A Question on EMP Protection From Sideliner 1950

I just read “BlogRot’s” excellent 2013 article on “How to Build A Faraday Cage in a Few Easy Steps” that you hosted on your website. It generated a lot of comments and raised a lot of good discussion regarding EMP. There’s so much to know. I ran across this article while researching a question that came up in another article recently published on The Prepper Journal: Standby Generators for Use During Power Outages.

The question I have for anyone with the answer is this: How would a generator Automatic Transfer Switch (ATS) fare in an EMP event?

I am torn as I ponder and weigh the variables I come up with. For example, on the one hand, the electronics are contained in an all-metal “box” (is that not a “Faraday Cage” in itself?) But on the other hand, the contents of that metal box are literally hard-wired to the grid, or could be for that instant before the Main Breaker is commanded open isolating the house electrical system from the grid, following an instability or interruption of “street power”.

Other considerations include the fact that that the wiring (to the Main Distribution Panel) within the box is grounded, as are the circuits in the house electrical system. Also, the controller’s normal source of power — while in its “standby state” — is indeed street power, although a small backup battery supports operation of the electronics during the brief moment after the system is isolated from street power (to prevent backfeeding) while the generator is coming up to speed, but before picking up generator power. These are questions far above my pay grade and expertise, and I would appreciate any help or other guidance you could provide.

A corollary question is this: How would the generator connected to that Automatic Transfer Switch fare in an EMP event?

My gut tells me that the answer to both questions is that it could go either way — bad or good — perhaps depending on the duration of the EMP event (is it a discreet event lasting a mere fraction of a second, or is it a repetitive pulse occurring over a protracted period of time?)

Seems to me that if the EMP event were a single, brief (if massive) burst of energy that disrupted the Electrical Grid, the ATS “brain”, upon sensing instability in voltage and/or frequencies of “Street Power”, would instantaneously attempt to command the Main Breaker to open, disconnecting and isolating the house electrical system from “Street Power”. If the EMP event ended soon enough, that is, before the ATS commanded the now-operating generator’s breaker to close and re-power the house, things might just be “ok”…with the EMP event over, conditions would(?) resemble those following a simple “street power” failure.

But if the EMP event lasted long enough for the Generator Breaker to close, connecting generator power to the house and its components while the EMP event was still taking place, then maybe — probably — not so ok. Since I’m no Electrical Engineer, I know I could be way off with my reasoning, and could probably be overlooking other important factors.

Again, any guidance you could provide would be welcome and sincerely appreciated.

Thank you very much for all you do.

Sideliner 1950


  1. PrepperDoc says:

    Oh my. I’ve sent an article on E3 protection to MD, but he seems absolutely overloaded with articles right now (and he has CERTAINLY published a bunch of mine!) , and it hasn’t published yet. I’ve previously written an article on how to protect electronic-type-things (radios) from E1 (they are different) which was published at SurvivalBlog.com Suggest you goggle it and read that as background info.

    I was unable to find the actual inner schematic for any commercially produced auto-transfer switches in five minutes of googling. I did find a homebrew schematic, which was based on monitoring a 12-volt DC signal derived from a power supply plugged into the AC mains, and then had the appropriate transistors, relays, latches, timers, etc to make the appropriate connections in the right order.

    In general, since these sorts of circuits are both connected in some fashion to the power grid, and also tend to involve LONG WIRES, they are at risk for destruction BOTH from E1 and E3. Luckily the power switching is usually done by relays.

    To protect them, I would place an appropriate MOV (metal oxide varistor) on the external side of their power-wiring & sense wiring across all pairs of wires (hot-neutral,hot-ground,neutral-ground) at every place where there are wires exiting the transfer device. Use good wiring and short (1″ or less) wires on the MOVs so that they are not rendered ineffective for the higher frequency components. Just INSIDE of those protective MOV installations, I would place low-pass filters — there are many for sale commercially, with different ratings. On my solar panel system I put two 20A units in parallel to give me 40A worth of current carrying capacity. Obviously, the “sense” wires can be handled by a low-power low-pass filter, but the power wires need heftier ones. Now, putting low pass filters on wires entering the cabinet that merely go right to relay contacts is probably overkill, whereas the SENSE wires (& wires that power the auto switch itself) DEFINITELY need this protection. If you can carefully shield the generator-output-power-wires and the AC-mains-power-wires and the wires-t0-your-loads (think, copper braid or aluminum foil wrapped around the wires and grounded right to the enclosure) , so that they don’t RADIATE lots of radio frequency right inside your shielded enclosure, it would probably be reasonable to only protect those high-power wires with MOV’s and not low pass filters if you want to save $. The MOVs are CHEAP from DigiKey. The ones I pick resemble ceramic capacitors in outward appearance and are simple to wire.

    Now as for the generator: Its internal voltage regulator may be fried by the E1 component, and its power wiring MIGHT be. I just don’t know. Not sure anyone does about the latter. Here is what I would do: 1) buy a spare voltage regulator for the genny (see generatorguru.com or your dealer). 2) If you HAVE to leave this generator CONNECTED, put MOV’s on its output wiring, probably inside its metal enclosure if possible or via a plug right at the outlets. Put an appropriately rated low-pass power filter inside the MOV’s between the MOVs and the generator windings. Consider building a plug that has three fuses — across every pair of wires– that will keep the output shorted for the brief EMP E1 event, but blow quickly and safely if the generator cranks up automatically. 1 amp fuses would do well for most generators and harmlessly blow when the genny starts up. If there is an E3 pulse, your generator will have already kicked ON as the auto transfer switch detected the abnormal power grid voltages, and your house wiring MAY pick up some spurious voltages for many seconds due to the E3 geomagnetic shifting event. I am not sure how great those voltages may be, and because your house wiring generally has black and white wires fairly close (limited the enclosed surface area), the induced voltages (which are proportional to the enclosed area, based on Maxwell’s equations) are not that great. (Power lines are damaged by virtue of the huge geometric area between the wires up high, and the conductive ground at the base of their towers, setting up potentially damaging neutral-ground currents.) The low pass filter & MOV on the output of your genny MAY suffice to protect it even if the induced voltages in your house wiring are significant. If not, you’ll be using that back-up generator voltage regulator I had you buy.

    Hope this helps.

    • PrepperDoc says:

      Some MOVs tell you what AC voltage they are meant for; “140VAC” might be ok for a 120 leg, given typical excursions. Remember, 120VAC is “RMS”– peak voltage is 1.414 times this, or up to (allowable) 1.414 x 140 = 198 volts! (DC rating for MOV…). Some trade offs here… clamp too tight & your MOV dies an early death with normal line perturbations & ceases to protect against REAL hazards. They do wear out!

    • Hildegard says:

      Play it safe and use extension cords.

      • Sideliner 1950 says:


        You write, “Play it safe and use extension cords.”

        I take your suggestion to mean that I should leave the generator isolated from any wires in or out, including the ATS, and allow it to “stand free” until needed, at which time I should fire it up and connect it to individual loads…is that correct?

        Thank you for your input.

        • Buy extra regulator boards/circuit boards and sink them in water if you want to be absolutely sure you can get her running again should the diodes/transistors/ICs be damaged. 5 feet of water will stop EMP.

    • Sideliner 1950 says:


      Thank you very much for your informative contribution. I especially appreciate your suggestion to have a spare voltage regulator for the generator to give us a chance of restoring function to the generator should it be inoperable after an EMP. I will look into that.

      As far as the ATS goes, having contacted and spoken at length with a tech rep at a major manufacturer of generator equipment, including a number of ATS models, I now have virtually no expectation that an unmodified ATS could survive one of the several extreme “space weather events”, whether EMP or CME or other.


  2. Wow, PrepperDoc did a much more comprehensive answer than mine.

    I read an article where the guy simply covered the electronic lock on his safe with metal foil for EMP protection. My only other recommendation would be based upon the cost of the unit; can you afford having a replacement sitting around in a cage?

  3. Does anybody have any information if an EMP would set off blasting caps?

    • Do they have long wires attached? If they do, there is a chance (probably small) that what they would be set off: the entire e1 event is over in a few nanoseconds. Unlikely that ignition temperatures would be reached unless there is discontinuity and a spark.

      If they have no wires, and kind of look like primers for a 50 BMG, it is extremely unlikely that they would go off.

      • thank you don’t have any now but used them a lot when I was in the army and people don’t understand how powerful just the blasting cap can be.

        • PrepperDoc says:

          I googled images of blasting caps. They all seem to have short wires. Do not connect them to very long wires! Keep the 2 wires close together, and probably short them out to each other at their tips. If that is normal practice then do it for sure. If normal practice is not the short them out, then just keep them close together. Avoid letting a space develop between the two wires.

  4. Bob Myers says:

    Most houses are not much better shielded than the open wire transmission lines that bring our power, eventfully, to the house.

    Protecting the alternative source of power is the thing to do, i.e. not have an uncontrolled connection between the load (house) and the alternative power source (fuel powered generator, wind powered generator or photovoltaic system).

    That device is called an interlock. It is a manually controlled device that only allows one power source to be connected to the load. If the interlock is in the mains position, the mains circuit breaker is physically allowed to be closed/connected to the load/house, while the alternative power source is physically prevented from being connected to the load/house. In order to put the interlock in the position to allow the alternative power circuit breaker to be moved to the on position, the mains breaker must be in the off physical position.

    There is no electrical way an electrical connection can be made to both power sources.

    Protecting the automatic emergency light(s) from the mains sensing device become necessary. Solid state relays can short long enough to connect the mains directly to the emergency light. The way to protect the emergency light is a normally (de-energized) closed electro-mechanical relay. The mains energy keeps the emergency light off by energizing the relay coil to pull the contacts into the open position. Whether the relay coil looses power because of mains failure or because the coil is destroyed, the emergency light will still light.

  5. Montana Rancher says:

    My generator/solar system is off grid and I believe that insulates me from most of the harmful effects of EMP.
    That being said I also have several lightning surge arrestors installed that provide additional protection.


    Mine are the 300v models and are installed as follow
    1x on the PV combine fuse box (DC leads to the charge controller)
    1x on the DC input from the charge controller to batteries/inverter
    1x on the AC input from the generator
    1x on the AC output to the house (loads)

    The video shows the item being tested with a 22,000 volt / 40,000 amp surge and not only protecting the equipment but also continuing to operate, though the power that gets through would probably blow every breaker in the system, which IMO is a good thing.
    EMP can be hardened against, I am guessing it would look a lot like my setup. There is no reason the same protections could not be done for a grid tied system.

    • PrepperDoc says:

      Montana rancher, thanks very much for that information, I learned a lot! The devices inside the midnight solar SurgeArrestor are almost certainly metal oxide varistors (MOV). They look quite beefy! I had not known that inverters could tolerate up to 2 kilovolts or more, and their testing certainly showed good clamping. I was very impressed, and although my solar system is from a different manufacturer, I think I’ll buy their arrestors and install them much as you have done. My installer company was not quite as concerned but I think I will add them.

      I’m not quite as certain that the charge controllers and the photovoltaic panels will be perfectly protected by the system, they may be slightly more vulnerable than the inverters… I have more to learn on this subject!

      The high pulse created in the video would likely have many high-frequency components, making it not that dissimilar to the E1 EMP event. Perhaps not totally identical but in the right ballpark.

      If you’re not grid connected, and have wiring lengths in the range of less than 100 feet, the E3 wave may not bother you that much. I don’t have hard numbers on that yet however.

      I think somebody wrote a book on this somewhere, I need to order it and read it. But certainly you are ahead of most people by a longshot

  6. Response to Sideliner 1950 on A Question on EMP Protection Nov 2015-thesurvivalistblogNET

    Sideliner 1950,

    To answer your question on EMP Protection, particularly an Automatic Transfer Switch for a generator or off-grid electrical system, one must understand what a Farady Cage is, what an EMP or CME is.

    An Electromagnetic Pulse or EMP (human created) and a Coronal Mass Ejection or CME (naturally created) are both electromagnetic “storms” that are the strongest “waves” of the electromagnetic energy spectrum.

    A CME comes from the sun while the EMP is caused by human weaponry and comes in one of 2 forms:

    • A high altitude detonation, which will have a greater radius of electromagnetic damage and smaller radiation radius, along with less structural damage.
    • A ground level detonation, which will have greater structural damage and radiation radius, with a smaller electromagnetic damage radius.
    • A “specific target” blast (like a shotgun) which will have limited radiation radius, very little if any structural damage and a very specific range of electromagnetic damage.

    The Electromagnetic Spectrum is the entire range of all the various kinds or wavelengths of electromagnetic radiation or light, including (from long to short wavelengths): radio, infrared, visible light, ultraviolet, X-rays and gamma rays.

    We commonly think of these wave lengths as being radio waves. However they are much more than that. Its light (both visible and invisible to the human eye) and radiation too. Keep in mind that the range of visible to the human eye light is a very small portion of the entire electromagnetic spectrum.

    A Farady cage is an enclosure made of conductive material that blocks both static and non-static electrical fields and is grounded. The key here is enclosure, meaning all 6 sides of the ‘box’ or ‘cage’. The first such ‘cage’ was made of a fine ferromagnetic metal mesh or screen. However to protect devices from a weapons EMP strike, a solar CME event, or a lightning strike, one needs a good solid metal enclosure that is grounded.

    Everyday Applications of the Farady Shield Principle

    • Safety against lightening: The cage protects the interior of the vehicle from the strong electric fields. Metal Cars and aircraft act as a type of Farady shields to protect people when the vehicle is struck by lightning, however it will NOT protect against the much higher electromagnetic frequencies of a CME or EMP.
    • Protection for electronic goods: Electronic equipment can be shielded and protected from stray electromagnetic fields (much smaller surges) by using coaxial cables that contain a conducting shell that acts as a Farady shield. This will NOT protect against a lightning strike, EMP or CME.
    • Protective suits for linemen: linemen often wear protective suits that act as Farady shields while working with high voltage power lines. These suits protect them from getting electrocuted. This will NOT protect someone from radiation or the much higher electromagnetic frequencies of an EMP or CME.
    • MRI (Magnetic resonance imaging) scan rooms are good examples of a Farady Shield principle. External radio frequency signals are prevented from interfering with the data coming from the patient. Most of these machines are also in a room that prevents the various radio signals from entering or leaving the room. The same can be said for X-ray rooms. No one has actually tested these rooms against the much higher electromagnetic frequencies associated with a CME or EMP.
    • Microwave: the microwaves inside the oven are trapped and used for cooking. The metal shell of the microwave acts as a Farady cage. The fine metal screen in the microwave’s window completes the 360 degree surround.

    Note: I question the lightning strike part as in the late 70’s I saw an IBM System 68 mainframe that was struck by lightning thru a glass window and the metal outer shell of the mainframe CPU. It was a fried mess inside after the strike.

    As you can see the Farady Shield Principle has many applications in our modern world. However note that these applications may or may not protect a device or person from the extraordinary ranges of electromagnetic energy generated by a CME or EMP.

    The top 6 conductive materials (stick to the good and cheap ones) are: copper, aluminum, iron, steel, brass or bronze.

    It must be understood that not all conductive materials have the same level of conductivity and not all insulators are equally resistant to electron motion. It should also be understood that some materials experience changes in their electrical properties under different conditions. Glass, for instance, is a very good insulator at room temperature, but becomes a conductor when heated to a very high temperature.

    A Faraday cage that uses only mesh or sheet metal can only shield against a magnetic frequency up to the RF range. Electronics nowadays are useful in the SHF, UHF and VHF range (such as your television). To efficiently protect your electronics from an EMP that is higher than an RF range (which most are), you need some steel, iron or thick copper.

    Aluminum can work, however, remember that just as aluminum wire generated house fires when overloaded, so to can any Faraday Cage made of aluminum.

    Some Key Points:

    • Just because your car has rubber tires, it will NOT be impervious to the effects of an EMP of CME. A car is NOT a Faraday cage sufficient to withstand an EMP incident. It has some similar components, yes. Most cars made today consist of fiberglass and disjointed parts, not a continuous metal material. In addition to that, they are on tires. Tires on a car do NOT serve as grounding. IF you had an old fashioned car that was made of metal, that had its tires removed, that was also attached to an Iron or copper pole and that was ALSO on dirt—not gravel—then yes, you may have a car that doubles as a Faraday cage.
    • Rubber containers are insufficient protection against an EMP or CME.
    • Faraday cages DO need to be grounded. If it’s NOT grounded, then the Faraday cage merely becomes a reflector or an amplifier.
    • Faraday cages do NOT have to be solid, but they do have to be constructed continuously without gaps between the protective material. Thus the name “cage” instead of the oft misused term—“box.” In fact, many of them that you can build yourself or will see on the internet will resemble a bird cage or a very finely meshed chicken coop wire. These are great for stopping radio signals, but will NOT protect the device from the extreme electro and ferro-magnetic frequencies of an EMP or CME.
    • Contrary to what you may see on the internet, a sheet of foil on a box will NOT protect you or your electronic devices. It’s not thick enough to withstand the pulse. However, you CAN protect your foil insulated items if they are buried a couple of feet underground in every direction (up, down and sideways).
    • Unless the material is also ferromagnetic, ALL magnetic fields are NOT blocked. Low-frequency radio waves are primarily magnetic waves (although with an electric field component), and may penetrate a Faraday cage because the varying magnetic field induces an electric field on the other side. Ferromagnetic materials are those substances, which when placed in magnetic fields are strongly magnetized the direction of the magnetizing field.e.g.: – Nickel, Iron, cobalt, rare earth metals.
    • The cages must be grounded, continuously connecting, and the openings of them cannot be too large. Chicken coop wire would work, but only if you double or even triple layered it as the opening are too large. For a reference of opening size, look at the front of your microwave door. It’s a small mesh. Just a like a snake can slither its way through the right sized hole, so can an electronic wave.

    A Faraday cage is NOT fool proof. The higher the frequency of the magnetic pulse, the faster and stronger it is. This is what causes the burn out.

    Note: Faraday Shield or Cage protection is NOT protection from the possible radiation (gamma rays) from CME’s or EMP’s; rather this protection is from the electromagnetic effects of these things on our technology. Hence, you will still need some kind of radiation protection for you and yours.

    Creating a Farady Cage

    There are tons of ‘Farady Cages’ you can purchase, from cheap to expensive, including a suit jacket that blocks your Wi-Fi and cell iPhone transmissions and there are tons of instructions available on the internet. Just remember that the “strength” of protection from the “cage” will depend on:

    • the ferromagnetic property of the metal the “cage” is made of
    • the thickness of the metal used for the “cage”
    • the size of the openings in mesh of the “cage”
    • how continuous the connection of the 6 sides of the “cage” are
    • how well the “cage” is grounded
    • the other protective material(s) surrounding the “cage”
    • the quality of the insulation protecting the “device” inside the “cage”
    • the strength of the electro and ferro-magnetic charge the “cage” is being exposed to

    Yet, when considering a Faraday Cage for your electronics it still pays to Keep It Simple and Cheap!

    Take advantage of some things you may already have in or around the house:

    • An aluminum or galvanized garbage can with a lid
    • A metal filing cabinet
    • A metal tool box
    • A microwave oven – unplug it before protecting anything in it
    • A metal oven – be sure to disconnect any electrical plugs or trip the circuit breaker before storing anything in it.
    • A clothes dryer, unplugged (washers are not ‘sealed’ enough)
    • Tin canisters (holiday popcorn cans) or ammo cans
    • Metal lunch pail
    • Metal locker, footlocker or steamer trunk
    • Metal suitcase or briefcase
    • Altoid tin for those smaller items
    • Any safe large enough to hold your item
    • Large stock pot (Be sure to clamp the lid down. Remember—continuous connection is key. (Since Farady cages are not fool proof, depending on the strength of the pulse, I would recommend burying such containers 2 feet under the ground, storing survival electrical and battery items; Including the batteries themselves).

    Tip: To secure a lid on a metal trash can or the like, purchase a roll or two of the metallic tape used to seal seams in heating/cooling duct work. Use this to seal the lids and cover hinges.

    A common steel garden shed, grounded using 1/4″ ground wire: The insulated ground wire does not touch the base/floor of the shed so things inside are safe.

    Basically a Farady Shield can be any conductive metal ‘container’ that has 360 coverage or encompasses all 6 sides of the enclosure, is substantial enough to take the projected electromagnetic energy, is grounded and is large enough to hold your insulated electronic device(s) in it.

    Tip: If you think your Farady shield may still be too weak, wrap it in heavy duty aluminum foil and burry the cage where it is surrounded by about two feet of good old dirt.

    Important Things to remember besides having a conductive metal container:

    • It is vital that none of your electronics directly contact the metal of the container. Insulate items by lining the container in a non-conductive material, like cardboard, foam, Styrofoam or wrapped in several layers of newspaper. You can also make cardboard sleeves for your devices.
    • Technically any make-shift or purchased Farady cages should be grounded in order to disperse the energy. The easiest way to do this is to have a wire lead from the metal skin of the ‘cage’ to the ground (good ol dirt) or the wire can go from the metal skin of the cage to a conductive metal pole that is stuck in the ground (like the old fashioned lightening rods).

    So having say, a laptop, in a Farady cage but still plugged into a power outlet or cable connected network will NOT work. Nor will sticking your emergency radio in your microwave, but not unplugging the microwave work.

    Remember these devices do not need to be in the ‘cages’ for long. To protect a device from the effects of a natural CME would be a few hours at most; for a human created EMP, a matter of a few minutes.

    The important aspect of this to remember though is that mesh or sheet metal only shields magnetic fields if the frequency is up in the RF range. To properly stop the wave, you need some iron, steel, or some slabs of thick copper. Most electronics are useful in the VHF/UHF/SHF range today and will need more substantial protection.

    I firmly believe in redundancy, and when it comes to protecting electronics, even more so. Considering this it would be wise to double or triple Farady-ize your emergency and important electronic devices.

    You do this by using the cheap cardboard box/aluminum foil cage type of Farady shield for smaller electronic devices and then placing those inside a larger Farady shield made of more substantial materials and containing more smaller pre-Farady caged items; Lastly – burry it in the ground with at least two feet of dirt ALL around it. Triple Farady protection!

    Now of course you can’t do that with items you use everyday like your laptop. That is why many sites suggested purchasing an old cheap laptop and backing up your extremely important digital information on it and then storing that laptop. As you accumulate more important digital doc’s, save them to a CD or DVD that the older stored laptop can read and store these items in one of the cheaper Farady cages.

    Note: Thumb drives, USB drives, diskettes, cassettes and any magnetic ‘tape’ or ‘disk’ recording medium will most likely be erased by a CME or EMP, so if these are important to you they need to be stored in some kind of Farady cage. This is where the smaller items are used that can be opened easily like: Holiday metal popcorn tins, metal lunch boxes or even Altoid tins (thumb & USB drives fit perfectly after being wrapped in paper or thin foam padding) that can then be placed in say a metal file cabinet or even thrown into your unplugged dryer in a pinch.

    Remember when you’re browsing the internet – Protecting against sparks, radio waves or lightning is NOT the same as protecting against a strong magnetic pulse.

    You can make your “cage” as small or as large as you’d like. It wouldn’t be out of the question to continuously line a basement storage room or hole in the ground with copper mesh wire and a grounding rod.

    Farady Cage Recap:

    • Farady cages are made of continuous (all six sides of the cage) connecting, conductive, metal mesh or sheets, that are grounded. What is inside the “cage”, must be insulated from the conductive metal (does not touch it).
    • The screen type Farady cage will stop radio transmissions from entering or escaping, however will NOT protect the enclosed device from the super extreme electromagnetic and ferromagnetic charges emitted by some space weather events, most particularly a coronal mass ejection or CME (like the 1859 Carrington event) or human created EMP.
    • Aluminum foil or other aluminum containers and such are NOT good materials to protect what is inside from a CME or human created EMP. Aluminum shorts out too quickly. Just remember all the house fires caused by aluminum wiring. However, you can burry something at least 3 feet in the ground that is wrapped in aluminum foil or in an aluminum container with a grounding wire and it will most likely be enough to protect the item.
    • During a Carrington type CME or human created EMP, anything that can conduct electricity (metals, air, ground, water, plumbing, wiring, etc.) and is exposed to the environment – WILL ; plugged in or not, connected to something or not, even a PC motherboard in the shipping box, on a shelf in the warehouse.
    • Faraday Cage strength is determine by:
    o the ferromagnetic property of the metal the “cage” is made of
    o the thickness of the metal used for the “cage”
    o the size of the openings in mesh of the “cage”
    o how continuous the connection of the 6 sides of the “cage” are
    o how well the “cage” is grounded
    o the other protective material(s) surrounding the “cage”
    o the quality of the insulation protecting the “device” inside the “cage”
    o the strength of the electro and ferro-magnetic charge the “cage” is being exposed to

    with an appropriately constructed Farady cage, you can likely protect that which is inside it from the electromagnetic attack of an EMP or CME incident, thus preserving the function of all that is contained therein (provided you have an alternate power source).

    Bottom line, your automatic transfer switch may or may not be “protected” from an EMP or SME depending on what it is made of and how it and its connecting parts are grounded.

    For additional information on Farady Cages see CME? EMP? Farady Cage? – Oh My! (includes Electromagnetic Spectrum Frequency & Radiation Charts) http://formerlynmurbanhomesteader.weebly.com/uploads/2/2/5/0/22509786/cme_emp_farady_cageoh_my_ver_2_includes_electromagnetic_spectrum_frequency__radiation_charts_new_site.pdf


    A 60 Something, no longer so urban or in NM, homesteading Prepper; I share Preparedness, Homesteading, Self-reliance knowledge & doc’s at: http://formerlynmurbanhomesteader.weebly.com/

  7. PS to my previous post:
    First please excuse me for my typos: The “2 ways” one can be hit by an EMP is really “3 Ways” and the SME mentioned is really a CME.
    Next let me quantify my repsone: The information I post was the result of 3 years (2008-2010) of research consisting of interviews with a handful of professors from several universities in several states; reading research studies from several universities from several states; electrical engineers/scientists from Sandia National Laboratories; from a closed lecture at the Alamagordo Space Museum on the Trinity Site and the Nuclear Age.

    • Sideliner 1950 says:

      A million thanks for taking the time to try to get me “smarted up.”

      OK, then, specifically regarding an (my) Automatic Transfer Switch and the metal container (box) in which it resides:

      I take it that the effects of the EMP or CME or other “event” could reach my system either “directly” (struck by the “blast”) or “indirectly” (pulse “imported” through the grid”)…correct?

      Since the electrical “box” containing the ATS does indeed have holes in it where the wires pass through, and a hinged, operable access door, around which there is an unsealed gap, I conclude that my “stock” (read: “unmodified”) setup would indeed be a poor example of a reliable “Faraday Cage” and therefore vulnerable to damage from an EMP, a CME, or any of the other “space weather events” mentioned or alluded to here and in the recently published government’s “National Space Weather Action Plan” https://www.whitehouse.gov/sites/default/files/microsites/ostp/final_nationalspaceweatheractionplan_20151028.pdf

      Further, I take it that the generator connected to and controlled by my “stock” (read: “unmodified”) ATS may or may not be damaged by one or more of the above-cited “events”, depending on the kinds of electronics integrated into it, depending on the kind, intensity, and duration of the “event”, and depending on how the generator is connected to all components (e.g., the ATS itself, and/ or any other component it may be operating)…

      How am I doing?

      By the way, the “lightning surge protector” video cited by Bob Myers (above) is really entertaining, and quite clear and easy to understand. Worth a look, I think. Here’s the link again:


  8. PrepperDoc says:

    Not to pick an argument here, but I want to assert some items regarding Faraday cages / shields / boxes.

    Electromagnetic waves (radio, light) propagate in certain mechanisms that involve an awful lot of mathematics to completely understand. The most important waves are the TEM modes (transverse elecrtic-magnetic) where the lines of electric / magnetic forces are at right angles. There are more than one type of mode of TEM waves. This stuff is complicated and the last time I formally studied it was 40 years ago.

    TEM waves have BOTH electric and magnetic components; they are in FIXED interrelationships deteremined by the epsilon and mu constants of the medium. These are known for air, glass, many other media. If EITHER of the components is unable to exist, the wave simply can’t pass in that form.

    The reason that a conductive box works as a Faraday Shield is that (and this is glossing over the math, which I did understand 40 years ago) it is impossible to sustain an E field within a conductor, which means you can’t have the TEM wave….in fact, it gets destroyed in the top layers of the conductor, called “skin effect.” The higher the frequency, the thinner the layer of the skin that is important. The lower the frequency, the deeper the conduction goes.

    EMP E1 components are extremely broad band but most of the power is below 100 MHz and most all below 1 GHz. Concentrate your efforts on 100 MHz and below.

    There is a reason that tiny holes are OK: there is a “waveguide beyond cutoff” phenomenon that stops waves larger than roughly the size of the holes, from getting through. This is complicated and I am overly simplifying it. You do NOT want long slits if possible.

    There is NO need for the Faraday box to be grounded. The earth is just a huge somewhat conductive item. The inability of the TEM wave to get inside a conductor has NOTHING to do with whether the conductor (the Faraday box) is connected to another conductor (the earth). You’re welcome to ground yours, but it makes little difference.

    I do think it is wise to put some insulation (cardboard?) on the inside to keep your precious electronics from touching the inside — I do NOT know if this makes any difference, because due to skin effect, it is possible there will be little going on, on the INSIDE surface. On the other hand, if your conductor is thin, there may be a lot going on !!! The math is complicated….

    All of this is somewhat MOOT when we are discussing an automatic transfer switch, which HAS to be connected to outside things….as I wrote above, you try and shield any wiring that will pierce the “shielding” around your transfer switch etc….. but you have to deal with the CONDUCTED radio frequency that can get in VIA the wiring that you have to connect to.

    I hope that makes some sense and helps someone. I have several new trash cans with some cardboard, and lots of important electronics secreted within. That’s my effort. If I were less lazy, I would seal the edges of the lid with aluminum tape….. been meaning to do that.

    • PrepperDoc says:

      Just to be clear: the garbage cans were my effort on STORAGE. I have done ENORMOUS work to have up-and-running communications systems that are relatively immune to EMP. That is an entire other subject, on which I’ve already written a lot.

  9. Jim from Whitefish says:

    Question from a not electrical savvy prepper: If you have a backup system gen and solar but are connected to the grid. Would not an EMP pulse knock out the grid thus blowing all the transformers etc along the line before it could reach you and your electronics? I realize a CME would get you if you were on the grid or not.

    • PrepperDoc says:

      The E3, similar to the coronal mass ejection, would likely take outquite a few transformers from the highest to the lowest, possibly to the neighborhood level.

      I’m not a power engineer, however I believe there are mechanisms to blow out your equipment connected to your local distribution system, depending on the level of its protection. My solar power inverters appear to have considerable protection and would disconnect, where as consumer electronics would likely be destroyed unless you have a system to disconnect, of which I have written.

    • Any long wire (even your own power cords, plugged in or not) will couple with the pulse and kill your stuff.

  10. How can I protect my batteries for my flashlights and radio? Will an EMP destroy them? If I place them in a Faraday box will that protect them for future usage?

  11. JustAnotherGuy says:

    Just to throw in my 2 cents and a bit more….

    I work on RVs, many of them having on board generators with shore power being 30 amp (120vac) 3 conductor and 50 amp (120/240vac) 4 conductor service. On an RV, the neutral is never connected to ground except at the source of power, is the pedestal or the generator. Grounds are not switched, just neutral and line. For 30A transfer switches, the contactor is 2 pole, 50A has a 3 pole contactor. Typically, the transfer switch has a delay on the axillary input (generator) of a few dozen seconds up to a couple of minutes. Contactor coils have been seen as both 12vdc and 120vac.

    That being said, I was first surprised at just how easy it was to burn up the xfer switch. In the case of the DC contactor coils, the switch mechanism / delay timer is powered by the 120vac on one of the aux line legs, no transformer. For the 120vac contactor coils, there is typically a transformer that creates a regulated DC supply, which powers the delay, and ultimately closes a relay to energize the aux contacts. This delay board is incredibly easy to damage, especially the ones that have an onboard transformer. A power surge, especially common mode, is disastrous. So is an ungrounded box- I have gotten tingles working on a box that had a line leg loop that induced a voltage to the box (bad install).

    A neutral failure can burn up the contactor, typically welding the contacts if they happen to be switching during the neutral event. The coils themselves can also be burned out on the 50amp variety if neutral is lost, and most certainly will be burned out on a 30A contactor where the plugin outlet is miswired 240vac instead of 120vac). If there is a large load present, particularly inductive, the contacts will arc somewhat when the contactor closes, and will arc copiously when opened. Please bear in mind that this is gear designed for use in a recreational vehicle. It takes some things from a commercial / residential design, and made them more compact.

    Given the nature how the coils are powered by the source being switched, I would not trust them to hold up to an EMP scenario. They all seem to be barely hanging on for everyday application. That being said, I built in some immunity when I first implemented my xfer switch. I built mine using latching contractors. Once the coil was engaged, the contactor was physically held closed but without using a magnet. Pulse coil once, contactor is engaged. Pulse coil in reverse direction, contactor is disengaged. In addition to a physical interlock between the 2 contractors, the coils were wired backwards. Pulsing one on turned the other off. Physical interlock was achieved with a traveling arm between the 2 contractors. Coil power was derived from a small 12v Lithium battery. Even with a handful of pulses each day, battery would have lasted several years. The coils were switched using a magnet that closed a reed switch through the metal enclosure (aluminum). Did I trust it? Nope. In case I needed it, I had a 50amp 240vac range receptacle (think RV 50a receptacle) wired for each circuit. The xfer switch connected to each receptacle using 50A plugs.

    Was my setup ideal? For me yes. I had autonomy when I needed it (built in delay driver), manual operation using a magnet (once delay driver unplugged inside), and a fall back when things went seriously sideways by using a double ended 50A jumper that was connected first to the load side, then to the supply In wanted to use. Yes, I realized that I had created a dangerous situation that could expose the user to 240vac. I wanted everything mounted on the wall, and 50A male plugs for this were not available. Would I do it again? Yes, but now would use a commercially available 50A 4Pole power inlet for load side, and a regular male/female jumper. Then no high voltage exposure.

  12. Sideliner 1950 says:

    Holy mackerel…I’m overwhelmed…

    First, many thanks to all the authors of responses to my query. Not only am I humbled by the obvious wealth of knowledge out there, but I am sincerely grateful (and apologetic) for all the time you have all committed and spent in providing me and others with the benefit of your knowledgeable replies. This is a wonderful, powerful example of the spirit of helpfulness I have found among the prepper community, and I take great comfort in it. Many thanks.

    Next, I’d like to express my sincere thanks to MD for putting my question “out there” in search of answers. Another example of that helpfulness and cooperation of which I speak.

    Finally, please know I will try my best to put all this knowledge to effective use. It will probably take me some time to optimize my own backup power solution, but I do believe I am far better armed now with all this information than I was before I asked the questions.

    Good luck to us all.

  13. Foil, MOVs, and a standard Faraday Cage is useless against a true nuclear EMP event. We used contiguous welded steel sheet with all external I/O running through tuned waveguide. A well was drilled for the ground.

    To protect your own gear at home… Just ensure you have spare critical electronic items, such as: control boards, HH radios, and the like, seal them in a water tight container, and let em rest at the bottom of a pond or stream – 5 feet minimum.

  14. Wow! Complicated. Way over my head. I have heard that the wave of an EMP is about 5 inches and therefore any mesh smaller than that would protect. True or false? I have a shop with a metal roof and stucco with wire mesh embedded. I have grounded the roof to water pipe. Will this provide protection? Does EMP travel like light, in other words, it does not bend or turn corners? Therefore, would my shed need protection in the floor? How would EMP come back up through the floor? Thanks for all your effort.

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