Repeated Surge Damage to Rooftop Air Handlers at a Church Campus, South Texas (2021)

In 2021 a church in South Texas asked us to look at a run of electrical damage in its main building, after a single event took out four of its five rooftop air handlers at once. The church is not named.

Two years of trouble

The building takes a 600 A, 480/277 V service. Its main distribution panel feeds the five rooftop air handling units, a chiller and three subpanels, and the HVAC system had been replaced in 2012. For about two years the building had seen recurring power problems. In the event that prompted the call, four rooftop units lost their control boards together. A later event damaged several condenser fan motors and left the 600 A main breaker tripped. Earlier damage to LED lighting and computers had also been reported, though the client described it as unrelated.

What we could check without opening the gear

Our examination was limited to what could be seen without cutting into walls or removing covers on energized 480 V panels. We looked over the rooftop units for signs of lightning damage and found none. Two of the four replaced control boards were still on site, and neither showed visible damage. We measured the resistance of the building ground to remote earth by the fall-of-potential method and got 1.17 ohms, a good result.

Utility surges, not a direct strike

The control boards showed no visible damage, the building ground was good, and the main breaker had tripped. Together, those observations made a direct lightning strike less likely and pointed to surges arriving on the utility service as the probable cause of the recent damage. A direct strike could not be ruled out entirely, and the report said so.

Recommendations

We recommended surge protective devices on the line side of the main service entrance for this building and for the other buildings on the campus with the same 480 V service, with matching devices for the 208/120 V services. Surge protection needs monitoring and maintenance once it is in place. If damage continued after that and direct strikes were confirmed, the next options would be moving the air handlers to ground level or adding lightning protection designed by a licensed professional engineer. How we separate lightning from other surge sources is described under lightning damage, and the ground measurement under grounding system tests.