Portable Earthing and short-circuiting equipment is temporarily installed on isolated power circuits to provide a control path for short-circuit current and to prevent voltage rise in the earth circuit. The equipment is essential for ensuring worker safety by conducting the short-circuit current for a specified time enabling automatic protection to operate.
TMAC has been designing and developing portable earthing and short-circuiting equipment for more than 25 years. We offer an extensive range of reliable equipment, adaptable to numerous types of installations.
In addition we are able to cater for customers' specific needs and provide:
Portable Earthing Components
The required cable cross-section depends on the rms short-circuit current (IR), the duration of the fault and the type of installation. The graphs below help to determine the required cable size for a given fault current (IR) and fault duration (sec).
For outdoor use the highest possible temperature rise is adopted to keep the weight to a minimum.
For indoor use, the cable temperature is limited to a maximum temperature of 250 °C, to prevent gas emissions from the insulated covering, which may pose a risk to personnel.
The length of the cables should correspond to the installation dimensions and distance between connection points.
Cables less than 1.2 times the distance between connection points may lead to more severe conditions than designed for. Cables more than 1.5 times the distance between connection points will cause unacceptable movement under fault conditions. Longer cables may be anchored by a non-conductive rope to reduce the movements.
Reduction in size of earthing cable
Earthing cable cross-section in multi-phase sets may be reduced when used on a non-solidly earthed system.
Earthing and short-circuiting devices may be used in parallel to achieve a greater fault capacity.
The following conditions must be adhered to:
Portable Earthing Clamps
Clamps must be suited to the connection points that they are to be attached to. The table of standard clamps indicates their suitability. In situations where a suitable clamp cannot be found, it is recommended that a fixed connection point is installed.
Portable Earthing Maintenance
Every Tmac® portable earthing device must be handled and stored with care to ensure it remains capable of achieving its full rating during its service life. Maintenance includes periodic visual inspection of all components and the cleaning of conductor clamps, cables and insulating sticks. Although the connections are engineered for a long service life, particular care should be taken to ensure that strands are not broken in the vicinity of the cable lugs.
Users should be aware that application, use and maintenance of Tmac® portable earthing and short-circuiting equipment may be regulated by government legislation or codes of practice.
Users should ensure that all applicable regulations and legislative requirements are complied with when selecting, using and maintaining Tmac® portable earthing and short-circuiting equipment.
Action in the event of a fault
If the portable earthing or short-circuiting device has been subjected to fault current, it should be removed from service immediately and disposed of.
For further information on selection, use and maintenance of portable earthing refer to IEC 61230:2008 Annex.C.