How to Ground a Rooftop Signal Booster or DAS Antenna

While cell phone boosters and distributed antenna system (DAS) have become an increasingly common accessory for businesses and households, many people are overlooking a vital component of their set-up that will protect their investment and ensure the longevity of their equipment: properly grounding the antenna system.

Grounding the antenna protects your signal booster or DAS from damage in case of lightning strikes. Lightning can strike the antenna and travel through the coaxial cable to your device, which will not only damage the signal boosting equipment but can cause a fire or shock people in the vicinity. Lightning doesn’t have to physically strike the antenna itself to cause damage: nearby lightning strikes and static charge build-up during storms can also create voltage surges which, although smaller, can damage the filters and amplifiers inside the booster or DAS headend.

To completely protect your device from lightning, two layers of protection are recommended: installing an in-line lightning surge arrestor and grounding the antenna mast. We’ll delve into each of these below.

Installing a Coaxial Surge Protector

Installing a coaxial surge protector in the path from the outdoor donor antenna to the signal booster protects both the booster and the inside of your home by disconnecting the circuit if an excessively high voltage flows through the cable.  According to the National Electric Code (NEC), it should be installed as near as possible to the point where the cable enters the house, but not near combustible materials.

Since many attic crawl spaces contain combustible material, we suggest installing the surge protector outside the building, near the point of entry.

Choosing the correct surge protector is vital because the wrong device can degrade the signal and reduce the performance of your signal booster or DAS. It is important that the impedance rating of your booster match the impedance rating of the surge protector. Boosters with F-type connections have an impedance rating of 75 Ohms, whereas boosters with N-type or SMA connectors have a 50 Ohm rating.  We offer a range of lightning surge protectors on our Surge Protector page.

Grounding the Antenna Mast

While a coaxial surge protector will protect a device from lightning strikes and transient voltages, grounding the antenna mast is also important—so much so that it’s mandated by the National Electric Code (NEC). Grounding this mast is absolutely critical if you are using a tall antenna mast since they are a prime target for lightning strikes because of their height and tendency to accumulate static electricity. The only equipment needed ground your antenna mast is the grounding cable. If your antenna mast is painted, you should make sure that you scrape off any paint before attaching the grounding wire.

Choosing and Installing Grounding Cable

The NEC recommends 10 AWG or lower gauge for your grounding cable. Cable gauges become thicker as the AWG gauge number decreases, so if you’re unsure which to use, go with a thicker wire (lower gauge). Stranded cable is recommended as it tends to be more flexible.

Installing the grounding cable is relatively simple; the main consideration to keep in mind is to not create any sharp bends in the cable.

You can connect the cable to any of five suitable grounding locations:

  1. A ground rod. A ground rod is typically installed outside homes, and is basically a simple metal rod buried in the ground, with just a foot or so visible above ground.
  2. The metal electrical service panel. This panel is typically connected to the grounding rod of your home or office.
  3. A metal electrical raceway or conduit. Conduit and raceway are typically grounded, so you can simply attach a strap to existing electrical conduit or raceway.
  4. A water pipe. This is acceptable, but only within 5 feet of the water pipe’s entrance to the structure, and if the pipe is metal and in direct earth contract for at least 10 feet before entering the property. You shouldn’t attach a ground wire to a water valve.
  5. The metal frame or structure of a building. If none of the options above is feasible, you can ground by connecting to the metal structure of the building, as long as the structure is grounded.

While we are able to give you advice on grounding your donor antenna, we recommend calling an electrical contractor if you are experiencing difficulties. Electrical contractors are highly trained in installing ground wires and can help make sure your cell booster or distributed antenna system is completely safe.

Summary

When grounding an outdoor antenna, you should ground the antenna mast and install a grounded lightning surge protector. Use 10 AWG or thicker wire to ground the mast and surge protector, and make sure you're grounded to a suitable ground location. Not only will this keep your equipment safe, it will also potentially save you if there is a lightning storm.