Why is there so much extra Romex zigzagging behind the master bath mirror?

That zigzag is basicly a service loop on steroids, and it's standard practice for bathrooms where the final fixture layout is still up in the air. When we're doing a rough-in on a new build, we often don't know the exact dimensions of the vanity or the mirrors the homeowner is eventually going to pick. If the plans change from a single massive mirror to two smaller ones with sconces in between, that extra cable lets us pull the wire wherever it needs to go without having to rip out drywall later.

ussually, we leave that wire loosely stapled or just tucked into the framing so it doesn't get pinched during the hanging process. Once the drywall is up and the cabinets are acutally on-site, the trim-out crew will come back, measure for the exact center of the sink or the mirror, and cut in a **remodel box** right where the fixture needs to sit. Having four or five feet of slack behind the wall means they can reach almost anywhere in that stud bay without a struggle or a junction box in the wrong spot.

And it's not just about the placement; it's about the type of lighting too. Some of those high-end LED mirrors or heated defogger setups require the power to come in at a very specific spot, often near the bottom or the side of the mirror frame rather than the center. If the electrician just stubbed out a single box in the middle of the wall, they'd be stuck. By leaving a big "S" curve of Romex, they've basically future-proofed the wall for whatever the buyer ends up ordering. It might look like a waste of copper, but the labor cost of moving a fixed junction box after the walls are painted is way higher than the price of an extra ten feet of 14/2. It’s a common trick to keep the job moving forward when the design details are still fuzzy. If you see it tucked behind where a vanity is going, that’s almost certainly what’s happening.

That makes a lot of sense. I didn't realize they'd just cut the hole later. How do they actualy find the wire once the drywall is up, though? Do they use a magnet or somthing, or do they just have to remember roughly where that stud bay was? Also, does having that much extra wire coiled up behind the wall cause any issues with heat? I’ve heard about wires getting hot if they’re bundled too tight, but maybe that’s only for high-voltage stuff or when they’re under a lot of load. It's wild how much planning goes into just a simple bathroom mirror setup.

Finding the wire is usally just a matter of taking a quick measurement from the nearest stud or the floor before the rock goes up. Most guys just jot it down on the subfloor with a Sharpie. Regarding the heat, you won't have an issue with standard lighting loads. Derating and heat buildup really only kick in when you've got several high-draw circuits tightly bundled together for long distances. A few loose loops of 14/2 for an LED mirror or a small defogger pad isn't pulling enought current to get warm. It’s way better to have that slack than to be fishing wire through finished drywall becasue the homeowner changed their mind.

I've seen plenty of guys lose those Sharpie marks when the flooring goes down or things get messy. If that happens, we ussually break out a circuit toner to sniff it out thru the rock so we aren't poking "exploratory" holes everywhere.

One thing to watch out for is making sure that slack is tucked way back in the cavity. If it's sitting too close to the face of the stud, a drywaller might catch it with a RotoZip or a long screw. Repairing a nicked wire behind finished tile or a heavy vanity is a total nightmare compared to just being careful during the rough-in.

I'd also keep an eye on how it interacts with the insulation if that's an exterior wall. Shoving a big bundle of copper behind fiberglass batts can compress the material and create a cold spot. Another thing I've seen is guys forgetting to staple the top of that loop loosely. If the whole 'S' curve is just hanging by the switch box connection, it can actually put a wierd amount of tension on those terminals over time. I ussually throw one loose staple up high to support the weight while still keeping the wire mobile for the trim-out.