Original subtitles

Over the years, I've had many interesting troubleshooting challenges.

And some of the most interesting problems were

caused by ground loops.

And you might ask, well, what is a ground loop?

Well, one definition would be simply just too many grounds.

And at first, you might think, well, how can that be a problem?

This could be a drawing of a telephone central office, a

computer lab, recording studio, or radio or TV studio.

It has lots of equipment.

And what I want to point out here is notice the blue lines.

Those are the grounds from each cabinet.

And they are all connected in one direction toward that blue

ground bar at the left.

And that goes outside to the earth ground.

So any noise that is developed by the equipment or outside.

noise is grounded and it runs outside into the ground.

There are no ground loops in this drawing but if a new piece of equipment

installed like this you can see that there are now two ground connections and

those connections cause a ground loop

And there's a possibility that some of the equipment

that's in that ground loop can cause interference with an unrelated

piece of equipment, causing some really bizarre troubles.

Audio equipment uses a lot of shielded cable.

And here's a representation of the inside of a chassis.

And we've got at the left an input.

And it has a shielded cable.

And you can see that the shield is connected to the chassis.

And the chassis is usually connected to earth ground.

But the other end of the shielded cable

The shield is not connected.

And here's why.

This is the end view of that shielded cable.

And if there is some interference,

what that shield does is

when that interference hits the shield,

it is drained away and it goes into the chassis.

And no noise gets to the center lead.

Now I have modified the drawing and added another shield connection

to the chassis at the other end.

Let's take a look and see what happens now.

when the interference hits that shield.

Now we have current flowing in the shield and in the chassis.

We now have a ground loop.

And when we have current flowing in that shield, that means that that

shield is going to produce a magnetic field.

And that is going to induce noise into that center conductor.

So too many grounds can be a problem.

And the idea is to drain the noise away in one direction

from the equipment to an earth ground.