Lightning suppressors


Senior Member
Lightning season is back upon us in the northern hemisphere at least. ( Aussie's can go snow skiing!) All electronic equipment, no matter how well it is designed can be damaged from nearby lightning transients. The easiest entry points for home automation controllers is the AC power lines and the telephone lines because they connect to the outside world. Zone wiring and data bus wiring can also be succeptable in near direct strikes.

A lightning strike 1 mile away can induce 30 volts per meter of wire. 100 meters of wire could induce 3000 volts into the control system. Most controls can handle this level of transients. Powerlines and telephone lines running down the road could be many times more induced voltage into the control system.

Transient suppressors are a great insurance policy. They are relatively inexpensive and can save you hundreds of dollars in damage not to mention the headaches of being out of service.

There are 3 main types of transient suppressors: gas tubes, metal oxide varistors (MOV), and silicon based suppressors:
1. Gas Tubes - Higher voltage protection and the slowest reaction time. More than 10 nano seconds.
2. Metal Oxide Varistors - MOV's. Used widely for transient protection because they are inexpensive. Reaction time about 5 nano seconds.
3. Silicon Based Suppressors - Two trade names are Transorb and Sidactor. Fastest reaction time, less than 1 nano second. More expensive.

In one nano second, the lightning transient can travel about 1 foot down a wire. In the case of a MOV, the lighting can travel 5 feet before the transient suppressor starts to kick in and limit the transient. That could be too late. Even the fastest silicon based suppressors could not be fast enough if the suppressor is mounted on the control's PC board.

A separate transient suppressor from the control board is better because you can put some wire distance between the supressor and the control equipment which allows the transient suppressor to kick in and limit the transient before it reaches the control board.
Example transient suppressors would be the ELK950 which incorporates the silicon based suppressor and induction coils and Ditech's transient suppressor line. In any case put at least 10 feet of wire between the suppressor and the control board. If you do not have that much distance, roll up the wire in a tight coil. A coil works better because it forms an inductor which lightning hates.

A great inexpensive inductor is to take nails and drive them into the wall and wrap all incoming and outgoing wires around a separate nail about 20 turns. This forms a very good inductor that will greatly limit lightning transients. It would be better to mount any transient suppressors between the nail based inductor and the control. The nail based inductor will limit or slow down the transient enough so that the transient suppressor can be more effective.

Multiple ground stakes in a house that are not unified or connected together are bad. A common or unified ground stake system works the best. Multiple, unconnected, ground stakes allow one type of lightning transient which is running through the ground to go up one ground stake, run through the house, and back down another ground stake. You may have heard of the story of cow's being killed from a nearby lightning strike. The lightning strike did not kill them, but the "Step Voltage" between their legs did. The lightning ran up one leg, through their body, and down another leg. So during a lightning storm, stand on one leg!!! :huh:

Every year go out and hit the top of your ground stack with a hammer to break up any glassification around the ground stack from any previous lightning strikes. Especially in sandy soil because a lightning strike can insulate the ground stake with layers of glass from the soil. It is also a good idea to replace or add a new ground stack next to the old one every few years. Make sure they are connected together for a unified ground.

Lightning suppression is a GREY art. Once you think you have it figured out, it will find another path to get you.

edit: Thanks Carry15+1 for the unified ground stake reminder.
Awesome post! As someone who has lost thousands of dollars in equipment to lightning, I can't help but stress that this can happen to anyone, and to prepare as much as you can. Even with a good insurance policy (which I did have), it can be a major hassle to replace everything.
I agree, a timely and interesting post - thanks Spanky.

I must say though that multiple rods can reduce the resistance of your grounding system. The multiple rods should be located close to each other and be tied together - esothermic welds are ideal. And you should probably make all your house connections to one rod. Also, if you have good soil you can drive LONG ground rods. Back in Illinois I picked up a few of these screw together rod sections from the power company and drove them over 18' deep using a impact hammer. Here in Missouri this would be a dream because of all the rock so it's multiple rods.

I like my primary brute force surge arrestors at the service(s).

Post reminds me I bought the Elk telephone surge arrestor and never did install it :huh:
I will have to agree. My elk took a hit, but tech suppport performed CPR and saved it. I now have a supressor.