LIGHTNING!


Background

I maintain the base station of a small Internet Co-Operative.  I bring in high speed Internet by radio from a town 12 miles away and redistribute on 2.4 GHz to some of my neighbours. The network also has a weather station and a PC acting as a server  to provide network news and local weather.

At the top of the 68 foot tower (left) is the high speed link to Richer and below it is the 2.4 GHz antennas for re-distribution.

On the shorter tower, the weather station wind speed and direction sensor is just below the rotator for the 2M beam antenna and the temperature, rainfall, and humidity sensor is located in the black box on the short tower just below the ridge of the house.

 

All the cables from both towers enter through a cable bulkhead through a lightning protector of some sort. The high speed link is a Cat-5 signal protected by an ITW Linx Cat-5 Power-Over-Ethernet protector (small gray box mounted directly on the metal bulkhead).  The 2.4 GHz cable for the Access Point is protected by a 1/4-wave shunt (to the left of the Linx protector).  The assorted rotator, switch, and weather station signals are protected by 300V 3-element gas tube protectors (in the small aluminum box just below the bulkhead. RF coaxial cables have the sheaths grounded at the bulkhead and are protected by 300V (for VHF) or 500V (HF) gas tubes. Both towers, the entrance bulkhead, and the house electrical service ground are bonded by a buried 2/0 conductor.  The taller tower was built on a 32" corrugated surface well that extends 15 feet into the water table and provides an excellent ground.

Inside the house is the Linksys router (right) and the Access Point radio, both powered from a UPS with surge suppression, and on the other side of the room is the display for the Davis Vantage Pro 2 weather station. The Co-Op server is located in the basement and connects to the router with a Cat-5 cable and to the weather display with a serial cable.
 

 
Also, around my property, I have a low-voltage control system that allows remote control of a number of lighting circuits (1 in the house, 2 in the garage), activation of the garage door, and conveys the door bell signal to both the house and workshop from any of three pushbutton stations in various places.

 

Left to right: one of the button stations, one of the relay panels, the surge suppression on the 12 pair cable between the house and the garage/workshop.

Having been in "the lightning business" for many years, I thought everything was well protected!

The Event

On the night of August 12/13 a severe electrical storm moved through southern Manitoba. Hot muggy weather gave rise to a lot of cloud to cloud lightning and around  11:30 p.m. the power went off. With no fan, I moved down to the main floor where it was cooler and since the power outage was wide-spread, I shut off the UPS that protects and backs up the Internet Co-Op and settled in to a chair near the weather station display. At 12:28 (approx.) lightning struck somewhere on the property and I saw an electrical flash between the cable on the weather station display unit. I mistakenly assumed lightning stuck the 68 foot tower.

The following morning, with power restored, I powered-up the Internet Co-Op and found everything was in working order. The weather station was dead however. Subsequent investigations showed the weather station display, its power supply, and the serial interface module had all been damaged and were replaced. I also later found one of the protectors on the 12 pair low-voltage control cable had failed short.


I  could not understand how the lightning energy reached the weather station display despite the extensive protection until I noticed the top of the power pole in the yard. Lightning struck the west face of the wet pole (note the blackened pebbled texture), wrapped around the pole and picked up the drop-wire insulator frame (very bottom of the picture) thus causing a surge on both phases (to the house and garage) as well as the electrical ground.

To combat repeat performances, I installed a "whole house surge suppressor" that protects against power line surges.


 





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