Point-to-Point Grounding Survey and Fall-of-Potential Test at a Corrugated Packaging Plant, San Antonio Area (2023)

A corrugated packaging plant near San Antonio asked for an assessment of its grounding in June 2023. We spent July 28 measuring the ground path from the building ground rod to nearly every piece of electrical equipment in the plant.

Walking the ground path

A point-to-point test reads the resistance between two grounded points, so it shows whether an equipment ground actually connects back to the system. We started at the building ground rod and the main switchboard sections, then worked outward through the panels and transformers and down each production line: the corrugator with its roll stands, splicers and single facers, the folder gluers, stackers, bundlers and conveyors, the slitter and knife cabinets, the starch kitchen, the boiler, the compressors and the baler room. Each step used the last tested point as its reference, about 150 measurements in all. The test leads add their own resistance, about 0.95 ohm with two leads and 1.57 ohms with three, and we subtracted it from every reading.

What the readings showed

None of the paths failed. Nearly half read under 1 ohm. Four read above 5 ohms, on equipment along three of the lines, the highest about 7.2 at a conveyor, and we flagged those as marginal and worth watching. A high reading on one machine usually means a loose or corroded ground connection at that unit, which is a simple repair. The fall-of-potential test, three poles from the building ground rod, gave 0.92 ohm to remote earth, a passing result for this installation.

A survey like this is a snapshot of one day. Connections loosen with vibration and corrode with time, so we recommended repeating the survey about once a year.

Related services

The methods are described under grounding system tests. Plants often pair the survey with infrared inspections.