I'm running 100 AMP service out to a shed/workshop - and while I see a TON of posts floating around about how to do this and all the codes, this isn't my question.

After consulting with a local electrician, I've agreed (and understand) everything BUT one bit - once the THHN 3 gauge wires are pulled on either end to a junction box, and the 3-3-3-5 SER cable meets it in there - how does one connect these things together?

I've seen people suggest copper crush bolts, and others say no. I can see that granger sells a plastic case for these things so it's POSSIBLE they can all be insulated from each other.

I've seen the polaris fittings, but can't seem to find something that supports 3 AWG wire.

Any tips/links/etc? Even if it's just to some additional reading material, that'd be HUGELY helpful!

  • They make split bolts with nuts that will accept the size and number of said wires. Also make sure you buy the ones that are for your type wire. Then you cover and tape the connections for safety.. Some of the electricians that follow this site will have more and maybe better recommendations for you. – d.george Aug 6 '17 at 13:20
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    I am curious as to why the cable is not run fully from source service panel to the outbuilding sub-panel eliminating the need for splices. What am I missing here? – Michael Karas Aug 6 '17 at 16:12
  • Maybe because I just don't know better. Here's the plan, from the main panel to a junction box inside the house I'll be running 3-3-3-5 SER and connecting to 3 AWG THHN. The THHN will be in conduit buried betweeen 20' and 24". Then at the workshop, the THHN will meet up with another small section of the 3-3-3-5 SER inside a junction box. I'm pretty sure I couldn't run one contiguous THNN without it being inside conduit everywhere. I thought this may give me all the flexibility I may need for future work. Thanks for the feedback! – EJC Aug 7 '17 at 13:07

I recommend the ISR-10 by NSI Industries or equal. They splice and are completely insulated. Pretty much foolproof. You can Google them and you will see what I mean.


This might get you there. You can probably buy them online or from a wholesaler or someone like grainger.

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  • Yes, those, except one that's just the right size for the wire (can't accept a larger wire). That way the insulation fits snug. Torque it to spec. You buy them from your friendly neighborhood electrical supply house, the one intended for use by the trade. If they don't have those in stock, they super suck. – Harper - Reinstate Monica Aug 6 '17 at 17:08
  • Holy MOLY the NSI Polaris ones are expensive! I'm looking at four at either end (8 total). At $75 - $100 a pop, it's a pass. Morris has similar ones for $15 - $30 a pop - hoping they are as reputable as NSI. – EJC Aug 7 '17 at 13:24
  • I just checked with a local supplier and I can purchase a Polaris ISR10 type connector for $14.73 ea. That is probably a contractor price so your might be 30% higher but not any more than that. Check with a local wholesaler and see what you can work out. – Retired Master Electrician Aug 8 '17 at 21:20

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