Another dreaded grounding question. Grounding to copper bus bar

[K8MHZ]

Sorry.

It is not convincing.

The problem is lightning has tremendous power but only limited energy due to its very short duration.

Because of it, lightning can not melt any 'thick' metal such as a 2/0 conductor.

First, 2/0 isn't that thick, only about 1/2 inch. Additionally, it will be stranded. I personally haven't seen 2/0 melt, but I know it will. I have seen lightning melt glass. My friend has a pane of glass with a 2 inch hole melted through it by lightning. I have seen lighting split pine trees that were more than a meter in diameter right in half. I have seen a video where #6 on a power pole didn't just melt, it vaporized in a flash. Lightning also melts sand together in the dunes nearby. I have shown this before, the result of the molten glass is called a 'fulgurite'.

From Wiki - Click here for pics.

Fulgurites (from the Latin fulgur meaning thunderbolt) are natural hollow glass tubes formed in quartzose sand, silica, or soil by lightning strikes.[1] They are formed when lightning with a temperature of at least 1,800 ?C (3,270 ?F) instantaneously melts silica on a conductive surface and fuses grains together; the fulgurite tube is the cooled product.[2] This process occurs over a period of around one second,

I can understand your doubt about flat conductor. I remember the first time I saw it used for lightning protection and I thought someone was either very stupid about lightning or playing a joke. No way did I think that thin, flat strap would conduct lightning without fusing open.

My mind changed when I did some study. My resources of study were not just from the electrical side of things. I have been doing volunteer work on and off for the National Weather Service for 15 years. In order to do so, we have to have storm training. A good part of that training is centered around the behavior of lightning. Since I am a ham radio operator, I also get to see how towers are installed and protected on a scale larger than all but the most experienced sparky or electrical engineer.

You never did tell me what your exposure to real lightning is. It seems all you are doing is guessing that 2/0 stranded wire will carry a bolt of lightning without fusing open. You need convincing that flat strap is the way to go, like I did many years ago, and you may not get that if you live in an area that does not have to contend with thousands of lightning strikes each season.

 

[T.M.Haja Sahib]

Hmm..
The maximum time of flow of one stroke of lightning current may settle the matter once for all. If P is power, V is voltage I is current and T is time of flow of one stroke of lightning current, its Energy E is

E=V*I*T=P*T.

 

[SG-1]

Why you think flat conductor is better than round conductor despite permitted by codes for lightning protection? Any formula for skin effect for round conductors demonstrating their inferiority over flat conductors for lightning protection?

A simplified formula is here: http://www.allaboutcircuits.com/vol_2/chpt_3/6.html

 

[K8MHZ]

Hmm..
The maximum time of flow of one stroke of lightning current may settle the matter once for all. If P is power, V is voltage I is current and T is time of flow of one stroke of lightning current, its Energy E is

E=V*I*T=P*T.

You like math, so here are some figures and facts for you, courtesy of Wiki:

a leader of a bolt of lightning can travel at speeds of 220,000 km/h (140,000 mph), and can reach temperatures approaching 30,000 ?C (54,000 ?F),

Lightning can occur with both positive and negative polarity. An average bolt of negative lightning carries an electric current of 30,000 amperes (30 kA), and transfers 15 coulombs of electric charge and 500 megajoules of energy. Large bolts of lightning can carry up to 120 kA and 350 coulombs.[16] An average bolt of positive lightning carries an electric current of about 300 kA — about 10 times that of negative lightning.[17]

The potential ("voltage") gradient inside a well-developed return-stroke channel is on the order of hundreds of volts per metre (V/m) due to intense channel ionization, resulting in a true power output on the order of one megawatt per meter (MW/m) for a vigorous return stroke current of 100 kA.[18] The average peak power output of a single lightning stroke is about one trillion watts — one terawatt (1012 W), and the stroke lasts for about 30 millionths of a second — 30 microseconds.[19]

High speed videos (examined frame-by-frame) show that most lightning strikes are made up of multiple individual strokes. A typical strike is made of 3 or 4 strokes, though there may be more.[35] Each re-strike is separated by a relatively large amount of time, typically 40 to 50 milliseconds. Re-strikes can cause a noticeable "strobe light" effect. Each re-strike is separated by a relatively large amount of time, typically 40 to 50 milliseconds. Re-strikes can cause a noticeable "strobe light" effect.[34]

 

[T.M.Haja Sahib]

Well.

The power of one lightning stroke is one trillion watts lasting for 30 microseconds. So its energy=(10^12) * (30*10^-6)=(30*10^6)Ws
=8.333 Kwh

Taking the specific thermal capacity of copper wire 2/0, and its initial temperature and assuming the entire energy of 8.333 Kwh to be dissipated in length of 30 or 60 meter length, it may be checked if the final temperature of the wire exceeds its melting point temperature.

 

[iwire]

Well.

The power of one lightning stroke is one trillion watts lasting for 30 microseconds. So its energy=(10^12) * (30*10^-6)=(30*10^6)Ws
=8.333 Kwh

Everyone knows it is 1.21 gigawatts.

 

[T.M.Haja Sahib]

Back to the future?

 

[K8MHZ]

Well.

The power of one lightning stroke is one trillion watts lasting for 30 microseconds. So its energy=(10^12) * (30*10^-6)=(30*10^6)Ws
=8.333 Kwh

Taking the specific thermal capacity of copper wire 2/0, and its initial temperature and assuming the entire energy of 8.333 Kwh to be dissipated in length of 30 or 60 meter length, it may be checked if the final temperature of the wire exceeds its melting point temperature.

That is the math per stroke. A bolt may have 3 - 20 strokes. Here is another link that shows a bolt (multiple strokes) of lightning has about 125 kWh of energy:

http://www.weatherimagery.com/blog/lightning-facts/

And, where do you get the 30 - 60 meter length?

 

[K8MHZ]

View attachment 6907

Major fire damage to NFPA-780 lightning-protected mansion in southeast USA.

View attachment 6908

NLSI engineers discuss lightning damage (see burn mark on wall at center electrical panel) to electrical system at military defense factory in New Hampshire.

View attachment 6909

Typical tree damage caused by lightning strike.

 

[K8MHZ]

More to figure in while sizing lightning conductors:

1.1 Ohmic Heating: Thermal Damage. When a lightning current pulse whose instantaneous value is i flows through a conductor of resistance R, the heat generated by the whole pulse is RSi2dt joules. The quantity Si2dt is called the action integral of the pulse and is measured in A2s or joules per ohm. Practically the whole of this heat is devoted to raising the temperature, since no significant portion of the heat can flow to the surroundings during the very short duration pulse. Thus the temperature rise is proportional to the resistance of the conductor multiplied by the action integral of the pulse. Parts of the AFS which may carry the lightning current therefore need to be designed with a cross-sectional area large enough to keep the temperature rise well below a critical value such as the ignition point or melting point of the material. The design also needs to account for the fact that rapidly changing current in the lightning pulse tends concentrate at the surface of the conductor (skin effect). The maximum surface temperature reached is greater therefore than it would be if the current was distributed uniformly over the whole cross-section.

http://www.lightningsafety.com/nlsi_lhm/effect.html

And lest we forget about inductance:

Whatever the size of the conductor, a wire has inductance. However larger is the wire size, lower is its inductance. Then to reduce the skin effect, the fact that the RF energy travels near the surface of the wire instead of using the central core, we should use oversized conductors to get the best path to the ground. That means that a railroad bar should be the best connector; it is massive and offers a large surface. Unfortunately this solution is not really conceivable as such a bar is first prohibitively expensive but also extremely heavy and cumbersome. So we need to find a cheaper solution but offering similar performances if possible.

KC2TN's SPGP. Note above left the braid grounding all chassis and very below the large copper strap going to the external grounding system.

To meet all these criteria at low cost but without impacting the security, there is a solution, and very easy to handle. It is using a copper strap in #26 AWG or 0.4 mm thick and at least 38 mm wide (1.5"). Displaying a lower inductance than the big #4/0 AWG cable (?16.4 mm), it is also much cheaper and lighter (14 kg/100m vs. 110 kg/100m). With its 38 mm wide, its cross sectional area is similar to the #6 AWG wire (?6.95 mm, over 9 kg/100m) and almost as light.

http://www.astrosurf.com/luxorion/qsl-lightning-protection3.htm

 

[T.M.Haja Sahib]

The resistance of lightning conductor taking into account skin effect would only change the proportional amount of lightning energy to be dissipated in it in relation to the amount dissipated in the ground. For the sake of simplicity, it is assumed that entire lightning energy is to be dissipated in the lightning conductor itself to see even in this case whether the conductor reached the melting point temperature or not.

 

[K8MHZ]

The resistance of lightning conductor taking into account skin effect would only change the proportional amount of lightning energy to be dissipated in it in relation to the amount dissipated in the ground. For the sake of simplicity, it is assumed that entire lightning energy is to be dissipated in the lightning conductor itself to see even in this case whether the conductor reached the melting point temperature or not.

Not according to this site:

Unfortunately, recall that you cannot maintain low impedance by a long run of wire no matter how heavy the wire is. If your station equipment is more than a few feet from the service mains ground rod, the voltage-differences along the bonding conductor will be significant to the massive energy of lightning. This is minimized by choosing the largest surface-area conductor you can get, and installing intermediate ground rods along the path to the utility service entrance ground.

http://www.3955.us/grounding.htm

 

[T.M.Haja Sahib]

Sorry. I am not able to see the relevance of your quote.

 

[K8MHZ]

Sorry. I am not able to see the relevance of your quote.

They support the use of flat conductor due to skin effect. I thought that was relevant to the OP's topic, which is about an inspector not allowing him to use flat conductor for the grounding of his radio tower.

If you don't see said relevance, sorry..... but trust me, it's there.

 

[klillemo]

Energy in Lightning strike

Energy in Lightning strike

If we accept that there can be 500MJ of energy in a lightning strike, this is equivalent to 139KWH, much more than 8.3KWH.
http://www.onlineconversion.com/energy.htm

Realize it is only an approximation that the current flow is uniform during a lightning strike. I would not be surprised to find that the peak instantaneous current would be more than ten times the average.