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Electric and magnetic fields and health

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  • What are EMFs
    • Terminology – an introduction
    • Electric fields
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    • 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 / Fields from specific power lines / 400 kV

400 kV

thumbnail photo of L6 pylon    thumbnail photo of transmission pylon
400 kV is the highest voltage in use in the UK.

All 400 kV lines are compliant with the public exposure limits, though this needs demonstrating on a case-by-case basis - see more details

Magnetic field

The maximum field is produced by the largest design of line – the L6 – when the ground clearance is the minimum allowed – 7.6 m – and the loads are the highest allowed – 4.7 kA in each circuit.  The field also depends on the phasing. Transposed (T) is higher close to the line and Untransposed (U) is higher away from the line.  This graph shows both .

graph of maximum field 400 kV

The maximum fields come from a design of line called the L6.  This was used extensively when the transmission system was built in the 1960s and 70s.  More recently, new 400 kV lines have often been built using a slightly smaller design of line, the L12.  This produces smaller fields than the L6.  We give here graphs showing the maximum fields from an L12 line at 400 kV.

graph showing maximum field 400 kV L12

see also an example of unusually heavily loaded lines.

Typical fields are lower than the maximum field because the clearance is usually higher and the loads are usually lower.  Also, many lines are a slightly smaller design – the L2.  Both L6 and L2 are shown on the following graph.  The phasing here is T as this is more common. It is rare for the two circuits to carry exactly the same load.  That is why the magnetic field shown here is not symmetrical.

graph of typical field 400 kV

The data

This table gives some actual field values for the same conditions.

magnetic field in µT at distance from centreline

maximum under line 10 m 25 m 50 m 100 m
400 kV largest lines L6
quad bundles
0.305 m
zebra
maximum clearance 7.6 m
phasing U
load 4.7/4.7 kA
108.422 95.780 38.422 11.697 3.096
typical clearance 13 m
phasing T
load 0.4/0.6 kA
5.783 5.247 2.194 0.578 0.119
smaller lines L2
twin bundles
0.305 m
zebra
maximum clearance 7.6 m
phasing U
load 2.4/2.4 kA
54.142 46.300 16.283 4.865 1.278
typical clearance 13 m
phasing T
load 0.4/0.6 kA
4.971 4.158 1.557 0.400 0.084
typical design used for new lines L12
twin bundles
0.5 m
araucaria
maximum clearance 7.6 m
phasing U
load 3.5/3.5 kA
81.942 72.818 22.103 8.148 2.145
typical clearance 13 m
phasing T
load 0.4/0.6 kA
5.604 4.938 1.979 0.514 0.106

Note:

1. All fields calculated at 1 m above ground level.

2. All fields are given to the same resolution for simplicity of presentation (1 nT = 0.001 µT) but are not accurate to better than a few percent.

3. Calculations ignore zero-sequence current.  This means values at larger distances are probably underestimates, but this is unlikely to amount to more than a few percent and less closer to the line.

4. The “maximum field under the line” is the largest field, which is not necessarily on the route centreline; it is often under one of the conductor bundles.

5. Calculated fields agree well with measured fields. 

Electric field

The maximum field is produced by the largest design of line – the L6 – when the ground clearance is the minimum allowed – 7.6 m. The field also depends on the phasing. Untransposed (U) is generally higher and is shown here. (see also the maximum field produced by the slightly smaller L12 line.)

graph of maximum field from 400 kV

The maximum fields come from a design of line called the L6.  This was used extensively when the transmission system was built in the 1960s and 70s.  More recently, new 400 kV lines have often been built using a slightly smaller design of line, the L12.  This produces smaller fields than the L6.  We give here a graph showing the maximum fields from an L12 line at 400 kV.

graph of maximum field 400 kV L12

Typical fields are lower than the maximum field because the clearance is usually higher. Also, many lines are a slightly smaller design – the L2.  Both L6 and L2 are shown on the following graph.  The phasing here is transposed (T) as this is more common.

graph of typical field from 400 kV

This table gives some actual field values for the same conditions.

electric field in V m-1 at distance from centreline

maximum under line 10 m 25 m 50 m 100 m
400 kV largest lines L6
quad bundles
0.305 m
zebra
maximum clearance 7.6 m
phasing U
11400 10130 774 446 156
typical clearance 13 m
phasing T
4244 4206 962 106 32
smaller lines L2
twin bundles
0.305 m
zebra
maximum clearance 7.6 m
phasing U
9897 6618 283 357 118
typical clearance 13 m
phasing T
3128 2964 469 56 27
typical design used for new lines L12
twin bundles
0.5 m
araucaria
maximum clearance 7.6 m
phasing U
10642 8410 669 404 136
clearance 7.6 m
phasing T
9384 7933 737 151 30
typical clearance 13 m
phasing T
3704 3595 732 98 26

Note:

1. All fields calculated at 1 m above ground level.

2. All electric fields are calculated for the nominal voltage.  In practice, voltages (and hence fields) may rise by a few percent.

3. All electric fields calculated here are unperturbed values.

4. All fields are given to the same resolution for simplicity of presentation (1 V/m) but are not accurate to better than a few percent.

5. Calculations ignore zero-sequence voltages.  This means values at larger distances are probably underestimates, but this is unlikely to amount to more than a few percent and less closer to the line.

6. The “maximum field under the line” is the largest field, which is not necessarily on the route centreline; it is often under one of the conductor bundles.

7. In efforts to reduce aerodynamic problems, a small number of 400 kV lines with quad bundles have had expanded bundles fitted, e.g. 500 mm horizontally.  This produces slightly higher electric fields but is not included in these tables.

Underground cables

Three main types of underground cable are used.

  • Trough: the separate cores of the cable are in a concrete trough, typically only 0.3 m or less below ground, but also only 0.15 m apart
  • Direct buried: the separate cores of the cable are laid directly in the ground, typically 1 m below ground and 0.3-0.5 m apart
  • Tunnel: the cable is carried in a tunnel typically 20 m below ground
     

See photos and diagrams of these different types of cable and also details of a newer technology, Gas Insulated Lines, not yet used in the UK.

Cables in tunnels are so far below ground that the fields at ground level are usually below background levels.  Maximum fields from typical examples of the other two types are shown in this graph.  This is for 1 m above ground.  At this height, the direct-buried cable produces the higher field.  Closer to the ground, the trough produces the higher field. Fields from underground cables are very sensitive to the height above ground. more detail

graph of maximum field 400 kV underground

Typical fields are lower than the maximum field because the loads are usually lower.  Typical fields are shown in the following graph.

graph of typical field 400 kV underground

Underground cables do not produce any external electric fields.

Obtaining a higher rating with an underground cable can involve installing multiple groups of conductors - see how this affects the magnetic field.

This table gives some actual field values for the same conditions.

 magnetic field in µT at distance from centreline
0 m5 m10 m20 m
400 kVtrough0.13 m spacing 0.3 m depthmaximum83.307.011.820.46
typical20.831.750.460.12
direct buried0.5 m spacing 0.9 m depthmaximum96.1713.053.580.92
typical24.063.260.900.23

Notes

1. All fields calculated at 1 m above ground level

2. All fields are given to the same resolution for simplicity of presentation (0.01 µT = 10 nT) but are not accurate to better than a few percent.

3. Calculations ignore zero-sequence current.  This means values at larger distances are probably underestimates, but this is unlikely to amount to more than a few percent.

4. Cable designs are not standardised to the same extent as overhead lines and the examples given here are representative.

5. The trough calculation is for a double circuit and the direct buried is for a single circuit, but in practice there may be other nearby circuits which affect the field.

 

Alternative designs of lines

This page deals with the great majority of lines so far, which are carried on lattice steel pylons.  On a separate page, we give details of some special situations or new designs:

  • the T-pylon
  • low-height pylons
  • single-circuit lines
  • unusually heavily loaded lines

Other voltages

  • 400 kV
  • 400kV special cases
  • 275 kV
  • 132 kV
  • 66 kV
  • 33 kV
  • 11 kV
  • 400 V/230 V

See also:

average fields calculated from one year of actual load data

These graphs are for lines carrying typical loads, but some lines carry larger loads - see here for an example

National Grid is consulting on an alternative pylon called the "T-pylon" - see here for the fields it produces

a specific comparison of replacing a 132 with a 400 kV 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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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