A coaxial cable that leaves a building and comes back is a conductor from outside connected to equipment inside. That single fact is what grounding requirements exist to manage, and it has nothing to do with whether the picture is good.
Getting it right is straightforward. Getting it wrong produces two distinct problems — a safety exposure and, less obviously, hum.
Quick answer
| Question | Answer |
|---|---|
| What has to be grounded? | The coaxial shield, at or near where the cable enters the building |
| What component does it? | A grounding block, bonded to the building’s grounding electrode system |
| Are the dish and mast grounded too? | Yes. The outdoor structure is bonded as well |
| Does grounding cause hum? | A single, deliberate bond does not. Random, multiple bonds do |
| Does a surge protector replace grounding? | No. It is an additional layer |
| What governs the details? | Your local electrical code, and it should be followed |
Why the shield is the thing being grounded
In a coaxial cable the shield surrounds the center conductor and behaves as the return path for the signal. It is a continuous metal layer running the length of the cable, and it is the part that couples to external fields.
When a surge is induced on an outdoor coaxial run — from a nearby strike, or from the potential difference created when lightning raises the ground potential over a wide area — most of the current appears on the shield. Providing a deliberate, low-impedance path to the building’s grounding electrode system at the entry point is what gives that current somewhere to go other than through the equipment.
An ungrounded shield does not stop the current. It just picks where it goes.
The grounding block
The component that does the work is a grounding block: a small fitting that passes the coaxial connection through and provides a lug or terminal bonded to the building’s grounding electrode system.
Two placement rules matter. It goes at or near the point where the cable enters the building, so that the surge reaches the ground path before it reaches the equipment. And it is bonded to the building’s grounding electrode system — not to a convenient water pipe, not to a separate rod driven for the purpose. The system is what gives the current a low-impedance path; a separate isolated rod does not.
Some cable and satellite services place the block where the service enters. Where the cable run leaves and returns — a dish on a roof feeding a receiver indoors — the same principle applies at the building entry point.
Grounding the structure as well
For a satellite dish or an antenna mast, the coaxial shield is not the only path. The metal structure outside is itself an exposure and should be bonded to the grounding electrode system.
Where the structure and the cable both bond, both bond to the same system. That is what keeps the arrangement single-point rather than creating separate references that can differ in potential.
Why random grounding creates hum
Ground loops are the reason grounding has a bad reputation in audio and video work, and the mechanism is straightforward.
Two pieces of equipment that are bonded to ground at two different points with different impedances sit at slightly different potentials. A coaxial cable connecting them provides a path, and current flows along the shield. You hear it as hum, or see it as a bar rolling up a picture.
The lesson is not to avoid grounding. It is that grounding should be deliberate and single-point: the shield bonded at the entry point, and the equipment grounded through its own power connection, with no additional bonds added at intermediate points to see whether they help.
Where a hum problem exists and the installation is already grounded correctly, the cause is usually a second path — a cable TV service and a dish both bonded at different points, for instance. Locating and resolving the second bond is the fix.
Surge protectors
A coaxial surge protector adds a component that diverts surge energy to ground, usually at the same entry point as the grounding block. It is cheap relative to the equipment it protects.
Three things worth knowing.
It does not replace the grounding block or the bonding. Without a ground path, a protector has nothing to divert to.
It has an insertion loss, small but real, which matters on a run whose loss budget is already tight.
And it is a layer, not a guarantee. A close strike can exceed what any single device handles.
Scenarios
A roof antenna feeding three televisions. A grounding block where the cable enters, bonded to the grounding electrode system, with a coaxial protector on the same bond. The mast bonded to the same system.
A dish installation with a receiver in a different room. Ground the shield at the building entry point, not at the receiver.
A carriage house with a coax run to the main building. Both ends are separate structures with their own grounding. The run between them needs the same treatment at each entry, and the two systems’ relationship should follow local code.
A system that hums after a cable television service was added. Two services, two bonds, at different points. Resolving the multiple bond is the fix, not removing grounding.
FAQ
Does coaxial cable need to be grounded? An outdoor run entering a building does, and the shield is the part that is bonded.
What is a grounding block? A fitting that passes the coaxial connection through and provides a terminal bonded to the building’s grounding electrode system.
Where does the grounding block go? At or near the point where the cable enters the building, ahead of the equipment.
Can I ground to a water pipe? Modern practice is to bond to the building’s grounding electrode system. Follow your local code rather than choosing a convenient pipe.
Will grounding cause hum? A single deliberate bond does not. Hum usually comes from multiple bonds at different points.
Do I still need a surge protector if the cable is grounded? It helps and it is inexpensive relative to the equipment. It is not a substitute for grounding.