MIL-HDBK-274 Electrical Grounding For Aircraft SafetyThis handbook has been prepared to provide U.S. Navy and Marine Corps aircraft maintenance and operations personnel with the background and technical details of the different types of aircraft grounds and how they are applied. In addition, this handbook provides background information for aircraft grounding, static electricity theory and how it affects aircraft, and techniques used for measurement of grounding points. This handbook is intended for use by all U.S. Navy and Marine Corps aircraft maintenance and operations personnel for the purposes of ensuring that aircraft are properly and safely grounded. This handbook is for guidance only and cannot be cited as a requirement.

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b. Direct injuries.  Electrical effects may result directly in injury.

4.6.3 Range for reflex actions.  Reflex action appears in the area of 10 to 30 mJ (1 to 3 mA across 10,000 ohms); a representative voltage is approximately 50 V (30 mJ and 1,500 ohms).  The threshold level for potentially lethal shock was established at 30 VAC and 45 VDC at energy levels of 600 mJ AC and 1.35 J DC, assuming a body resistance of 1,500 ohms.

4.6.4 Equipment damage level.  The threshold level for equipment damage is a function of dielectric breakdown (high-voltage effect), high temperature damage (high-power effect), or a combination of both.  One mJ can cause upset when directly injected into sensitive circuits. However, since direct injection is unlikely, a coupling factor of approximately 1/10 is assumed to establish a minimum threshold of 10 mJ for the practical lower limit of sensitive equipment

upset.  Damage levels are taken as 35 mJ, comparable with ordnance thresholds.

4.6.5 Summary of damage threshold levels. In summary, the levels of electrostatic and electrical energies considered are tabulated in Table IV.

4.7 Analysis. The basic purpose of the material in 4.5 through 4.6.5 has been to establish the data which verify or disprove the hypothesis that an electrical hazard exists and grounding will eliminate or reduce this hazard.  The first hypothesis (hazard exists) is assessed by a comparison of energy source levels with hazard threshold levels and scenario particulars.  The second hypothesis (grounding reduces hazard) is assessed by considering the extent to which application of an electrical ground alters the available energy, location of discharge, or duration of hazard.  The results of the analysis are summarized in 4.7.3 following the detailed analysis in

4.7.1 through 4.7.2.2.

TABLE IV.  Summary of hazard threshold levels.

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