Living Under Or Near High Voltage Transmission Lines
- Andy Hooley
- Jun 11
- 5 min read
Electrical standards in New Zealand allows homes and other structures to be built very close to high voltage transmission lines. These are the lines spanning across the large pylons we see running up and down the country. The NZ standards covering this subject are centred around minimum safe distances between buildings and overhead electric line supports. There is absolutely zero consideration towards the electromagnetic exposure on a home located under or near these lines. Searching the internet, you will find there is little official information available on EMF influences from this infrastructure that may affect a home or other building. It would therefore come as no surprise that there are indeed a number of factors to understand about living near these lines that can infect living spaces. Some are electromagnetic, some are not. Let’s get into the detail
Magnetic Fields
First of all, the biggest factor by far is the AC magnetic field which extends out perpendicular to the line, along its full length. These mag fields expand and contract in a relationship with the amount of current in the line and this can vary hour to hour, day to day and season by season. As customer demand increases or decreases, the current changes to meet this demand. You can imagine on cold winter nights there is more demand for electrical heating, lighting and other appliances. This equates to a stronger and further reaching mag field. Magnetic fields penetrate most building materials and so being close to lines, means that the mag field will flood all areas of a house. The closer you are to the lines, the higher the mag field. Other materials in the house that are conductive like corrugated iron roofing or cladding will also add to the spread of the magnetic field.
In thinking about distances in and out of the field, the general rule of thumb, in the Building Biology world is to take the kiloVolt (kV) rating of the line and convert to meters. For example, a typical 220kV line would be 220 meters, which is your safe distance outside of the magnetic field. In reality, the mag field would drop off to normal background (street) levels after about 120m or so. So there is a good margin there to cover the seasonal variance.
A typical home with no outside electrical or magnetic influences or wiring errors will generally have an AC magnetic field around 10 to 20nT (nanoTesla) over beds and lounge seating. This is low. In the Flatbush suburb in Auckland, there are multiple HV transmission lines stretching across the streets and over homes. In the garden of a house we measured here which had a pylon a handful of meters over the fence we recorded around 5000nT. Inside the house we recorded a range of 2500 to 3600nT at ground level. These numbers increased at a 2m height by another 20%. Magnetic field recordings inside the house like this are 125 to 180 times greater than a typical home.
Another factor to consider here is fluctuation. Being this close to lines means you are in the magnetic bubble and will be exposed to rapid changes in current which makes the magnetic field move up and down. The house mentioned above may see readings in the lounge increase or decrease 20% in seconds.
How high is the magnetic field in a house 50m from a normal 220kV transmission line?
As with any EMF that radiates from a source, its strength decreases with distance. At around 50m you may find AC magnetic fields ranging from 200 to 500nT. But consider other factors like time of the day, season, materials of the house inside and outside etc. A two storey home would be higher.
Is there any way to shield the magnetic field from these transmission lines?
In short no. From line sources like transmission lines, there is no practical solution to shield from magnetic fields unless you can build a Chernobyl size sarcophagus over the top of your house. EMF shielding paint is not designed for mag fields. Other structures in the vicinity may reduce or even increase the mag field. Tall trees would also do nothing to reduce the field strength. When there is no physical way to shield or to disable the source of the EMF, what we are left with is distance. Moving away from the source is the only way to reduce exposure. Even buried powerlines and transmission lines have a strong magnetic field above ground as the earth does not reduce the field strength.
Electrostatic Activity
There is another effect taking place which is called Electrostatic Coupling or Capacitive Coupling. This is caused by the electrostatic field that surrounds the conductor (lines) effectively jump conducts on to other conductive objects. Basically this means that any conductive surface in the vicinity can become charged. The size of the charge depends on the receiving objects material, the size and its isolation position with respect to ground. Touching such surfaces while touching ground may result in an electrical discharge. This charge can appear in two ways with either a spark (also called a nuisance shock) which will be instant, or a steady state current that has the ability to build up into a sufficient charged state which can give a prolonged shock. I’ve seen these in effect around farm gates and posts. Under these lines in urban areas, cladding materials of homes, cars, fences, Waratahs, and other conductive surfaces even ones buried underground have the potential to become charged.
A second variant of this electrostatic coupling is Inductive Coupling. In short, the magnetic field interference induces an electric field in a conductive object charging it and releasing it with the two above mentioned pathways.
Other Interesting Effects
Ozone Gas
The air around the lines can become ionised from corona discharge. This can produce ozone gas and oxides of nitrogen in the air around the lines.
Noise
Transmission lines can producer noise in different circumstances. In some damp weather conditions they can create crackling sounds due to the electricity ionising the moist air around the wires. There can also be noise from wind vibration through the lines and pylon.
Radio Interference
Most likely your AM radio will give you a good clue that you are under transmission lines. While the lines are designed to not cause issues with some frequency modulations like digital TV or FM radio, they will fuzz out your AM radio listening. Turn a car radio to AM the next time you drive under transmission lines.
Balance of Charged Particles
The balance of nature with respect to environmental charged particles between positive ions and negative ions is influenced by your surroundings. In a forest, coastal region or waterfall there is a high concentration of negative ions vs lower numbers of positive ions. These are balanced areas and as we all know healthy places to be around. Move in to a city, commercial area or other location with infrastructure and there is an imbalance of much high positive ions over lower negative ions. This is the same under transmission lines. There is a constant very high concentration of positive ions.
Synthetic Materials
It should come as no surprise that synthetic materials in carpets, curtains, bedsheets and clothing can create static electricity. In a home that is influenced by EMF from transmission lines, the electrostatic activity is higher in these materials. This adds to a higher positively charged environment.
Sum this up for me
In summary and very basically, living under high voltage transmission lines, affects and influences your EMF footprint. Inside the house, outside in the garden, the driveway and follows you a world record javelin throw down the road. Avoid.
The standard NZECP 34:2001 covers the safe electrical distances from infrastructure.
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