Why a house built decades ago can carry field levels a new build never sees, and what an instrument reading tells you.
Wiring errors are one of the most common sources of elevated AC magnetic fields inside older homes, and they are invisible to a standard electrical inspection because the circuits still work. A wiring error means current is returning on a path the original electrician never intended, often through a neutral shared between circuits or through metal plumbing. That stray current creates a magnetic field that penetrates walls and floors and cannot be shielded in any practical way. FieldWise measures AC magnetic fields in milligauss (mG) with a Gigahertz Solutions NFA1000 analyzer, room by room, and compares every reading against Building Biology SBM-2015 guidelines. Finding the pattern is the assessment; fixing it is usually one visit from a licensed electrician with the map in hand.
The Mechanism
In a correctly wired circuit, the outgoing and returning current travel together, and their magnetic fields largely cancel. When the return current takes another path, the cancellation is lost, and the loop becomes a source. Homes wired before modern code, and homes extended repeatedly over decades, are where this shows up most.
Knob and tube wiring, still present in many pre-war homes, has no grounding path at all, and later additions frequently sit on top of the original wiring rather than replacing it. None of this shows on a breaker panel. All of it shows on a properly taken AC magnetic field reading.
What We Measure
A wiring-error signature is a magnetic field that stays elevated when you would expect it to fall: it persists across a whole room rather than dropping sharply with distance from an appliance, and it often tracks a wall or floor line. During an assessment, readings are taken with major loads switched on and off, which separates a wiring pattern from an appliance pattern.
AC electric fields matter here too, especially around sleeping areas. Voltage on energized wiring creates an electric field, measured in volts per meter (V/m), even when nothing is drawing power. Older ungrounded circuits tend to read higher, and the bed is where proximity makes it count.
What Happens Next
the written room by room report documents where the elevated fields are, what pattern they follow and which rooms they affect, with room-by-room scores against SBM-2015 guidelines. That written map is what an electrician needs to find and correct the actual fault, so the repair visit is short and targeted rather than exploratory.
The goal is not elimination, but intentional optimization: most homes cannot reach zero, and they do not need to. Sleeping areas get priority, because that is where hours of proximity accumulate.
Questions
Yes. Electrical inspections confirm circuits work safely by code; they do not measure magnetic fields. A shared neutral or a current path through plumbing can pass inspection and still produce a clearly measurable field.
Consumer meters can show that something is elevated, but single-axis readings and uncalibrated scales make the pattern hard to trust. The assessment uses a 3-axis calibrated analyzer, which is what makes the on-off load comparison meaningful.
No. FieldWise measures, maps and documents. The repair belongs with a licensed electrician, and the report is written so the electrician can go straight to the fault.
AC magnetic and electric field measurement is part of the Foundational Assessment at $850, and a Focused Visit can be arranged where a wiring pattern is the main concern. Call and describe what you are seeing.
Every assessment is performed personally by founder Cameron Castaneda and ends with a written room-by-room report with prioritized next steps. Appointments run Monday through Sunday, 8am to 6pm. Call (970) 436-7611 or book a discovery call.