Grounding Your Cable

Don't let this happen to you

I heard a story the other day (thanks Eric) about a badly installed cable and the disaster that ensued from it. The cable in question was a cable TV line entering a home, now this was several years ago but it still applies today to any cable that enters a building from the outside.

In this case it seems that the cable installer (not Marty or Bill) failed to ground the in coming Cable TV coax, it was then split several ways to feed several TV sets in the home, this worked fine for several years. Then one day, one of the high voltage lines carried at the top of the telephone poles broke free a few blocks down the road. The 6KV line fell across the cable TV line. This stuff had been up there for many years   and the insulation had decayed  so the 6KV made contact with the cable TV shield.

At all the houses the 6KV ran up to the home on the cable TV coax and hit the ground connection

Cable box, where the ground is attached

and promptly burned up the coax and it dropped to the ground. But not at the house we are talking about. Without the ground attached to the Cable TV coax shield where it entered the home, that 6KV went looking for a ground.

The 6KV was fed directly to every TV set in the home where they promptly caught fire, remember TV sets are not required to be grounded, as the cases are all plastic and there is no metal to get shocked from. In one room there was a coil of Coax on the floor and it quickly burned a hole right through the floor. Now there were several fires going in this one house all from the missing ground on the Cable TV coax entering the house. One set was older and used twin lead for the antenna input so it had a balm that burned up and saved the TV set.

I run a AWG 1 wire to the house ground for all incoming wires

The fire department had been called out because of the brush fires that had started do to the falling charged wires. Someone ran up to tell the firefighters that there was a house on fire down the street. The home was not a total loss but it was extensively damaged, all from a missing ground wire.

 

A related story comes from my old TV station where we had our transmitter and studio together on a mountain top. The mountain was San Bruno mountain and it is composed mostly of rock. We had a large satellite dish installed down in a ravine and in those days we used LNAs. Those are Low Noise Amplifiers that took the received satellite signal, amplified them and then sent them to the receiver, on frequency, with no down conversion. We used some large helix to bring the signal from the dish to our building, also there was a thick, multi pair control cable that ran from the dish to our building.

So useful, yet so dangerous

The building was old, it had been built decades before and was properly grounded on this rock of a mountain. One day a High Voltage line on one of the poles arced across to the the low voltage line that fed our satellite dish. As you may know, rock is not a good conductor and the high voltage could not find it’s way to ground. So it saw our nice fat control cable and decided to run up to our building. We had grounding on the Helix where it entered the building so it was protected but not on the control.  And so the high voltage found it’s way to the satellite dish controller and popped the tops off several chips and burned up the PC board. I was told there was a loud bang and smoke poured out of the racks.

Now theses two tales are about power lines failing but as I am sure you are aware lightning is a much more common problem and can strike anywhere. SO, be safe and check your grounds on everything that enters your station and especially your home.