Does the NEC require wire nuts for splices?

No. NEC 110.14(B) requires splices to be made with a device identified for the purpose, or brazed, welded or soldered, then insulated. Lever connectors, push-in connectors, crimp sleeves and set screw connectors all qualify when listed.

Are lever connectors code approved?

Yes. Lever connectors listed under UL 486C are identified for splicing and are accepted the same as twist on connectors, provided the conductor size and material fall within the listing.

What do I use to splice conductors larger than 6 AWG?

Split bolt connectors with a listed insulating cover, insulated multitap set screw connectors, or crimp sleeves. All must be torqued or crimped per the manufacturer instructions as required by NEC 110.14(D).

What are common alternatives to wire nuts?

Wire nuts are the default in residential work, but NEC 2023 never names them. Section 110.14(B) simply requires that splices and joints be made with a device identified for the purpose, or brazed, welded or soldered, and then covered with insulation equivalent to that of the conductors. Anything listed for the conductor sizes and materials you are joining is fair game. The realistic alternatives are lever connectors, push-in connectors, crimp sleeves, split bolt connectors, set screw connectors and insulation displacement connectors.

Lever and push-in connectors

Lever connectors are the fastest growing replacement for twist on connectors in device boxes. Each conductor gets its own port with an independent clamp, so a loose or short strip on one conductor does not compromise the others. They are listed under UL 486C the same way wire nuts are, and most are rated for both solid and stranded conductors, which twist on connectors often are not. Push-in connectors work the same way without the lever and are usually cheaper, but they do not release cleanly, so they are better for splices you never expect to open again.

The main field advantage is box fill and repeatability. A lever connector produces the same clamping force every time, while a wire nut depends on how hard the installer twisted it. The main disadvantage is cost per splice and the fact that some models limit you to a single conductor size range.

Crimp sleeves, split bolts and set screw connectors

Crimp sleeves with an insulating cap or heat shrink are the go to for permanent splices in commercial and industrial work, especially where vibration is a concern. Use the crimp tool the manufacturer specifies, because 110.3(B) makes the listed instructions enforceable.

Split bolt connectors handle the large conductors that no wire nut covers, typically 6 AWG and up, and get taped or covered with a listed insulating boot. Set screw connectors, sometimes called king grip or Polaris style insulated multitap connectors, are the cleanest option for splicing feeders inside a junction box because the insulation is molded and no taping is required. Torque them to the value stamped on the body, since 110.14(D) requires terminations to be torqued to the manufacturer value using a calibrated tool.

What all of them still have to satisfy

Whatever device you use, the same rules apply. The connector has to be listed for the conductor material, so a copper only connector cannot splice aluminum to copper, which needs an AL/CU rated device and often an oxide inhibitor. The connector rating cannot be the weak link on temperature, since 110.14(C) forces the whole circuit to be sized on the lowest rated component. The splice must stay inside an accessible enclosure under 300.15, and box fill under 314.16(B)(1) counts each splice device as one conductor volume based on the largest conductor in it.

Field takeaway

There is no code preference for wire nuts. Pick a listed connector that matches conductor size, material and temperature rating, install it per the printed instructions, and any of these options passes inspection.