# how does current flow over coaxial cable?

Discussion in 'General Electronics Chat' started by antennaboy, Jan 20, 2011.

1. ### antennaboy Thread Starter Active Member

Jan 31, 2008
45
0
Hello Forum,

in a simple abstract experiment, if we connected a DC voltage source to a load (lightbulb)using a a coaxial cable, the bulb would normally light up. The current will flow through the inner conductor and "return" to the voltage source by flowing through the outer conductor. (viceversa is possible too I guess).
This concept is based on the current/water analogy where current flows as water.

If the voltage source is an AC voltage source instead, and the coaxial cable outer conductor is connected to earth ground, will the current only flow through the inner conductor with no current inside the outer one? or will we have currents in both conductors?

In terms of voltage, I guess the outer conductor will remain to the same 0 voltage and the voltage on the inner conductor will go up and down with respect to the outer conductor voltage. But how will AC current flow in this case?

thanks
antennaboy

2. ### Accipiter New Member

Sep 20, 2009
9
0
Current will be in both conductors, although if the outer conductor is grounded at the source and load end, you will also have some current flowing through ground. However, if there is only one point in your circuit that is grounded, then no current will be flowing through ground. Just think of the ground as being a parallel resistor with the outer conductor if you have two ground points.

3. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
202
With DC it's just wire,with low Hz mains it's still just wire. With RF its a different story altogether.