Part 1 (Minimum Insulation Resistance)
A very good and practical change to the AR-100 is the minimum insulation resistance for DC armatures being lowered to 5
Mohms. Yes, 5 Mohms! In previous revisions of AR-100 the minimum insulation resistance for most DC armatures was 100
Mohms. For anyone who has ever been covered in carbon dust while trying to keep a DC armature at or near 100 Mohms this is a sigh of relief. When you have the open atmosphere of a copper DC commutator and expected heavy contamination from the brush wear, it is nearly impossible to maintain 100 Mohm resistance-to-ground values for continued operation. With the AR100 2020 revision, the DC armatures have joined the random wound stator coils where they belong and the form wound coils built after 1970 retain the 100 Mohms minimum insulation resistance recommendation.
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