# Question about electricity

Does an electrical wire expand when an electrical current is sent through it ?

No.

The electrons are aready there, all the time. An electric current is just a movement of a small number of electrons in the wire. So there’s nothing extra there to make the wire expand, no extra mass being added.

Hmmm. Well, maybe it does, just a little. The movement of electric charge is accompanied by the generation of a little bit of heat, or sometimes a lot of it. This heat causes the wire to expand. In addition, moving charges generate magnetic fields. Since all the electrons that are moving are moving in the same general direction the charges repel each other a little more than they normally would and this might cause a slight expansion. The wires in the coils of a transformer have to be well anchored or the thing wants to fly apart under heavy loads because of the magnetic field repulsion.

I think that aluminum wire connected to copper binding post screws in outlets was the cause of fires in mobile homes when aluminum wire was used. The differential thermal expansion of the copper and aluminum gradually loosened the screws which lead to higher resistance which lead to more heat, etc. etc. et voila!, a fire. The electrical wires in your house operate at a rather surprisingly high temperature (like maybe 40[sup]o[/sup]C), especially the connections, when operating at the full current the codes allow.

Electrical current in a wire will cause some heating, and heating up most metals causes some expansion. However, when sized correctly for the load, wires don’t heat up very much. If you can feel the increase in heat, you’re overloading the wire. And even under an overload so severe as to cause problems, the increase in diameter will be small compared to the increase in length.

But the increase in diameter is not because there is current flowing. It is because the wires are not perfect conductors, and therefore heat up a little, and therefore expand a little. If you cooled the wires as the current increased, there would be no expansion at all, even under high current conditions.

So the answer is “Yes, but not so you’d notice it” as long as you’re talking about the wires in your home.

Ugly

Wow, what amazing replies.This qewstion is in reference ,mainly to the high tension wires that can be seen along the Hi-Ways of our Great Land. Thank You Responders One & All.

The same would be true for the high-voltage transmission lines. They would heat up a little. They actually carry a surprisingly small amount of current. That’s 'cause power is voltage times current, and the power lost due to heat is proportional to the current, so they minimize that by cranking up the voltage.

By the way, “high tension” is a term I’ve never heard in engineering. A lot of laymen seem to use it, so I think it’s like the term “tarmac” to refer to the ramp area of an airport - laymen use a term because they think it’s the right one, but no one on the “inside” uses it. I believe “tension” is French for “voltage,” and I’ve seen some warnings posted on high-voltage equipment that reads “Haute Tension,” so that might be the source of it.

Overheated high voltage lines definitely are an issue: http://www.msnbc.com/news/566732.asp?cp1=1