Complex continuous run vs easier single junction boxes

Question

I am currently in the process of finishing my basement and I am doing the electrical wiring of all my rooms. The work will be checked by my electrician before he connects everything to the electrical panel.

For all of my electrical outlets and other appliances, I have used a continuous circuits that have no unnecessary junction box. The junctions take place from one outlet to another, etc.

However, for my light and my heating circuits (one of each), I am considering using two single junction boxes at the center of my basement that would have 4 load romex going out to each of the rooms of my basement. That would save me from using a continuous circuit that would require hundreds of feet of cabling passing through weird places (under sheetrock ceiling, around staircases, etc.) instead of going through the middle of the main room that has dropped ceilling for easy access. Also, if I want to add lights in the future, I would be able to just add a cable to this 4x4 junction box.

I know that the use of junction box is frown upon, but since they would be under a drop ceiling (easy access), would you consider that this design is justifiable?

Also, I know having a single light circuit is not ideal, but that would power a few low wattage LED and won't utilize 10% of this 15 amp circuit. Again, having a center junction box could enable the addition of another 15 amp circuit load line, but I highly doubt this would be required.

Answer 1

It seems the heart of your question is topology. "Bus" topology is what you have for your outlets, in which power comes from the distribution panel to one outlet, then to the next, and so on like a chain. "Star" topology is one in which power comes from the distribution panel to a central point and then branches out in multiple directions. It sounds like this is what you're entertaining for the lighting.

Both bus and star are acceptable. Wire sizing, demand calculations, and so on are the same regardless of the topology.

As for the junction box at the heart of the star topology: it needs to be in an accessible place, and it needs to be sized appropriately to contain the wires. "Accessible" means it can be reached without removing any part of the building. Drop-in ceiling tiles seem to be accepted as "accessible" virtually everywhere, so if you make the junction in a box (don't forget the cover) and put it above a drop-tile ceiling that'll be fine.

Junction box sizing is determined with an exercise called "box fill calculation." It considers the number and gauge of conductors being joined or merely passing through, any devices like switches or outlets also in the box, etc. Boxes are marked with their cubic inch volume; the box fill calculation tells you the minimum number of cubic inches needed.

Answer 2

What Greg Hill says about topology.

You can branch out anywhere you want. It's not down to only 2 choices of "string" vs "hub and spoke". Each outlet on a circuit can simply go to the nearest and most convenient outlet that has already been reached. Or to a junction box you choose to create somewhere.

The only thing you have to watch for is junction box size, as Greg discusses. "Octagon boxes" (round boxes) intended for lamps are the most troublesome here.

For very large boxes, use 4-11/16" square deep boxes, with an appropriate 1-gang, 2-gang or round mud ring or domed cover.

You seem to be in North America, so this answer is based on that.