Electric Fields in Your Home

Everything in your bedroom is off. The lamp, the charger, the clock, all unplugged. The room is dark and quiet. But the wiring inside the walls is still energized at 120 or 230 volts, radiating an AC electric field into the room.

You are lying in that field for eight hours a night. If you measured your body voltage right now, the voltage your body has picked up from the surrounding electric field, most bedrooms would put you somewhere between 200 and 2,000 millivolts. The SBM-2008 standard considers anything above 100 mV a concern for sleeping areas.

Electric fields are the overlooked EMF type. People focus on magnetic fields and RF radiation because those are more familiar and their sources more obvious. But electric fields are present in every room with powered wiring, and unlike magnetic fields, they couple directly to your body. The fix for most bedrooms is straightforward and inexpensive: a demand switch that cuts voltage on the bedroom circuit when nothing is drawing current.

What Are AC Electric Fields?

An electric field exists whenever voltage is present on a conductor, whether or not any current is flowing. In your home, every wire that connects back to the panel and carries 120 V (or 230 V in most of Europe) produces an electric field around it. That field radiates outward from the wire, passes through drywall and plaster, and fills the room.

Magnetic fields are produced by current, they exist when a device is actually running. Electric fields are produced by voltage, they exist whenever the circuit is live, even if every switch is off and nothing is drawing power. Your bedroom wiring is energized 24 hours a day. The electric field is there all night.

What this means in a house:

• Electric fields are present whenever wiring is energized. Turning off a lamp stops the current (and the magnetic field) but does not stop the voltage (or the electric field). The only way to eliminate the electric field from a circuit is to cut the voltage entirely, at the breaker, or with a demand switch.
• They couple to the body. Your body is conductive. When you're in an AC electric field, a small alternating current is induced on your skin and through your tissues. Body voltage measures this, the voltage your body has acquired from the surrounding field.
• They are blocked by grounded conductive materials. Unlike magnetic fields, which pass through everything, electric fields can be shielded. A grounded metal surface, grounded shielding paint, or grounded shielding fabric will block an electric field. This makes them more controllable than magnetic fields, though the simplest fix is usually to cut the voltage at the source.
• They decrease with distance. Moving away from the energized wire reduces the field, though in a typical bedroom with wiring in multiple walls and sometimes the floor or ceiling, distance alone rarely brings levels below SBM thresholds.
• They are measured in volts per meter (V/m) or as body voltage in millivolts (mV). Both measurements reflect the same underlying field. Body voltage is the more sensitive and practical measurement for sleeping areas.

Electric Fields vs. Magnetic Fields

Both are low-frequency (50/60 Hz) fields from household wiring. Both are assessed in a building biology EMF assessment. But they need different measurement techniques and different solutions. You can have low magnetic fields and high electric fields in the same room, and in most bedrooms, that is exactly the case.

Health Considerations

AC electric fields at residential levels do not produce acute effects. The currents induced in the body are far too small. The concern in building biology is chronic nighttime exposure, sleeping in an elevated electric field for years.

Research on low-level AC electric field exposure is thinner than the magnetic field and RF literature. The SBM-2008 standard takes a precautionary position: sleeping areas should have the lowest possible levels of all fields, including ones that couple directly to the body's electrical system during sleep.

Government limits are not informative here. The ICNIRP reference level for 50/60 Hz electric fields is 5,000 V/m for the general public. The SBM-2008 "No Concern" threshold is less than 1 V/m, roughly 5,000 times stricter. The two frameworks answer different questions. ICNIRP protects against immediate nerve stimulation. Building biology asks what levels are appropriate for long-term sleeping exposure.

For broader context on EMF health research, see EMF and health.

SBM-2008 Threshold Values for AC Electric Fields

The SBM-2008 standard provides thresholds for AC electric fields as field strength (V/m) and body voltage (mV). Body voltage is generally the more practical measure for bedrooms because it reflects what the body is actually experiencing in its sleeping position.

Field Strength (V/m)

Body Voltage (mV)

Most bedrooms in standard construction fall in the 200–2,000 mV range when measured at the bed, squarely in "Severe Concern" or "Extreme Concern" territory. Not because of unusual wiring or faulty construction. Standard residential wiring is not shielded, and the voltage on those wires radiates electric fields into every room they pass through. A bedroom with wiring in three walls and the ceiling below (common in multi-story homes) can read well above 1,000 mV with no devices turned on at all.

Sources of Electric Fields in Bedrooms

Wiring in Walls

The dominant source in nearly every bedroom. Standard Romex (NM-B) cable, the type used in the vast majority of residential construction in North America, is unshielded. The hot conductor carries 120 V, and the plastic jacket does nothing to contain the electric field. Every run of Romex in the walls behind your bed, beside your bed, and in the ceiling or floor near your bed contributes to the field at your sleeping position.

The field is strongest closest to the wire. A bed pushed against a wall with a wire run directly behind the headboard will have higher body voltage than a bed centered in the room. But most bedrooms have wiring in multiple walls, so moving the bed may reduce the field without eliminating it.

Extension Cords and Power Strips

An extension cord plugged into an outlet is energized at full voltage whether anything is connected to its other end or not. A power strip under the bed or a cord running along the baseboard behind the headboard puts an energized, unshielded conductor within centimeters of your body. These are among the easiest electric field sources to address: unplug them.

Bedside Lamps and Chargers

A lamp plugged into the wall produces an electric field along its entire cord, even when switched off. The switch breaks the circuit, stopping current flow and eliminating the magnetic field, but the cord remains energized up to the switch point. Chargers plugged into outlets do the same. If the cord runs behind or beside your pillow, body voltage at the head position will be elevated.

Unshielded Cables Running Under or Behind the Bed

In some homes, wiring runs through the floor cavity directly beneath the bed, or vertically through the wall cavity behind the headboard to feed outlets or fixtures on the floor above. These hidden conductors can be the primary electric field source at the mattress, and they are invisible without knowing the wiring layout or testing with a meter.

Ungrounded Metal Bed Frames

A metal bed frame sitting in an electric field acts as an antenna, it picks up the field and re-radiates it across the entire frame surface. If the frame is grounded (connected to the grounding terminal of a nearby outlet), it drains the field to ground and can actually reduce body voltage. Ungrounded makes things worse. Grounded helps.

How to Measure Body Voltage

Body voltage is the most practical way to assess electric field exposure in a sleeping area. It is inexpensive, and it tells you directly what voltage your body carries in your actual sleeping position.

What You Need

• A digital multimeter that reads AC millivolts. Most multimeters in the $20–50 range can do this. You need the AC voltage function with millivolt resolution. A meter with high input impedance (10 megaohm, standard on modern digital multimeters) gives accurate results.
• A grounding rod driven into the earth outside, with a wire running to your measurement location, or access to the ground terminal of a properly wired outlet. A dedicated grounding rod gives a cleaner reference, but an outlet ground works for screening purposes.
• A length of wire long enough to reach from the grounding point to the bed. Standard insulated copper wire is fine.

Step-by-Step Measurement

1. Set the multimeter to AC voltage (V~), millivolt range. If your meter does not auto-range, select the lowest AC voltage range that includes millivolts, typically the 200 mV or 2,000 mV range.
2. Connect one probe to the ground reference. Attach one test lead to the grounding rod wire or clip it to the ground terminal of an outlet (the round hole in a North American receptacle, or the earth pin in a UK/EU socket). This probe stays at ground potential throughout the measurement.
3. Hold the other probe against your skin. Grip the metal tip of the second test lead in your hand, or hold it against your forearm or ankle. You are now measuring the voltage difference between earth ground and your body.
4. Lie down in your sleeping position. Get into bed the way you normally sleep. Hold the probe against your skin and watch the meter reading stabilize. Do not touch the grounding wire with any part of your body other than through the meter, you want to measure the voltage, not drain it away.
5. Record the reading. This is your body voltage in millivolts. Compare it to the SBM table above.
6. Test different positions. Move to the other side of the bed. Try the head end and the foot end. Body voltage often varies across the mattress depending on proximity to wiring in different walls.
7. Test with changes. Flip the breaker for the bedroom circuit and measure again. Unplug bedside devices and measure. Turn off adjacent rooms' breakers. This tells you which circuits and sources are contributing to the field at the bed.

For measurement of all four EMF types, see the home EMF assessment guide. For meter recommendations beyond a basic multimeter, see the EMF meters buying guide.

What to Do If Levels Are High

If your body voltage exceeds 100 mV, and in most standard bedrooms it will, work through these steps in order.

Step 1: Unplug and Relocate Cords Near the Bed

Unplug bedside lamps, chargers, extension cords, and power strips. If you need a lamp, plug it in across the room rather than at the headboard. Move any cords that run behind or under the bed. This step is free and takes five minutes. In some cases it alone drops body voltage by 100–500 mV, especially when an extension cord or power strip was running under the bed.

Step 2: Install a Demand Switch

A demand switch (also called a circuit cut-off switch or automatic circuit disconnector) is installed at the breaker panel and monitors a specific circuit. When no current is being drawn on that circuit, meaning every device on it is off, the demand switch automatically replaces the 120/230 V supply with a small DC test voltage (typically 2–5 V). This eliminates the AC electric field from all the wiring on that circuit. When you flip a light switch or a device calls for power, the demand switch detects the draw and instantly restores full AC power.

For a bedroom, this is the highest-impact fix. A demand switch on the bedroom circuit eliminates the electric field from every wire in the walls, ceiling, and floor that belongs to that circuit. Body voltage typically drops from several hundred or thousand millivolts to under 10 mV, from "Severe" or "Extreme Concern" to "No Concern."

Practical details:

• Cost: The device itself runs $80–150 depending on manufacturer. Installation typically adds $70–150, bringing the total to roughly $150–300. A fraction of the cost of shielding a room or rewiring with shielded cable.
• Installation: An electrician installs it at the panel. No changes to room wiring are needed. The work usually takes 1–2 hours.
• Limitations: The demand switch only controls one circuit. If your bedroom has wiring from multiple circuits in its walls (common when an adjacent room's circuit runs through the shared wall), you may need demand switches on more than one circuit. The breaker-off test during body voltage measurement will reveal which circuits matter.
• Night lighting: Since the demand switch cuts power when nothing is drawing current, you cannot leave a night light plugged into the bedroom circuit. Use a battery-powered light if needed. Some people also switch to a battery-powered alarm clock.
• Popular models: Gigahertz Solutions and Biologa both make demand switches designed for building biology applications. Your electrician can source standard automatic circuit disconnectors that serve the same function.

Step 3: Ground Metal Bed Frames

If you have a metal bed frame, connect it to the ground terminal of a nearby outlet using a wire with a ring terminal or grounding clamp. This turns the frame from an antenna (re-radiating the field) into a shield (draining it to ground). The effect on body voltage varies, noticeable reduction in some setups, minimal in others, but it costs nothing and takes minutes.

Wood bed frames and wooden slatted bases do not pick up and re-radiate electric fields the way metal does. If you're choosing a new bed frame, wood is simpler from an electric field perspective.

Step 4: Shielded Wiring in New Construction or Renovation

In Europe, shielded cable (NYM-J with a grounded shield or BIO cable) is available and commonly used in building biology projects. The grounded shield contains the electric field within the cable, preventing it from radiating into the room. If you're building new or doing a gut renovation, specifying shielded cable in bedroom walls eliminates the need for a demand switch and the limitation of losing circuit power at night.

In North America, standard shielded residential cable is less commonly available. Metal conduit (EMT) with standard wiring inside serves a similar function, the grounded metal conduit acts as a shield. MC (metal-clad) cable also provides partial shielding. These options cost more than standard Romex but far less than retrofitting later.

In existing homes with standard wiring, a demand switch is almost always more practical than rewiring.

Step 5: Shielding Materials

Grounded shielding paint (carbon-based conductive paint applied to walls and then grounded) and grounded shielding fabric (canopies or curtains) can reduce electric fields from wiring in walls. The paint must be properly grounded to work, ungrounded, it has no effect. These solutions are labour-intensive and more expensive than a demand switch. They are most useful when the field source is wiring in an adjacent unit you don't control (apartments, condos) or when a demand switch cannot cover all contributing circuits.

Measurement with a Professional Meter

Professional building biologists also measure electric field strength in V/m using specialized meters. The Gigahertz Solutions NFA1000 and ME3951A are common choices. These meters read field strength directly and can locate the direction of the dominant source, which wall, which cable run.

For most homeowners, body voltage measurement is enough. It answers the question "what is my body experiencing in this bed?" and maps cleanly to SBM thresholds. If you hire a building biologist, they will typically measure both field strength and body voltage.

Prioritizing Your Efforts

Electric field reduction in a bedroom follows a clear sequence:

1. Unplug everything near the bed. Free. Five minutes. Removes the closest sources, cords and chargers within arm's reach of your pillow.
2. Install a demand switch on the bedroom circuit. $150–300 installed. Eliminates the dominant source, energized wiring in the walls, automatically, every night, with no change to your routine.
3. Ground a metal bed frame. Free if you have wire and a grounding clip. Stops the frame from amplifying the field.
4. Check adjacent circuits. Use body voltage measurement with individual breakers off to find out whether wiring from other rooms passes through your bedroom walls. Install additional demand switches as needed.
5. Consider shielding for sources you can't control. In apartments or condos where wiring from other units runs through shared walls, grounded shielding paint may be the only option. Budget $200–500 for materials per wall, plus labour.

Most people will get their bedroom into "No Concern" territory with steps 1 and 2 alone.

Next Steps

Electric fields are one of four EMF types assessed in building biology. The home EMF assessment guide covers the full protocol, electric fields, magnetic fields, RF radiation, and dirty electricity, with step-by-step instructions for each. For a focused look at the bedroom across all exposure types, see the EMF bedroom guide.

If you're choosing a meter, the EMF meters buying guide covers options from a basic multimeter for body voltage through professional-grade field meters. If you'd rather have someone assess your home, the building biologist directory lists certified practitioners by location.

For the precautionary standards referenced throughout this guide, see the full SBM-2008 standard reference.

The wiring in your walls carries voltage to every outlet and switch. The electric field is a side effect that standard construction never addressed. Now you know what to measure, what the numbers mean, and where to start, unplug what you can tonight, and consider a demand switch for the circuit that feeds your bedroom. Most people who take those two steps wake up in a room that finally matches what they assumed it was all along: off.