Grounding and surge Protection: The Shocking Truth
Compliments of Rain Bird

Why Does Your System Need Surge Protection?
Today's electronic equipment and solid-state components are very vulnerable to voltage surges - small or large. Electrical surges are by far the biggest cause of problems with electrical circuits. Damaging surges may be produced by lightning, pumps being turned on or off, the energizing or de-energizing of a transformer, or a power source short. a typical 120 volt power line each year can have as many as 2,500 surges of over 6,000 volts.

"But I don't have a lot of lightning in my area."
Lightning and Surge Protection Facts

*Over 80% of lightning and surge problems are due to bad earth grounds.
*A "good" earth ground should have a resistance of 15 ohms or less.
*Protect primary voltage source using a LPP-K across the supply power.
*Use M.O.V. (metal oxide visitors) in secondary power (24 vac).

While lightning is, in fact, more common in certain areas of the country, it happens everywhere. Damage can be instantaneous. About half of all lightning strikes are 20,000 volts and 20,000 amps, but strikes can exceed 100,000 volts and can travel 3 miles through the ground. Each flash of lightning can contain as many as 45 strikes. The average region in the United States can expect 2 to 30 strikes per year within a square mile.

Irrigation systems are particularly susceptible because they have large amounts of wire buried in the ground that can attract lightning. While you cannot protect against a direct lightning strike, you can protect against its indirect electrical energy with surge protection and proper grounding.

Surge damage happens in the first few milliseconds of the surge. Because surges are so fast, even fuses, circuit breakers and GFIs are not quick enough to protect from the damage.

For Your System's Protection
The theory behind most surge protection is to provide a path of least resistance from electrical surges so they dissipate harmlessly in the ground. Such surge protection involves both surge arrestors and proper grounding.

Surge Arrestors - Varistors and Metal Oxide Varistors
Rain Bird uses varistors as surge arrestors because they are much faster than the other products available on the market today. Varistors "clamp" voltage that exceeds a certain level and shunts the excessive energy to a harmless path in the ground.
An M.O.V. or Metal Oxide Varistor is a bilateral device (with no polarity) that is particularly effective at redirecting surges. It is small and easily mounts on PC boards. It is very fast, can handle moderately high power surges and is self-extinguishing.

Protection From the Ground Up - Your Grounding System
Grounding is the essential back bone of a lightning protection system. No matter how much you spend on surge equipment and how you install it, it's only as good as the grounding the system you connect to.

Good grounding breaks up the electrical energy of lightning then directs it to a path to the ground that has less resistance than the path through the irrigation equipment.
Components of an effective grounding system include a grounding conductor, bonding connector or clamp, one or more grounding rods, the soil in contact with the electrode (s) and the surrounding earth.

Grounding Rod
The ground wire from the device you are protecting to the grounding grid should be at least one wire size larger than any other wire connected to the device. Rain Bird recommends a number 9 solid, bare copper wire.

A good grounding system has low resistance to electrical current. You want the ground to be as close to 0 ohms in resistance as possible. Having 0 to 5 ohms is excellent, 6 to 10 is good, 11 to 15 is marginal, and anything over 15 is not effective. Rain Bird specifies 0 to 10 ohms for a grounding grid, or the system warranty is void.

Using soil additives and keeping the ground moist with a dedicated sprinkler can reduce resistance and encourage energy to travel to the ground.

A soil moisture level of 17% offers the best soil conductivity. Soil resistance can also be lowered by adding chemicals, but care should be taken to avoid damaging surrounding landscaping.

Note: When a grounding grid is first installed, you will be unable to get a true ohms reading because the rod surface will not be in good contact with the soil. Wait 5 to 6 weeks for a meaningful reading. Then check the grounds at least once a year.