sizing the bare copper counterpoise conductor

H

HANY

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Location
Egypt
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technical support
Considering a linear grounding counterpoise installed along a steel sunshade structure (300mt) , used for lightning air terminals and equipotential bonding, and noting that two local LV panels are supplied from a remotely grounded MDB,


what is the appropriate basis for sizing the bare copper counterpoise conductor:


  • when it is treated only as a lightning protection system, and
  • when the LV panels are bonded locally to this counterpoise?

Specifically, should the conductor size remain governed by lightning protection requirements, or should it be increased to account for possible power-system ground-fault current contribution?
 
I like to make these as large as possible. Spend as much of the client's money and waste as much copper as you can.

Seriously though, this will serve no purpose for the electrical system so don't even bother. If this is a component of a lightning protection system, what did the person who designed the lightning protection system say? If this wasn't designed by someone who is familiar with lightning protection systems, I wouldn't even bother.
 
Electrofelons comment is right on the mark. Counterpoise had no role in ground fault current for typical NEC but I don’t know what a 300 mt is
Lightning protection is not a a subject that most, maybe all, can answer. Best to get a professional and pay for a set of engineered drawings
 
the 300mt is the length of the sunshades (12 sunshade x 25 mt each) ,,, and this will be the length of the linear grounding counterpoise which will be connected to the air terminals down conductors along this 300mt
 
HANY said:
the 300mt is the length of the sunshades (12 sunshade x 25 mt each) ,,, and this will be the length of the linear grounding counterpoise which will be connected to the air terminals down conductors along this 300mt
Click to expand...
Regional terminology gets in the way again.

In the US we abbreviate the measurement meters as simply the letter m, so we would say 25m.
the NEC uses the term 'ground ring' instead of 'counterpoise' when discussing a buried conductor surrounding a structure. The last time I used counterpoise was when describing an arrangement of ground rods into a triangle.
 
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In my opinion Egypt is connected with IEC standards. Then IEC 62305-3 for Lightning Protection and BS 7430/BS7671[or IEC 60364-5-54] for electric system grounding- for instance.
 
IMHO the size of the ground ring doesn't change because of the (tiny) contribution to soil current from the power system ground fault. This ground fault current into the soil is tiny compared to lightning induced currents.

Where it _might_ pay to increase the size of anything, it might be the power system EGCs cables ('ground wires') that connect from the main service to the sunshade structure. My reasoning is that these EGCs act as jumpers that connect two _different_ ground electrodes separated by some distance, and these EGC may be called upon to conduct current between the two grounding electrodes if there is a nearby lighting strike.

I don't have the necessary experience to analyze this.
 
You are right, Winnie.
So, according to NEC art.250, Main Bonding Jumper [or EGC] it is an effective ground-fault current path.
But the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 V. The earth shall not be considered an effective ground-fault current path.
 
My point is that the EGCs are sized per NEC article 250 with considerations for the _power system_ but have probably not been sized with considerations for lightning protection integration.

However in the system being considered these EGCs will _also_ be jumpers between two different grounding electrodes, and this aspect might be important.
 
FWIW regarding NFPA 780; it still exists because people are familiar with its style, but its really a boiled down version of IEC 62305, with limited scope, both are easy to understand if you have a EE background.
I don't think NFPA 780 is even intended for protection of equipment, if your doing utility work I think your into IEC 62305-3. Last I checked the scope of NFPA 780 excludes the protection of the equipment specific to generation, transmission and distribution systems.
IEC 62305 IMO is a more complete standard and thats where the latest research and development is, it covers everything lightning related for transmission and distribution systems and I think thats what is more commonly used, over time you can see the NFPA 780 standard has moved more and more to the exact the IEC 62305 alignment as its all the same experts, all the same lighting. References to IEC 62305 can be found throughout NFPA 780 and increase each edition.
They have been doing work to harmonize the lighting standards for along time now since I think 1980's, as lighting does not check what standard your covered by before it strikes.
 
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