Hello,

We get our share of thunderstorms and lightnings around here, and I'd
like to protect the electric supply of our home -- somewhere near the
entry. The=20

The supply is a three-phase system with a neutral wire (four wires) and
the neutral wire is grounded (typically a grounding rod) at each
connection point.

Our connection point is at the property boundary, where the four wires
come in from the street. As required, the neutral is grounded there and
there is a master circuit breaker. This would be the first possibility
to place overvoltage protectors, between the three phases and the ground
rod (which is connected to the neutral).=20

My question with this is whether this makes sense, considering that the
neutral is connected to the same ground rod where I'd connect the
protection devices -- and the neutral comes from the same "problem zone"
where the 3 phases come from. But OTOH it's supposedly well grounded and
probably already reasonably clean when it reaches my property. (I don't
expect to have good protection if a lightning strikes within a few
meters... :)

>From there, the four wires go through some 20 m underground to reach the
house. There I have a ground rod for the protective earth wire in the
installation inside the house (separate neutral and PE). This would be
another place to put the protection devices (and I've seen quite a few
installations that do this).=20

However, I don't think I'd like to connect the protection devices to the
protective earth grounding rod; after all, it's directly connected to
many exposed surfaces all over the house. Connecting them to the neutral
there would beg the same question as in the first option, with few if
any advantages. (If a lightning strikes directly on the property, I
don't think there's much that these protection devices can do anyway.)

It's not easily possible to use a third ground rod that is far enough
away from the other two. I'm tending to prefer the first option, placing
the protective devices right at the entry point, and connect them to the
neutral/ground connection there.=20

Does anybody have any ideas what is the best solution here? What do you
guys do for lightning protection?


BTW, how would this earthing scheme be called? It seems it is a mixture
between TN-C-S and TT. AIUI, it would be TN-C-S if I hadn't used a
separate ground rod for PE and connected PE to the same ground rod where
the incoming neutral is connected to, and it would be TT if the incoming
neutral weren't grounded at each connection to the grid.=20

The overvoltage protectors they sell for TN-S and TT systems have four
protection devices, and the ones they sell for TN-C systems have three.
Another question I have is how many overvoltage protection devices I
need. I figure I only need three... no use trying to protect the
combined neutral/PE wire that comes from the pole, since it is grounded
anyway. Right?

Thanks,
Gerhard
--=20
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