I have a need to splice a 6/3 romex and 4/3 romex in my attic. It would look something like this:

4/3  |-- (6/3) new destination
     |-- (4/3) original destination

I am looking at purchasing the following connector: https://www.amazon.com/gp/product/B00UKGG0C6/

The current breaker is 70amp. I will downgrade that to 50amp because of the 6/3 wire.

I have read conflicting reports on whether these connectors require a junction box or not. Can someone please give guidance? Please cite any references rather than just opinions!

  • 3
    What size breaker do you have feeding that original 4/3 cable? – brhans Jul 10 '18 at 18:31
  • 1
    It was 70amp. It's my intention to go down to a 50amp breaker because of the 6/3 cable. – Bryan Frederick Jul 10 '18 at 19:06
  • You do understand you'd need four of those, yes? That thing is not 3 poles x 3 ports, it is 1 pole x3 ports and can only accommodate 3 wires period. The wires can enter either from left or right but not both at once. The top "port-like-thing" is actually where you put the allen wrench to torque it. Go to the local electrical supply and ask for those with maximum size is #4. It will fit your wires better and be cheaper also. I paid $11 last time I needed a 3-wire #2. – Harper - Reinstate Monica Jul 10 '18 at 19:09
  • Yep. I understand that I'd need 4 of them. Anyone know if I require a junction box? – Bryan Frederick Jul 10 '18 at 19:53
  • From "Amazon Customer" so not necessarily a reliable source - in the Amazon Q & A: Do these connectors need to be enclosed inside a junction box? For household usage, yes. And if behind walls, without a doubt yes. – manassehkatz-Reinstate Monica Jul 10 '18 at 19:57

You'll need a box, and a pretty chunky one at that

Splicing wire this large is indeed done with insulated mechanical splice connectors like the one you linked -- you will need one per wire, and a torque screwdriver or wrench, marked and calibrated in inch-pounds, to install them properly. As to containing the splices, you will need something larger than a normal junction box -- in fact, what you need is called a pull box, and needs to be sized according to NEC 314.28(A):

(A) Minimum Size. For raceways containing conductors of 4 AWG or larger that are required to be insulated, and for cables containing conductors of 4 AWG or larger, the minimum dimensions of pull or junction boxes installed in a raceway or cable run shall comply with (A)(1) through (A)(3). Where an enclosure dimension is to be calculated based on the diameter of entering raceways, the diameter shall be the metric designator (trade size) expressed in the units of measurement employed.

(1) Straight Pulls. In straight pulls, the length of the box or conduit body shall not be less than eight times the metric designator (trade size) of the largest raceway.

(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.

Given that you are splicing in this box, and that a 4/3 W/G cable is equivalent to 4 4AWG THHNs (actually a bit less due to the ground being bare, but lets ignore that for now) or 212mm2 of fill, which barely fits down most types of 1" conduit, we wind up needing at least a 6" square box, and likely something more like an 8" square box. Fortunately, a NEMA 1 pull box of that size (such as this) isn't too hard to get one's paws on -- your local electrical supply house should definitely be able to get one in for you.

Grounding the pull box, by the way, will require you to use either:

  • a four-way insulated mechanical splice for the ground wires as well as an 8AWG copper pigtail from the insulated splice to the green ground screw in the box.
  • or a ground bar in the pull box, attached to the box where the green ground screw goes, with the ground wires landed on that.
  • Thanks for the thorough answer. For clarification, how would I go about grounding this setup? I assume I can't just use one of these 3 way connectors and not ground the metal pull box? – Bryan Frederick Jul 11 '18 at 3:27
  • 1
    @BryanFrederick -- edited in details on grounding – ThreePhaseEel Jul 11 '18 at 3:41
  • Something else to think about... at what point does it become easier to replace the entire run of wire, instead of trying to splice? – longneck Jul 11 '18 at 13:31

Yes, it must be in a junction box. There are splice connectors available for installation in a space where a junction box is not possible, but those splice connectors are explicitly rated for such a purpose; the connector you have proposed is not.

Putting a junction box in an attic is not that big of a deal. Just do that.

  • How large / what type of junction box would be appropriate? I read that there are size limitations for any junction box with wire 4/3 and larger? – Bryan Frederick Jul 10 '18 at 21:58
  • 1
    An ordinary junction box won't do here...4AWG puts you into pull box territory. – ThreePhaseEel Jul 10 '18 at 22:42
  • Good point. I missed how big that wire is. – longneck Jul 11 '18 at 2:38

Your Answer

