2.15 Conventional enclosed thermal current Ithe Is the manufacturer defined current for temperature testing of the device, when the device is fitted into a specifed enclosure. IEC/EN 60947-1; 4.3.2.2 Conventional free air thermal current Ith The conventional free air thermal current ist the maximum testing current for temperature testing of devices in free air. The conventional free air thermal current must at least correspond to the maximum rated operational current of an open device during an eight hour operation. Free air is understood as air in common interior rooms almost free of airflow and radiation. IEC/EN 60947-1; 4.3.2.1 Conversion factors for permissible current Conversion factors for permissible current loads of PVC-insulated lines and cables at ambient temperatures other than 25°C. See table on page 2.23. EMC EMC is defined as the ability of a device to work satisfactorily in it‘s electromagnetical environment without any unacceptable disturbances for this environment or other devices. (definition by IEC) Devices without electronic circuits as e.g. disconnect and cam switches can emit electromagnetic interferences during occasional switching operations only, which last for ms merely! As a result it is assumed that they do comply with the requirements. No verification is necessary. Situation is different if switches are part of an installation and used as repair and maintenance switch upstream of a frequency controlled motor. The frequency controller can emit interferences making necessary an electromagnetic shielding of the supply line. Of course in this case the switch must be integrated into the shielding. MERZ offers a complete range of EMC shielded enclosures in plastic and metal. Cam switches MN and compact switches ML are completely resistant and cannot be influenced by external interferences. Emergency stop switch With certain machines the main switch must fulfil the function of an emergency stop unit. In order to separate from standard functions the handle must be red whilst the background has to be yellow for safety reasons. The switching contacts of manually operated emergency stop units must be positively driven. Easy access in case of an emergency shut-down is a must whenever the device is fulfilling the function of an emergency stop switch. Extension shaft To adapt MERZ switchgear to various installation depths of switchboards and enclosures, a large range of shaft extensions is available for the MERZ cam switch series (MN) and the MERZ disconnect switch series (ML). Distances from 18mm to 405mm can be covered. Supports for big distances avoid a deviation of the extension shaft. Faulty signal resistance The ability of a contact to switch current and voltages without faulty signals. The contacts of cam and compact switches are designed for bigger currents and ratings, as a result small ratings can be transferred limited only. The critical values are 1A and 24V. In case of values smaller than the said ones gold plated contacts are recommended.
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