Checks a measured bonding/grounding connection's resistance-to-ground (e.g. at a tank truck/rail car loading rack, drum-filling station, or other flammable-liquid transfer bonding point) against the commonly-cited threshold for adequate static-electricity dissipation, and flags whether an unusually high (but still 'passing') reading might indicate a connection problem worth investigating.
Standards followed
NFPA 77 (Recommended Practice on Static Electricity) — the commonly-cited 1 megohm (1×10⁶Ω) threshold for adequate static-charge dissipation
What it can do
- Pass/fail check of measured resistance against the (adjustable) static-dissipation threshold, defaulting to NFPA 77's commonly-cited 1 megohm.
- Quality flag distinguishing a tight all-metal bond (≤10Ω) from a merely-adequate-for-static-dissipation reading, since a high reading on what should be an all-metal path often indicates corrosion or a loose connection even though it still numerically passes.
Example problem
A tank truck bonding cable measures 25,000Ω to the grounding grid.
- 25,000Ω is well below the 1,000,000Ω (1 megohm) NFPA 77 threshold for static dissipation.
- It's also well above the ≤10Ω expected of a tight all-metal path, suggesting some resistance in the connection (e.g. a clamp with light corrosion) — still functionally adequate for static dissipation, but worth a look.
Passes the static-dissipation threshold, flagged as 'acceptable' rather than 'tight metallic bond'.
Want the full step-by-step version?
1 megohm is the commonly-cited NFPA 77 threshold specifically for static-charge dissipation — it is NOT an equipment-grounding (fault-current) requirement, which needs a much lower, low-impedance path. Don't use this threshold for equipotential bonding required for electrical safety/fault-clearing purposes — those systems are properly all-metal, low-resistance connections (typically well under 10Ω).