Installation technology: Staying cool with AFD units

Low temperatures, moisture, and wetness – harsh ambient conditions pose fundamental challenges in cold stores and freezer rooms. The components built into these rooms must therefore be suitably robust. cool it Isoliersysteme GmbH installs the 5SM6 AFD (arc-fault detection) unit from Siemens in its doors.

The door and gate systems from the company based in Melle near Osnabrück in the German state of Lower Saxony are used all over Europe. In addition to the specific conditions, high mechanical loads also play a major role in the cold-storage industry as collisions with doors and gates can’t always be avoided in busy operations that use forklifts and other material handling equipment. This can result in damage to the concealed built-in electronics that isn’t detectable from the outside. 


Therefore cool it installs protection systems into the door control unit itself. These may be miniature circuit breakers (MCBs) or residual-current circuit breakers (RCCBs). MCBs provide protection in the event of a short circuit and against overloading. They isolate the circuit in the case of parallel arc faults occurring between outer conductors or between outer conductors and neutral conductors. RCCBs detect fault currents and arc faults to ground. However, neither device type is technically capable of detecting serial arcing faults. These faults frequently occur in trapped or otherwise damaged cables. Because they can cause hotspots reaching temperatures up to 6,000° Celsius, they can lead to smoldering or even fire.

Automated safety

The 5SM6 AFD unit automatically detects hazardous arc faults with a high degree of reliability and is used in combination with MCBs or RCCBs. It not only records current and fault voltage, it also continuously measures the intensity, duration, and intervals between high-frequency noise. Integrated filters in conjunction with intelligent software process, analyze, and evaluate these signals based on a wide range of criteria. If the conditions of a serial or parallel arc fault are met, the connected circuit is shut down within fractions of a second.

Further enhancing standards

With the Siemens development, cool it will be able to enhance its already high safety standards. “The AFD unit, and the extra protection it offers, adds a new element to our safety package that was not technically possible in the past,” says cool it Technical Director Alexander Rolf.

Since the summer of 2015, cool it has been offering the AFD unit as an option and as standard on certain models, such as its Flex door. The fast-moving, two-leaf sliding door for logistics applications features flexible door leafs and is better equipped to withstand the impact of a forklift than a conventional door. However, this means that the load on the built-in electronics is correspondingly high. That’s why the Flex door model was already equipped as standard with a dedicated RCCB, which has now been replaced by a combination of AFD unit and both RCCBs and MCBs. The protection component is installed directly in the door’s control unit housing. “That also offers the advantage that when tripped, the fault is selectively displayed,” Rolf explains. “That means that the fault doesn’t have to be first discovered on some centralized distribution panel; rather, it’s immediately localized. And that means we can respond quickly to restore regular operation.”


Picture credits: Siemens AG/W. Geyer


The 5SM6 arc fault detection devices are part of the integrated Sentron portfolio from Siemens. The technical basis of the arc fault detection devices is the SIARC patented detection technology from Siemens: The devices continuously measure the intensity and duration of episodes of high-frequency (HF) noise associated with the voltage and current and the gaps between them. An integrated microcontroller analyzes these signals and triggers the disconnection of the connected circuit within fractions of a second if anything unusual is detected. The arc fault detection devices are able to distinguish harmless causes of faults, such as can arise when operating power drills or vacuum cleaners, from hazardous arcs.

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