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I'm planning on replacing a 100A stab-lok (house burner) sub panel enter image description herewith a QO Mains box enter image description here but I may need about 6 more inches of SER to get connected comfortably. The original box is already about 12 in from ceiling (I know, too high, but it's neigh impossible to run a new service feed). Can the SER conductors be extended, inside the box, with a butt connector and shrink tubing? Or other thoughts? This is a sub panel in the basement fed off 100A breaker at main box in garage. It's not my first box conversion, but the first time I've worried about service cable length. Thanks in advance..

  • What gauge are the existing SER conductors? – ThreePhaseEel May 23 at 18:23
  • Thanks for reading, it's labled '#2' aluminum. It's a fused 100A feed from a breaker box. – Chuck May 24 at 16:20
  • Does this breaker panel serve an entire dwelling unit (apartment or ADU) by its lonesome? What make and model is the upstream breaker box? – ThreePhaseEel May 24 at 16:38
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It is acceptable to splice additional wire to a feeder, as long as that feeder is not an unfused conductor (service entry). Keep in mind that improperly installed splice can become a real nightmare. It might be better to try and raise the new panel up if there are no obstructions rather than try extend the feeder.

Also if an AHJ gets involved they may want to see if the panel has the proper clearances to legally install the splice. That would be wire bending area and proper fill.

Good luck.

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  • Thanks RME, just trying to keep my options open and it is a fused feeder from the main box (100A circuit). No plans on AHJ nosing around, either, but would you have a recommendation on splice hardware for #2 Alu? The splice will be inside the new box, too. Thanks again for the input – Chuck May 24 at 16:27
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    @Chuck - I would use an insulated tap connector. They are made by Polaris, Ilsco, Burndy, or any connector manufacturer. You can get them in many configurations depending on your need and space requirements. – Retired Master Electrician May 25 at 13:07

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