Voltage on Lan Lines

[kilmarac]

Greetings,

I have a netgear R6300 Wireless router. Recently, I was experiencing trouble with the internet connectivity, so I called a technician in to look for what I couldn't find.

At first the problem was that there was a bad ground outside, and the cable line was pushing voltage into my modem. This was fixed, and we went over all the rest of the components. We discovered that the Netgear router is pushing a measurable voltage over the lan ports.

By measurable, I mean he head his meter about 1-3 inches from the lan cable and the meter lit up four of its 8 LEDs. We double checked and made sure it wasn't coming from the modem, or the attached devices.

Is this normal, or something I should be concerned about?

 

[bill001g]

If the device functions then who knows what he is measure. The voltage on ethernet is under 2 volts. The twists in the wire are designed to reduce the radiated signal....ie something his meter could detect.

Now if the device is dead maybe you could have power running over the ports if it is all shorted out.

Ethernet cable is magnetically isolated for safety and for it to work properly. There is no connection between the power or ground or anything in the router and the lan ports. Some device also have optical isolators.

I have no clue what kind of meter he had. Most non contact voltage meter only measure very high voltages.

 

[kilmarac]

He was using a non contact meter, and that's why we were confused. The router is working (as far as I can tell) normally. We checked it at both the port and at the end of the cable and got the same reading when not connected to the modem. If we disconnected the cable from the router and let it connected to the modem, we did not get a reading.

-confused

 

[bill001g]

If it works then there is not high voltage and the grounds are not connected. The grounds are the key reason for the isolation transformers. Since at the 100 meter limit you can easily be on a different power system there is concern you can get different ground levels. In worst case it can kill someone but mostly it is there because of the interference it would introduce.

This is a fundamental to the operation of ethernet so its not like you would find equipment that does not have isolation transformers.

It is extremely strange that a non contact meter could detect anything. They are designed to operate at low frequency ie like 50 or 60hz. Gig ethernet is running at 125mhz. On top of that the twisted pairs are designed to prevent leakage of that signal...mostly into the other pairs in the cable. You would think that if the signal has issues getting to the other pairs inside a cable it would be almost undetectable from outside the cable.

I suspect the meter was reading something else.

 

[kilmarac]

I would agree, but the reading came only from within 3-4 inches of the cable and nowhere else nearby. You've answered my question, I need to investigate into getting a new router. 🙁