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Lightning Arrestors

Lightning is the number one cause of catastrophic failures in solar electric systems and components. The first major reason is that many PV systems are poorly grounded and poorly protected. That is also the 2nd and 3rd major reasons.

The purpose of lightning protection is NOT to stop the lightning from striking. You can’t do that. Lightning protection controls the PATH of the lightning after it hits. Like it or not, that is about the best you can do. It’s not lightning that causes the damage, its lightning going through places you don’t want it to.

Almost nothing can offer 100% protection from lightning strikes or damage – but it can be reduced 95% or more with simple precautions and relatively inexpensive installation methods.

Surge arrestors act like “clamps” in most cases. They go across the live wires with another wire going to ground. Normally they just sit there, but if the voltage goes above a certain level, they start to conduct, shorting the higher voltage to ground. In lighting prone areas you should also install a surge capacitor – this is not really an arrestor, but acts extremely fast, and will catch those high voltage spikes on the AC line that are too fast for a surge arrestor. For most systems to get the best protection you should have a DC surge arrestor, such as the LA302DC on the side coming from the array – this should go on the INPUT to the charge controller. It should be as near the charge controller as possible. On the AC side (and this applies to BOTH the inverter AC input and AC output (for generator and/or grid tie systems) you should have both an AC surge arrestor and a surge capacitor.

Most inverter damage is caused by surges on the AC side coming in through house or generator wiring. In many systems with a backup generator, the generator is located outside, quite some distance from the inverter, and is a common hit point for lightning strikes. The Delta LA302R AC surge arrestor and the CA302 surge capacitor should be used on the AC portions. The benefits of also putting arrestors at the generator end are not all that great, and if installed you will probably need a separate ground rod system.

For most mid size and larger systems we recommend the solar surge arrestors. For smaller systems or for general household AC protection the Delta brand will offer some lesser protection but are quite a bit cheaper.

The Delta arrestors are not perfect, but they work a lot better than nothing. Better arrestors are available, but the problem is price – complete system protection using the Polyphaser units could easily cost over US$1000. The biggest problem with the Delta arrestors is that they may not always trigger on “low “level” spikes, but if you also have a surge capacitor installed, that will catch most of those.

It may seem a bit high to spend over US$200 on surge arrestors, but the typical repair bill for large sine wave inverter that has been lightning hit can run well over US$1000. We carry a complete line of Delta Surge arrestors and capacitors.

Most surge arrestors that we sell have 3 wires (a few, for pumps, have 4). In all cases, the GREEN wire is ground; the black and white wires are wired across the AC or the DC power side. Even though the white in most AC systems is neutral, and is supposedly grounded, don’t count on it – make sure you have both sides protected. In DC systems, such as PV arrays, it really does not matter much which of the two wires go to what, but again both sides of the input to the charge controller or whatever the panels are feeding should have one wire from the arrestor attached. To protect a 3-phase submersible pump motor, connect the black wires to the line terminals and the white and/or green wire to the casing ground. Most of the arrestors that we sell have a separate green ground wire – this wire should ALWAYS be attached to a good ground.

Q. Does a lightning rod or grounded tower or high structure makes it more likely that lightning will strike?

A. No, it will have little or no effect on how likely it is that it will strike in the immediate area, the important thing is it will be conducted directly to ground, without having to go through your inverter first. It does make it more likely to strike where you want it to. There is some evidence that a few strikes can be prevented with the use of special sharp-pointed “air streamer” lightning rods, which bleed off some of the accumulated charge. However, that has been a controversy for at least 50 years.

Q. Does lightning always strike the tallest objects?

A. No, it can strike anyplace – although it is most likely to hit the highest object, there is no guarantee. It is also more likely to strike something with a good path to ground, such as a steel tower. Sometimes, even if it strikes the highest object, you can get side flashes if the object it hits is not well grounded.

Q. Does fuses and breakers offer protection from lightning?

A. Fuses and circuit breakers offer no protection at all to lightning strike, that is not their purpose. Lighting usually lasts for only a few microseconds – much faster than any fuse or breaker can blow. It’s pretty unlikely that a one-inch fuse gap is going to offer much protection from a bolt that just cut through two miles of open air. Yet the myth persists that a fuse will offer lighting protection. It will not.

Q. What the Purpose of Grounding?

A. Equipment: Panel frames and mounts are grounded in order to provide the easiest path for lightning to get to ground. You would much rather have it go down the mounting pole or your ground rod than down your wiring to your controller or inverter.. Without proper grounding, lightning can do some really strange things, and can jump around all over while trying to get to earth. If your inverter happens to be in the way, you will probably be buying a new one. You cannot stop lightning, but you can usually direct it where you want it to go.

Q. What is Single Point Grounds?

A. The importance of a single-point protection ground cannot be stressed enough. All equipment should normally be bonded to one single good earth ground. If you have some equipment on one ground and other equipment on another ground, it is quite likely that in a nearby strike that there will be a large voltage difference between the two grounds. This means that the equipment will be at different voltages, sometimes high enough to get arcing from one to another. There is an exception to this: If you have a panel array that is more than 50 to 75 feet or so from the rest of the system, it should have it’s own frame/mount ground (not electrical ground).