FAQ on Powerlines & Cables

1. I’d like information concerning the parameters of a high voltage power line crossing my garden.

For this kind of inquiry, you can directly contact:

On the basis of your address, the line will be located and you will obtain its characteristics.

2. How far from underground cables should humans remain, so as not to take more risk than in their normal everyday life?

In the absence of Belgian standards, being mindful of European guidelines, there is no safe distance to respect insofar as all installations to which the public may be exposed follow the guidelines.

If you desire to stay under “0.4 microT” in maximal exposure conditions (e.g. 150 kV underground cable under maximal load), you have to move away from the cable by a distance of 25 m. However, in practice, underground cables, like overhead powerlines, are rarely operated at their maximal load. Hence, the mean current carried is always lower than the maximal current. Therefore, to stay under 0.4 microT of exposure, a separation distance of 25 meters (as mentionned above) should be maintained.

For other information, feel free to contact ACE team.

3. How far from overhead power line should humans remain, so as not to take more risk than in their normal everyday life?

Knowing that maximal magnetic field level under an overhead powerline (measured with respect to the legal safe distance) is always under 50 microT and that international guidelines advise not to exceed 100 microT, we can state there is no safe distance to respect with regard to magnetic fields.

However, if you desire to keep out of the range of influence of the line where the mean level goes up the epidemiological cut-off point of 0.4 microT, you must be aware of the load of the line, which varies greatly over time and from one line to another. On average, we can evaluate the half width (i.e. the distance from the axis of the line) at about 80 m for a 380 kV powerline, 40 m for 150 kV, and 15 m for 70 kV.

4. Our office is located under a high voltage power line. We’ve noticed that our computer screens are not stable. Is it possible to correct this?

It is well known that computer equipment (cathode-ray screens and non liquid crystal flat screens) is sensitive to magnetic fields (flickering of the screen) from 1 microT, which gives rise to inconveniences in particular environments. (Magnetic field sources are numerous: from power lines or underground cables, from our own wiring at home, or from the transformer of a nearby halogen lamp…)

We suggest that the family or company who use the computer in this environment change to flat screens to avoid flickering. It is worth noting that new equipment is usually less sensitive because the electronic components are better shielded. This problem is typical in banks and other environments that contain many electrical devices close to each other, and that may be on the floor with a UPS system (which sustains the flow of power when it is interrupted in an inopportune manner). All of these disturbances require specific arrangements.

We add that it is not because a computer is sensitive to electric and magnetic fields that these fields are harmful to human health.

5. Are there any data available on underground cables and the fields they generate?

Underground cable issues are similar to the ones for overhead power lines, given that, in both cases a current is carried at 50 Hz. However, the exposure is different: it is more significant directly above the cable, but declines rapidly with distance. You will find information about this characteristic of cables on the following page: Outdoor ELF exposure.

6. I own a land (with a 12 % slope) bordered at the top by a 20 kV powerline (height = 12 meters). My home will be located several meters below. Could you roughly indicate to me the maximal and mean values of an electromagnetic field that would expose me?

In your case, a magnetic (induction) field (B) is mainly measured (in microTesla). It depends on the load of the line and thus varies during the day.

Few measurements exist for this very low voltage. With the assumed data, you should be under 0.4 microTesla around 5 meters from an external phase of the line (which is located 12 meters high according to your information).

A measurement would allow us to ascertain the data. Your electric company should be able to do it. It also should give you with certainty maximal and mean loads on the line. The magnetic field is directly proportional to this value.

The weekly mean value is noticeably lower, but obviously depends of the proportion of the use of the line, which we are unable to ascertain. However, a reduction by a factor of 2 seems plausible. These rough estimates are close to the ambient fields created by your own house wiring.

7. Our garden is overhung by a 380kV line. We installed a trampoline with a safety net linked to metal tubes (total height 2.5 m). Could the electric field of the high voltage line be dangerous?

In the present state of our knowledge and our experience, here is what we can answer:

Any metallic object in the electric field of a high-voltage line is crossed by electric charges moving to the rhythm (ie the frequency) of the ambient field. These variable charges are likely to cause contact current when touching the object (similar to static discharge when touching a car in dry weather). This current is usually not dangerous (except for very large objects) but it can be unpleasant. Therefore it is recommended to ground the object, here the metallic supports of the trampoline, with a simple ground stake (about 1 m long is enough). For very large objects (such as a crane or a truck) when contact currents may exceed the value of 1 mA, this grounding is mandatory (in Belgium , see RGIE art 139).

8. I’ve noticed that my dairy cows drink less when they’re in the meadow where there’s a power line. They seem to be more nervous than usual. Is it caused by the power line?

Power lines are used to transport and distribute electricity. This creates magnetic and electric fields. When metal structures such as fences or troughs are close to a power line, parasitic currents can occur. In the case of a metal drinking trough insulated from the ground and located close to a power line, such parasitic currents can be generated by the effect of electrical induction, also known as capacitive coupling (see diagram). The electric field generated by the nearby power line induces a change in the distribution of electric charges on the surface of the metal trough. This creates a potential difference between the trough and the ground. As a result, when a cow comes into contact with the trough, a current flows through it. If this parasitic (because uncontrolled) current is strong enough, the cow can feel it and be disturbed. This could explain the problem described for the cows in the question above.

The solution to prevent parasitic currents due to capacitive coupling is to earth the trough. This can be done by planting a metal rod in the ground and connecting it to the trough with a conductive wire.

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