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I have an electrician running a 220 line out to my shed, using 4-4-6 braided aluminum run underground. The wire is about 3 feet too short (after running about 150 feet). He wants to just use 3 wire nuts for #4 gauge wire and tie the 3 right above the circuit panel and then make the connection to the breaker.

Is that legit? I'm okay with it if it isn't going to cause a problem, but I just wanted to make sure.

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    The pros will give the exact answer - but the short version is: It is OK as long as (a) the wire nuts are rated for aluminum and are the correct size and (b) the connection has to be inside a junction box. – manassehkatz Dec 30 '18 at 17:17
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    What's he doing for a ground wire? Or is this 220V-only?. – Harper Dec 30 '18 at 17:20
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    What type of wire nuts? I have not seen that large "purple" aluminacons , usually I use lugs for splices above #8 even with copper, if they are listed for aluminum to aluminum connection at this size it would be legal but I prefer Polaris style because they are already insulated and the lock screws hold as well as split bolts. – Ed Beal Dec 30 '18 at 17:51
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    I don't believe they even make wire nuts for that wire size, your options are split bolts or Polaris connectors when the wire gets that big... – ThreePhaseEel Dec 30 '18 at 19:09
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    @manassehkatz, I think the question is about stranded wire not "braided" wire, right? – Jim Stewart Dec 30 '18 at 23:50
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He'll need to use a pull box to house this

Splicing of wire that fat can't be done in a regular junction box due to the fact regular junction boxes are too small to let the wire be bent in conformance with bending radius specifications. Instead, what's needed is a NEMA rated (NEMA 1 if it's inside, NEMA 3R if it's outside) pull box, as these are available in dimensions that conform with the specifications in NEC 314.28(A)(2):

(2) Angle or U Pulls, or Splices. Where splices or where angle or U pulls are made, the distance between each raceway entry inside the box or conduit body and the opposite wall of the box or conduit body shall not be less than six times the metric designator (trade size) of the largest raceway in a row. This distance shall be increased for additional entries by the amount of the sum of the diameters of all other raceway entries in the same row on the same wall of the box. Each row shall be calculated individually, and the single row that provides the maximum distance shall be used.

Exception: Where a raceway or cable entry is in the wall of a box or conduit body opposite a removable cover, the distance from that wall to the cover shall be permitted to comply with the distance required for one wire per terminal in Table 312.6(A).

The distance between raceway entries enclosing the same conductor shall not be less than six times the metric designator (trade size) of the larger raceway.

When transposing cable size into raceway size in 314.28(A)(1) and (A)(2), the minimum metric designator (trade size) raceway required for the number and size of conductors in the cable shall be used.

Note that for large raceways, this can lead to rather large boxes, so it may be best to mount the box to one side of the panel and leave a bit of slack length in the too-short run instead of mounting it above the panel, although mounting it below a bottom-fed panel may not be an issue, depending on the depth of the box.

4AWG Wirenut Not Found

Wirenuts are generally not made in large enough sizes to splice 4AWG wires, so your electrician will be using a different splicing device -- a mechanical setscrew connector, or Polaris™ connector as it is often called. These, like wirenuts, are one-piece splicing units, but instead of twisting the wires together, each wire is individually attached using screws that clamp the wires down into a block of plated aluminum, much like a breaker box neutral or ground busbar. While they are available in different configurations (one-sided, two-sided, in-line), most are like the picture below in that the screws sit under the caps on top while the wires go into the ports on the front and/or back (or each end) of the connector. Furthermore, as a result of their construction, they can handle a variety of wire sizes (even in a single connector -- the smallest ones go from 14AWG to 4AWG, and the next smallest size starts at 6AWG and goes to 3/0 or more), and can handle any mix of copper and aluminum wire.

picture of a mechanical setscrew connector

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