quality control checks.

1. Look inside the connector. You should see an intact spring, fully seated. If in the unlikely event that the spring has fallen out, discard the connector.

2. Strip the correct length of wire. This varies widely and can range anywhere from ¼ inch all the way up to 7⁄8 inch, depending on the type of connector.

3. Check for nicks before making the splice. A nick created from the stripping tool leaves a stress focal point and an area of hardened material. Both of these can cause a crack to propagate in the spliced wires, leading to electrical failure, overheating, and, perhaps, an electrical fire.

4. With the conductors stripped to the correct length, line up the insulation on the conductors.

5. Seat the connector over the conductors and twist very firmly in a tightening, clockwise, motion. Some manufacturers even recommend that the connector should not only be fully tightened but that the conductors should themselves have two to three twists in them. There are several types of twist-on wire connectors with wings that facilitate both twisting by hand and by using a connector-tightening tool, which may be anything from a specially equipped screwdriver or as simple as a nut driver. Shapiro cautions, however: “These (tightening) tools are really handy, but you can crack a connector with them if you’re not careful.”

6. Check the connection by pulling firmly on the conductors. Don’t jerk on the wires; rather, exert firm and increasing force. Shapiro notes that the UL standard for these connectors varies from 25 pounds for 14-gauge wire to 35 pounds of pulling force for 12-gauge. That’s a lot of force. As for the pull test, Shapiro says, “Don’t be shy.”

To Pre-Twist or Not to Pre-Twist

Want to spark (if you’ll pardon the pun) a lively debate between electricians? Ask them if they pre-twist conductors before applying a twist-on connector. That is, if they twist the wires together beforehand and then add the connector as insurance or if they allow the connector to twist the conductors together. The UL requirement for listing is that the connector itself must provide sufficient binding force so that it will form an electrically reliable connection without this pre-twisting.

Shapiro, with countless splices behind him, is firmly in the pre-twist camp. “I just about always pre-twist,” he says.

Other electricians nix the idea because pre-twisting makes it all but impossible to untwist the wires without damaging them in the event that you need to make a change to the circuit.

wire connectors

The Push-In Versus Twist-On Debate

What’s more, push-in connectors are flourishing in the electrical aisle because they’re simpler and faster to use than their twist-on cousins. You strip the wire and push it into the connector. Push in the wire (or wires) that you want to bind to it. Done.

With some connectors, such as the Wago above, you open a small lever on the device, insert the stripped wire, and close the lever.

wire connectors

Still, Shapiro is no fan of push-in wire connectors and prefers twist-on types because when properly done they provide more contact area between or among conductors. “Yet I know colleagues who swear by push in connectors,” he says.

Connecting Stranded to Solid Conductors

Handypeople and electricians both have been frustrated by the inability to form a good splice when connecting stranded conductors to solid conductors. The stranded conductor doesn’t seem to get braided in very easily.

The solution is easy, says Shapiro. When splicing stranded to non-stranded, strip slightly more stranded wire. Try adding an extra 1⁄16 inch to the length of stripped wire, line up the insulation, and twist on the wire connector (or pre-twist the conductors first). Then try the pull test.

wire connectors
When bonding solid and stranded conductors, strip slightly more stranded conductor, maybe 1/16 inch.
Roy Berendsohn