This article was posted 02/13/2006 and is most likely outdated.

How to Protect Your House and It’s Contents from Lightning
 

 
Topic - Grounding and Bonding
Subject - How to Protect Your House and It’s Contents from Lightning

February 13, 2006 

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How to Protect Your House and

It’s Contents from Lightning

 

This guide is intended to provide useful information about the proper specification and application of surge protectors, to protect houses and their contents from lightning and other electrical surges. The guide is written for electricians, electronics technicians and engineers, electrical inspectors, building designers, and others with some technical background, and the need to understand lightning protection.

 

Click here to download: This IEEE Guide for Surge Protection of Equipment Connected to AC Power and Communication Circuits

 

Mike Holt Comment: This document is an excellent, but I have a problem with the statement

“High surge currents impinging on a power distribution system having a relatively high grounding resistance can create enormous ground potential rises, resulting in damage. Therefore, an evaluation of the service entrance grounding system at the time of the SPD installation is very important [2.3.1]”.

 

Grounding. The contact resistance of the electrical system to the earth (ground resistance) plays an insignificant role in reducing ground potential rise (GPR) of surge protection devices at a residence. It’s unfortunate that all surge protection writings make the same statement, because this gives the impression that ground resistance of the grounding electrode system serves a purpose in surge protection, that it doesn’t.

 

If you feel that the contact resistance of the electrical system to the earth does reduce ground potential rise, please send me a copy of a study that supports your position.

 

Bonding. Now I do agree that a low-impedance path from the surge protectors to the source, such as the equipment grounding conductor, or the neutral conductor at service equipment is critical in reducing ground potential rise. But this really has to do with bonding, not grounding!
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Comments

  • MIKE, Low earth resistance is important. Otherwise, ground potential rises during operation of SPD and if the earth of the neighbour is within the resistance area of the earth to which the SPD is connected, there will be rise in potential in any grounded metallic surface of the neighbour and he will be shocked touching it and standing bare-footed on the ground!

    T.M.haja sahib

    • Reply from: Mike Holt   
    I'm not saying a low earth resistance is not important to reduce voltage on metal parts as well as conductors from induced voltage from lightning.

    This issue si SPD and earth resistance and voltage rise. Please give me an example to support your comments. You are free to use any values that are reasonable.

    Note: SPD shunt transient voltage back to the power source (typically the transformer) via a low impedance path, the earth only can become part of this path at service equpment and since the earth resistance as compared to the service neutral so so large, it doesn't help that much at all, so the earth is not the importnat issue, it's the service neutral.

    But I've been wrong many time before and I'm willing to learn more. Maybe your example will help me understand the issue you are trying to describe.

    Reply from: T.M.Haja sahib   
    Mike, Kindly note that high voltage transient currents caused within a properly designed system such as by switching will be confined within the system and will not fiow through ground.So low soil resistance is not important in this case. But lightning current[via SPD also]tends to go into ground in which case ground potential rises at the point of entry depending on the earth resistance.Also ground potential is greater farthar the distance from the earth this again depending on the soil resistance.But I can proceed further if you agree with me sofar!

    Reply from: Mike Holt   
    Surprotection for lightning transients (to earth) would be by a lightning arrestor, not a Surge Protection Device SPD. The 2008 NEC is changing Article title from TVSS to SPD, but Article 280 remains as Lightning Arrestor.

    So if you are referring to lightning arrestor, then I agree with your comments.

    Reply from: T.M.Haja sahib   
    Mike,not all lightning current would be by-passed by LR and some will be passed on to SPD to deal with and I referred to that above.In the meantime, kindly clarify regarding NEC rules for safeguarding against touch and step voltages in the circumtance mentioned above. Thanks.

    Reply from: Mike Holt   
    When any lightning current flows through a SPD, the current travels from the circuit conductors to the 'equipment grounding conductor', then the current travels to service equipment the service neutral, then it goes to the utility transformer. Oh yea, some of the current then flows into the earth as well.

    What are the NEC safeguards against touch and step potential? Well grounding is not one of them. How do I know that? The NEC does not have any maximum resistance value, and grounding would never lower the voltage from any energized part to a safe level.

    What can one do to ensure a safe installation? Well the question is safe from what? Lightning - Nothing, Ground Fault - Clear the fault with proper bonding.

    So that we don't continue in a loop, please give me a call, 352.429.5577.

    Based on your comments, I pickup that you are an engineer that thinks that grounding will reduce touch voltage to a safe value. I'm guessing you are an engineer that uses IEEE 80 and you design substations. There are computer models that will demonstrate the Ground Potential Rise (GPR) based on fault current and ground resistance. If you happen to have access to such a program, take a minute and simply work a few examples out. I'm sure you know the IEEE 80 formulas on how to calculate the maximum touch/step potential.

    Understand the original discussion was related to Grounding and SPD, not Lightning Arrestors, not Substations, and not how to make an installation safe from touch/step potential (which the earth doesn't help to reduce to a safe level).

    Again call me so that we can separate the issues, and I'm 100% sure we can come to an agreement.

    Reply from: T.M.Haja sahib   
    Mike,Thank you very much for spending your precious time in giving replies.I learnt a thing or two and continue learning from your website.

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