An electromagnetic field (EMF) acceptance survey is a documented measurement program that quantifies the magnetic field strength present in and around a new or substantially modified electrical facility or installation - substations, switchyards, cable vaults, control rooms, or other areas where workers or the public may be exposed to fields during normal operation. The survey team records field readings at multiple heights and locations throughout the area under study, identifies the primary sources (overhead lines, underground cables, bus structures, current-carrying apparatus) that generate the fields detected, correlates the measurements to the electrical system conditions and current magnitudes present during the survey, and documents all findings in a formal report with conclusions and recommendations per NETA ATS-2025 10.
Electromagnetic fields from power conductors and energized equipment pose occupational and public health considerations that must be characterized before a facility is put into service so that engineered controls, administrative practices, or spatial arrangements can be implemented if needed. A baseline survey performed at acceptance establishes the field profile the installation was designed to produce, creates a record against which future maintenance or modification decisions can be assessed, and demonstrates compliance with any regulatory or consensus thresholds that may apply to the facility's geographic jurisdiction or industry sector.
Acceptance: the survey is conducted after the electrical installation is complete and ready to carry normal operating current, but before the facility is turned over to the customer for independent operation. The measurement is taken with the system in its as-designed steady-state condition - typically at or near rated load or a representative load scenario - so the captured field profile reflects the actual electromagnetic environment workers and neighbors will experience during routine use.
Before measurements begin, the survey scope is defined to identify the areas, worker exposure points, and equipment or conductors that will be studied. Electrical system single-line diagrams, cable route drawings, and conductor configuration details are assembled so the field sources can be identified and correlated to the measured readings. The survey team positions calibrated electromagnetic field meters at specified heights (ordinarily 1 meter above ground or at the elevation of exposed worker positions such as equipment platforms), records readings at regular grid intervals or at locations judged representative of exposure points throughout the area, notes the date, time, ambient conditions, and the electrical system current and operating voltage present during each measurement set, and documents the equipment and meter identification so the work is reproducible. The measurements are then evaluated against IEEE 644 recommended practices per ATS-2025 10.1.3, and conclusions and recommendations are developed based on the field pattern found.
For each survey location: the measured magnetic flux density in appropriate units (typically mG or µT), including the resolved x, y, z, and resultant components at each grid point, the measurement height and exact location on a site plan or coordinate system, the date and time of measurement, the electrical system current (in amperes) and voltage condition at the moment of measurement, the identification of nearby conductors or equipment judged to be the dominant field source at that point, ambient temperature or environmental notes if relevant, and the test instrument make, model, serial number, and most recent calibration date. The survey report consolidates these readings into a basis, description, purpose, and scope summary per ATS-2025 10.2.1, along with conclusions and recommendations per ATS-2025 10.2.6.
No single numeric acceptance/rejection criterion applies to all EMF survey results; instead, the measured field profile is evaluated descriptively against the survey's stated scope and purpose, against IEEE 644 recommended field practices for worker safety and exposure, and against any specific regulatory or consensus thresholds that apply to the facility or jurisdiction. A well-executed acceptance survey documents the electromagnetic field environment the installation produces, allows the client and testing professional to assess whether any localized high-field areas warrant administrative controls or re-siting of worker stations, and provides a baseline record for comparison if system modifications are contemplated in the future. See the purchased NETA ATS-2025 Section 10 and IEEE 644 for the complete survey framework and any applicable field-strength guidance.
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