It is commonplace for firecodes to tell us not to use extension cords. But for living in a rental, sometimes there is no other way to transmit datalines between rooms securely. A reasonable person would infer this fire code is talking about full AC current extension cords, since many of these cords aren’t rated for the full amperage provided by typical fuses.

I have always understood this to be about AC extension cords. When it comes to Ethernet extension cords, I assume it’s fine because they don’t carry any power. Though I’ve never bothered to ask.

For USB extension cords though, there is about 5V carried through the cords, maybe up to an amp typically (5W). Still nothing that would cause a fire.

What is the line though? Certainly fire codes must recommend a typical wattage for these cords? And they must be safe to run under doors as well?

  • 1
    Fire codes will differ from country to country and sometimes from region to region... You may want to add which place you're interested in!
    – MiG
    Commented Feb 22, 2022 at 15:42
  • Low voltage(~ below 50v) is usually not given any love or care in codes. About the best they can get is done with good workmanship(look neat) by an inspector.
    – crip659
    Commented Feb 22, 2022 at 15:42
  • The wires inside of the cables are usually weak and break easily, stopping their usefulness. Best practice is to place them where they are not underfoot or under chair wheels,and away from cats/dogs to chew/pull out, so they last longer.
    – crip659
    Commented Feb 22, 2022 at 16:15
  • 1
    At least in the US, NFPA 70 (the National Electrical Code) does have Articles including 800 - General Requirements for Communications Systems and 770 - Optical Fiber Cables. Generally speaking, these are mostly concerned about fire resistance of the cabling used and not mixing them in with power conductors.
    – Jon Custer
    Commented Feb 22, 2022 at 17:06
  • 1
    You've obviously never heard of "power over ethernet".
    – Simon B
    Commented Feb 22, 2022 at 20:53

2 Answers 2


Except fiber optic, all computer cables carry power. Electrical codes generally don't apply to low voltage (typically less they 50V), so telephone, network, USB, serial (RS232), parallel etc. have almost no rules in most places.

The two major exceptions I know of are:

  • Plenum cabling - cables run through walls and ceilings have special rules, and especially if they run through areas where area can travel between parts of a building (plenum). Primarily this relates to the type of insulation and jacket so that if there is a fire the spread of toxic fumes is minimized. There are also rules on sealing around cables going through firewalls.

  • Tripping Hazard - this applies to extension cords of all types (even fiber optic). Often this means using a longer cable so that you can route it up over a doorway instead of across the floor.


USB cables and/or the batteries that feed them can and do catch fire from overcurrent. I've seen it multiple times. I do not think, however, that making one very long or running it along a floor, through doors, etc, would make it more likely to catch fire. In theory it would make it less likely by adding resistance and limiting the current somewhat. The hazards from long USB cables are more about tripping etc.

USB cable fires MIGHT be less likely to ignite nearby objects than mains-powered cables due to the limited power they are capable of carrying and the limited energy in most batteries. Less likely, not impossible.

I have never heard of an ethernet wire, plugged in to an ethernet device at both ends, causing a fire. But like all other cables, fire is not the only hazard when stringing them all around an apartment.

Ethernet cables can be much longer than USB ones so you can run them around walls, over doors, etc to avoid most hazards.

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