Grounding Continuity and Testing Under TRGS 727

Section 3.1 requires, depending on ignition probability, conductive objects and equipment to be grounded and dissipative objects and equipment to have earth contact. The connection may be omitted only where dangerous charging is excluded.

For bulk-solids requirements and exceptions, see grounding combustible-dust equipment under TRGS 727.

Under section 8.3.4, where insulating pieces separate conductive components, the conductive parts must be interconnected and grounded. Alternatively, each installation part may be grounded individually.

The rule calls particular attention to parts hidden from outside view, including:

• Ball valves with insulating seals.
• Shafts with insulating collars.
• Metal nozzles at the end of plastic pipes.

A conductive or dissipative coating on an insulating object must itself be grounded or connected to earth. In Zones 0 and 1, proof of its durable effectiveness is also required (section 3.2).

Section 8.3.5 distinguishes two cases:

• Above 10 pF: Conductive objects must be grounded unless dangerous charging does not occur.
• Below 10 pF: Apply Table 11, which sets maximum permitted capacitances for ungrounded small objects by zone and explosion group, where no strongly charge-generating processes occur.

Small conductive objects must also be grounded regardless of capacitance near strongly charge-generating processes or when they contact the product stream in an apparatus.

Determine capacitance in the installed state, using simulated conditions where appropriate.

Section 8.4 requires grounding and equipotential-bonding equipment to be clearly marked and prohibits interrupting or switching it off.

Section 8.5 requires grounding clamps to be attached before work starts and retained until all dangerous charges have dissipated. The equipment must be designed and maintained so that clamps can penetrate paint, rust, or liner-bag films where used.

Under section 8.7, static-grounding and equipotential-bonding tests must be performed independently of other electrical tests. Testers must be qualified under the provision cited by TRGS 727: Annex 2, Section 3, Number 3.1 of the Betriebssicherheitsverordnung (BetrSichV).

Where charge dissipation depends on temperature or humidity, account for their expected operating range (section 3.1).

For floor-specific requirements, see TRGS 727 floor and person-to-earth resistance limits by zone and testing installed flooring when a product certificate exists.