On 1/13/2012 9:54 AM, Jim Lux wrote:
> On 1/13/12 5:39 AM, Stan Labinsky Jr. wrote:
>> John, your understanding that short is better is correct, however, taking a
>> path right through your house is not, never, ever!
>> Consider also that the outside path, if accomplished with bare wire will
>> create a more intimate connection to earth which is what you want. I'd
>> suggest that at the corners of the run, that you drive ground rods.
>> Lightning doesn't like sharp bends, but having the rods at those points will
>> augment the strike energy's access to ground.
> I don't know if there's any truth to the "lightning doesn't like sharp
> bends"... I'd like to see some physics behind that.
> 90 degree bends don't have much inductance over the length of the wire
> (that is, measure the inductance of a meter of wire in a straight line,
> and then measure it after being bent in a 90 degree arc, or a sharp
> angle, and it will be the same).
> There are mechanical reasons why bends are bad: the electromagnetic
> forces tend to pull the turn apart.
> Something to think about, length wise... Either route is "long" in terms
> of the inductance (i.e. it's many microhenries). Either route will
> have many kilovolts of drop with a typical lightning rise time of 1-2
This is why I say that having everything at the same potential in the
house from a nearby strike is a myth.
Each room is a different distance from the strike, and voltage induced
at one end of the house will not be in phase with voltage induced at the
other end of the house by the time it gets there even with an SPG. Even
when the SPG is at the house entrance there may be multiple circuits in
rooms that follow different routes and are different lengths. There are
3 circuits in my den and one takes the long way around going through the
living room, a bed room, the bath room and then in here. The other two
circuits for the station are run by direct route to the panel. So when
the computers are connected to the rigs their electrical neutrals are at
least 50 feet longer.
I still need to do something about the circuit that is longer. I really
need to replace it with separate circuits to the bedroom, bathroom, and
in here for the computers.
BTW I have a single #2 running direct through the ceiling of the
basement to tie the bulkhead to the house ground which is only #6. The
bulkhead OTOH is tied into over 600 feet of bare #2 with 32 or 33 8'
ground rods and two tower bases.
To go around the house which would have been preferable would have
required going under a 40' wide slab of concrete which is the approach
for a 3 car garage. Going the other direction would have added 130' of
copper although the house ground would have benefited from it, the
timing would have been lousy for pulses coming from a lightning strike
on one of the towers.
> V = L di/dt... If the full 20kA stroke is the i, you're looking at di/dt
> of 20E9 Amps/sec... 20kV per microhenry.
But Di is probably on the order of 0.001 or less for the typical stroke.
> As Jim pointed out.. the whole goal is to get everything that is
> physically close to move together, so you don't get large "box to box"
> currents (or arcs). It's inevitable that one side of the house is going
> to be different than the other.
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