I recently drilled through the floor to run a CAT6 cable and hit the main feed to our panel. I'm in a duplex with a meter main panel with 2 meters and 2 100A breakers, one for each unit. The cable that runs from the meter main to the sub-panel in my unit got damaged. Basically a big arc and flash as I bridged the hot and neutral, the tip of the drill bit was vaporized.

It did not trip the main 100A breaker. I temporarily fixed it by opening up the cavity between the ceiling and the floor, and insulating the damaged conductors after I removed the sheathing. I estimate that maybe 20% of the conductor is locally removed when I hit it with the drill. I'm not sure what the gauge of the wire is. I've included some pictures from the sheathing where I could see it. I think it is #1 or #2 aluminum. Based on the fact that it supplies the entire dwelling, I think the cable needs to be rated for 83A, even though it is a 100A service. I've learned in the past on this forum that "2AWG aluminum SE is allowed to carry 90A when terminated on 75°C lugs as per 338.10(B)(4)(a)".

I would like to repair the cable, and I'm thinking that the inline splicers from Polaris can be used for this, specifically a ISR-1/0. I would need to put a box around this to make it an accessible junction box. Would this be an acceptable permanent repair, or are there better ways to fix this cable? And what do you think is the gauge of the cable?


Damaged cable from drill Conductors with sheathing stripped A fuzzy pictures of damaged conductors Markings on sheathing More markings on sheathing Temporary fix

Opening in ceiling Closeup of ceiling cavity

  • How much space is there to fit a box there? Jul 21 '19 at 23:49
  • The space is 5.5" tall, the slot in the drywall is 10" by 24" or so. I've added a couple of pictures, you see it is fairly busy in that space, but I can probably pull those other NM wires out of the space because I'm relocating the panel. Unfortunately I probably can't reach the new panel location with the un-damaged part of the wire. BTW the quote about 83A is from a previous answer from you. Thanks for your advice Jul 22 '19 at 0:36
  • This is one of the rare cases I've seen where a box and a splice will work out. Jul 23 '19 at 2:19
  • Thanks @Harper, the electrician is proposing a mechanically crimped splice, rather than the Polaris connectors, which I assume is fine for an inline splice. A bit harder to do for a tap, but this is just an inline splice Jul 25 '19 at 19:53

You'll need a pretty chunky box for those splices

Wires 4AWG and up can't be spliced in any old junction box as they're simply too stiff and fat to fit into junction-box-sized boxes. Instead, you need to use what's called a pull box in the trade to house your splicing job, which invokes the box sizing rules in NEC 314.28(A), specifically (A)(2):

(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 314.28(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.

(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.

As a result of this, we come up with 477mm2 for a 1-1-1-3 aluminum SER cable at slightly under 1" diameter, which fits into a 1.5" conduit (it's slightly too large for a 1.25" conduit). So, we'll need an 10" by 10" by 4", NEMA 1 (indoor rated), screw cover pull box (the Wiegmann SC101004 should do the trick), along with a matching flushmount cover (Wiegmann SCF1010), and cable entrance fittings that can work with such a large cable. The Polaris connectors you have chosen will work fine for splicing, by the way: the only caveat with them is that you'll need to use an inch-pound torque wrench to tighten them to their specification torque for a reliable connection (this is required by 110.14(D) of the 2017 NEC).

  • Thanks for your usual thorough answer. I cut away the jacket to fix the wires, if you look at the last picture on the left side, you can see the jacket. Also the pictures 1,3 and 4 show the cable with jacket. Is that not a proper jacketed SER cable? I think I can fit a 8x8x4 pullbox up there. I'll have to see if there is enough jacket left on either end to use the SE entrance fitting. Do you think the inline Polaris connectors are good as a permanent splice? Jul 22 '19 at 5:24
  • @ChristianK -- edited that for you Jul 22 '19 at 11:42
  • Well done sir.... Jul 23 '19 at 2:18
  • Thanks, a 10x10x4 box should work. Sorry to ask again, but what is the max current that the 1-1-1-3 Al SER cable can handle. I think I can use the 75C column (100A), because I don't think my SER cable runs through insulation, but I've also heard mentioned that I should use the 60C column (85A?). I know there is a derating of 83% because it serves the entire unit, but I would like to know the max the cable can handle, and if it is OK to be protected by a 100A breaker. Jul 25 '19 at 5:09
  • 1
    @ChristianK First off, due to the fact your cable is larger than 10AWG, there are no issues with running it at 75degC ampacities, even through insulation. Second, since just about all modern distribution hardware has terminals that are rated 60/75degC, you can use 75degC wire at 75degC ratings with it provided the other end is also rated the same way, independent of wire gauge, as long as the small conductor rules in 240.4 don't kick in. Jul 25 '19 at 22:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.