Repeated Lightning and Surge Damage at a Communication Tower Site, Texas Hill Country (2019)

In 2019 a rural telecommunications provider asked us to examine one of its tower sites in the Texas Hill Country, where lightning and surges had damaged equipment again and again. The job was to work out how the damage was getting in. The provider and the site are not named.

The buried ground was not the problem

We started where most people would, with the buried grounding system. The grid tested continuous between the tower and the equipment building, which is the correct arrangement, and its resistance measured 1.9 ohms, which met the recommended value. The main ground bar in the building was solidly connected to the building ground loop. No changes to the buried system were needed, which moved the investigation indoors, to the paths a surge can take between pieces of equipment.

Paths a surge should not have

The equipment racks were anchored directly into the concrete floor. Concrete and its rebar conduct, so a surge can return to the racks through the floor and pass through the equipment on the way. We could not find any connection between the rebar in the slab and the ground system. If that rebar is floating, the best path to the copper ground may run straight through the racks. On the cable tray we found a single bonding jumper, and the other tray joints were not bonded.

What we recommended

Our report set out seven measures in two groups. For grounding: give the sensitive equipment and the trays an isolated, single point ground with one path back to the buried system; mount the racks on insulated anchors; bond the slab rebar to the ground system; and add bonding jumpers and a copper ground runner along the tray. For surge protection: protect the low voltage power feed to the tower; add a surge protector at the main electrical panel; and put protectors at both ends of every copper cable that runs outdoors or underground, data cables included. For the radios on the tower, we suggested hybrid multistage filters and a larger protector at the base of the tower, so DC power could still reach the radios.

Sites that keep getting hit

When one site is damaged over and over, the energy usually has a way into the equipment that nobody intended. Finding it takes measurements and a careful look at how everything is bonded together. Our lightning damage work covers single events and sites like this one, and the measurements themselves are described under grounding system tests.