The best ways to run phone and cable lines through a block wall

Green Cables image by Charlie Rosenberg from

Once you have decided that you need a phone in the breakfast nook or that new flat screen TV must go over the fireplace, you then have to figure out how to get the phone or cable lines to these devices to make them work. Most of the time this is a simple task of routing these lines under the edge of the carpet or along the skirting board. Sometimes there is just no way around that block wall. If you absolutely have no alternative route available except going through a block wall to run these cables or wires, then just go ahead and do it. The best and the only way to do this is to drill a hole through the block wall. Drilling the actual hole through the wall is the easy part. The "Best Ways" part is all about what must be considered before, during and after you drill through the block wall.


There are some common sense considerations to keep you and your property safe while you are doing this job. Before you start drilling make sure you know what's on the other side of the wall. Never operate a power drill while you're standing in water. Make sure to use a grounded extension cord. Do not drill into existing house power lines which may be "hidden" inside the wall. Make sure that the cables you are running, phone, TV or data, have been properly grounded between their respective utility systems or antenna and the new lines that you are now installing. This grounding should already have been completed by the telephone or cable providers.

Determine the hole size

Your goal is to drill a hole that will accommodate whatever cables you want to run through this concrete block wall while keeping the hole size as small as possible. Include in your calculations any future need to run additional cables.

It is easy to calculate the size. For example, if you are running a single coaxial television cable you just have to measure the outside dimension of the cable and then select the next larger sized drill bit. The most common cable line is RG-6 Quad shield coaxial cable and it has an outside dimension of 7.5 mm (0.298 inches). The next larger size drill bit is 8 mm (5/16 inch). That is the size you should use.

If you are running multiple cables you can simply bundle these cables together in your hand and measure the outside diameter of the bundle. Then choose the next larger size drill bit. Keep in mind that you may need to step up even one more size larger to keep the hole large enough to easily place the cables through the hole without damaging the cables. Now you know the size of the hole and the size of the drill bit. Don't try to shortcut on the drill bit by using anything other than a masonry type bit.

Determine the location for the hole

You may not have any choice on the location because of the physical limitations of the cable route, the wall itself or restrictions on the interior of the wall. If you do have choices here are some considerations.

On an outside wall, exposed to the weather, you want to keep the hole up off the ground to avoid any water ingress problems. You also want to keep the cables away from lawnmowers and bush trimmers. Cosmetically, you want to hide the cables as much as possible and where you place the hole can help or hinder this effort. If the hole must go near the edge of the wall make sure to leave room for any wall on the inside which is perpendicular to the wall which you are drilling. You do not want to drill inside an existing wall or drill so close to an existing wall that you are unable to put on a wall plate or other covering on the interior side of the wall. Avoid drilling between the concrete blocks in the cement seams.

On the inside, consider the proposed cable route from the new hole to wherever the cable is going. Naturally you want to minimise exposed cable whenever possible. Most likely the cable(s) will exit the hole and go straight down to a skirting board and then on to wherever it's must go. Remember that there will be a bending radius associated with the cable(s). It is unlikely that it will be able to make a hard 90 degree turn and will end up sticking out of the wall approximately 2.5 cm (1 inch) to accommodate this bending radius without kinking the cable. Don't forget to mark the spot once you have determined the location for the hole.

Drilling the hole

Ideally, your power drill motor will have a "Roto Hammer" feature that vibrates the masonry bit as you drill through the wall. If this is a one-hole project, a regular power drill motor without this "Roto Hammer" feature will get the job done, it'll just take a little longer. The masonry bit should be 45 cm (18 inches) long. When drilling try to keep the drill bit level, horizontal and perpendicular to the wall. Don't forget that concrete blocks are hollow on the inside. Keep consistent pressure on the drill as you push it through the wall and let the drill bit do its job. Too much pressure can cause the concrete block to shatter around the exit hole when the drill bit finally breaks through.

Cable(s) placement

Do not place any connectors on these cables lines until you have completed routing them. Connector placement will be the last thing you do when you hook up the equipment to the cables and lines. Most likely you can simply push the cable through the new hole without much difficulty. If you have trouble pushing the cable straight through the concrete block and finding the exit hole, use a coat hanger to push/pull the cable through the block. If the concrete block wall is an exterior wall, exposed to weather, you need to leave enough slack in the cable to form an outside "drip loop" with the cable. This "drip loop" will prevent water from running down the outer sheath of the cable and into the hole. If the exterior cable is vertical on the outside wall, its route should take it down the wall and past the hole and then make a 180-degree turn up and into the hole. This way, any water running down the cable cannot travel back up the cable into the hole, this is why it is called a "drip loop." Even if the cable is horizontal, it should curve down and then up in a half circle before entering the hole.

If you plan to use plastic inserts to seal each end of the hole or a wall plate on the interior wall, don't forget to place these parts onto the cable before running the cable through the hole and permanently attaching the cable to the wall.

Sealing the hole

It is important that you seal both ends of the hole. You want to preserve the integrity of the block wall and you also want to protect the cable's entry and exit points. A silicon sealant is available, at your local hardware store, in either clear or light/dark colours to match its surroundings. The silicon sealant will not crack and deteriorate over time and if you need to replace cables or add cables at a later date, the silicon is easy to remove.

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