With the talk of vehicle bonding, I'd like to talk about bonding of a different sort at home. I'm finally getting time to finish some installations at home and while it's been in the back of mind I haven't done a good job engineering a grounding solution thus far.
So what are you guys doing for your single point ground and lightning suppression?
My question most revolves around where the lightning path is located and is it your station ground as well? I'm torn between hanging a box on the wall outside to put the arrestors and have a second plate inside for the single point ground or to share these two functions on one plate mounted right on the inside side of the coax entry.
From a safety standpoint, the outside/inside solution is better, but this means I can create ground loops much easier. When I think about it performance-wise, I start to convince myself that a single ground plate with the arrestors and single point ground is better.
I have not checked the NEC or local codes, so the decision might already be made if the NEC says that lightning arrestors cannot be mounted inside the dwelling. I have a feel that it does not specify, though.
I am also thinking of getting a couple of nice, old knife switches and putting them as close as I can to the antenna feedpoints and just hard grounding the antennas (I already physically disconnect the radio feeds) as storms pass overhead. That would not substitute for the inline arrestors, which are mostly to dissipate close-in energy and static. Those little suppressors aren't going to survive a direct lightning strike anyway.
I was listening on the 145 a couple years back and these fellers were talking about using a glass jar as an insulator. so that's what I do in the spring to fall months, is unscrew the antenna and put the connector into an empty glass, supposedly that's enough insulation from any badness should lightning hit the antenna on the roof? That's as fancy as it's gotten over here in the shack.. http://www.risingsun4x4club.org/uplo...s/electric.gif
That's a very old myth. Whatever you do make sure that jar is in safe place! The only way that's not gonna be a grenade in a strike is if you have a very good vacuum inside, otherwise the moisture and air inside is going to heat up quickly and you are mostly containing the expanding gas as it expands. BOOM!
The theory goes that since glass is an insulator that this is somehow better than just an open coax. It is not. The strike made it 15,000 feet from the cloud to the ground causing air the break down, do you thinking another few mils of glass are gonna stop it? You know what might work is to fill your sink with salt water and dunk the coax in that. It would short the feedline to your plumbing and might do the trick. The salt water would ruin the coax, though. :-)
What you are after with lightning and static suppressors is controlling and routing the current away from your stuff, not stopping it. That is why you ground things, give the strike a path of lesser resistance around your radios and house. I only pull my coax off because I don't have antenna switches to connect to a real discharge ground yet. But don't forget that anything hit with lightning is gonna be toast, so think about your physics and thermo classes, things are gonna burn, heat, expand, etc.
I am interested in this topic, Dave.
I am interested in the topic for:
B: Electric Shock
C: Radio Frequency Energy
2: NEC code concerns
3: Thrift. (I don't want to buy/do more than I need to to meet the above)
I understand that we live in HOUSES and not wireless telecomunication huts. There will have to be compromises.
Number 1A concern for me is lightning protection for people and structure.
I understand the desire to ground everything together so that voltages come up and fall back down together. The smaller the voltage difference, the less current that actually flows. As my friend Tyler sings in his local geek rock band, "The Bluebird Equation" as part of a tribute song to Nicoli Tesla, "Amplitude not voltage will burn you down."
There is a ton of "information" both good and bad out there to sift through. As with most things, I have to filter the information using my personal experiences. For lightning, I have a few. The neighbor's chimney got hit and exploded. The flying bricks dented the siding on my parent's house a good 10 feet away. A tree at the cottage got hit in the front yard. It blew the bark off the trunk in a spiral all the way to the ground. Tree died. Next door, two trees got hit in a different storm. Trees fell down. 4 cottages up was hit by lightning. Burned to the ground. My cousin and I saw a bolt hit the water in the cove 2 cottages down. lit up the water in the cove, killed some small fish and wow was it loud.
So yeah, I've been close to lightning and it is totally destructive. What can I do to minimize the risk/impact of a lightning strike?
It looks like just as much damage comes from power, phone, and cable TV lightning hits as direct strikes to people's antenna systems. So protecting the house power, phone and cable TV might be equally important to protecting the antenna system?
If my house gets struck by lightning I'm not sure what a little extra broken glass on the floor is going to matter, but if it's a myth alright I'll quit doing the glass jar thing, and instead just leave the coax laying on the desk.
Right now the antenna is on the top of the house- how much would I lessen my risk if I moved that to the top of a tree in the back yard 30' away?
So what have I done.
I have a roof mounted antenna re-using an existing 2' satelite TV dish tripod.
I ran a 6 AWG bare copper wire down from the antenna mount, over the lip of the roof and down to the ground. There are no standoffs attached to the house, but I might have to add a couple in the future if the wire bangs the house in the wind. The wire is about a foot from the house on the way down. Not a foot away at the roof. I used a large radius curve underground to traverse 5 feet or so the the existing house ground rod. I used nolox under a UL listed, designed for direct burial, clamp to attach the 6 AWG wire to the ground pole. I was surprised that the ground pole wiggled when I hit it with the shovel. It might not be an actual 8' ground rod. The rod is not marked on the end.
I removed the 24 AWG ground wire and 2 pieces of RG58 coax that were screwed to the roof, the eves, and the side of the house. They were well within 4' of the old tripod mounts on the roof, but cut off and left when the dish was removed (which must have been more than 10 years ago since it was gone when I moved in.)
The dish ground wire was attached to a spigot on the back of the house. Which would route a lightning strike into the house via the plumbing. sounds like a bad idea. The cable TV guys did a little better and ran a coated 14 AWG wire from their ground block, stapled to the bottom of the house around the side and attached it to the phone company's bare ground wire, which is attached to the main breaker box coming in from the street. I see some potential ground loops there.
So, what can I do to improve at least what I already have?
Removing the old wires from the roof was probably a good thing. Now lightning won't travel down those wires and light the roof, eves, and side of the house on fire where it is attached to the house before entering the house via the copper water pipe it was attached to.
My #6 ground wire on the antenna is a good start, but the 90 degree bend at the top will probably let the lightning short-cut through the roof and light the roof on fire anyway. *shrugs* Maybe the rain will put it out. ;)
I think it would be wise to put a ground rod in directly below the copper antenna ground wire, but leave the wire continuing along to the original ground rod. but...The rods would be less than 6 feet apart. I think, (but don't know) that the NEC doesn't allow ground rods that close together (because it doesn't really help ground things)
The next good thing to do might be to simplify the grounds on the phone and cable TV. We don't actually have cable TV anymmore, so maybe the best thing to do is to remove the ground block and wires and make the cable TV company re-do everything again the next time we switch back to cable. Yeah right. I bet they would hook right to the handy spigot on a do-over.
Can I install more ground clamps directly on the main ground rod like I have already done and still be National Electric Code compliant?
I think it's important to distinguish between equipment damage and safety. I think we can all agree that if a radio or computer dies due to a discharge, that it sucks but isn't critical. If a person is killed or hurt or a house is burned down, that is critical.
We can also agree that an antenna that works well for RF signals is going to be conductive and tall, also making them better at lightning attraction!
OTOH, if you think about it, they are also very good to have around because they can protect your house. This requires that you consider the equipment damage potential because you in a way make the antenna the conduit to route lightning away from the house. Which means that you need to think about the current flow and don't do something to make it neutral or worse. This is why I want to put lightning arrestors in a box on the outside of the house connected to a ground rod.
When placing protective device consider the case where they are destroyed, there is a lot of energy in a lightning strike and it has to go someplace. Think about what would happen if a device arced over say near a gas line or where you store paint. Most houses would sustain non-structural damage in a strike, like you mention blowing off bricks or localized burning. But if the strike hit your gas line that creates a secondary problem which isn't really a direct electrical effect per say.
One thing is that the chance for shock is low with a lightning strike unless you are touching the antenna or equipment during the actual strike. A small window of time. However, an electrically floating antenna during a storm, really anytime, can build a large charge that can be painful or fatal, not to mention damaging. The static needs to be bled off even during normal conditions, so all external antennas should be grounded. This, though, has to be a DC ground and not an RF ground. Your radio does not like to see an RF short (although an antenna tied hard to ground is not necessarily an RF short at the radio end). Also there is a non-trivial chance that antennas can carry commercial power, so before touching them make sure they are not touching overhead wires, underground wires or otherwise. That is the main shock danger, that a loose wire touches your antenna.
BTW, only your /cold/ water pipes can be considered for grounds.
|All times are GMT -6. The time now is 05:37 PM.|
Powered by vBulletin® Version 3.7.1
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.