This article was posted 02/13/2006 and is most likely outdated.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

    • 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 to Mike Holt

    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 to T.M.Haja sahib

    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 to Mike Holt

    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 to T.M.Haja sahib

    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 to Mike Holt

    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.
    Reply to T.M.Haja sahib

  • Lemme see if I've got this right: we want to keep the voltage between the hot wire and the metallic ground and neutral conductors (presumably bonded together) from rising. A surge protector is a clamping device that limits the voltage between the hot wire and the neutral/metallic ground wires. This is important because our equipment is connected across these two wires.

    The IEEE paper seems to imply that the voltage of the hot wire, (and by extension the metallic ground or neutral conductors) with respect to the soil outside the building is important. Mr Holt contends that this is not the case, and I tend to agree. The only exception would be if there was equipment that is somehow connected to the soil outside.

    But there may be some virtue to the IEEE paper's statement. First off, I think some lightning people like to think of the neutral to earth path as an extra bypass for the lightning current. The source is connected to the low side of the load through the neutral, and also through the earth, and so a good path through the soil can parallel the path through the neutral. The trouble with this is that it's an unreliable assumption because ground conductivity varies so widely with location.

    Another possible objection to a high impedance between neutral and soil is that a great rise in the voltage between neutral (and metallic ground) conductors with respect to the soil may result in an arc between the neutral and the soil, even though the voltage between hot and neutral is kept within range. As we all know, open arcs mean trouble wherever they may occur.

    Corrections are invited; I may have interpreted the IEEE statement wrong.

    Mark Kinsler
    Reply to this comment

    • Reply from: JD Miskell   
    Isn't your equipment 'required' to be attached to the 'soil outside' by the NEC? (Note: some are not in specifically engineered cases) Keep in mind that the capacitively coupled voltage induced by a lightning strike to your 'bonding' ground is likely to be millions of times higher than utility power and at frequencies that can penetrate their insulation and/or feet of air gap. Be careful about mixing metaphors - thyristor SCD's are limited to shunting short duration, utility generated voltage spikes on the incoming 'hot leads' of your service back to the utility neutral. If I am not mistaken this is the reasoning for Mike's statement. This function is more correctly 'power conditioning' and not surge suppression. There are no thyristors on the market at any price that have an throughput breakdown voltage that can withstand any lightning strike. Thus, if both the transformer lines and the house wiring are energized to the same potential, the only path available is to ground whether the connection is via capacitive coupling or insulation breakdown. The step voltages created are directly proportional to the ground to soil impedance. Thus, the IEEE's statement is correct in the imperical case, and takes into account more sophisticated surge (and lightning) suppression schemes already in existence. Neither statement directly takes into account lightning 'ground strike' which enters through your ground rod and seeks neutralization via the utility wiring. This is very destructive. A low impedance ground at the very least makes designing realistically useful (as opposed to 'consumer' commodity, wishful thinking/band-aid, or fraudulent) surge suppression less complicated. Most importantly, power conditioning should be optional, and efforts to 'codify' this misinformation should be resisted.
    Reply to JD Miskell

  • Did the IEEE forget that lightning can travel and usually does both directions. It does so from the earth end at points of low impedance. I was one of the Navy techs for lightning strike tests of digital communications and targeting systems. High impedance points heat up and fuse.

    Kid Stevens
    Reply to this comment

  • Actually, there is difference when talking about LIGHTNING protection. Lightning protection will only be as good as the grounding electrode. A surge between conductors is not affected very much by the grounding resistance but a common mode surge from lightning is.

    Mike Cole mc5w at earthlink dot net

    Michael R. Cole
    Reply to this comment

    • Reply from: George T Hummert, PE   
    I agree with Mr. Cole -- currents caused by lightning are capable of lifting a high impedance ground connection to significant potentials. Lightning currents or lightning-induced currents are most likely associated with a path through the earth, and therefore impedance of the "earth ground" is an important parameter that helps determnine the common-mode voltage at the ground point.
    Reply to George T Hummert, PE

  • Mike:

    I think you are right that the bonding together of the various systems (Electric, Phone, Communicationms, CATV) is a primary factor in reducing damage by maintaining a common potential rise on all systems. However, the resistance to ground will play a part in determining the quality of the lighning stroke drain off. The analysis would be similar to that performed for substation ground systems as detailed in the IEEE 80 standard. Its not a question of potential difference - the bonding deals with that, its a question of potential magnitude - this could ultimately failt the surge protector and/or bleed thru. This is why coordinated and cadscaded surge protection is recommended.

    Bruce Rockwell
    Reply to this comment

  • Good artical.

    Jeffrey Basiaga, Jr., PE
    Reply to this comment

    • Reply from: solidrock   
    article Jeff, article
    Reply to solidrock

  • I would try talking to Franklin Electric in Indiana. I know they have a lab and do such testing.

    Rex Cauldwell
    Reply to this comment

  • It has been my experience that induced EMF from lightning strikes even at considerable distances from a system can cause damage. It would seem that the least amount of impedance would be optimal. It may be that length and orientation (in relation to vertical or horizontal) of conductors is a factor. Lightning is a stranger to convention. Mark (one wire) Prairie

    Mark Prairie
    Reply to this comment

    • Reply from: Kid Stevens   
    Induced EMF in an open field drops within a mile in most cases but induced emf in lines of all types can reach out for several miles, I tested a phone KSU that died at 5 miles from the mapped lightning strike. It died on the telecom side from EMF that came down the power line. Adding gas discharge tubes at the entrance to the office did not prevent a reocurrence problem on the power lines due to their high impedance
    Reply to Kid Stevens

  • The paper's Article 2.3.1 refers to Section 4 to support its position that "...high grounding resistance can create enormous ground potential rises." Section 4 doesn't address the issue of high grounding resistance; it's more focused on high rate-of-rise surge currents getting into the grounding system from other sources and causing potential gradients on the grounding conductors. I agree that the grounding electrode-to-earth resistance has little effect on the voltage "seen" by the SPD. However,with a high grounding impedance, a surge will result in the voltage on the electrical conductors being higher than if the impedance was lower, even after the SPD has operated. This won't effect the protection level of the equipment in the building as long as it's isolated from "remote" earth.

    James Wilson
    Reply to this comment

    • Reply from: Bruce Rockwell   
    What is "Remote Earth"?

    What are you indicating isolated from "Remote Earth"

    Earthing, as long as it is done correctly, is a good thing. This does not necessarilly mean we are direct connected into the soil, just that there is proper connection to an electrode (via throundinmg electrode conductor). All electrodes present in a facility need to be bonded together. Remember the ground system is made up of a few unique components:

    Equipment Grounding Conductor

    Grounded Conductor

    Electrode (Sometimes referred to as "Earth")

    Grounding Electrode Conductor

    Isolated Ground - Just an equipment grounding conductor isolated from its utilization point back to the source. The source being a separately dervived system (ups/transformer/generator) or the building service if there is no transformer in between..

    Lets not forget the MBJ - Main Bonding Jumper which is the neutral to ground connection at the service and the BJ - Bonding Jumper needed at separately dervied systems to connect neutral and ground and sometimes allowed elsewhere.

    When considering grounding issues, always be clear about what part of the system you are investigating. Missing a component or having one where it should not be is never good.


    Reply to Bruce Rockwell

    Reply from: Mike Holt   
    Remote Earth is a term indicating a point in the earth that is at least 50 ft away from any metal parts that you are attempting to measure voltage-to-earth from.
    Reply to Mike Holt

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