# Current over ethernet?

It seems that the voltage over ethernet ranges from 2 to 3 volts. How much current typically runs through the wires? I tried Googling with no success.

I ask this because I'm looking for components that are able to switch on and off an ethernet connection.

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I assume you're not considering a power-over-Ethernet type of connection, which is typically ~48V and ~350mA. en.wikipedia.org/wiki/Power_over_Ethernet –  HikeOnPast Jul 29 '12 at 0:36
Just to summarize, excluding power over ethernet, your primary challenge would not be the current-handling capability, but instead the maintenance of characteristic impedance through the switching path. –  Chris Stratton Jul 29 '12 at 16:30

Physically switching Ethernet is hard to do, for the following reasons:

• Ethernet is high frequency. In this area, you have to watch out for reflections of the electrical wave, which happens when the "characteristic impedance" of the transmission path changes. Ethernet cables have a char. imp. of 100 Ohms. You would have to design your switch so it has a characteristic impedance of 100 Ohm, but a specific (DC) impedance of 0 Ohm, like the cables.

• The whole point of structured cabling is to remove physical connections in the cabling between the endpoints for this very reason. You connect each unit to a switch with a separate cable, so there are no disruptions in the characteristic impedance.

• Ethernet is not meant to be physically switched. A network switch device does not switch the cabling, it does receive, manage and forward the packages.

About voltages and currents: Ethernet voltages mostly use -1 to +1 Volts. Currents would be in the range of a few 10 milli-Ampere, depending on frequency and length.

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Line is 50 ohm impedance - with driver IC's driving a 100 ohm impedance line balanced around ground with a transformer coupling.
Here is a typical driver IC data sheet TLK110.
They note a drive r power consumption of 250 to 275 mW in operation so actual circuit power will be below that.
At say 3V RMS equivalent into 50 Ohm power would be V^2/R = 180 mW so that's in the order of right.

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So current is 60mA RMS. –  starblue Jul 31 '12 at 7:29

Are you sure you are asking the right question? There are lots of Ethernet standards, I assume your are talking about 100BASE-TX?

You can not directly put a DC voltage on an Ethernet connection using standard hardware (beyond other problems it is physically impossible because it is transformer-coupled on both sides). You can transmit a message (frame), which is a one-time thing. Or you can transmit repeatedly, but that still won't get you a DC signal. And if you transmit nothing, that will not guarantee that there is no signal on the Ethernet connection!

In short, you won't be able to do much with your Ethernet connection without an intelligence (microcontroller) on the oher side.

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I don't understand how this addresses the question. –  Rocketmagnet Jul 29 '12 at 13:24