Static grounding and bonding: maintaining the path from clamp to earth
At a glance
Bonding electrically connects conductive parts; grounding connects that path to earth. Metal parts that appear to touch can still be electrically isolated by paint, corrosion or insulating components. In hazardous-liquid transfer equipment, inspect isolated metal components in hoses and nozzles as well as the tank body.
A monitored grounding system monitors the connection in a specified circuit. A green indication does not establish that the liquid's flammability or surrounding gas concentration is safe. The tanker-grounding Earth-Rite II RTR also requires a distinction between grounding-path monitoring and the process interlock. Product-specific values are not universal statutory criteria for grounding.
Bonding and grounding serve different connections
Static charge can develop as liquid flows through pipes, valves and filters. An isolated charged conductive part can discharge to a nearby conductor at a different potential. Bonding connects parts electrically; grounding provides a path to earth. Grounding the tank alone can leave a hazard if metal parts of the filling nozzle remain isolated.
- 1 Bonding between partscheck interconnections so small conductive components do not remain isolated.
- 2 Grounding to earthCheck the charge path to earth and the air measurement separately.
- 3 Clamp and cableCheck contact, electrical continuity and cable tension at the designated contact point to prevent loss of connection during operation.
- 4 MonitorIdentify the circuit represented by the green indication in the installation drawing, and check isolated parts and other ignition sources separately.
- 5 Process interlockverify the actual shutdown and remaining flow as well as the signal.
The conductive path runs from the clamp contact through the cable and junction box to the designated earth point. Closing the clamp is only the beginning of that path. Check whether it is attached to the tanker’s designated grounding point, whether electrical contact is established and whether cable tension could dislodge it during the job.
Three checks behind the indication
The Earth-Rite II RTR datasheet describes tanker recognition, verification of earth connection and continuous circuit monitoring. This model uses capacitance to recognize a tanker, helping distinguish connection to a tanker from attachment to an unrelated metal structure. Other grounding monitors do not necessarily operate in the same way.
The system then monitors whether the path from the tanker contact to the designated earth remains intact. The circuit-resistance criterion in the datasheet belongs to this model and configuration. That model-specific criterion does not apply universally to every Korean transfer installation. Installation must follow the product instructions, the facility's grounding design and hazardous-area conditions.
Verify the monitored boundary on the installation drawing. A clamp connected to the tanker body does not separately verify continuity through every component. The datasheet warns against isolated metal components on the tanker. Use the designated connection point rather than a detached conductive part that could be mistaken for the tanker body.
- Monitor: use the installation drawing to identify which transfer action is linked to its indication.
- Vehicle connection: verify the manufacturer-designated tanker grounding point, then connect at that location.
- Cable route: check slack and movement paths so tension does not break contact during the job.
A pump-stop signal is not necessarily the end of flow
The output contacts can interlock with process equipment such as pumps. An indication-only installation is different from one connected to the actual transfer shutdown circuit. Establish what stops when the green indication is lost: whether the response is only an alarm, and which pumps or valves are acted upon.
The manufacturer's datasheet warns that product movement can continue after a pump or impeller stops, allowing charge generation to continue. Distinguish receipt of a lost-ground signal from actual cessation of flow, and address this residual transfer in the operating procedure.
An interlock test should not end at the clamp-system indication. The monitoring circuit and the process equipment receiving its signal are separate components. Check the signal and resulting shutdown through the prescribed test procedure; simulating a healthy signal with improvised resistors or jumpers defeats monitoring.
Match the vehicle, container and enclosure to the model
A tanker-recognition system should not simply be transferred to small portable containers or unrelated equipment. First verify the manufacturer's intended target and connection method. Check the type of explosion-protected enclosure and whether the cable entries, junction box and clamp are included in the approved configuration. A product-family name does not combine different enclosure types and regional certifications into one approval.
The manufacturer's page separates certificates by region. Check the certificate matching the exact enclosure and model used in Korea and implement any special conditions in the installation. A certificate number in a datasheet and a compliant installation at the site are different determinations.
Why the clamp goes on first and comes off last
For this product, connect to the designated grounding point before transfer procedures begin and retain the connection until those procedures are complete. Attaching the clamp only after hose connection or product movement leaves the earlier phase without the monitored path. At the end, switching off the pump alone does not justify immediate clamp removal.
Before use, inspect the clamp contacts, spring, cable and quick connectors for damage. During use, prevent excessive cable tension and interference by other work. If the indication changes, do more than reattach the clamp until green returns: resolve the unstable contact or cable strain that caused the change.
No calibration requirement does not mean no testing
The official Earth-Rite II RTR page states that calibration is not required at installation or during its service life. That describes the monitoring technology; it does not eliminate checks for clamp wear, cable failure or interlock operation. The manufacturer separately describes a dedicated tester for the system, cable and clamp.
The tester and procedure must suit the installed model. A clamp that appears intact at its stowage point does not establish a healthy circuit when connected to a vehicle. Record the method and scope of testing; after replacement, recheck the grounding path and process interlock. Set inspection arrangements through manufacturer instructions and the site's maintenance plan rather than inventing an interval.
Isolated metal parts beside a steel tank
On 29 October 2007, fire and explosions occurred while ethyl acetate was being transferred into a portable steel tank at Barton Solvents in Des Moines. In its 18 September 2008 findings, the CSB identified a static spark associated with inadequate bonding and grounding. Metal components in the plastic filling nozzle and hose were not bonded and grounded, and the equipment was unsuitable for flammable-liquid transfer.
The CSB explained that charge likely accumulated on the metal components and discharged to the tank, igniting vapour around its opening. This illustrates why inspection must extend beyond the metal tank to small isolated conductors inside nozzles and hose connections. The incident is not a performance test or use history of a particular grounding monitor.
The rule requires controls suited to the static hazard
Article 325 of Korea's Rules on Occupational Safety and Health Standards requires appropriate controls where static electricity could cause fire or explosion in the specified filling, storage and handling equipment. It lists measures including grounding, conductive materials, humidification and non-igniting charge-elimination devices. It is not a requirement to fit one particular device everywhere. Electrical equipment in hazardous locations also requires suitability and maintenance under Article 311.