Wich is the best way to protect equipment from earth spikes and surges?

[mcinque]

I'd like to protect my home devices (like tv, sat etc) from any spikes or surges that could came up from the earth wire. I mean: a lightning drops on the ground few hundreds of meters far from my house and a little part of its energy raise from the earth wire up in my devices.

I know that:
- some (but not all) devices are engineered keeping in mind that low energy spikes can raise up thru the grounding
- surge arrestors sockets or DIN dischargers modules works only for spikes and surges that come from live or neutral, using varistors or gas dischargers to drive the energy thru earth, not for the opposite

So, if you had to protect your devices, what solution would you use? (pulling out the power cord from the wall socket is not the reply I'd like to read  )

[Marco]

Why would a MOV/TVS/GDT care whether the surge is on the ground or on phase/neutral? It's meant to divert surges to ground, but the devices don't really care about what they are meant to do. AFAICS they'll happily clamp Vphase-ground and Vneutral-ground regardless.

[HackedFridgeMagnet]

A good earth is critical to a Lightning protection system as you want most of the energy shunted to ground and absorbed before it gets into the internal wiring.

In Australia we use a modified TN?C?S electrical system called MEN. This means we have the neutral shorted to the local earth within the building.
Other systems have different requirements.
This type of protection works on the assumption that the Earth and the Neutral are tied together very close to the filter. So Earth Neutral protection is not necessary. If this is not the case then you can add a gas arrestor between Earth and Neutral.


With MEN:
For a standard say 100A installation, pretty reasonable protection can be had by putting Class I MOV protection say 50kA 10-350uS between active and neutral . Then a low pass filter on the active L+ C with a 3db around 1000hz. then another MOV after the filter maybe 50KA 8-20uS or so. The secondary MOVs will dampen any ringing that could occur after a surge.
Make sure there is plenty of iron in the inductor to avoid saturation as much as possible.
You probably want a circuit breaker too depending on where the surge protector is situated as the MOVs will blow short.

Heres a link to a company that makes this sort of stuff.
http://lpi.com.au/ProductsServices/PowerLineProtection.aspx

[johansen]

the second set of MOV's should be connected to a different grounding rod.

if you really want something lightning proof you need lots of ground rods. the number depends on the conductivity of the soil and how long you want  them to last. you can buy copper plated grounding rods or you can use rebar, and a lot of it.

best to bury the lines connecting the ground rods as well. # 8 copper is good enough.

earth and neutral should be bonded together at lots of locations, however the code requires that a single point ground be used in residential areas. the reasons are numerous but they cause lots of problematic issues when dealing with making a structure lightning proof.

for example, the equipment can be connected through a big common mode choke, but then you have equipment in the home connected to ground through the cable line, internet, etc. phone.. so the only thing you can do is try to network all the grounds together and have lots of MOV's everywhere shorting out all the signal lines.

you probably want to put the lightning arrestors at least 50 feet apart, each connected to several ground rods radially connected together.

[jahonen]

Basically preventing the ground potential from raising is pretty much impossible since ground conductivity is nowhere good enough to prevent significant potential differences from happening. Typical lightning current is around 30-100 kA, and keeping a potential difference below safe level, say 1000 volts or so (even that might be too great), would require that ground impedance should be below 10-30 milliohms.  Soil resistance is quite low (maybe tens to hundreds of ohms depending on the soil) but nowhere that low. Add relatively fast rise time of the lightning current and inductive effects come into play and it is even more difficult.

But what you can do, is to add just those din rail surge protectors to tie all the electrical lines together (also antenna and telephone/DSL lines), so all grounds rise potentials together, and no large voltages exist between them. That is all it takes to protect the connected equipment. Idea is a bit similar than power companies use to work on live high voltage lines, using an insulated lift so that workers are at the same potential than the high voltage line and no current flows.

Regards,
Janne

[G7PSK]

The probability is that if the lightning strike is that close to your domestic earthing point it's not your TV you will be worrying about more likely the house itself. Most domestic earthing rods are close to the point of entry into the house of the incoming mains, the house being much higher than the surrounding ground will be struck first, therefore the best solution is with your insurance company.

[mcinque]

Why would a MOV/TVS/GDT care whether the surge is on the ground or on phase/neutral? It's meant to divert surges to ground, but the devices don't really care about what they are meant to do. AFAICS they'll happily clamp Vphase-ground and Vneutral-ground regardless.

I understand.

In Australia we use a modified TN?C?S electrical system called MEN. This means we have the neutral shorted to the local earth within the building.

This is a smart solution. It's a shame that europe doesn't use a similar system.

If this is not the case then you can add a gas arrestor between Earth and Neutral.

I like it. I guess I should use this. Do you confirm that?

if you really want something lightning proof you need lots of ground rods. the number depends on the conductivity of the soil and how long you want  them to last. you can buy copper plated grounding rods or you can use rebar, and a lot of it.

Yes, this is probably the best thing. But unfortunately I can't do that kind of job. I was thinking to use some kind of domestic device to save my devices from low energy spikes.

But what you can do, is to add just those din rail surge protectors to tie all the electrical lines together (also antenna and telephone/DSL lines), so all grounds rise potentials together, and no large voltages exist between them.

It's a good idea.

The probability is that if the lightning strike is that close to your domestic earthing point it's not your TV you will be worrying about more likely the house itself.

I agree 

[mtdoc]

Consider installing one of THESE at your electrical service entrance.

Originally designed to protect from spikes coming in from solar PV array inputs, they also work well to arrest spikes coming in through the electrical grid feed.

Of course if there's a direct hit or very close strike, all bets are off...

[HackedFridgeMagnet]

I like it. I guess I should use this. Do you confirm that?

No.

I cant really even confirm it is a gas arrestor. It may be, but the pdf link says it is a spark gap.
3000volts breakdown might be a bit high, MOVs will break down at a lower voltage, can't remember the breakdown voltage of a gas arrestor.

My understanding is the gas arrestors are better for situations where the conductors are nominally the same voltage. Such as Neutral and Earth. It cant self extinguish if mistakenly put on the active, it needs the two conductors to settle to the same voltage again to extinguish.

The spark gap which is sort of a gas arrestor using just air instead of an inert gas across the spark gap. It will extinguish once the voltage falls back to normal AC levels.

So yes a gas arrestor for N/E.
I am not sure how to rate it though. Key parameters are breakdown voltage, let through voltage, breakdown time, surge current, possibly energy rating.

Also a lot of electronic equipment needs protection against dv/dt whereas the straight electrical stuff doesn't.
A surge pulse can produce a dv/dt that turns  on fets resulting in failure of electronic equipment. This is where series protection via a Low Pass Filter comes in to it's own.
It is much more expensive and so you only put it where it is needed.

As jahonen says getting the earthing right is so so important. The energy needs to go somewhere and go somewhere fast so as short as possible to a good ground is the only solution.

[madires]

earth and neutral should be bonded together at lots of locations, however the code requires that a single point ground be used in residential areas. the reasons are numerous but they cause lots of problematic issues when dealing with making a structure lightning proof.

RCDs are a good reason to have a single connection between N and PE ;-) Another thing to consider is that a real LPS is not an overvoltage protection. If the building is hit by a lightning you want to have the LPS take the pain and not also some PE or neutral wires in the building which aren't capable of passing 100kA.

for example, the equipment can be connected through a big common mode choke, but then you have equipment in the home connected to ground through the cable line, internet, etc. phone.. so the only thing you can do is try to network all the grounds together and have lots of MOV's everywhere shorting out all the signal lines.

At every cable entry add an overvoltage protection based on the type of signal/cable to ground. Don't use PE of the nearest wall socket! Install a proper PE wire connected to the nearest PE bar which is connected to a grounding system (ring armature for example). Install a dedicated PE/earth wire for antennas and sat dishes (at the mounting pipe, use >= 16mm² solid copper). For antenna cables there are special grounding bars with matching connectors and overvoltage protection adapters. If you got a multiswitch or similar stuff for your antenna/sat dish put one bar between antenna/LNB and multiswitch and a second one between multiswitch and receivers/TVs. Connect the grounding bars to the grounding wire of the antenna, assuming their are close together.

[Kremmen]

jahonen is correct and not only because he is a fellow countryman 

Against a surge from direct lightning strike the best protection is fervent prayer. The next best solution is a well laid out grounding system that bounces the whole installation more or less along the same potential, while minimizing differences in live and neutral wiring to prevent flashovers and dead gadgets. Achieving this is no mean trick and i guess the majority of installations will fare badly if ever put to the test. The key item is solid grounding of all projections such as antennas etc on the roof. All roof furniture must be hard interconnected and grounded using large gauge copper, preferably employing the Ufer layout. This will have a descending conductor at each corner of the house, bonded to the foundation rebar and additionally to a heavy gauge copper electrode completely circling the building at sufficient depth to guarantee reasonable conduction to the ambient. A single rod kicked half-ass into ground somewhere is a joke best forgotten in this context.

Against conducted surges from grid entry to premises, the standard solution is a coordinated protection scheme. Also this scheme builds on solid grounding being available at each barrier point.
The first stage is the heavy protection provided by arc electrodes and/or gas discharge tubes from incoming conductors to actual ground (depending on the system used, this can be a PE wire as well). These arrestors are always outside the building, either at the transformer pole or the entry panel.
The medium protector is usually a relatively heavy set of MOVs in the main distribution panel inside the house. For proper coordination a minimum inductance is required between the heavy and medium stages; this is usually sufficiently provided by the cable connecting the 2, unless it is very short. The medium protectors also need a solid ground directly from actual earth or the main entry or both. Many mfgs provide ready made units to fit the system in use at a particular location.
After that is is up to the fine protectors, of which more and less professional implementations are available. Mine are installed into the distribution panels protecting individual wiring groups, but you also get them integrated into extension cords or as wall plugins or whatever. During a lightning strike it is anybody's guess how the voltages will behave at each point of the wiring, but as a whole these devices hardly make it worse.

The Ufer grounding system AFAIK was developed to protect high risk premises the common lightning bait such as transmission towers etc. When done right it can actually prevent destruction of equipment, but whether it will prevent a fire hazard in a typical house is another thing. Anyway, mine is so constructed and i have had zero damage from overvoltages (well, one PIR did blow a fuse some years ago in a severe thunderstorm, but then they are known to be prone). And we do get a lot of surges from the air transmission lines in this rural area.

[mcinque]

Against a surge from direct lightning strike the best protection is fervent prayer.

true.

I appreciate your suggestions.

I live in a city area, I have a garden and some treees around me, and I have my own ground earth pole.

Since I don't live in a rural area and since I'm not connected by aerial powerline but I have some trees very close to my house (close to my earth ground pole) I guess it's mostly probable that those low energy spikes and surges would come come up from the ground earth, generated by a lightning strike that hit a tree, near the ground pole.

I fear that in that case, the most of the energy will discharge to the ground, but some surges and spikes could rise the ground earth wire up to my house.

What do you think about this?

[G7PSK]

Against a surge from direct lightning strike the best protection is fervent prayer.

true.

I appreciate your suggestions.

I live in a city area, I have a garden and some treees around me, and I have my own ground earth pole.

Since I don't live in a rural area and since I'm not connected by aerial powerline but I have some trees very close to my house (close to my earth ground pole) I guess it's mostly probable that those low energy spikes and surges would come come up from the ground earth, generated by a lightning strike that hit a tree, near the ground pole.

I fear that in that case, the most of the energy will discharge to the ground, but some surges and spikes could rise the ground earth wire up to my house.

What do you think about this?

Three options. one] Buy a chain saw. 2] move you ground rod as far from the trees as possible.  :-+3] do nothing, stop worrying and claim on your insurance if the worst happens.

[mcinque]

Buy a chain saw.

2] move you ground rod as far from the trees as possible. 

By now is not possible. During the construction of the house the electrician decided the worst place where to place the rod and now I can't do anything (apart from killing him).

3] do nothing, stop worrying and claim on your insurance if the worst happens.

[saturation]

A whole dissertation about surge protection:

https://www.eevblog.com/forum/suggestions/surge-protectors-scams-and-saints/msg7581/#msg7581

Updated NIST page:

http://www.nist.gov/pml/div684/spd.cfm

The whole story of all the above in a nutshell:

A electrical code quality ground;
surge protection at the mains panel;
plug in or installed surge protection to each electrical socket leading to the device;
surge protection to every data line connecting the end device to outside ambient: i.e., TV cables, external TV antenna, satellite dishes, telephone lines, etc..

The actual surge devices used are far less an issue today, i.e., MOV vs gas discharge etc., so long as its not a passive line filter alone but a redirection device that shunts energy to ground.

The above covers lightning strikes including induced EMI by nearby lightning or man made surges [e.g. collapsing magnetic fields in inductors] , that is then transmitted atmospherically, or via cables, or generated in your own home.

[mtdoc]

Keep in mind not all SPDs are created equal. stay away from the sand filled Delta arrestors....   This video is worth a look.

Skip to 2:18 to get to the testing:

[HackedFridgeMagnet]

Here is an Isokeraunic map. Show the density of lightning strikes.

Midnite Solar is not the only company using MOVs. They are also not the only company employing FUD either.

Spark Gaps work differently to MOVs so it is hardly a fair comparison. Normally I would think that Spark Gaps can handle bigger surges, so I am not sure how they made the Sand filled one fail so easily.
IIRC Spark Gaps are a bit slower and also have a higher let through voltage.

[mcinque]

I doubt anything realistically will save your stuff if a bolt of lighting strikes close enough.

Me too. The only safe thing is a Faraday Grid that I've seen in some military ammo depot. But I think that my wife wouldn't like it. 

I need only some basic protection from low energy spikes and sourges, I've a couple of APC basic sourge arrestors sockets and as I said in the first topic, I'd like to have something in case the lightning strikes the GROUND, HUNDREDS of meters away from my house, and a LITTLE part of it's energy raise the ground earth wire.

I know that if it strikes few meters far the house, I'm fried 

[mcinque]

Maybe a well isolated UPS would work. Can't remember off hand which type you need.

I was looking for a pure sinewave model, but probably any online model should be a good victim of spikes or surges...

[dfmischler]

My worst lightning experience was at an installation with a 200' (~61 meters) microwave tower on top of a hill.  It seemed like you could see for 50 miles in all directions from the base of the tower.  Even with Ufer grounding of the building and tower, we experienced a direct lightning strike that left burnt crunchy bits of microwave radio gear all over the radio room, turned the Racal modem into a cinder, and blew holes in the chips of the smart interface (DMV11) in the DEC minicomputer.  Fortunately, I was not responsible for cleaning up the mess nor for preventing repeat occurrences.  I wonder how many repeats they've had in the last 25 years...

[G7PSK]

My worst lightning experience was when the house I was in got hit, the radio never worked again. It was smashed to bits when the gas stove was blown across the room and shoved the radio through the brick wall. To top it all the next door neighbour came around to complain that our chimney stack was now in his bedroom.

[mcinque]

To top it all the next door neighbour came around to complain that our chimney stack was now in his bedroom.

It seemed like you could see for 50 miles in all directions from the base of the tower.

Someone would say "they asked for it!"