Ensuring that a rotating drum or impeller is correctly grounded may be difficult as it is not always possible to rely on the connection made from its shaft to the body of the machine, owing to the design of bearings, etc.  A popular method of guaranteeing ground continuity is to use a ground monitoring module to test the ground connection to the drum or impeller via a pair of carbon brushes or a slip ring, acting on the shaft.

Such modules may also be used to test the ground connection to key items of fixed plants, such as large storage vessels for flammable liquids.

NFPA 77, when discussing the static dissipation path through bearings (in this case, in rail car wheel assemblies) states that: resistance to ground ... might not be low enough to prevent the accumulation of static electric charge (7.8).

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