IEEE 80 Clarified: Substation Grounding Safety Uses Step & Touch Voltage (Not a ≤ 1 Ω Rule) Substation Grounding per IEEE 80: Why Step/Touch Voltage Beats a Fixed 1‑Ohm Target
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IEEE 80 Clarified: Substation Grounding Safety Uses Step & Touch Voltage (Not a ≤ 1 Ω Rule) Substation Grounding per IEEE 80: Why Step/Touch Voltage Beats a Fixed 1‑Ohm Target

Jezcoolin' 11:07 PM

IEEE 80 Does Not Mandate “≤ 1 Ω” Substation Ground Resistance — Safety Is Based on Step & Touch Voltage

Executive Summary: IEEE Std 80 (2013) designs substation grounding for personnel safety using tolerable touch and step voltage limits—it does not specify an absolute grid-resistance limit like “≤ 1 Ω.” The oft‑quoted 0.5–1 Ω and 1–5 Ω figures are historical/typical values clarified in the IEEE Standards Interpretation for IEEE‑80. For measurement and acceptance, use IEEE‑81 methods and confirm that actual touch/step voltages are ≤ the IEEE‑80 tolerable limits. IEEE‑142 (Green Book) values (often 0.5–5 Ω) are informative recommendations for industrial grounding, not prescriptive limits for substations.

Contents

  1. #ieee80-what-it-requiresWhat IEEE‑80 Actually Requires
  2. #one-ohm-mythWhere the “≤ 1 Ω” Myth Comes From
  3. #ieee142-contextIEEE‑142 (Green Book) Context
  4. #measurement-acceptanceMeasurement & Acceptance (IEEE‑81)
  5. #design-notesPractical Design Notes
  6. #contract-languageRecommended Contract / Spec Language
  7. #referencesReferences

1) What IEEE‑80 Actually Requires

Scope & intent: IEEE‑80 is a Guide for Safety in AC Substation Grounding. Its primary objective is to design a grounding grid so that the calculated touch and step voltages around equipment and structures remain below tolerable limits during fault conditions, given the site’s soil resistivity, prospective fault current, protective clearing time, and surface layer properties (IEEE SA overview; Electrotechnik paper).

Design sequence (typical):

  • Establish inputs (soil model, fault current to grid, clearing time, surface layer). (IEEE‑80 Tutorial slides)
  • Compute tolerable limits using IEEE‑80 formulas based on Dalziel’s allowable body current, Ib=k/√t (k=0.157 for 70 kg; k=0.116 for 50 kg), including surface-layer corrections. (Electrotechnik paper)
  • Lay out the grid, estimate grid resistance Rg and GPR, then compute mesh/touch/step voltages; iterate spacing, perimeter conductors, rods, and surface layer until actual values ≤ tolerable limits. (IEEE‑80 Tutorial slides)

Key point: IEEE‑80 provides no mandatory “≤ 1 Ω” requirement. Safety compliance is proven by the voltage limits, not by a single grid-resistance number. (IEEE Interpretation)

2) Where the “≤ 1 Ω” Myth Comes From

The widely repeated figures—“~1 Ω or less” (transmission/generating plants) and “1–5 Ω” (distribution/industrial)—are described by IEEE as typical values observed historically, reflecting site size and grounding geometry. They were useful for protection performance (relays/fuses) but are not the safety design criterion of IEEE‑80. (IEEE Interpretation)

Industry summaries and training materials often echo these ranges (e.g., Vertiv), but they consistently present them as recommendations/targets, not mandates. (Vertiv educational note; again see IEEE Interpretation)

3) IEEE‑142 (Green Book) Context

IEEE‑142 addresses industrial/commercial grounding practices and discusses achieving low earth-electrode resistance (commonly ~0.5–5 Ω) for robust performance. These are recommended/typical values, not prescriptive for substation grid acceptance. For substations, IEEE‑80’s touch/step voltage limits remain the governing criterion for personnel safety. (IEEE‑142 SA page; IEEE‑142 (2007) text)

4) Measurement & Acceptance (IEEE‑81)

Commissioning and verification should follow IEEE‑81 methods:

  • Soil resistivity surveys (e.g., Wenner/Schlumberger) to validate the design model. (IEEE‑81 SA page)
  • Ground impedance/resistance to remote earth at power frequency. (IEEE‑81 SA page)
  • Step/touch potential verification (measurement or targeted checks) to confirm that actual voltages ≤ IEEE‑80 tolerable limits for the site’s clearing time and surface conditions. (IEEE‑81 SA page; Electrotechnik paper)

5) Practical Design Notes

Grid resistance & GPR: Engineers often estimate grid resistance Rg from IEEE‑80 (Sec. 14.2, Eq. 57) to predict Grid Potential Rise (GPR) = Igrid × Rg, then compute resulting mesh/touch/step voltages. (ELEK IEEE‑80 grid‑resistance equation)

If limits are exceeded, IEEE‑80 suggests effective mitigations: tighten perimeter spacing, add deeper/longer rods, enlarge grid area, increase surface resistivity (thicker/higher‑ρ crushed rock), and/or reduce clearing time—each reduces actual touch/step voltages. (IEEE‑80 excerpt (design guidance))

6) Recommended Contract / Spec Language

Design Compliance: The substation grounding system shall be demonstrated per IEEE‑80 by calculations showing actual mesh/touch/step voltages ≤ tolerable limits for the specified fault current(s), clearing time(s), soil resistivity, and surface-layer parameters.

Field Verification: Perform commissioning tests per IEEE‑81 (soil resistivity, ground impedance, and selected step/touch checks) to confirm inputs and validate performance.

Informative Targets: Where project documents reference IEEE‑142, acknowledge that 0.5–5 Ω grounding resistance values are recommended/typical for industrial practice. Acceptance shall be governed by IEEE‑80 touch/step voltage limits, even if Rg differs due to local geology.

Optional Numeric Cap: Any project‑specific numeric grid-resistance cap (e.g., “≤ 1 Ω”) may be used as a performance target, but it shall not replace the IEEE‑80 safety criterion.

References

Note: IEEE‑80 focuses on AC substation grounding safety at 50/60 Hz and tolerable human limits. If you align with IEC practices, consult IEC 60479 (physiology) and EN/BS 50522 derived methods for cross‑comparison, but maintain consistency within your project standard.

Author’s intent: This article is informational and standards‑based; it is not legal or regulatory advice. Always follow your project specifications and the Authority Having Jurisdiction (AHJ).

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