Lightning Protection

nothing is perfect

surely

I guess somebody may have wondered what happens if there is a huge potential rise in the building earthing system. Then I think we must know how a spd behaves.

indirect lightning might mean that there is an overvoltage coming from earth via a strike , so what I wonder is if this spd acts as a blocking element against these type of faults/HAZARDS.

Jinsnao-

Lighting arrestor system should never be connected to the building grounding electrodes. To do so would subject the building system to large surges and spikes in voltage. This would "kill" many electrical devices from the partial surge in voltage. building grounding systems are not completely perfect. Also if you connect a meter 1/10th of the way up a wire leading from the lightning rod to the grounding electrodes it will be subjected to 1/10th of the lightning surge voltage to the ground.

Good Luck, Old Salt

retracted after reading further...

As in all things electrical, check your local codes.

The comments from old salt in this instance are faulty. It is code in Canada and I am sure it is also code in the US that such grounding electrodes (power system grounding electrode and all other ground electrodes, no matter their purpose) be interconnected.

Why? So that a voltage impressed on one grounding system is impressed on all grounding and bonding systems in a given building. If such was not done, an impressed voltage on one of the systems could present as a voltage potential difference between the grounding/bonding systems. That is a dangerous condition.

The voltage rise on lightning grounding electrodes during a fault, while potentially quite large, they are of very short duration.

As to the suppression device you mentioned... got a make and model number?

North of 60-

Source, very old, very experienced lightning system contractor from the Mid-West some years ago. I don't dispute you but I don't dispute him.

Good Luck, Old Salt

well... my source is a code book.

North by 60-

Was just going to send you a note when I saw your reply-----

Just checked my NEC code book. I now dispute him.

Sometimes I suffer from cranial flatulence. Sorry about that. Thanks

Good Luck, Old Salt

If you connect building earth,lightning earth,telephone earth,computer earth,TV earth etc together the combined earth resistance become very low & is an advantage for earth current to flow to earth

North of 60 -

I agree with your response, simply because of the different ground loops that will be created when there is no common ground in a system. Ground loops sitting on different planes causes several, varying equipotential problems to most electrical-electronics equipment.

You are so nice to answer my question. What I wonder is, if there is such a striking on the electrodes there will be a huge potential rise, so this will be carried to all the protective grounding conductors of the building, then there will be a reverse ground-phase voltage is not it? So is it not important to wonder if this spd guys works in such a situation , (I think this case is inevitable, but I have not met any case in which there is insulation failures with a usual bonded or not lightning protection scheme). I do not give model name but say I ask about MOV surge arresters, in practical they all work same way.

Also it is said that type 2 and 3 spd 's are used for indirect lightning situations, I can not understand what does it mean with indirect, I am asking you if there is a lightning on the installation, this will come up through grounding system of the building, and this potential rise will be reverse as I described above.

I am in such a confusion,is there an illogical thought in my writings?

Jinxnao -

Metaloxide variable resistors (MOV) are excellent transient voltage surge protectors commonly used or found in highend electronic devices. One of its terminals is directly connected to the ground potential. Their function is to protect sensitive electronic components. Similarly behaving like a zener diode clamping action. It tends to serve as a direct path to ground during a transient high voltage is sensed or when a certain predetermined threshold is reached.

Also, its clamping effectiveness is only limited to an indirect hit! It cannot sustain nor dissipate the amount of energy discharges carried by a lightning hit in a very close proximity or in the immediate vicinity of where the equipment is located!

Also, its clamping effectiveness is only limited to an indirect hit! It cannot sustain nor dissipate the amount of energy discharges carried by a lightning hit in a very close proximity or in the immediate vicinity of where the equipment is located!"

All true statements, no argument, but as noted below, they CAN serve in a limited fashion to protect against directs hits, also.

I used some MOVs in a design for lightning drains in Colorado Springs, Colorado, USA. One of the speaker clusters on a pole took a direct hit, which roared down the 000 gauge cable heading for the amps, hit the MOV (which had been flooded in a manhole by rain attendant on the lightning storm) and the MOV lit up like a christmas tree (beautiful colored flashes, as it arced and the charge drained off through the water filling the manhole). The light show was spectacular, and the speakers (3@$15USD each) and cable (45 feet of 000) were a total loss. Not so the remaining "downstream" cable, about 4K feet of it, also 000 gauge, nor the 150KW audio (bridged) amps in the racks inside the building.

The MOVs were intended to be sacrificial (they cost the US Air Force about $3.35 each, in quantities of 500+, if I remember correctly) in the event the lightning charge hit, and subsequent charge, as opposed to a ground surge, or a charge-coupled surge from a nearby strike), and they were perfect for the purpose, and the price. But they were NOT useful for a follow-on strike after a direct hit.

Surges, on the other hand, which were in a manageable range, left the protector MOVs intact, and ready to do it again.

Most important, they saved the lives of the system operators inside the building in what would have been a catastrophe.

So, MOVs CAN be used to protect against a direct strike, properly installed, but they only do it once, and then require replacement.

I appreciate your helps, but I think I have trouble in explaining myself here.

I wonder if there is a striking near a building, does it mean that if we have a joint (perhaps even with a separate one) grounding system (lightning bonded to building grounding systems) a very big potential rise will occur in the building protective grounding system,

if positive does this not mean that a very high voltage will turn up between PE and phase conductors, then it will cause an insulation failure perhaps,

If SPD's are protecting against these reverse overvoltages is unknown to me,

I am waiting your answers..

Jinxnao-

If lightning strikes and scores a direct hit on the building, the energy will be and should be dissipated to the earth assuming the building is equipped with a properly designed lightning arrester system. Since it is a direct hit any electrical/electronic devices that are equipped with MOVs may still get damage. The building itself may have some structural damage due to being hit directly!

If the lightning strikes is nearby, (indirect hit), some of the electronic devices, not all may also be affected? The potential surge in this situation may not be as high as compared to a direct hit but may still create some damage to some sensitive electronic devices ..

If it does, then either some protection system will operate, or there will be a fire, depending on how up-to-local-code the building is, and how intense and local the strike is.

The solution is therefore adequate building insurance cover.

"The comments from old salt in this instance are faulty. It is code in Canada and I am sure it is also code in the US that such grounding electrodes (power system grounding electrode and all other ground electrodes, no matter their purpose) be interconnected."

This is a code requirement in the US to interconnect all grounding systems. Agreed.

If ground potential rises, as it does in a direct lightning strike, then yes, that includes all ground potential. Will electronic devices be damaged? Most likely yes. The realistic intent of a lightning protection system is to protect the structure from burning down, not to protect every 3 VDC device therein.

Also, I have designed many LPS and best practice is to use a full ground loop plus radials off of that.

SPDs are not intended to divert 1 Million volt direct strikes and are not rated to do so.

Not necessarily true in the USA.

It depends on the application.

Many communications, instrumentation, and PLC based controlled systems such as DCS require separate grounding systems that are not tied to the building or other equipment systems ground grid.

The reason they are not interconnected is to prevent the circumstance the OP is concerned with in their post as well as preventing other ground noise being reflected/imposed into the electronics that negatively affect the controls and cause component failure .

If lightining is of huge concern, it would be wise to implement a lightinging strike prevention system that creates a neutralizing cloud above the area.

Above all else; consult the manufacturer's technical service group of/for each section of equipment affected and follow their grounding recomendations exactly.

Lightning is trying to go to earth. Buildings and other such enclosures will not take a hit unless struck directly. That is what a lightning system is for. The same goes for a car in a lightning storm. If you are in a car that is hit, the bolt will use the metal container around you , pass through the tires, continuing to earth.

If you ever see a bucket truck when it touches a high voltage line, it will track down the arm of the bucket, through the tires(usually causing the tires to blow), and go to earth.

"Buildings and other such enclosures will not take a hit unless struck directly."

True. The damage is done in an indirect (near strike, or even with an unusually large "ground surge") when the voltage rise, and attendant current discharge, is coupled into the building, or into it's structure, by nearby power or signal lines. Small enough gauge lines, and they will melt down without delivering the charge. Bad, but not as bad as the arcing that occurs inside the building (I've seen what it can do in both comm centers and UPS/Generator housings). But proper MOV installation on all lines coming in will protect against that surge.

In the event of a direct hit (I've seen those, too, and have been inside two buildings that took direct hits) of which I've seen a few, damage tends to be more physical than electrical.

Holes were ripped in the roof of both buildings I was in, but, happily, neither building had a flammable roof. One was ceramic half-pipe tiles, and the racket was deafening. The other was a "Butler" type building in Japan, and the metal roof suffered what looked like burnt gashes where the metal melted away from "God's Plasma Cutter". The noise there was just the "ripping of a huge sheet of canvas" that you normally get as the Plasma Channel of the Stepped Leader in a stroke is forming. Ugly sound, and LOUD, but not near as loud as the tiles being blown apart by the other bolt. I THINK the instantaneous super-heating of the tiles is what blew them apart, but when we went up on the roof to cover the resulting hole, it looked like a series of bomblets had hit the roof and detonated. Messy as all get out. Not pretty.

Happily, not common, either.