Electrical – Are service loops allowed by US electrical code in residential wiring

I will not speak to the code issue as other already have. But, I did use them when building my new home a few years ago and, for me, they passed inspection.

While the package does say they can be used for stranded wire, I did not find that they worked that easily with stranded wire (I was using some computer controlled switches with pigtails instead of screws). But, they did work. I just had to twist the strands fairly tight first.

As far as coming loose? Not the ones I was using. If memory serves me correctly, I think there is a little hole that you can push the spring up with to release the wire because it is so tight.

Leave just enough "extra" wire to route the wire along the edge of the board so it looks clean like the image below. Otherwise, do not bother leaving extra wire. You can splice more wire within the panel if you need to move things around later. Leaving a lot of additional coiled wire to try to account for the future could result in excess heat build-up and potentially an electrical fire. Note: Some excess wire is harmless, but if the panel begins to look like a mess of coiled wires, then you are likely creating the following situations the NEC tries to protect against in several areas of code (though not necessarily specific to the panels) to make sure the wire will not exceed the heat rating of its insulation at the expected current load:

• Current running through a wire generates heat and relies on air to carry that heat away from the conductor. Therefore, the NEC protects against too many current-carrying conductors in close proximity for other areas of wiring:

  310.15(B)(3)(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(3)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.

  314.16 Number of Conductors in Outlet, Device, and Junction Boxes, and Conduit Bodies. Boxes and conduit bodies shall be of sufficient size to provide free space for all enclosed conductors. In no case shall the volume of the box, as calculated in 314.16(A), be less than the fill calculation as calculated in 314.16(B). The minimum volume for conduit bodies shall be as calculated in 314.16(C).

• When wire is coiled or there are more than one conductor, there is potential to induce additional currents in the wires due to the additional electromagnetic fields not otherwise present with a single conductor. The NEC protects against this related to ferrous metal enclosures and raceways:

  300.20(A) Conductors Grouped Together. Where conductors carrying alternating current are installed in ferrous metal enclosures or ferrous metal raceways, they shall be arranged so as to avoid heating the surrounding ferrous metal by induction. To accomplish this, all phase conductors and, where used, the grounded conductor and all equipment grounding conductors shall be grouped together.

  Exception No. 1: Equipment grounding conductors for certain existing installations shall be permitted to be installed separate from their associated circuit conductors where run in accordance with the provisions of 250.130(C).

  Exception No. 2: A single conductor shall be permitted to be installed in a ferromagnetic enclosure and used for skineffect heating in accordance with the provisions of 426.42 and 427.47.

Image obtained from https://en.wikipedia.org/wiki/File:EEUU%28GE%29BreakerpanelInnards.jpg