Dear Mr. Electrician: Can I prevent lightning strikes from doing damage to my house by grounding? My neighbor was blown out of her chair when lightning hit her TV. How can I prevent that from happening to me?
Answer: There is no 100% full proof method of stopping a lightning strike from doing damage. However several things can be done to prevent or reduce the damage. Basically everything electrical needs to be properly grounded and bonded in such a manner as to provide a good direct path for lightning to flow to the earth.
The photos below depict an actual job of mine correcting the grounding for a 1940’s single family detached house. Article 250 in the National Electrical Code concerns grounding and bonding. Some relevant sections are: 250.8, 250.52, 250.90, 250.94, 250.104. Also read article 800.100 on grounding communication circuits and 820.100 which concerns the grounding of cable TV systems. NOTE: Some text links below go to applicable products on Amazon.com
Lightning Protection for Power, TV, and Telephone
The above photo depicts how I found the TV and telephone lines grounded. It turns out that this pipe was not connected to anything. It was in the ground only a few inches and contained a piece of cut electrical cable, the remains of which is protruding from the pipe. Needless to say, this would not be adequate protection if lightning were to strike.
The telephone demarcation point and the cable TV demarcation terminal both need to be bonded to the grounding electrode conductor for the main electrical service. Newer electrical installations have an intersystem bonding termination for the grounding conductor from the telephone and cable TV to connect to.
On older houses the telephone and cable TV grounding conductors are sometimes connected to an existing ground rod, or have their own ground rod, or are connected to the grounding electrode conductor.
Above was the existing ground connection for the cable TV service to the house. I installed a new #10 copper wire and clamped it to the grounding electrode conductor which was connected to the water pipe inside of the house.
The copper wire for grounding TV and telephone must be no smaller than #10 AWG. #8 wire would probably be too big for most demarcation terminals.
Additionally all interior metal piping must be bonded to each other with jumpers around water meters, water filters, and other devices whose removal would interrupt ground continuity.
The hot and cold metal water pipes must have a jumper between them. This is usually done at the water heater. Although the code requires gas pipes to be bonded, some local areas do not want that. Best to check with your local building department about bonding the gas pipe.
The arrow in the photo above indicates the existing grounding terminal on the original telephone demarcation point. It was still active with it now being fed from the new outside telephone demarcation box. The existing ground wire was attached to a water pipe at a sink in the back of the basement instead of the water main near the water meter.
The grounding electrode conductor from the main electrical panel is connected to the metal pipe water main before the water meter. If there was only a plastic main water pipe, then one or more ground rods are required for lightning protection.
In the first main disconnect after the electric meter the neutral conductor is bonded to the grounding electrode conductor. After that neutral and ground are always kept separate from each other.
The photo above depicts the old water main and the old grounding electrode conductor connected to the copper pipe. When the new copper piped water service main was installed, a new grounding conductor was installed. You can see below what the new connection looked like after several years.
As you can see in the above photo, the existing water pipe ground clamp is quite corroded. This is not an unusual sight. After years of being in a damp basement and ignored of maintenance the ground clamps tend to get corroded.
It is important for the grounding electrode conductor connection at the water pipe to be tight and free of corrosion. See what the replacement for the rusted clamp in the above photo looks like on page 2.