Living Under Or Near High Voltage Transmission Lines
Updated: Aug 21
Electrical Standards and Living Near High Voltage Transmission Lines in New Zealand
Electrical standards in New Zealand allow homes and other structures to be built very close to high voltage transmission lines. These lines run along the large pylons we see across the country. The NZ standards covering this subject focus on minimum safe distances between buildings and overhead electric line supports. However, there is absolutely zero consideration for the electromagnetic exposure on a home located under or near these lines.
Searching the internet reveals little official information on EMF influences from this infrastructure that may affect a home or other buildings. Therefore, it’s no surprise that a number of factors about living near these lines need to be understood. Some are electromagnetic, and some are not. Let’s go into detail.
Understanding Electromagnetic Fields
Magnetic Fields
The most significant factor is the alternating current (AC) magnetic field that extends out perpendicularly to the line, along its entire length. These magnetic fields vary with the amount of current in the line, which changes hour by hour, day by day, and season by season. As customer demand fluctuates, the current adjusts to meet this demand.
Imagine cold winter nights, where there is increased demand for electrical heating and lighting. This results in a stronger, more extensive magnetic field. Magnetic fields can penetrate most building materials. Hence, being close to the lines will lead to these fields flooding all areas of a house. The closer you are to the lines, the stronger the magnetic field.
In a typical home, away from external electrical or magnetic influences, the AC magnetic field generally measures around 10 to 20 nT (nanoTesla) over beds and lounge seating. This is considered low. However, in the Flatbush suburb of Auckland, multiple high voltage transmission lines stretch across streets and homes. In one garden we measured, which had a pylon just a few meters away, we recorded a staggering 5000 nT.
Inside that house, we found a range of 2500 to 3600 nT at ground level. These figures represent 125 to 180 times higher than a typical home.
Another concern is fluctuation. Living close to these lines places you in a magnetic bubble exposed to rapid changes in current, causing the magnetic field to shift up and down. In the aforementioned house, readings in the lounge could increase or decrease by 20% within seconds.
Safe Distances from Transmission Lines
How High is the Magnetic Field within a Home?
The strength of EMF decreases with distance from the source. At around 50 m from a standard 220 kV transmission line, you might encounter AC magnetic fields ranging from 200 to 500 nT. Several factors come into play, including the time of day, season, and the materials used both inside and outside the house. A two-story home would typically show higher levels.
Is Shielding Possible for Magnetic Fields?
In short, shielding from magnetic fields produced by transmission lines is practically impossible. The only method to effectively reduce exposure is to increase distance from the source. Using EMF shielding paint is not effective against magnetic fields. Nearby structures might alter, but not diminish the magnetic field. Tall trees do not provide any significant reduction in field strength.
Even buried power lines still emit strong magnetic fields above ground, as the earth does little to mitigate their effects.
Electrostatic Coupling and its Effects
Another effect to consider is Electrostatic Coupling, or Capacitive Coupling. This occurs when the electrostatic field surrounding the conductor jumps onto other conductive objects, effectively charging them. The charge size can vary based on the receiving object's material and its proximity to the ground.
Touching these charged surfaces while grounded can lead to electrical discharges. These charges can manifest in two forms: a quick spark, often termed a nuisance shock, or a prolonged shock from a steady-state current that has built up. This phenomenon can commonly occur around areas like farm gates or posts, and under urban lines, cladding materials, cars, and even fences may become charged.
Other Variants of Electrostatic Coupling
Moreover, inductive coupling is a secondary variant, where magnetic field interference induces an electric field in a conductive object, charging it. This results in potential electrical discharges.
Other Interesting Effects from Transmission Lines
Ozone Gas Production
The air surrounding the lines can ionize due to corona discharge, generating ozone gas and nitrogen oxides in the surrounding atmosphere.
Noise Generation
Under certain damp conditions, transmission lines may produce crackling noises from electricity ionizing the moist air around the wires. Wind vibrating through the lines and pylons may also add to the noise.
Radio Interference
You may notice radio interference while driving under transmission lines. These lines can disrupt AM radio signals, providing a clue that you are under high voltage lines.
Imbalance of Charged Particles
Your environment's balance concerning charged particles is also affected by these lines. Natural areas, such as forests or coastal regions, generally have a higher concentration of negative ions compared to urban areas dominated by positive ions. Living near transmission lines means exposure to a high concentration of positive ions.
The Role of Synthetic Materials
Synthetic materials found in carpets, curtains, and clothing increase static electricity in homes influenced by EMF from transmission lines. This makes the environment even more positively charged.
Conclusion: What You Need to Know
In summary, living near high voltage transmission lines affects your EMF footprint. The influence extends inside and outside your house, from the garden to the driveway, and even down the street. Awareness and understanding of these challenges can help residents make informed decisions about their living environment.
For further reading on electrical safe distances in New Zealand, please refer to the following documents:
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