[TowerTalk] Shack ground
K8RI-on-TowerTalk at tm.net
Wed Jun 16 22:43:39 PDT 2010
On 6/16/2010 9:55 PM, W2RU - Bud Hippisley wrote:
> On Jun 16, 2010, at 7:41 PM, Michael Baker wrote:
>> Relocation is also not always practical nor is it inexpensive.
> Agreed. But I found the losses from damage caused during three earlier storms not inexpensive, either. And unlike relocating either the shack or the service entrance, they were downright inconvenient because I had no control over their scheduling.
> In those three earlier storms, virtually all the damaged or destroyed equipment in the house was in some way connected to _both_ the AC power line and the telephone line. In particular, in one storm every PC in the house that had a fax/modem connected to the phone line was totally zapped. Unfortunately, one of those PCs was my rig control / logging PC, with a serial interface to my rig, so my rig experienced some damage, as well.
Although voltage spikes do come in on the phone, cable, satellite, and
power line, there is also the *induced* voltage in every conductor in
> These three lightning "events" were not caused by direct hits on my house; rather, they were "nearby" hits, perhaps a quarter-mile away, and the damage came from the surges on our (underground) power line and/or our(underwater!) telephone line.
Probably over 90% (educated guess) of lightning damage is caused like this
> When your AC service and your telco service come into the building at different locations and each is "grounded" at its own separate entry point, you're just asking for trouble if you have equipment connected to both.
They also need to be connected together. In the ham shack all grounds
need to go to the SPG as well. You can never prevent some differences,
but if the lines are properly bypassed and grounded it will minimize any
> So, clearly, some of the impetus to collect the entrance point for these utilities in one spot goes away if one takes care to _not_ connect anything of value directly to the telephone line.
Not necessarily. That is only one of several routes in.
> I no longer use PC-based fax/modems; they have been replaced by a single $50 el-cheapo fax machine for outgoing faxes and a free efax service for incoming.
It's very easy and simple to disconnect the fax/modem.
> Similarly, my DSL high-speed internet service feeds a telco-supplied modem which then connects only to an inexpensive WiFi node; there are no hard-wired connections from my telephone line to anything in my shack.
Every thing here is hard wired. The house and shop are on separate feeds
from the power company and I rarely disconnect anything.
> Unfortunately, there's not much I can do about the connection from my DirecTV receiver to the phone line
Why would you say that. We have DISH network and they have the same
arrangement. It's a simple manner to disconnect the phone line from that
and they aren't going to charge you extra for an hour or two of
disconnect. Also if you go on vacation, just call them and tell them
you will be gone and the phones will be disconnected.
> but since it's leased equipment the company replaces it when it dies and all I'm out is the inconvenience of a few days without television service.
You could also easily be out a television and any other equipment hooked
into the receiver.
> Next, the remaining issue is whether cables to/from the shack (for RF, rotor& remote switch control, etc.) go through a single-point ground that is allied with the AC entrance ground. I think, if I were looking at $5,000 or more to relocate the service entrance (or the shack, for that matter), I would simply lengthen all my cables and make sure they came into the shack the "long way around" -- that is, via the AC service entrance point. Alternatively, I would disconnect them all _outside_ the dwelling after each operating period.
Which is not always a good idea either. Leaving everything in the house
floating is inviting some mighty high induced voltages in said equipment.
As has been mentioned before, you can ground all the circuits in a room
or house to the SPG with a bit of extra work.
The idea is to have all the equipment that is any way connected together
to have a common ground that will allow all of that equipment to rise to
a given potential at the same time, not to prevent a rise.
If the phone line comes into a room have it bypassed with the ground
common to all the rest of the equipment in the room. If the phone line
then goes on to another room do the same thee. Here our phone lines have
separate runs from the entrance, so grounding them with every thing else
in a particular room is no big deal. This is where those bypass power
strips that also handle the phone line may be of some use. The strip is
grounded to the same ground as everything else in the room. The phone
line is bypassed in the strip and grounded like every thing else in the
Lighting prevention is not necessarily keeping the lightning out, but
having every thing raise to the same potential so there is no voltage
differential between any lines in the room.
> BTW, I am not located in an area of high lightning activity;
I recently found out that I am. Of course the 17 strikes to the tower,
averaging 3 a year should have told me something. OTOH the last two
summers were quiet. What this summer brings? I don't know, but they have
the entire lower peninsula painted in red for Thursday the 17th. So it
*could* get kinda noisy around here today.
> the three storms that caused damage to equipment were in the course of perhaps a decade. But one of those three storms occurred totally outside our normal thunderstorm season, on an Easter Sunday morning, with absolutely no warning whatsoever. It was a single bolt event. So I don't recommend leaving cables connected until you see a weather report that suggests a storm is coming; you might receive an unpleasant surprise.
If you disconnect cables you then need to ground said cables or they
become part of a giant antenna system and lightning can induce as much
as 3000 volts per meter of wire. Throwing the coax out the window is
often neither the best or safest route.
An alternative is to install and elaborate ground system and then tie
all systems into that.
> Bud, W2RU
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