What is it?
AC magnetic fields are physical fields generated by electric current flowing through a conductor. In Europe they are mainly associated with the 50 Hz frequency of the mains supply.
Unlike AC electric fields, they only exist when current is flowing: their strength varies with consumption and with the operation of the connected equipment.
They are one of the physical factors covered by the SBM-2024 and are not interpreted in isolation. The behaviour of a magnetic field depends on the current, the geometry of the wiring, the distance from the source and the construction of the building; that is why two properties with apparently similar installations can give very different results.
Where can it be found?
The most common sources are power supply lines, distribution boards, transformers, motors, pumps, lifts, heating and air-conditioning systems, appliances in use and certain wiring configurations.
Installations in neighbouring buildings, substations, nearby power lines and other infrastructure can also play a part when they produce appreciable levels inside the property.
During the inspection, particular attention is paid to bedrooms and areas where people spend long periods, because the aim is to understand how the indoor environment behaves in the spaces used every day.
How does it affect the space?
The distribution of these fields can vary considerably between rooms and even within the same room. That variability is why the factor is examined at the specific points where people spend time, rather than across the building as a whole.
Their strength also depends on electricity consumption, so the same space can behave differently depending on the time of day and on which equipment is running.
How is it assessed?
What the inspection looks at
The technical inspection identifies possible sources and analyses the configuration of the building’s electrical installation.
What is recorded for each measurement
Equipment, quantity, unit, location, date, measurement conditions and duration, together with the relevant limitations and the interpretation criterion applied.
How this factor is measured
Measurements are taken with specialist professional instruments at the points where people spend time: bedrooms, living rooms and workstations.
As well as recording field levels, where necessary we investigate return currents, current loops, nearby transformers or installation faults that might explain the values detected.
In assessments intended as expert evidence, calibrated instruments are used to ensure the reliability and traceability of the measurements. All the information obtained feeds into the overall analysis of the indoor environment.
Criteria
Interpretation follows the SBM-2024, which sets guidance ranges for assessing AC magnetic fields in spaces used for sleeping and for long periods of occupancy.
The technical assessment goes beyond the numerical value: the location of the sources, the intended use of each room, the spatial distribution of the field, how the measurements behave over time and the interaction with the other factors assessed are all taken into account.
This guide does not publish values or thresholds. Technical criteria, legal limits and recommendations are different things and are not presented as equivalent.
Improvement measures
Work always begins by understanding and, where possible, reducing the source, before acting on the path or on the space. Measures are prioritised by expected effect, feasibility and proportionality, and no products are recommended by default.
The action taken depends on the origin of the field detected. Options that may be considered include:
- Reorganising certain circuits.
- Correcting installation faults.
- Eliminating current loops.
- Relocating equipment.
- Optimising the electrical design.
- Adopting specific solutions where they are technically and structurally feasible.
There is no universal measure that applies to every case. Each recommendation is adapted to the characteristics of the building and to the results obtained, and action is always planned after an individual assessment.
How Cemprotecta helps
This factor is not assessed on its own. It is measured as part of an assessment that treats the space as a system, because its strength depends on consumption and its distribution changes from one room to another.
What an assessment gives you is knowing what is there, where it is and what can be done about it, with an ordered sequence of measures rather than a list of problems.
- Inspection of the space and of accessible installations.
- Measurement in the rooms where people spend most time.
- Combined interpretation with the other factors assessed.
- A report with measures ranked by their expected effect on exposure.
Request an assessment
If this factor concerns you in your home or workplace, tell us about your case. The prior inspection will determine whether it is worth measuring and what else should be assessed alongside it.