Running Ethernet cable seems straightforward enough. Drill holes, pull wire, crimp the ends, and you’re done. I ran Ethernet to over a dozen spots in my basement when we finished the space, and I thankfully remembered not to run them right next to power cables. Cable routing deserves way more attention than I gave it. The category printed on the jacket matters, sure. So do your connectors and how well you terminate them.
Whatever’s running next to your Ethernet inside those walls and ceilings can mess with performance just as much. Power lines throw off electromagnetic fields, and a surprising number of contractors—plus plenty of us DIYers—run network cable right alongside electrical wiring like it’s no big deal.
Electromagnetic interference is the enemy
Why power lines and network cables don’t mix
Every wire carrying electrical current generates an electromagnetic field. That’s just how electricity works. You don’t notice it day to day because your appliances and lights don’t care about a little EMF floating around. Ethernet is pickier. The data signals traveling through network cable are tiny compared to the 120 volts in your walls, and that makes them vulnerable to outside interference in ways that household appliances simply aren’t.
Run your network cable parallel to electrical wiring for any real distance, and the electromagnetic field bleeding off those power lines starts inducing noise into your signal. Packets get corrupted. Your devices have to request retransmissions. Speeds tank, connections drop randomly, and the whole thing looks like some other problem entirely. You might see random speed drops. Connections that work perfectly for an hour and then stutter. Streaming that buffers even though your speed test looked fine two minutes ago. The frustrating reality is that your hardware keeps functioning, just never at full capacity.
Crossing a power line at a right angle isn’t really a concern. The exposure is momentary, and the interference has no time to accumulate. Running ten or twenty feet alongside Romex in the same joist channel is where things get problematic.
Your cable category affects vulnerability
Shielded versus unshielded makes a real difference
The biggest factor in how well your Ethernet handles nearby electrical interference isn’t the category number—it’s whether the cable includes shielding. Unshielded twisted pair, or UTP, relies on the way those internal wires are twisted together to reject interference. It works, but only up to a point. Shielded twisted pair adds a layer of foil or braided metal around the conductors, and that physical barrier does a much better job keeping electromagnetic noise from bleeding into your signal.
Cat5 and Cat5e are almost always unshielded. Cat6 can go either way, which means you actually have to pay attention to what you’re ordering if EMI protection is on your radar. Cat7 goes all-in with foil around each individual wire pair, plus a braided shield wrapping the whole bundle. Cat6a lands somewhere between Cat6 and Cat7—more protection than the basic stuff, less bulk and expense than going full Cat7.
There’s a gotcha with shielded cable that people miss, though. The shield needs to be grounded at one end, or it doesn’t actually protect anything. Worse, an ungrounded shield can pick up interference like an antenna and funnel it straight into your signal. So if you’re specifically buying STP cable because you’re worried about electrical interference, double-check that your patch panel or keystone jacks support proper shield grounding. Otherwise, you’re paying extra for cable that might actually perform worse than cheap UTP.
Please stop using the wrong Ethernet cables
Using the wrong Ethernet cables can throttle the speed from your ISP.
What safe installation actually looks like
Distance, angles, and separation methods that work
The simplest rule is separation. Most guidelines say six inches minimum between Ethernet and electrical when they’re running parallel. A foot of clearance is better if your framing allows it, though I realize walls and joists don’t always cooperate with what we’d prefer.
When you absolutely must cross power lines, do it at 90 degrees. A perpendicular crossing minimizes the length of cable exposed to the electromagnetic field. I’ve got several spots in my basement where Ethernet crosses Romex, but they’re quick intersections rather than extended parallel runs.
Conduit helps too. Running Ethernet through its own plastic or metal pathway enforces separation and protects the cable from physical damage. If you’re dealing with a situation where Ethernet and electrical need to share the same general route, spending a bit extra on shielded Cat6a gives you meaningful insurance against interference. The price difference between basic Cat6 and shielded Cat6a has shrunk to maybe $30–$50 on a 500-foot spool.
Good cable management pays off here too, and not just because tidy runs look better. When you can actually trace where each cable goes, you’re far less likely to punch through one with a drill bit six months later—or accidentally run new electrical right on top of your network infrastructure.
The routing matters as much as the cable
Getting your Ethernet cable selection right is only half the job. A quality Cat6 run terminated perfectly will still underperform if it spends thirty feet running parallel to a high-draw circuit. If you have a new wiring project or nagging network issues you can’t explain, it’s worth thinking about what else shares that wall or ceiling space.
Interference from electrical wiring is one of those problems that tanks your speeds without giving you an obvious clue about the cause. The good news is that fixing it usually doesn’t cost much. Reroute what you can, create separation where it’s possible, or swap in shielded cable for the runs that have to live near power lines. A little extra effort during installation beats chasing phantom network gremlins for years.
