I'm no expert in this area, but have got into the topic a bit.
I thought that basically one ground rod, and on a single phase system,=20
the neutral is also grounded there for all loads supplied by that=20
supply. This minimizes ground loops. Then important not to tie together=20
anywhere else the neutral and ground. That also might create weird=20
issues with GFCI's. I assume the 3 phase is for heavy motors, etc., and=20
a normal 110/220 single phase is derived from that. Could you not then=20
treat the 110/220 single phase in the normal manner, providing surge=20
suppressor at main breaker box. For the whole house, I have had one of=20
these for maybe 5 years, and we are in an open area with lightning.
http://www.google.com/products/catalog?q=3Dwhole+house+surge+suppression&oe=
=3Dutf-8&rls=3Dorg.mozilla:en-US:official&client=3Dfirefox-a&um=3D1&ie=3DUT=
F-8&cid=3D2095718605650227831&ei=3Dc_JXTe2YHMKftgfZ2YXsDA&sa=3DX&oi=3Dprodu=
ct_catalog_result&ct=3Dimage&resnum=3D1&ved=3D0CCsQ8gIwAA#

This one mounts next to breaker box, connects to 2 existing breakers.

Here's a 3 phase:
http://www.grainger.com/Grainger/SQUARE-D-Surge-Arrestor-3-Phase-600vac-3XB=
87

And here's a bunch of them:
http://www.grainger.com/Grainger/ecatalog/N-/No-80/Ntt-surge+suppressor

On 2/13/2011 9:35 AM, Gerhard Fiedler wrote:
> 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
>
> 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).
>
> 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 th=
e
> 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).
>
> 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.
>
> 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.
>
> 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
--=20
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