Splicing 6/3 wire to multiple 8/3 wires (or even other 6/3 wires) inside a junction box

Question

I have a situation where my oven and counter-top range are split up, but fall within spec of being able to utilize one 50a breaker on the panel.

My plan is to pull a single 6/3 cable to a large junction box, inside which I’d splice the two sets of 8/3 wires from the oven and range with the 6/3 cable (hots and neutrals, the grounds are skinny enough to use a twist-connector). Because the all the cables combine to be pretty thick, I am not sure a twist-connector on the hots/neutrals would be a good choice (previous owner had it that way, but even with smaller cables it felt a bit sketchy).

With NEC 2017 in mind, what type of connectors can I use? In the automotive world I’m used to things like a multi-terminal connector/distribution block. Is there something like this in the home-owner world?

Tried searching and found some split-bolt suggestions - do I just wrap it with lots rubber tape to insulate? Can a split bolt be used to connect three wires (one 6ga and two 8ga or even just 3 6ga if a future oven has that)?

Another option I found are Polaris connectors. Expensive but seem straightforward. Would they or the split bolts need to be secured to the inside of the box, if used?

Any additional suggestions or recommendations are welcome.

Answer 1

I use Polaris and other brands for this, in the past I used to use cambric , linerless and super88 to insulate the split bolts the cost of the Polaris style pays the first time you reuse them and are much easier to use. I use a size 4-14 rated alcu Home Depot actually had a good price on these and I usually put tape on to hold the plugs in place but nothing is required to hold them in the box. Their are 2 lug 3 that I think you want up to 6 I have purchased all 600v rated and UL approved.

Answer 2

There's a neater way to do this

While Ed Beal's suggestion of "Polaris" type insulated mechanical lug connectors will work, it's a bit ugly to have big honking connectors flopping about in a box. Fortunately, there is an analog in the mains world to the distribution blocks you're used to in the automotive world. What you're looking for is also, aptly enough, called a power distribution block; however, in mains-wiring-land, you need to be careful not to confuse them with power terminal blocks, as you must use a part tested and listed to UL 1953 (QPQS category code in the UL database), not a part that's only been component recognized under UL 1059 (XCFR2 category code in the UL database).

Under these constraints, the cheapest option would likely be a Mersen/Ferraz MPDB63163 with a trio of MPDBC6263 covers; depending on where you shop, you'll be looking at about $40-$50 for that, which takes care of both hots and the neutral in one go. This compares favorably to having to get three insulated mechanical connectors at around $20/piece at the time of this writing, and also provides a neater installation as the PDB gets fastened to the back of the box so that nothing can flop about.

You'll want a big box in any case

The other factor in play here is that with either route you take, you'll want to use something larger than a typical 4 or 5" square junction box to house the splices. For starters, "Polaris" type connectors are fairly chunky creatures, with a 3-port, 4-14AWG splice taking up over 2.5 in³, far more than a wirenut or even a push-in type splicing device would use. Furthermore, the rules in NEC 314.28(E) regarding the use of power distribution blocks only permit their use in boxes upwards of 100 in³ in size, and also require NEC 312.6 compliant wire-bending space at the power distribution block's terminals.

As a result of this, I would recommend that you make these connections in a NEMA 1 pull box instead of an ordinary junction box. A 6"x6"x4" box with a matching flush cover will provide enough space for all of your splicing needs, and costs only about $20 at your local electrical supply house. (It also fits within a standard 2x4 stud wall, if only barely.) You'll want to use an appropriately threaded machine screw into the grounding hole on the box with a 10AWG solid copper pigtail to connect the box to the incoming ground wires, by the way, and don't forget to use NM clamps in the knockouts, just as you would with a regular junction box.

Answer 3

If you have a circuit rated for 50A using that sized breaker and 6/3 cable to distribute to the load then ALL wiring on that circuit must be rated for 50A. You may not splice in smaller gauge wires because they would not be rated to carry the full capacity of the circuit.

On the other hand you may use larger sized wiring to distribute to the loads receptacles as long as the circuit breaker rating does not exceed the current rating of the smallest gauge wire used in the circuit.

If you do use mixed gauge wiring in a circuit make sure to provide marking and tagging, especially in the main distribution panel, that such usage is being done so that someone in the future does not see large sized wire going to a circuit breaker and think that the breaker can be upgraded to a higher capacity.