{
  "id": "emitters:transmission-line",
  "collection": "emitters",
  "slug": "high-voltage-transmission-line",
  "name": "High-voltage transmission line",
  "summary": "Fields directly beneath a loaded transmission line reach tens of milligauss and fall off roughly with distance for a balanced three-phase circuit, reaching background at 30–60 m for typical loadings.",
  "status": "verified",
  "lastVerified": "2026-08-12",
  "data": {
    "aliases": [
      "power line",
      "overhead line",
      "pylon",
      "HV line"
    ],
    "category": "elf-magnetic",
    "environment": [
      "outdoor",
      "home"
    ],
    "bands": [
      {
        "label": "Power frequency",
        "minHz": 50,
        "maxHz": 60
      }
    ],
    "dutyCycle": "Continuous, proportional to circuit loading, which varies through the day and season.",
    "distanceProfile": [
      {
        "meters": 0,
        "value": {
          "quantity": "magnetic-flux-density",
          "unit": "mG",
          "value": 10,
          "max": 100,
          "basis": "measured",
          "note": "Directly beneath the conductors at mid-span, dependent on current, conductor height and phase arrangement.",
          "sourceIds": [
            "niehs-emf"
          ]
        }
      },
      {
        "meters": 30,
        "value": {
          "quantity": "magnetic-flux-density",
          "unit": "mG",
          "value": 1,
          "max": 10,
          "basis": "measured",
          "note": "Typical range at 30 m from the centreline.",
          "sourceIds": [
            "niehs-emf"
          ]
        }
      },
      {
        "meters": 60,
        "value": {
          "quantity": "magnetic-flux-density",
          "unit": "mG",
          "value": 0.2,
          "max": 3,
          "basis": "measured",
          "note": "Approaching residential background at 60 m for typical loadings.",
          "sourceIds": [
            "niehs-emf"
          ]
        }
      }
    ],
    "mitigations": [
      {
        "action": "Measure over 24 hours at the property line and inside the building, since line loading varies.",
        "effect": "A single daytime reading can understate or overstate the annual average by several times."
      },
      {
        "action": "Compare the annual average against the Swiss 1 µT installation value and the Dutch 0.4 µT policy target for new lines.",
        "effect": "Gives a defensible frame of reference; no regulatory limit anywhere is close to typical residential exposure.",
        "sourceIds": [
          "ch-onir",
          "sbm-2024"
        ]
      },
      {
        "action": "Treat magnetic shielding as a last resort; it requires high-permeability alloy and rarely gives more than 50% reduction in a residential retrofit.",
        "effect": "Sets expectations correctly — distance and source correction are the only reliable options."
      }
    ],
    "measureWith": [
      "elf-gaussmeter",
      "data-logger"
    ],
    "related": [
      "limits:ch-onir-power-lines",
      "limits:who-elf-leukaemia-association",
      "studies:iarc-elf-2b-2002"
    ],
    "questions": [
      "how-far-should-i-live-from-a-power-line"
    ]
  },
  "sources": [
    {
      "id": "niehs-emf",
      "title": "Electric and Magnetic Fields",
      "publisher": "National Institute of Environmental Health Sciences",
      "url": "https://www.niehs.nih.gov/health/topics/agents/emf",
      "kind": "government",
      "retrieved": "2026-08-12"
    },
    {
      "id": "who-elf",
      "title": "Electromagnetic fields and public health: exposure to extremely low frequency fields",
      "publisher": "World Health Organization",
      "url": "https://www.who.int/teams/environment-climate-change-and-health/radiation-and-health/non-ionizing/exposure",
      "year": 2007,
      "kind": "government",
      "retrieved": "2026-08-12"
    },
    {
      "id": "ch-onir",
      "title": "Ordinance relating to Protection from Non-Ionising Radiation (ONIR / NISV, SR 814.710)",
      "publisher": "Swiss Confederation",
      "url": "https://www.fedlex.admin.ch/eli/cc/2000/38/en",
      "year": 2000,
      "kind": "regulation",
      "retrieved": "2026-08-12"
    }
  ],
  "links": {
    "self": "https://emfbase.com/api/emitters/high-voltage-transmission-line",
    "html": "https://emfbase.com/emitters/high-voltage-transmission-line",
    "markdown": "https://emfbase.com/emitters/high-voltage-transmission-line.md",
    "collection": "https://emfbase.com/api/emitters"
  }
}