Faraday Cages: EMP Protection for Your Electronics

An electromagnetic pulse (EMP) is a burst of electromagnetic energy intense enough to damage or destroy electronic devices. Two sources are relevant to preparedness planning: a high-altitude nuclear EMP (HEMP) from a nuclear detonation above the atmosphere, and a severe geomagnetic storm (Coronal Mass Ejection, or CME) from the sun. Both are low-probability but high-consequence events — and unlike most disaster scenarios, they can affect electronics across an entire continent simultaneously.

This guide covers what an EMP actually does, what’s worth protecting, and how to build Faraday shielding that works.

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What an EMP Actually Does

An EMP produces three distinct pulse components (E1, E2, E3) that affect different systems in different ways. The short version:

E1 (fast pulse): Destroys solid-state electronics — microcontrollers, computer chips, anything with an integrated circuit. This is what fries phones, laptops, modern vehicles, and anything with a microprocessor.

E2 (intermediate pulse): Similar to a lightning strike. Most surge protectors can handle this component.

E3 (slow pulse): The component that affects the power grid itself — transformers, transmission lines, and large electrical infrastructure. This is what takes down the grid for months or years in worst-case EMP scenarios.

A geomagnetic storm (CME): Primarily produces E3-type effects — it threatens the power grid and large connected systems, but has less effect on small unconnected electronics than the E1 pulse from a nuclear EMP.

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The Realistic Threat Assessment

Solar CME (Carrington-level event): The 1859 Carrington Event was a solar storm powerful enough to set telegraph offices on fire. A comparable event today would damage or destroy large power grid transformers — replacing these takes months to years as they’re custom-manufactured. Most modern electronics sitting disconnected from the grid would survive a CME with no special protection, though connected devices might be affected through the grid.

Nuclear HEMP: A single high-altitude nuclear detonation above the continental US could produce an E1 pulse covering the entire lower 48 states simultaneously. This is the scenario that damages unconnected electronics. The probability of this event depends on geopolitical factors outside this guide’s scope, but it is a documented concern taken seriously by the US military and government assessments (EMP Commission reports, available publicly).

Local EMP devices: Non-nuclear EMP devices exist but have limited range. They’re relevant for targeted attacks, not the widespread grid-down scenario discussed here.

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What’s Worth Protecting

Not everything needs protection. Focus on items that:

• Would be difficult or impossible to replace post-event
• Are critical to your preparedness capability
• Would lose significant function without electronics

High priority:

• Backup radios (HAM, GMRS, shortwave receiver) — your communication capability post-event
• Medical electronics (insulin pump, pacemaker external equipment, CPAP — though implanted devices have their own shielding considerations)
• Backup solar charge controllers and inverters — allows rebuilding power generation capability
• Backup lighting (LED lights, solar lanterns)
• Backup tools (electric detonator-free items, electronic ignition-free items)
• Navigation (handheld GPS, though maps are more EMP-resilient)
• Important documents on USB drives or microSD cards
• Small backup generator (older carbureted if possible, or a unit you can afford to have a backup of)

Lower priority (already hardened or replaceable):

• Older analog equipment — already EMP-resistant by design
• Appliances with mechanical controls — less vulnerable than microprocessor-controlled devices
• Modern vehicles — if your vehicle survives, great; protecting a spare vehicle is expensive and may not be worth it relative to other prep priorities

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How a Faraday Cage Works

A Faraday cage is a conductive enclosure that redirects the EMP’s electromagnetic field around its contents, preventing the fields from penetrating to the electronics inside.

Key principles:

1. Continuous conductive enclosure: The shielding must form a complete conductive shell — gaps allow field penetration. The cage doesn’t need to be solid; fine conductive mesh works, as long as the holes are smaller than the relevant wavelength.

2. Grounding is optional for EMP protection: For static electricity and lightning protection, grounding is important. For EMP protection, an isolated (ungrounded) Faraday cage works — and some sources argue ungrounded is better because it can’t act as an antenna.

3. No direct contact between contents and cage walls: Items inside should not touch the conductive shell — this can transfer the induced current to the contents. Use non-conductive padding (cardboard, foam).

4. Nesting works: Double-layer protection (an item in a sealed bag inside a sealed metal container) provides more attenuation than a single layer.

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DIY Faraday Cage Options

Metal Garbage Can with Metal Lid (Most Practical)

A standard galvanized steel garbage can with a tight-fitting metal lid is the most commonly recommended DIY Faraday cage for preparedness. It’s cheap, large enough to hold multiple radios and devices, and reasonably effective for E1 protection.

How to set it up:

1. Line the interior with cardboard or foam (prevent contact between items and the can walls)
2. Place electronics inside, individually wrapped in a non-conductive layer (cardboard, zip-lock bags, foam)
3. Ensure the lid fits tightly — tape the seam with metallic tape for better shielding
4. Store in a location where it won’t move or the lid won’t be inadvertently disturbed

Metal Ammunition Cans

Military-surplus .50 caliber or 20mm ammunition cans provide an excellent small-format Faraday cage. They’re already designed to be dust-tight and water-resistant, and the metal construction provides good shielding. Used ammo cans cost $15–$30.

Setup: Line with cardboard or foam, verify the rubber gasket and lid latch are intact, add metallic tape around the lid seal.

Commercial Faraday Bags

Purpose-built Faraday bags (often used for forensic evidence preservation) provide portable device-level shielding. They’re convenient for protecting phones and smaller electronics but require testing to verify shielding effectiveness — quality varies significantly.

Testing a Faraday bag or cage: Place a phone inside, seal it completely, and try calling it. If the call connects, the shielding is insufficient. This is not a perfect test (phone signals differ from EMP frequencies) but provides a basic verification.

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What to Store in Your Faraday Cache

A practical Faraday cache for preparedness:

Item	Why
Backup HAM/GMRS radio (Baofeng UV-5R or similar)	Communications capability
Shortwave receiver	Receive broadcasts from distant transmitters
Spare solar charge controller	Rebuild power generation capability
USB drives with important documents	Records, manuals, maps
LED headlamps (spare)	Lighting
Backup glucose meter, medical monitors	If applicable
Handheld GPS with downloaded maps	Navigation
Small AM/FM/NOAA radio	Receive information
Spare vehicle ignition components (points, condenser)	For older vehicles

Keep the cache sealed. The entire value depends on it being sealed when the event occurs. Don’t open it to borrow the radio for a camping trip. Keep it sealed.

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The Honest Probability Assessment

EMP preparedness is the “black swan” end of preparedness planning — the scenario with severe consequences but genuinely low probability. It requires weighing a small investment ($30–100 for a basic cache) against the unlikely but catastrophic scenario.

A galvanized can with $100 worth of backup electronics is a reasonable hedge. Restructuring your entire preparedness around EMP survivability to the exclusion of higher-probability scenarios (storms, job loss, medical emergencies) would be misallocated effort.

Build the cache. Seal it. Then continue building your more likely-scenario preparedness.