UL listing of lightning arrestors [RE-wrenches]

[Bill Brooks]

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William,

I think you misunderstand how and why these devices work. Silicon-oxide
varistors (SOVs), by definition, must degrade as they absorb energy from a
lightning strike. In order to absorb energy, they must conduct some current
through the sand (silicon oxide) and turn the sand to glass. If enough sand
is turned to glass (glass is less dense than sand), the plastic case breaks
signifying that it is used up.

I have seen a spent SOV sitting next to an inverter that was fully
operational. The device obviously did its job. I'm sure there are many
examples where dead inverters were in the vacinity of unspent SOVs, but this
is likely due to improper installation rather than failure of the device to
work (although I'm sure Delta has its share of failures). 

When I lived in North Carolina, every local hardware store sold Delta
Lightning arrestors. These were mostly used on wiring for well pumps. These
folks were not the type to add cost to projects unnecessarily so I would say
that this is an additional evidence that these actually do something.

Every surge arrestor will wear out over time if it is exposed to surges so
if you are expecting to install something in a lightning prone area and
simply walk away, that will not happen. The more lightning a site is exposed
to, the more often the surge arrestors should be checked. If the site is
exposed to lightning storms on a monthly basis or more often, as much of the
eastern half of the U.S., then annual inspections of surge arrestors and
grounding should be conducted in the ideal situation.

Bill.




Bill and others,

I posed a question to the list several days ago about lighting 
arrestors. I still haven't seen a response---

So I'm wondering if anyone has seen or done testing that demonstrated 
any actual benefit to using lighting arrestors? That is, for an actual 
installation, they absorb a discharge and prevent damage that would have 
otherwise occured to inverters or solar panels... and at the same time, 
without self-destructing.

/wk


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