I hadn't thought about the lightning protection issues. Lightning occurs
infrequently here in Western Washington, so it isn't the first thing that
usually comes to mind. If I run the ground wire through the toroid also,
would I get sufficient lightning protection by adding a closely spaced,
large area (0.25 to 0.5 sq inch) spark gap across the two ends of the ground
wire that passes through the toroid? Low level static build up would
discharge through the toroid's dc path, but when the voltage increased past
a certain point (say 1-2KV), it would discharge through the spark gap. I'm
not sure if it would meet code, but it seems that it would give the best of
both worlds -- good RFI suppression and a safety ground for lightning.
Another thought -- if a single ground point is used at the cabin's service
panel, and the RFI filter is installed at generator 20' away, the most
important lightning protection would already be provided, since the most
likely path for lightning to take would be through the antennas and into the
house. If the safety ground passes through the toroid, it might even offer
some additional lightning protection for the generator.
On the subject on grounding, the generator is located in a separate shed
about 20' from the service entrance. If I use a single ground point, should
it be at the generator or at the service panel? When connected to a power
company, the ground is a the service panel and I assume that the power
company grounds their service at multiple points along the delivery route.
How is a generator supplying power (as the sole power source) different?
When connected to both the power grid and a generator though a transfer
switch, I believe a single ground at the panel is required and probably
preferable. However, when the generator is the only power source, I'm not
sure what the requirement is.
The topic of grounding (both RF and power) is one that I simple haven't
thought about enough during my ham career, although I'm starting to realize
how important it is, especially since I started running QRO last year. I
really appreciate all of the advice being offered here. This summer I hope
to put up a tower with a Steppir beam, a couple of wire antennas and a
beverage or two at the cabin. If I can eliminate my own man-made QRN, it
should be a great location for some serious DX work. The cabin is over 2
miles from the power grid and at 1700' in elevation on a mountain. Terrain
analysis shows that I'll have about 5db of gain over flat land towards the
southwest on 160/80M which will be perfect for working the South Pacific and
long path into Europe.
Clay W7CE
>
> The word "probably" in my reply is based on the potential for a conflict
> between safety grounding and RFI suppression. You MUST bond all grounds
> within an installation for safety, but these conductors can radiate RF
> current that is flowing on them. The obvious answer is to choke that
> current. BUT -- the reasons for the bond are 1) to provide a path for a
> fault current to blow a breaker or fuse; and 2) to equalize the very high
> potentials that can exist with a lightning strike. The choke will likely
> cause no problem with #1, but it CAN cause a problem with #2, because much
> of the energy in a lightning event is in the middle of the AM broadcast
> band, and, of course, continues above that range.
>
> Remember, it is the impedance of the bond at the frequency of the
> lightning strike that determines its effectiveness. We know this
> intuitively re: the lightning bonds for towers, masts, etc. -- lightning
> will jump across any bumps and grinds that we put in its way in the form
> of coils, loops, zig-zags, etc. Thus, to avoid compromising lightning
> protection, any choke added on such a bonding conductor must be designed
> to have minimal impedance in the part of the spectrum where lightning
> energy is concentrated. What might happen if there's a choke there and it
> has too much Z? First, it will overheat and self-destruct, but second,
> the lightning may not be discharged quickly enough to avoid damage
> elsewhere.
>
> Jim Brown K9YC
>
>
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