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Electric and magnetic fields and health

index/glossary | EMFs At A Glance | EMF The Facts (pdf)
  • What are EMFs
    • Terminology – an introduction
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      • “EMF Commercial”
    • Adding fields together
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    • Screening EMFs
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    • Overhead power lines
      • Fields from specific power lines
        • 400 kV
        • 400 kV – specific cases
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        • 132 kV
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        • 11 kV
        • 400 V/230 V
        • Replacing a 132 kV line with a 400 kV line
      • Summaries of fields from all power lines
      • Factors affecting the field from a power line
        • Voltage
        • Current
        • Clearance
        • Height above ground
        • Conductor bundle
        • Phasing
        • Balance between circuits
        • Balance within circuit
        • Ground resistivity
        • Two parallel lines
      • Calculating and measuring fields from power lines
        • Geometries of power lines
        • Raw data
        • On-line calculator
      • Fields from power lines – more detail on the physics
        • Field lines from a power line
        • The direction of the field from a power line
        • Power law variations in the field from a power line
      • Statistics of power line fields
    • Underground power cables
      • Different types of underground cable
      • Fields from cables in tunnels
      • Gas Insulated Lines (GIL)
      • Underground cables with multiple conductors
      • Effect of height on fields from underground cables
      • Screening fields from underground cables
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    • Field levels and exposures
      • Personal exposure
      • Other factors that vary with magnetic fields
      • Fields greater than 0.2 or 0.4 µT
    • Screening EMFs
      • Screening fields from underground cables
      • EMF Reduction Devices
  • Known effects
    • Induced currents and fields
    • Microshocks
      • Control of microshocks in the UK
      • Microshocks from bicycles
      • Bees and microshocks
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    • Childhood leukaemia
      • Survival from childhood leukaemia
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      • Childhood leukaemia and night-time exposure
      • The “contact current” hypothesis
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      • IARC
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      • ICNIRP 1998
      • ICNIRP 2010
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      • Power lines and property – UK
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      • SAGE First Interim Assessment
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        • SAGE Second Interim Assessment – the full list of recommendations
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    • Static fields – the expert view
You are here: Home / Sources / Overhead power lines / Factors affecting the field from a power line / Two parallel lines

Two parallel lines

Most of the calculations on this website of fields from overhead lines in general, from specific overhead lines, or demonstrating the effect of particular factors, are for a single overhead line.  What happens if there are two lines close to each other? 

General principles

The general principles of what happens are shown in this graph:

 graph showing effect of parallel lines

The blue curve shows the magnetic field from a single line.  It's calculated for the same standard conditions as many of the other graphs - an L12 line, with 500 A in each circuit, transposed phasing, and 12 m ground clearance.

The red curve shows the field when a second identical line is placed 50 m away from the first line.

Each line produces its own elevated field underneath it, falling off to the sides.  The maximum field under one line is affected by the other, but only by a few percent, as can be seen from the difference between the red and blue curves at the "0 m" point.  Close to a line, it is that line which dominates the field, and the other line has only a small effect.  In this particular case, the presence of the second line actually reduces the field under the first line slightly.  That is a fluke of the specific conditions, in particular the relative loads and the relative phasing, which determine the direction of the two fields and whether they add or subtract.  The field could go up or down depending on the specific conditions, but it will only be a slight effect either way.  And in a real situation, the loads in the two lines would be constantly varying anyway.  See more on adding fields together.

To the sides of the lines, where the field is lower, again, it is the closer line which dominates the field, with the farther line making a difference, but not a big one.  Only if you are half way between the lines is the combined field markedly greater than you would get from the closer line only.

Particular application: 132 kV + 400 kV lines

One situation is where there is an existing 132 kV line, and there is a proposal to build a 400 kV line alongside.  This graph shows what happens:

graph showing parallel lines 132 and 400 kV

The blue lines show the magnetic fields from each line separately - the left hand one the 132 kV line at 0 m, the right hand one the 400 kV line at 50 m.  The red line shows the combined field.  Again, the details of where the two fields reinforce each other and where they cancel each other depend on the relative phasing and loads in the line.

(In this example, the 400 kV lines has 500 A currents, 12 m ground clearance, and transposed phasing.  The 132 kV line has 130 A currents, 10 m grouind clearance, and untransposed phasing.)

 

We stress that these graphs illustrate the general principles only.  The details of what happens to the field are highly dependent on the specifics of each situation. 

See also:

  • The fields from the different voltages of power lines
  • These pages deal with the size of the field - see also the direction of the field
  • an alternative to parallel lines is when one line replaces another - see a specific comparison of replacing a 132 with a 400 kV line

Latest news

  • New publication on cancer incidence from the UK electricity industry Cohort Study August 27, 2019
  • How has the reported risk for childhood leukaemia changed over time? February 11, 2019
  • Media stories about microshocks in children’s playground September 10, 2018
  • New studies on leukaemia and distance from power lines June 1, 2018
older news

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To contact the electricity industry’s EMF Unit Public Information Line (UK only):
telephone 0845 7023270 or email [email protected].

See Contact us for more contact details including our privacy policy.

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Navigation
  • What are EMFs
    • Terminology – an introduction
    • Electric fields
    • Magnetic fields
    • Units for measuring EMFs
    • Measuring and calculating EMFs
      • “EMF Commercial”
    • Adding fields together
    • Radiofrequencies
    • Screening EMFs
  • Sources
    • Overhead power lines
      • Fields from specific power lines
        • 400 kV
        • 400 kV – specific cases
        • 275 kV
        • 132 kV
        • 66 kV
        • 33 kV
        • 11 kV
        • 400 V/230 V
        • Replacing a 132 kV line with a 400 kV line
      • Summaries of fields from all power lines
      • Factors affecting the field from a power line
        • Voltage
        • Current
        • Clearance
        • Height above ground
        • Conductor bundle
        • Phasing
        • Balance between circuits
        • Balance within circuit
        • Ground resistivity
        • Two parallel lines
      • Calculating and measuring fields from power lines
        • Geometries of power lines
        • Raw data
        • On-line calculator
      • Fields from power lines – more detail on the physics
        • Field lines from a power line
        • The direction of the field from a power line
        • Power law variations in the field from a power line
      • Statistics of power line fields
    • Underground power cables
      • Different types of underground cable
      • Fields from cables in tunnels
      • Gas Insulated Lines (GIL)
      • Underground cables with multiple conductors
      • Effect of height on fields from underground cables
      • Screening fields from underground cables
    • Low-voltage distribution
      • UK distribution wiring
      • USA distribution wiring
    • House wiring
    • Substations
      • National Grid substations
        • Static Var Compensators
      • Sealing-end compounds
      • Distribution substations
      • Final distribution substations
        • Indoor substations
    • Transport
      • EMFs from electric trains (UK)
      • EMFs from cars
    • Appliances
    • Electricity meters
      • Smart meters
      • Traditional meters
    • Occupational exposures
      • Live-line work
      • Static Var Compensators
      • Occupational exposures on pylons
    • Field levels and exposures
      • Personal exposure
      • Other factors that vary with magnetic fields
      • Fields greater than 0.2 or 0.4 µT
    • Screening EMFs
      • Screening fields from underground cables
      • EMF Reduction Devices
  • Known effects
    • Induced currents and fields
    • Microshocks
      • Control of microshocks in the UK
      • Microshocks from bicycles
      • Bees and microshocks
    • EMFs and medical devices
      • Standards relating to pacemakers and other AIMDs
    • Effects of EMFs on equipment
  • Research
    • Types of research
    • Epidemiology
    • Animal and laboratory experiments
    • Mechanisms
    • Specific studies
      • UKCCS
      • CCRG
      • French Geocap study
      • CEGB cohort
      • Imperial College study
  • Current evidence on health
    • Childhood leukaemia
      • Survival from childhood leukaemia
      • Childhood leukaemia and Downs
      • Childhood leukaemia and night-time exposure
      • The “contact current” hypothesis
    • Other health effects
    • Scientific review bodies
      • WHO
      • IARC
    • Electric fields and ions
    • Comparing EMFs to other issues
  • Exposure limits for people
    • Limits in the UK
    • Limits in the EU
    • Limits in the USA
    • Limits in the rest of the world
    • Limits from specific organisations
      • ICNIRP 1998
      • ICNIRP 2010
      • NRPB 1993
      • NRPB 2004
      • EU 2004
      • EU 2013
  • Policy
    • UK policy
      • Power lines and property – UK
    • Compliance with exposure limits
    • European EMF policy
    • Precaution
    • SAGE
      • SAGE First Interim Assessment
        • Government response to SAGE First Interim Assessment
      • SAGE Second Interim Assessment
        • Government response to SAGE Second Interim Assessment
        • SAGE Second Interim Assessment – the full list of recommendations
  • Finding out more
    • EMF measurement and commercial services
    • Links
    • Literature
    • Contact us
  • Static fields
    • Static fields – the expert view