First the lightning, then the thunder – this concept is not only true in meteorology, it also applies in all industrial areas where hazardous atmospheres are created when filling, mixing and loading combustible media or fine-grained bulk material. To avoid ignition hazards caused by uncontrolled discharge of electrostatic potentials, barrels, refuelling vehicles, big bags and tank containers need to be grounded reliably. This can be done using a simple cable. However, this method of "passive grounding" poses a significant hazard, namely the risk of interruptions in the dissipating connection going undetected. Even minor damage to cables or contact elements can render the safety devices ineffective. In a similar way, corrosion, dirt or coatings can impair the conductivity between the clamp and object to be grounded. Active, permanent monitoring of the connection between the object and equipotential bonding rails can be implemented as a countermeasure.
The explosion protection specialist R. STAHL offers a wide range of ground monitoring devices and accessories. With the 8485, 8146, 8150 and 9170 series for universal use in Ex Zones 1, 2, 21 and 22, the manufacturer meets the specific requirements for a range of usage scenarios. The 8485 device series for tankers, tank wagons or FIBC (Flexible Intermediate Bulk Containers, also known as big bags) uses red and green LEDs, which are optimally visible even in bright daylight, to indicate correct grounding. Automatic object detection in trucks prevents operating errors caused by incorrect connection.
This involves checking that the clamps are connected properly in a two-stage process before release. Firstly, an impedance measurement is performed in order to determine whether the device is connected to a truck, not to part of the loading equipment. In the second stage, the resistance is measured in order to establish that sufficient grounding is provided by the grounding device. For remote signalling or for direct disconnection of loading equipment, the devices in the 8485 series are available with up to four potential-free change-over contacts, which can either be operated with Ex i or Ex e degree of protection. Installation and commissioning are simplified by the splash-protected aluminium enclosure with IP65 degree of protection over a readily accessibly connection area. An integrated suspension point for the clamp prevents it from becoming worn prematurely. Designed for a temperature range of -55 °C to +60 °C, this series can even be used in harsh climatic conditions without a problem.
In the 8146 and 8150 series, R. STAHL has specifically adapted the measurement process for grounding monitoring in tank wagons or tank containers. The models in an IP66 enclosure made of plastic or weather-resistant stainless steel are fitted with an insulated suspension point and are approved for use in applications with SIL 2 (according to IEC 61508). Signalling to the process control technology or to external signalling devices takes place using a potential-free change-over contact.
Additionally, the manufacturer has also included the 9170 leakage monitor in their range – a two-channel monitoring solution for systems and containers that are grounded at multiple points, which requires minimal space in the cabinet as its enclosure measures just 18 mm in width. In order to optimally adapt all device series to varying on-site conditions, R. STAHL offers a comprehensive selection of optional accessories. This range includes UV-, oil- and fuel-resistant spiral cables measuring five or ten metres in length, as well as high-quality stainless steel clamps, automatic retractors, visual/audio signalling devices, and multi-signal devices in explosion-protected designs. On request, R. STAHL can also design customer-specific solutions with preferred fieldbus interfaces, integrated heating systems or NEC-compliant designs for use in the USA.
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