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I'm planning to mount a 12x12x6 junction box above my new panel to extend some wires that do not reach into my new panel and add CT's for energy monitoring. I saw an electrician on Youtube that mounted a box with 3 short nipples above his panel. He also added a ground bar in the junction box and used it to land the grounds for the circuits to be extended. I like this approach because it keeps the panel less crowded.

He ran one ground conductor (#6?) down to the panel from the ground bar in the junction box. I think I'm required to have a ground in each conduit (either a conductor in a PVC conduit or bond metallic conduit). Should I run one ground conductor from that junction box ground bar through each nipple? I'm assuming it should be sized for the largest conductor in that nipple, is that correct? I know it is important to keep the neutral paired with the hot conductors in the same conduit.

I'm going to have something like 20 circuits running through this box. I don't think I'll have an issue with box fill based on the 20 spliced circuits, but how do I account for CT's in the box fill calc?

Any issues with some cables running straight through (no splice) with just a CT clamped on the hot conductor?

Thanks

Junction box with 3 nipples above panel

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    Assuming that's a screen grab from the video rather than your (planned) installation, just use metallic nipples properly installed, and grounding is done. A pessimistic (thus unlikely to fail inspection) box fill might consider each CT as a "device" for box fill calculation purposes.
    – Ecnerwal
    Commented Mar 1 at 17:01
  • @Ecnerwal yes, that is a screen grab from the video. Are you suggesting that I use metallic nipples and don't run any ground wire through the nipples and use a bonding bushing on both sides of the nipples to run a jumper to the ground bar? All 20 incoming circuits would have their grounds terminated on the ground bar in the junction box, and the only connection to the ground bar in the main panel would be through the metallic nipples. Commented Mar 4 at 1:51

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You need to run a EGC in each conduit:

NEC 300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, conduit body, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

For calculating the box fill I don't find that the code provides clear instruction, so your best bet is to call your local inspector and ask his interpretation since:

90.4(B) Interpretations. The authority having jurisdiction for enforcement of the Code has the responsibility for making interpretations of the rules, for deciding on the approval of equipment and materials, and for granting the special permission contemplated in a number of the rules.

I don't see any problem with unspliced conductors running through the box being aware if you leave a loop big enough to cut and splice you need to count it twice.

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I've always been told that the ONLY place neutral and ground wires can be bonded together is in the main panel.

When I added a 60-amp sub-panel, I ran three #6 cables, one connecting the neutral bar in the sub to the neutral bar in the main. I also ran an earth ground from the grounding bar/structure of the new panel out and clamped it to the earth ground for the main panel. Maybe this was not necessary, as I did use a steel nipple with double conductive lock rings on each end.

I have had zero issues with it in the 5-6 years it has been in use.

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