Lightning detector and disconnecting utiliy earth.

dadams · November 2013

Greetings folks.

Sorry if this seems a bit off topic but I'm sure everyone will find it interesting.

Lightning, where I live, it's a real pain in the butt for about four months a year.
We get those serious angry purple rolling thunder storms. Replacing electronics in summer is an all too frequent event.

I'm about to install thousands of dollars of backup power and automation equipment and I'd rather not see the magic smoke leaving the building.
So, I plan to install something along these lines to allow me to disconnect my home from the grid when a storm approaches.

http://www.hobby-boards.com/store/products/Lightning-Detector.html

Now here's my worry, ok, A storms approaching and the electronics have disconnected the hot and neutral but I'm still connected to the utility earth.
When I've run my generator in the past, and there's been a nearby strike, I notice my genset load up like crazy for a couple seconds while the lightning is hitting the ground.
So, there has to be a complication here.
I'm assuming lightning getting involved with the power grid does strange things to everything running from the grid.
Or even striking the earth must do horrible things to earth potential in the general area.

I have my own earth buried in my garden, (A Caterpillar D7 radiator core at about 9 feet deep in a nice wet part of the garden) so my own supplementary earth is pretty good.

Would it be better to disconnect my incoming utility earth along with the hot and neutral during a storm or would it be better to disconnect my utility earth altogether and just use my own on a full time basis?

I'm worried about having my own earth connected to the grid as it might cause voltage potential and still blow things up during a storm.
I really don't know enough about this to even come up with any arguments. But, I have to come up with some way of completely isolating my house during a storm (and keeping things safe) so that only a direct strike will cause damage. I'm far more concerned about lightning blowing my electronics via the grid than I am about a direct strike.

Anyone got any ideas?

Thanks in advance

Dave

ggunn · November 2013

Re: Lightning detector and disconnecting utiliy earth.

To begin with, something you already know: lightning is weird. Nothing you can do will render you completely invulnerable to lightning.

That said, and I am no lightning expert, it seems logical to me that a strike out on the grid somewhere could bring woe down upon your head through the utility ground, so in that case you'd be better off cut off from it. OTOH, it also seems logical that if you took a direct strike, being connected to the utility ground could help take some of that charge away from you. But the grid is a lot bigger than you are, and therefore a lot more likely to take a strike than you.

I'd say disconnect from utility ground during a thunderstorm, but understand that is free advice and worth every penny.

Cariboocoot · November 2013

Re: Lightning detector and disconnecting utiliy earth.

Here's a question for you: where is your home Earth grounding connected to the system? Inside the house, or outside at a utility pole?

Because this is how lightning causes trouble: introducing very high Voltage and frequency spikes inside the home where everything is connected. If your ground sink is outside it stands a better chance of earthing any spikes coming down the utility ground wire than if it is inside. Inside, it can hit anything you've got, jump to another wire, find its own way around the place - and burn up everything in the process.

Lightning can jump miles. If you really want to disconnect from the grid you'd need to sever the utility feed at both ends. Things like a transfer switch are a complete joke to several hundred thousand Volts.

I would also be installing MidNite's protectors on the lines. You will never be able to do anything about a direct strike, but you can reduce the chances of damage from nearby strikes energizing the whole areas. As ggunn said, lightning is weird. It will do what it wants.

Oh one other suggestion: insurance.

BB. · November 2013

Re: Lightning detector and disconnecting utiliy earth.

One of the reasons lightning is difficult to "control" is that it is not just DC, but has lots of Radio Frequency Energy too (most is 10,000 Hz and below). So, while your buried core is an interesting idea--You can have several issues it may not work well with lightning.

First, what is the diameter and length of the cable? In the US, we usually use 6 awg (4.11 mm or 13 mm²) minimum (and 4 to 4/O is used too--many times thicker/and more expensive copper--Aluminum can be used for above ground cabling too). For lightning, that becomes inductive and of questionable use over ~10' / 3 meters of length. It is the "skin effect" that the higher the frequency, the more the electricity wants to flow in the "skin" of the conductor.

Simliar with the radiator core--the copper in the core is very thin--So it is not a very effective RF conductor.

Here is a site that sells grounding products:

http://stormgrounding.electrical-insulators-and-copper-ground-bars.com/lightning-protection.html

UL (Underwriters Laboratories) Installation Guidelines
Residential Lightning Protection and Grounding
Arborist (Tree-Top) Lightning Protection and Grounding
Barn and Outdoor Structure Lightning Protection and Grounding

BB. wrote: »

A couple threads about Lightning:

Off Grid Grounding Technique?
Another Question, this time about Lightning

Note, the above are discussions, not a do A, B, and C--and you will be "safe". There probably is no such thing with lightning. Several different techniques are discussed--and a few of those posters even have experience with lightning. :cool:

And our host's consolidated FAQ page:

www.windsun.com
Lightning Protection for PV Systems

From other past posts here, Windsun (admin/owner of NAWS), he said that most of lighting induced failures he saw were in the Inverters' AC output section.

Towards the end of this thread is a very nice discussion of proper generator grounding.

-Bill

[h=3]Off grid grounding technique?[/h]
http://www.copper.org/applications/electrical/pq/casestudy/nebraska.html

Lightning detectors seem to becoming more common--But usually these are used at outdoor events to indicate when people should evaculate the area (fields, stadiums, swimming pools, etc.).

Opening switches is, generally, not "good enough" to really stop lightning. You can easily get 25,000 to 250,000+ .... The little gap in a switch is not really doing to do a lot. Others have recommended separating tower/solar array connection by 10 feet (3 meters) minimum to avoid flash over.

-Bill

Cariboocoot · November 2013

Re: Lightning detector and disconnecting utiliy earth.

A note on what Bill was saying about wire: actual lightning protection systems use woven flat wire to help combat that skin effect he mentions. Large surface area, low core volume. This is one of the biggest problems with lighting; that whatever conductor it gets induced too can not handle the type of power so it easily jumps to other conductors rather than follow what would be the path of least resistance and normally able to take the Voltage under 'standard' conditions.

DanS26 · November 2013

Re: Lightning detector and disconnecting utiliy earth.

Dave, you mentioned in your original post that you have a separate ground buried in the garden. Is this ground bonded to the utility ground? If not I submit that is the problem. If not bonded then you are creating an electrical difference in potential between the two grounds or earths. What happens during a lightning strike is that electrical build up will search for the lower resistance ground through your sensitive electronic equipment. Make sure those two earth connections are bonded together so that electrical surges see a "single point" of ground.

dadams · November 2013

Re: Lightning detector and disconnecting utiliy earth.

Cariboocoot wrote: »

Here's a question for you: where is your home Earth grounding connected to the system? Inside the house, or outside at a utility pole?

Because this is how lightning causes trouble: introducing very high Voltage and frequency spikes inside the home where everything is connected. If your ground sink is outside it stands a better chance of earthing any spikes coming down the utility ground wire than if it is inside. Inside, it can hit anything you've got, jump to another wire, find its own way around the place - and burn up everything in the process.

Lightning can jump miles. If you really want to disconnect from the grid you'd need to sever the utility feed at both ends. Things like a transfer switch are a complete joke to several hundred thousand Volts.

I would also be installing MidNite's protectors on the lines. You will never be able to do anything about a direct strike, but you can reduce the chances of damage from nearby strikes energizing the whole areas. As ggunn said, lightning is weird. It will do what it wants.

Oh one other suggestion: insurance.

Hi Cariboocoot,
Home earth is connected in to the distribution board inside my kitchen. It's connected directly to the same busbar the utility earth is connected to.
Understand lightning which has just leapt a couple miles won't even blink at box of tricks or a half inch gap between wires.
Will look at midnites protectors, thanks.
Insurance is the cheapest and most reliable form of protection. Absolutely. But it still doesn't stop the pain of having to rebuild everything.
Where I live, all the power lines to within three miles of my house are underground so the nearest strike I'm likely to see (on the lines anyway) is about three miles away.
What I'm mainly trying to protect myself from is a few Kv coming down the line. Simple disconnection during a storm might do that. Obviously nothing will help if a few hundred thousand little blue men decide to jump in to the wire.
My thoughts are, some protection is better than none, and if I can protect against the smaller incidents, that has got to cover 90% of the risk.
where I live, it's very unlikely I'll have a direct strike on my house, surrounded by hills and such.
Also, I need to know if switching from utility earth to my own earth during a storm is a safe thing to do or not.
I don't see it making much difference from a human safety point of view but I really don't know enough about the subject to make a decision.

Just for a bit more info, the Cat radiator core is about 5'x5'x8" thick with a 5' earth spike bolted to each corner. (That'll make it a few hundred pounds of copper, brass and solder)25x3mm copper earth strip (00 gauge) bolted to the core and runs through the ground to my house. Once at the wall of my house, the rest of the wire run to the DB is 2gauge copper wire. Total run length from radiator to DB is about 150'

I nearly died a few years ago when I went for a bath and some prick hadn't earthed the geyser in the house I was staying in. The submersible element had blown and was juicing up the pipes. Thank god I didn't get in to the bath before I grabbed the tap. We run on 240v in this part of the world. Since then, I've taken earthing very seriously.
The radiator core was just a supplementary thing. was never intended to dissipate lightning.

Hope that helps :-)

Dave

dadams · November 2013

Re: Lightning detector and disconnecting utiliy earth.

Hi Dans,

Yes, the home earth is bonded to the utility earth.
My concern is, when we've had a storm in the past and I've been running on generator with the manual change over switch disconnecting the grid hot and neutral, the generator loads up like a bugger when there's a nearby strike within a couple miles of my house. I have no idea what causes this. In my limited knowledge, I can only assume the strike is causing some kind of major earth potential.
Anyone got enough knowledge to explain what's going on here?
I'm hoping that disconnecting the utility earth at the same time as the hot and neutral, and switching to run on my own earth during the storm will help solve the problem of the genset loading up during strikes?
Any ideas?

Thanks

Dave

DanS26 · November 2013

Re: Lightning detector and disconnecting utiliy earth.

dadams wrote: »

Hi Dans,

Yes, the home earth is bonded to the utility earth.
My concern is, when we've had a storm in the past and I've been running on generator with the manual change over switch disconnecting the grid hot and neutral, the generator loads up like a bugger when there's a nearby strike within a couple miles of my house. I have no idea what causes this. In my limited knowledge, I can only assume the strike is causing some kind of major earth potential.
Anyone got enough knowledge to explain what's going on here?
I'm hoping that disconnecting the utility earth at the same time as the hot and neutral, and switching to run on my own earth during the storm will help solve the problem of the genset loading up during strikes?
Any ideas?

Thanks

Dave

Is your generator a separately derived system? In other words is the neutral bonded to ground at the generator or floating. What you have described so far your neutral should float (ie not bonded). If bonded at the generator then it could explain the loading you describe. I see you are switching the neutral. You should not switch the neutral in a floating system.

Cariboocoot · November 2013

Re: Lightning detector and disconnecting utiliy earth.

If the concern is lightning-induced HV spikes coming down the utility wires then disconnecting all the utility wires, including ground, from the house is the best way to minimize this. This will eliminate the utility lines acting as an antenna to pick up stray Voltage and feed it to your house.

Since your house system has its own Earth grounding put the surge protection on the house lines to that to sink anything that may arise in your immediate area. Beyond that there's not much more you can do.

Insurance may not eliminate the pain of rebuilding, but it can ease the pain of paying for it.

DanS26 · November 2013

Re: Lightning detector and disconnecting utiliy earth.

I agree that complete isolation would protect your house from grid induced over voltages, but what a PITA. Every time you see a bad storm roll in you go to generator power? I don't think that is practical and also not possible when away from home.

First a proper grounding and bonding setup is required. Hire a licensed electrician, if you are losing equipment, that will be money well spent and cheap insurance.

Then a good system of SPD's is required. I'd start at the utility transformer. Many utilities in strike prone areas will put a SPD right on the transformer. Just ask them. Next put an SPD under the meter at the can. Most utilities will provide these also usually at a cost but you can find them on the net but the utility will probably want to install it. Next you could add another in the main distribution panel and also in each outbuilding sub panel. This is cheap insurance. Also any lines such as telephone, cable coax, satellite TV, etc should have grounding shunts installed. Solar inverters, controllers and combiner boxes should be protected by devices such as sold by Delta or Midnight Solar.

Finally, for all your sensitive equipment, then protected power strips are in order.

niel · November 2013

Re: Lightning detector and disconnecting utiliy earth.

the generator loading up with a strike is concerning me here. be very sure all connections are correct with polarities observed and good connections not only at the generator, but throughout your place. if all checks out try disconnecting totally from the grid upon the next storm and see if the lightning still loads down the generator. there may or may not be something amiss with the utility power setup and in reading up some on power there it is something less than desirable.

Lightning detector and disconnecting utiliy earth.

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