Correct, you aren't necessarily grounding the wire, you are grounding the device (speaker, WAP, satellite dish etc.) that the wire is connected to. This is more important on devices that are outside as they have more of a potential of being a conductor of lightning. If you can provide a path to ground from the device there is less chance the surge will travel down the connected wire and into the equipment.

crosen,

I hope that this helps:

We are generally very sloppy with our use of "voltage". We are similarly sloppy when we quote how "high" something is. We really don't know how "high" something is until a reference point is given. That four inch high step is usually understood to be four inches above the nearby floor or the next step in line, but it could also be 200 feet above the street and the street could be two thousand feet above sea level -- never mind that sea level is modulated by the moon. Consider a pilot flying at "2000 feet". If the pilot is using a sea level reference, I hope that he is not flying near the mountains.

In our trade we are sloppy with our use of "ground". Sometimes we literally mean earth, other times it is the shield on a cable, a point on a circuit board, or a screw on the outside of a box. Just as we measure "height" from a reference point, we measure signal "voltage" from a reference point -- that we sloppily call "ground". Dropping a marble from a "height" of two feet above the floor that we are standing on and landing on that floor is not a big deal, however, if we absentmindedly lean out the window from the tenth floor and drop that marble to the street, there will be consequences after the marble gains some kinetic energy. But, we could argue that we dropped the marble from the same "height".

Earth is not a very good conductor of electricity. Try measuring the resistance of earth. You'll likely come away wondering why we even bother to connect things to earth. If you drive a couple rods into the earth you'll get a better reading.

If we consider earth to be a wire and remember that when wires carry current there will be a voltage drop, consider what happens when the large current accompanying a lightning strike flows through the (somewhat conductive) earth. The water pipe, electric service ground rod, cable system, etc, that have contact with earth at different points around the property will have different potentials immediately after the strike. A person touching between these two "grounds" (say a water pipe and appliance surface) could receive quite a shock. This is why we "bond" all of these "grounds" together with a wire that has much lower resistance than earth.

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With respect to transients, there are large electric and magnetic fields associated with the lightning strike that can generate voltages within our signal wires. These voltages can be much higher than our equipment can deal with. In some respects you can think of our wires as transient antennas and the longer the wire, the better the pickup will be. We need to protect our delicate circuits from these transients.

The protection scheme inserts a resistance, perhaps using the wire's own resistance, between the transient antenna and our equipment. Between the resistance and the equipment is a varistor, gas tube, or diode arrangement. A common thread is that these devices do not conduct until the input voltage crosses a threshold, then the devices switch to a very low impedance mode that dissipates the transient -- into a "ground". If this "ground" is not the "ground" that the equipment is referenced to, the transient protector accomplishes very little. Proper "bonding" is important here too.

There are some nasty details to consider because some coax and CAT-5 transient protectors have limited bandwidth. Also, a 25V threshold might be great protection for a CAT-5 network cable (that does not carry PoE), but not so great for a 70V speaker line. Check the specs before installing.

Thanks, buzz. The second to last paragraph clarifies for me something I’ve been trying to understand about grounding data cables. Specifically, I had been trying to understand how you could connect, say, a cat6 to ground. I mean, you obviously could not simply provide continuity from each conductor to a grounding point as that would short the entire cable.

If I understand your explanation correctly, a cat6 can be grounded using electronics that provides this continuity at - and only at - the moment a transient appears. In other words, each conductor is electrically isolated from one another and from ground during normal operation, and the shorting to ground - and presumably to each other - only happens at the moment the surge occurs. .

Correct. A "gas tube" is similar to a neon bulb. At low voltage it is an open circuit. At about 90V a neon bulb will turn on and become a relatively (compared to an open circuit) low impedance. If this impedance is lower than the the impedance in the transient circuit, the transient is shunted through the bulb, away from our circuit. Literally, if you look inside a lot of telephone KSU's you'll see rows of neon bulbs.