Field discharge resistor. In the case of large magnetic coils with iron core (e.g. load lifting magnets) it is not sufficient to simply switch them off because part of the magnetic field of the ion stays due to remanence (remanent, Latin: remaining = residual magnetism). The magnetic field is eliminated by briefly applying a reversed polarity supply voltage, i.e. the coil is discharged. The field discharge resistor limits the current to the required value (approx. 20% of the nominal current) so that the coil is not excited again due to reversed polarity.

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