Het gaat waarschijnlijk om een borstel die voor het afvoeren van elektrische spanning naar aarde zorgt. Zie bijvoorbeeld
http://www.biname.be/catalogues/D-malt/pdf/D-MALT-page-30.pd... en http://www.analberswitgoed.nl/index.php/component/option,com... .



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Note added at 2 hrs (2010-12-30 11:32:41 GMT)
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Further references:

http://technicallyspecializedsolutions.com/Electrical_Flutin...
What is Electrical Fluting?
Electrical fluting occurs when a current is passed through the motor bearing instead of a grounded source. PWM (Pulse Width Modulated) drive switching frequencies result in undesirable motor shaft currents, a side effect that causes bearing damage within the motor through pitting and fluting. The audible noise generated by the damaged bearings is unacceptable and motor failure soon follows.
(…)
1. Shaft Grounding Kit - With this method of diverting motor shaft currents away from the bearings, a shaft grounding kit is installed with a conductive grounding brush that is in contact with the shaft. The brush conducts shaft currents to the motors ground. Eventual oxide buildup on the shaft reduces the brushes effectiveness. If the shaft gets covered with dirt or grease, the brush may fail to pick up the currents and sparking occurs across the brush or the bearing race. Regular maintenance is required to help ensure that this method is effective. In addition, there is no easy way to tell if the brush is working.

http://www.patentstorm.us/patents/5988996/description.html
This invention relates in general to electrical submersible pump motors, and in particular to a brush assembly for reducing arcing across bearings between a rotor shaft and stator.

http://www.sohreturbo.com/grounding-brushes/grounding-brush-...
Grounding Brush Features
For shaft grounding, shaft earthing of all types of stray shaft currents-such as found on turbine generators, gears, pumps, turbines, compressors, electric motors, ship propeller shafts or other rotating equipment. Failure to properly ground rotating shafts can result in expensive damage such as damage due to spark erosion (electrolysis). Also suitable for generator or electric motor diagnostic work.

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Note added at 3 hrs (2010-12-30 13:13:43 GMT)
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PS: De borstel kan worden geïmplementeerd als zg. sleepborstel. Die kunnen overigens ook voor andere doeleinden dan aarding worden gebruikt. De term aardings- of aardborstel is mijns inziens hoe dan ook een correcte vertaling (en ik spreek als HTS'er Elektrotechniek).