Electric and Magnetic Fields (EMFs)

Electric and magnetic fields are produced both naturally and as a result of human activity. The earth has both a magnetic field and an electric field. And wherever electricity is used, electric and magnetic fields also exist. 

We know that some people have genuine concerns about Electromagnetic Fields (EMFs) and health. 

Here, we explain the facts about electric and magnetic fields, based on the most up-to-date information from Irish and world-leading health and scientific agencies.

Electric fields occur naturally, as well as around sources of electric current. For example, electric fields are produced by a number of natural events such as storm clouds, blowing snow and swirling dust clouds. 

Common electric fields also include static electricity such as the electric shock felt after walking across a carpet and the ‘static cling’ that develops on a comb, balloon or on clothing. 

When occurring because of electric current, the strength of the electric field depends on the voltage within the wire. The higher the voltage, the stronger the electric field.

Electric fields are strongest when close to a power source and their strength reduces quickly with distance. Electric fields are blocked by grounded conducting objects like buildings, trees and walls.

For underground cables, the electric field from the voltage applied to the inner conductor is blocked by the outer grounded metallic sheath. This means the external electric fields associated with underground cables are insignificant.   

Electric fields are measured in volts per metre (V/m) or kilovolts (thousands of volts) per metre (kV/m).

The earth is a source of a static magnetic field produced by constant flow of current deep within its core. This is called the ‘geomagnetic field’, and it is this field that is used for compass navigation.  We also encounter higher strength magnetic fields from natural or manmade metal magnets. 

Magnetic fields are also produced by moving electric charges (also known as electric current). The strength of the magnetic field depends on the current flow in the lines or cables and their physical design. 

Unlike electric fields, magnetic fields are not blocked by common grounded conductive objects such as buildings and trees. Like electric fields, magnetic fields are strongest when close to an electricity line or cable and their strength reduces quickly  with distance from the line or cable.

Magnetic fields are measured in units of microtesla (μT).

The European Union recommendation (1999/519/EC) outlines a set of basic restrictions and reference levels for limiting overall exposure of the general public to electromagnetic fields and ensuring an increased level of protection.

This recommendation is based on ICNIRP guidelines (International Committee on Non-Ionising Radiation Protection) for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to 300 GHz) as the scientific basis.

The electric and magnetic fields associated with Ireland’s transmission grid do not exceed the EU recommendation (1999/519/EC). This is demonstrated in the infographics below where we have used the highest recorded values from this year’s review (more information below).   

What are electromagnetic fields (EMFs)?

When electric current flows, both an electric and a magnetic field form around this current. 

Electric and magnetic fields are separate fields. However, we refer to them as ‘electromagnetic fields’ or EMFs. Electric fields are measured in volts per metre (V/m) or kilovolts (thousands of volts) per metre (kV/m).

The electromagnetic spectrum

Electromagnetic fields are very common and can be found in the home, in the workplace, and anywhere we use electricity. This includes electrical appliances such as microwaves, mobile phones, ovens and hairdryers.

The frequency of a field determines where it lies on the electromagnetic spectrum which starts at 0 Hz and goes all the way up to X-rays. 

The electric current transmitted through Ireland’s power lines (as well as most appliances) is alternating current (AC) and has a frequency of 50 Hz.

The electric and magnetic fields that form around the electric current have the same frequency (50 Hz). 

How do we characterise EMFs?

EMFs are characterised by their energy, frequency and wavelength. 

Frequency is the number of complete cycles that pass a given point per second. Its unit is the Hertz (Hz), which is defined as one cycle per second.

Wavelength (λ) is the distance between two points of a field that define a complete cycle. These three characteristics are related, so the higher the frequency of the field, the greater the energy transported and the shorter its wavelength.

Extremely low frequency 

The electromagnetic spectrum shows the range of frequencies that exist in our universe. Included in this spectrum is sunlight. 

The main frequency of electric and magnetic fields produced by power lines (and all devices supplied with electricity) is 50 Hz and are classed as ‘extremely low frequency’ (ELF). 

At ELF frequencies, the electric and magnetic fields are independent from each other. This contrasts to higher frequency electromagnetic fields (such as TV or radio) where the electric and magnetic fields are coupled together.

Non-ionising 

All of the fields on the electromagnetic spectrum fall into one of two categories: ionising or non-ionising. Fields with frequencies below ultraviolet are called non-ionising. 

The electromagnetic fields that are produced by Ireland’s electricity grid are non-ionising. 

Non-ionising fields are not strong enough to damage DNA.

Distance

Distance affects the intensity of an extremely low frequency electric or magnetic field significantly. The strength of the field depends on how close you are to the source, with that strength weakening greatly the farther away from the source.

Therefore, the magnetic field from a household appliance can be similar – or even stronger – than that from more distant power lines.

In 2024, EirGrid reviewed the electric and magnetic fields produced    by overhead lines and underground cables across Ireland’s transmission system. 

The purpose of this review was to ensure EirGrid’s best practices are consistent with international safety standards and to include the data for 400 kV cables. 

 For this study, EirGrid reviewed the current and voltage of every transmission circuit in the country every hour for a year. These averages were then used to calculate* the typical electric and magnetic fields near our lines. 

How we calculated the typical electric and magnetic fields

For this study, EirGrid reviewed the current and voltage of the overhead lines and cables across Ireland’s transmission system, every hour for a year. These values were then used to calculate the typical electric and magnetic fields.

The review involved a desktop study using standard installations. This means we used EirGrid’s uniform technical criteria, methods, processes, and practices to calculate the data.

It is common to use the ‘peak load’ value when calculating the levels electric and magnetic fields. Peak load is the highest level of load on a circuit which occurs 1% or less of the time. The peak load is at or below this value for 99% of the time. 

Using the peak load value often results in higher values of magnetic field than on any randomly selected day of the year as the current used is typically higher than a normal average load current.

Voltage determines the strength of the electric field. However, voltage may vary slightly throughout the day. 

To calculate the electric fields, we used the average voltage for 110 kV and 220 kV cables. The average voltage for the 400 kV system is less than 400 kV, therefore we used 400 kV to calculate the electric fields.

The minimum conductor height at midspan was selected because that gives the maximum field levels at any point between two poles or pylons where the conductors are closest to the ground.

About our safety standards

EirGrid operates the electricity grid to stringent safety recommendations set out by the EU as well national and international agencies. These recommendations are based on peer-reviewed medical and health studies, independent of any grid operator. 

The European Union recommendation (1999/519/EC) outlines a set of both ‘reference’ and ‘restriction’ levels for limiting overall exposure to electromagnetic fields and ensuring an increased level of protection.

This recommendation is based on ICNIRP guidelines (International Committee on Non-Ionising Radiation Protection) for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to 300 GHz) as the scientific basis.

The purpose of the reference levels is to prompt further investigation to ensure the restriction levels are not exceeded. 

Dimbylow (2005) has calculated that the field levels above 9.2 kV/m and 364 µT would not exceed EU or ICNIRP basic restrictions.

EirGrid designs the electricity network to make sure that public exposure to EMFs does not exceed EU restriction levels. 

What were the results?

Below are the highest levels for both electric and magnetic waves produced by Ireland’s electricity grid. 

We have also included the safety restriction levels we work to for reference.

Restriction level: The basic restriction levels in this table were based upon calculations by Dimbylow (2005) of the levels of electric and magnetic fields which would produce current densities within a model of the human body equal to the basic restriction limits specified in EU 1999/519/EC and ICNIRP (1998). These are just some of the many safety restrictions that EirGrid adheres to.

Highest level calculated: These tables show the highest values captured for both the electric and magnetic fields throughout the year. At closer distances the field levels are higher but still fall under the EU 1999/519/EC and ICNIRP (1998) restriction levels. 

How does distance impact the strength of electric and magnetic fields?

It’s important to know that the strength of both magnetic and electric fields drops significantly with distance (away from the source) which you can see in the diagram below.

What can I take from the study?

For both the magnetic fields and the electric fields, the levels recorded are below the restriction levels set by ICNIRP. 

To further demonstrate EirGrid’s stringent safety precautions, ICNIRP released a new set of restriction levels (in 2010) which allow higher limits than the 1998 levels. However, EirGrid continues to adhere to the stricter, 1998 levels. 

The EMFs created by the electricity grid are not high enough to be considered harmful to humans.  

The consensus from health and regulatory authorities is that extremely low frequency electromagnetic waves – like those from power lines – do not present a hazard to our health.

We obey all laws and meet all applicable health and safety standards. 

We work for the benefit and safety of every citizen in Ireland.

Electricity is a very safe way to provide energy to homes and businesses, and we use a lot of it in our daily lives. 

This requires EirGrid to transmit large amounts of electricity.

Alternating current (AC)

AC or ‘alternating current’ is the most common way to move electricity around an electricity grid. It is called alternating current because it continuously changes direction. 

Annual peak load

The highest level of load on a circuit which occurs 1% or less of the time. The peak load is at or below this value for 99% of the time. 

Conductor 

A type of material that allows the flow of electric current. 

Direct current (DC)

DC or ‘direct current’ is used for long distances and for undersea cables. Direct current flows in one direction only.

Electric current

Current refers to the number of electrons flowing between two points. It is measured in Amperes or more commonly, Amps. 

Electrified

Electrified means that an electric current is passing through.

Electric field 

An electric field is a region that forms around a charged particle or object. The strength of an electric field is determined by the voltage. Electric fields are measured in Volts per metre.

Electromagnetic spectrum

There are different types of electromagnetic fields. Those that are extremely low frequency (such as those produced by power lines) and those that are higher, such as sunlight. We can put these in order of frequency called the electromagnetic spectrum. 

Frequency 

The strength and direction of electromagnetic fields vary in a continuous cycle that repeats multiple times per second. The number of cycles per second is the frequency of the field. 

Hertz (Hz)

Hertz is the unit used to measure frequency. For example, the electric and magnetic fields from the electricity we use in our homes have a frequency of 50 Hz. 

ICNIRP 

International Commission for Non-Ionizing Radiation Protection (ICNIRP). This is an independent body, funded by public health authorities around the world. ICNIRP has investigated the safety of EMFs for decades and provides guidance on safe levels of exposure.

We design the electricity network to make sure that public exposure to EMFs complies with these guidelines.

Insulator

A substance or material that does not allow electrical current to flow easily. 

Magnetic field

Magnetic fields are produced by moving electric charges (also known as electric current). The strength of the magnetic field depends on the current. Magnetic fields are measure in Microteslas.

Microtesla (μT)

The unit of measurement used for magnetic fields (see above).

Overhead line

A transmission (or distribution) electricity line which is strung overhead between pylons or wooden polesets.

Polesets

Wooden poles used to hold up overhead lines. They are similar to pylons. 

Pylon

Pylons are tall structures used to support high-voltage overhead lines. They keep these lines high enough from the ground, so they don’t come into contact with passing vehicles, people or animals.

Underground cable

A transmission or distribution cable which is buried underground. These are most commonly used in urban, congested areas, or in environmentally sensitive areas.

Voltage

Voltage refers to the amount of electrical force or ‘push’ behind an electrical current, flowing between two points. It is measured in volts.