Is "don't mix data and power cables" and "don't loop power cables" still valid nowadays?

Question

There are two sayings I keep hearing when talking about wiring e.g. home cinema or computer hardware;

• Don't wrap data/network cables and power cables up in the same loop because the power cables will mess up the streams of your data cables
• Don't loop power cables because it can produce an induction effect.

I'm interested in whether these two theses are still valid with the current coating and shielding of modern day data/network and power cables.

So, when I wire my home cinema and the power cables lie next to the data cables, will that cause any effect on the quality of video/audio I am likely to perceive?

And is wrapping three or four meters of power cables in a coil actually in any way dangerous, seeing how thick the coating and shielding is on them?

How else should you manage the power cables that are too long to just let them lie around? Maybe a different wrapping/looping technique?

Answer 1

Yes, its still valid.

Power and data cable coatings are insulation - designed to protect from electric shock and to avoid short circuits. They do not interfere with magnetic fields.

I do not know what kind of shielding you are talking about - I have never seen any modern power or data cables with shielding that blocks magnetic fields. Magnetic fields are quite pervasive.

In response to your follow up question:

The size and strength of a magnetic field is relative to the amount of current flowing through the wire within. For very low voltage wires, like network cables, bundling them together generally doesn't create a strong enough field to disturb the other lines in the bundle.

However, if you loop the cables, you end up running the same current through very nearly the same space - over, and over, and over - and this can amplify the magnetic field that's created, enough that it can interfere with other signals.

With power cables, they run much more current and so create much bigger fields. Big and strong enough to interfere with the tiny currents going thru the other cables. Looping them is even stronger and more problematic.

Answer 2

In addition to the other answers which correctly note that it is hard to block magnetism, it is a very bad idea to run power and data together because some unfortunate person in the future -- possibly a future version of yourself -- is someday going to try to hang a picture and drive a nail through the wire, just nicking both the data and power cables enough to connect the power to the data, and suddenly your XBOX has 120 VAC going to the video port instead of the power port. Just don't do it; keep high voltage and low voltage as far apart as you reasonably can.

Answer 3

You're missing the point.

You're not allowed to mix mains and data cables in the same cable, bundle, raceway or conduit because mains power can kill you.

The issue is the chance of damage to the cables mutually, e.g. someone drives a nail into a wall and nicks both L1 of your mains and the TX1 of your data cable. Now your computer (which coincidentally is plugged into an ungrounded socket) has its chassis energized at 230V; you touch this and BLAMMO. You are dead.

This prohibition is handed down from the Electrical Code; i.e. the authorities that govern mains power. A related rule prohibits using electrical mains cable, raceway, gutter or conduit to attach anything else -- be it a PEX line to a water fountain, an ethernet cable, or some clothes to dry.

Now as far as induction, yeah, that's a big problem -- but a keystone of mains power design is all conductors in a circuit are bundled in the same cable, raceway or conduit. Which means their rather considerable magnetic fields cancel each other out as all the currents in all the wires balance each other, as well they should. If you took a single conductor and coiled it, yeah, that would create a hefty magnetic field, causing eddy current heating in anything metallic nearby, and vibration which would fatigue the copper wires, causing cracks, local heating and series arcing. But multiple conductors in a cable will cancel if coiled, so that should not be a practical issue.

Heat, however, is always a practical issue; try to avoid tightly bundling electrical cables under load. The core of that bundle will get too hot. "No more than four" is our rule of thumb.

Answer 4

I just experienced this issue. I bought a second hand light with a DIY cable that has exposed ground wire. Not pretty but i tucked it nicely, thought electrical tape would do. Had it plugged into the same powerbar as my modem and router...cables were touching. Few hours after plug in my internet goes down and I have a tech come. He said my wires are good so I must need a new modem. While going to unplug it (my modem/router) I noticed noise coming from my speakers. So I separated everything and rebooted my modem/router just to see.....guess what? It works like a charm now. Exposed wires + power + coiling data and power cords = No.

I feel silly now that I did something so careless and dangerous!

Answer 5

Henry's laws of induction are still in effect as well as Hertz and Maxwell's observations on electromagnetic radiation. The less noise you induce into your data cables the better, especially now that stuff's going to Gigabit. The inverse square law says that distance is a good thing. Keeping things straight and not having loops reduces the magnetic field as you aren't creating a transformer coil. And if they do have to come close, having them cross at a 90 degree angle keeps inductive coupling down to a minimum.

Also, don't use metal drive rings for data cables, they can act like ferrite chokes and reduce signal strength. For POTS they're just fine, but for the frequencies used in Ethernet, not so hot.

So much for in the wall and ceiling.

Once it exits the wall, things get nasty. I just figure 8 loop the electrical cable with a tie wrap in the center and keep the data cables as far away as I reasonably can get them. There isn't an easy answer here, basically if you start having problems, move things apart until the problem goes away. USB cables have a Faraday shield, so they're less of a problem. This has worked pretty well on the 27 computer network I run.

Answer 6

Even more so today than before with high speed data networks. Physics hasn't changed lately so follow the same rules. Whether you notice this in a home entertainment system could be debatable.

Answer 7

Yes, physics laws haven't changed, however most video/audio signals are digital nowadays.

This means that even if the signal is slightly degraded in the cable, you will still get the maximum quality.

Unlike analogic transmission where each small signal degradation was causing a small loss of quality, with digital transmission you have a "threshold". When your signal is above the threshold, you got the maximum quality. When it drops below the threshold, you have no signal at all (or a very jammed one).

Also for audio you may use optical cables which are completely immune to magnetic fields from a power line.

For looping the power cables, it's not recommended, and can be dangerous if you roll many hundreds metres (there have been some cases of fire started by this).

However, if you need to do a couple of loops, I don't think it will have a significant effect.

Bottom line: magnetic fields decrease quickly with the distance, so if you can keep your video and audio cables a few centimetres away from your power lines, that should be good enough.