Electrical Grounding: Learn the Fundamentals

Many years ago, I was installing an audio system in a suburban Minneapolis neighborhood.

The system included a preamp, amp, VCR, laser disc player, cable box and big screen television. It was built into a cabinet and, when the system was turned off, it looked good.

Unfortunately, it didn't sound very good and, further, the television had very faint rolling bars going from the bottom to the top of the picture no matter what the video source.

The audio was plagued by a buzzing sound that never seemed to change pitch -- a constant tone, in the middle bass frequency range.

I was baffled.

At wits' end, I contacted tech support at one of my suppliers. There, a kind individual suggested that I might have a ground loop in my system.

I started to research that explanation, and here's what I found:

It turns out that not all electrical grounds are rated equal. Each ground may have its own value, or potential. When different ground potentials are present in a system, the resulting product is often a 60-Hz hum and/or rolling bars on the video display.

I apparently had hit the daily double, but still wasn't clear where the ground potential difference was coming from. All the equipment was plugged into a good quality component-style surge protector and, as such, all of the equipment had to have the same ground.

Or so I thought.

"Ground Breaking" Hum Prevention

It turned out in this instance that it wasn't just the electrical ground that I was having trouble with.

When I started troubleshooting, I eliminated equipment.

First off the system was the VCR. With its removal, the hum diminished somewhat. The CD player and the laser disc player's removal had no effect whatsoever on the hum.

When the cable box was removed, though, the hum dropped dramatically. There was still a bit of hum left, though, so I continued yanking patch cords.

When I finally disconnected the big screen TV from the preamp, the annoying remnants of hum disappeared.

What I discovered was that the cable signal coming in had a different ground potential value than the electrical ground inside the house. Even though all the electronics shared a common ground point of reference, the cable was grounded to a different spot.

In this case, and probably others, the cable guy had not run the cable through a grounding block when he installed the service several years prior.

The shield of the coaxial cable was essentially connecting my system up to a grounding block somewhere upstream in the cable system. Like water spilling on a tabletop, the ground potentials tried to equalize and the result was hum.

The kind soul at tech support (probably either Ken Manson or Tony Trimble) taught me an easy way to check to see if it truly was a ground potential problem.

By unscrewing the incoming coaxial cable from all the devices, and then just putting the stinger of the coax into the F fitting on the back of the cable box, I was able to instantly determine whether that was my problem. If the hum disappeared but the picture and soundtrack remained, my problem was the grounding of the RF signal.

The way an F connector works is by the signal's being carried down the center conductor, with the foil and braid providing the ground connection.

By having the center conductor only making contact, I was essentially lifting the ground from the external cable and removing the ground potential differences that caused my problem. At the time, a simple $5 part from Xantech solved the problem.

I installed one of their ground breakers on the incoming cable just prior to the RF splitter behind the rack of equipment and took away the ground potential differences that the VCR, cable box and TV were all suffering from.

The rolling picture problem went away as well.