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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
    • Electric fields
    • Magnetic fields
    • Units for measuring EMFs
    • Measuring and calculating EMFs
      • EMF instruments and other commercial services
    • 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
      • Fields in different countries
      • How fields vary with time
    • Reducing your exposure
  • Known effects
    • Induced currents and fields
      • Numerical calculations of induced currents
      • Details of numerical calculations of induced currents and fields in the body
    • Effects of EMFs on equipment
    • EMFs and medical devices
      • Types of medical devices
      • Real-life experience of interference with Implanted Heart Devices
      • Laboratory Tests of Implanted Medical Devices
      • Consequences if interference does occur with an implanted heart device
      • Manufacturers of Implanted Heart Devices
      • Standards relating to pacemakers and other AIMDs
      • Interference with hearing aids and cochlear implants
    • Microshocks
      • Control of microshocks in the UK
      • Microshocks from bicycles
    • EMFs, agriculture and the environment
      • Bees and microshocks
      • Behaviour of large mammals in magnetic fields and near power lines
  • Evidence on health
    • Childhood leukaemia
      • Pooled analyses of childhood leukaemia and magnetic fields
      • Number of children affected
      • Childhood leukaemia and night-time exposure
      • Survival from childhood leukaemia
      • Childhood leukaemia and Downs
      • The “contact current” hypothesis
      • The causes of childhood leukaemia
    • Other health effects
      • Other childhood cancer
      • Breast cancer
      • Other adult cancers
      • Cardiovascular disorders
      • Neurodegenerative disorders
      • Epilepsy
      • Reproductive outcomes and disorders
      • Suicide and depression
      • Sleep disturbance
      • Asthma
      • Hypersensitivity
      • Effects of parental exposure to EMFs
    • Scientific review bodies
      • WHO
      • IARC
      • ICNIRP
      • SCENIHR
      • PHE (formerly HPA, formerly NRPB)
      • IET
      • NAS
      • NIEHS
      • California
      • Bioinitiative
    • Electric fields and ions
      • Electric fields and ions – a commentary on the suggestions
      • Electric fields and ions – NRPB comments
      • Skin cancer
      • Air pollution and childhood cancer
      • How many corona ions do power lines produce?
    • Comparing EMFs to other issues
      • EMFs compared to other issues: smoking
      • EMFs compared to other issues: passive smoking
      • EMFs compared to other issues: coffee
      • EMFs compared to other issues: shift work
      • EMFs compared to other issues: cholera
      • EMFs compared to other issues: BSE and variant CJD
      • Comparative risks
  • Research
    • Types of research
      • Research ethics
    • Epidemiology
      • Causation – what can epidemiology show and what can’t it?
      • Confounding
      • Clusters
    • Animal and laboratory experiments
      • Behaviour of large mammals in magnetic fields and near power lines
    • Mechanisms
      • Energy issues in mechanisms
      • Free radicals
      • Melatonin
      • Cryptochromes
      • Total field and AC field
    • Specific studies
      • UKCCS
      • CCRG
        • CCRG distance study
        • CCRG magnetic fields study
        • CCRG “corona ions” paper
        • CCRG follow-on paper
        • CCRG Underground cables paper
        • CCRG “wrap up” paper
        • CCRG Note on distance
        • Responses to the various CCRG papers
      • French Geocap study
      • California power lines study
      • Imperial College study
      • CEGB cohort
      • Transexpo
    • Ongoing research
      • UK electricity industry research
    • Non peer-reviewed science
    • Abstracts of papers
      • Childhood leukaemia abstracts
      • The CCRG (or “Draper”) study abstracts
      • The UKCCS abstracts
      • The CEGB cohort abstracts
      • Alzheimer’s disease abstracts
      • Breast cancer abstracts
      • Suicide and depression abstracts
      • Animal toxicology experiments abstracts
      • Numerical calculations of induced current – abstracts
      • Abstracts related to the Contact Current Hypothesis
      • Abstracts relating to research on fruit flies
      • Abstracts relating to animal behaviour: orientation in magnetic fields and sensing of power lines
  • Exposure limits
    • Limits in the UK
    • Limits in the USA
    • Limits in the EU
    • Limits in the rest of the world
    • Limits from specific organisations
      • ACGIH
      • NRPB 1993
      • ICNIRP 1998
      • EU 1999
      • ICES 2002
      • NRPB 2004
      • EU 2004
      • SBM 2008
      • ICNIRP 2010
      • EU 2013
      • The Control of Electromagnetic Fields at Work Regulations 2016
      • International Guidelines on Non-Ionising Radiation 2018
      • Comparison of exposure limits across frequencies
    • Indirect effects in exposure limits
    • Compliance with exposure limits
  • Policy
    • UK policy
      • Consent for power lines
      • Cross-Party Inquiry
      • Early Day Motions
      • Parliamentary Questions and Answers
      • UK Government and Parliament
    • European EMF policy
    • Power lines and property – UK
      • Corridors round power lines
    • Power lines and property – USA
    • Precaution
    • SAGE
      • SAGE First Interim Assessment
      • Government response to SAGE First Interim Assessment
      • SAGE Second Interim Assessment
      • Government response to SAGE Second Interim Assessment
    • Public Opinion on EMFs
      • Opinion polls conducted by Ipsos MORI on power lines and EMFs
    • Communications on EMFs
    • Litigation on EMFs
  • Finding out more
    • Links
    • Literature
    • Contacts
    • Finding out about other issues
      • Finding out more: Wayleaves and easements
      • Finding out more: Safety clearance distances
      • “Danger of death” notices
      • Finding out more: Audible noise
      • Finding out more: Power lines and satellite navigation
      • Finding out more: Radio and TV interference
  • Static fields
    • Sources of static fields
      • Fields from underground DC cables
      • Effects of static fields on compasses
    • Effects of static fields
    • Static fields – the expert view
      • Types of medical devices
      • WHO – static fields
      • IARC – static fields
      • ICNIRP – static fields
      • PHE – static fields
    • Static field limits
You are here: Home / Sources / Overhead power lines / Calculating and measuring fields from power lines / Geometries of power lines

Geometries of power lines

To calculate the field from a power line, you need to know the geometry of the conductors.  On this page we provide the necessary details for some standard UK power lines.  If you use these dimensions, you should be able to get the same results for fields as we present on this site. (see also a tutorial on how to calculate the magnetic field from a three-phase circuit.)

We give details at present for three specific power lines:

thumbnail photo of L6 pylonL6, the largest design in normal use for 400 kV and 275 kV lines

thumbnail photo of transmission pylonL2, a smaller design used for 400 kV and 275 kV lines

thumbnail of L12 L12, a more modern design used for most new construction at 400 kV and 275 kV.

Most of the calculations on this web site are for the L12 design.

The following figure defines the dimensions.  For an explanation of the different parts of a power line see here.

 diagram defining tower dimensions

 

The dimensions

 

dimensioncode on diagramtower typeunits
conductordirectionL6L2L12
earth wirehorizontal from tower centre-000m
vertical above bottom phaseey29.5121.2627.668m
top phasehorizontal from tower centretx6.985.4866.30m
vertical above bottom phasety19.5415.62118.00m
middle phasehorizontal from tower centremx10.44655.7159.12m
vertical above bottom phasemy9.007.8498.70m
bottom phasehorizontal from tower centrebx8.446.0967.12m
vertical above bottom phase-000m
conductor bundlenumber of conductors 422 
spacing 305305500mm
diameter 28.6228.6237.26mm

 

Commentary

Accuracy

Values are entered in this table to the same resolution as in the underlying data we use in National Grid for our own calculations.  In some cases these will have been converted from imperial units and the amount of rounding may be variable.

Relative positions of conductors

The table gives the dimensions relative to the centre of the tower at the level of the bottom phase conductors.  All normal UK towers are symmetrical about the centre line. Dimensions are to the "bottom centre" of the conductor bundle - the horiziontal midpoint at the level of the lowest conductor - not to the end of the crossarm - on tension towers with a horizontal insulator it's the same thing, but on suspension towers the conductor hangs from a vertical insulator below the end of the crossarm.

Conductor bundle

The table gives the commonest conductor bundles used on these towers.  But many other variants are used as well, with larger spacings or different size conductors.  Earth wires are sometimes smaller than the phase conductors.  Bundles of 2 conductors ("twin") are horizontal, bundles of 4 ("quad") form a square.

The conductor bundle has no effect on the magnetic field, which simply depends on where the current flows, not what it flows in.  But it does affect the electric field.  More on the effect of the conductor bundle here.

Ground clearance

The positions of the conductors relative to each other stays the same throughout the length of the line, but the clearance above ground varies from span to span and along each span as the conductors sag.  The minimum clearance to ground for 400 kV is 7.6 m but is rarely found in practice.  When we want a typical clearance we often use 12 m.  If there are buildings nearby the clearance is likely to be even higher, and the clearance is clearly higher at the towers than in the middle of a span. More on the effect of ground clearance on the field.

Height above ground

We usually calculate fields at 1 m above ground level for reasons explained here.

Exceptions

Several different manufacturers built L6 lines and the dimensions varied subtly, and there is a variant of the L2 where the middle crossarms are wider. 

Also, where lines go round corners, the towers are designed to keep the horizontal spacing of the two circuits the same, but nonetheless the spacing can vary slightly at corners.

Questions?

If you have questions about these data, or you'd like us to provide dimensions for a further different design, please contact us.

See also:

  • a tutorial on how to calculate the fields from a power line

Latest news

  • 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
  • UK media interest in the causes of childhood leukaemia May 22, 2018
older news

Contact Us

To contact the electricity industry’s EMF Unit Public Information Line (UK only):
telephone 0845 7023270 or email EMFHelpLine@nationalgrid.com.

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

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Specific questions

  • Affected by a new power line or substation?
  • Building or developing near a power line or substation?
  • Terminology – an introduction
  • Microshocks
  • Pacemakers and other medical devices
  • EMF policy in the UK
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Navigation
  • What are EMFs
    • Terminology – an introduction
    • Electric fields
    • Magnetic fields
    • Units for measuring EMFs
    • Measuring and calculating EMFs
      • EMF instruments and other commercial services
    • 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
      • Fields in different countries
      • How fields vary with time
    • Reducing your exposure
  • Known effects
    • Induced currents and fields
      • Numerical calculations of induced currents
      • Details of numerical calculations of induced currents and fields in the body
    • Effects of EMFs on equipment
    • EMFs and medical devices
      • Types of medical devices
      • Real-life experience of interference with Implanted Heart Devices
      • Laboratory Tests of Implanted Medical Devices
      • Consequences if interference does occur with an implanted heart device
      • Manufacturers of Implanted Heart Devices
      • Standards relating to pacemakers and other AIMDs
      • Interference with hearing aids and cochlear implants
    • Microshocks
      • Control of microshocks in the UK
      • Microshocks from bicycles
    • EMFs, agriculture and the environment
      • Bees and microshocks
      • Behaviour of large mammals in magnetic fields and near power lines
  • Evidence on health
    • Childhood leukaemia
      • Pooled analyses of childhood leukaemia and magnetic fields
      • Number of children affected
      • Childhood leukaemia and night-time exposure
      • Survival from childhood leukaemia
      • Childhood leukaemia and Downs
      • The “contact current” hypothesis
      • The causes of childhood leukaemia
    • Other health effects
      • Other childhood cancer
      • Breast cancer
      • Other adult cancers
      • Cardiovascular disorders
      • Neurodegenerative disorders
      • Epilepsy
      • Reproductive outcomes and disorders
      • Suicide and depression
      • Sleep disturbance
      • Asthma
      • Hypersensitivity
      • Effects of parental exposure to EMFs
    • Scientific review bodies
      • WHO
      • IARC
      • ICNIRP
      • SCENIHR
      • PHE (formerly HPA, formerly NRPB)
      • IET
      • NAS
      • NIEHS
      • California
      • Bioinitiative
    • Electric fields and ions
      • Electric fields and ions – a commentary on the suggestions
      • Electric fields and ions – NRPB comments
      • Skin cancer
      • Air pollution and childhood cancer
      • How many corona ions do power lines produce?
    • Comparing EMFs to other issues
      • EMFs compared to other issues: smoking
      • EMFs compared to other issues: passive smoking
      • EMFs compared to other issues: coffee
      • EMFs compared to other issues: shift work
      • EMFs compared to other issues: cholera
      • EMFs compared to other issues: BSE and variant CJD
      • Comparative risks
  • Research
    • Types of research
      • Research ethics
    • Epidemiology
      • Causation – what can epidemiology show and what can’t it?
      • Confounding
      • Clusters
    • Animal and laboratory experiments
      • Behaviour of large mammals in magnetic fields and near power lines
    • Mechanisms
      • Energy issues in mechanisms
      • Free radicals
      • Melatonin
      • Cryptochromes
      • Total field and AC field
    • Specific studies
      • UKCCS
      • CCRG
        • CCRG distance study
        • CCRG magnetic fields study
        • CCRG “corona ions” paper
        • CCRG follow-on paper
        • CCRG Underground cables paper
        • CCRG “wrap up” paper
        • CCRG Note on distance
        • Responses to the various CCRG papers
      • French Geocap study
      • California power lines study
      • Imperial College study
      • CEGB cohort
      • Transexpo
    • Ongoing research
      • UK electricity industry research
    • Non peer-reviewed science
    • Abstracts of papers
      • Childhood leukaemia abstracts
      • The CCRG (or “Draper”) study abstracts
      • The UKCCS abstracts
      • The CEGB cohort abstracts
      • Alzheimer’s disease abstracts
      • Breast cancer abstracts
      • Suicide and depression abstracts
      • Animal toxicology experiments abstracts
      • Numerical calculations of induced current – abstracts
      • Abstracts related to the Contact Current Hypothesis
      • Abstracts relating to research on fruit flies
      • Abstracts relating to animal behaviour: orientation in magnetic fields and sensing of power lines
  • Exposure limits
    • Limits in the UK
    • Limits in the USA
    • Limits in the EU
    • Limits in the rest of the world
    • Limits from specific organisations
      • ACGIH
      • NRPB 1993
      • ICNIRP 1998
      • EU 1999
      • ICES 2002
      • NRPB 2004
      • EU 2004
      • SBM 2008
      • ICNIRP 2010
      • EU 2013
      • The Control of Electromagnetic Fields at Work Regulations 2016
      • International Guidelines on Non-Ionising Radiation 2018
      • Comparison of exposure limits across frequencies
    • Indirect effects in exposure limits
    • Compliance with exposure limits
  • Policy
    • UK policy
      • Consent for power lines
      • Cross-Party Inquiry
      • Early Day Motions
      • Parliamentary Questions and Answers
      • UK Government and Parliament
    • European EMF policy
    • Power lines and property – UK
      • Corridors round power lines
    • Power lines and property – USA
    • Precaution
    • SAGE
      • SAGE First Interim Assessment
      • Government response to SAGE First Interim Assessment
      • SAGE Second Interim Assessment
      • Government response to SAGE Second Interim Assessment
    • Public Opinion on EMFs
      • Opinion polls conducted by Ipsos MORI on power lines and EMFs
    • Communications on EMFs
    • Litigation on EMFs
  • Finding out more
    • Links
    • Literature
    • Contacts
    • Finding out about other issues
      • Finding out more: Wayleaves and easements
      • Finding out more: Safety clearance distances
      • “Danger of death” notices
      • Finding out more: Audible noise
      • Finding out more: Power lines and satellite navigation
      • Finding out more: Radio and TV interference
  • Static fields
    • Sources of static fields
      • Fields from underground DC cables
      • Effects of static fields on compasses
    • Effects of static fields
    • Static fields – the expert view
      • Types of medical devices
      • WHO – static fields
      • IARC – static fields
      • ICNIRP – static fields
      • PHE – static fields
    • Static field limits