Siemens SIMOTICS XP 1LA5 Compact Operating Instructions page 25

Tandem operation
If you connect two motors in series in "tandem operation", install an insulated
coupling between the motors.
①
Driving machine
②
Motor
③
Coupling
Figure 4-2 Schematic representation of a tandem drive
NOTICE
Bearing damage
If the coupling between the motors of the tandem drive is not insulated, bearing
currents can cause damage to the drive-end bearings of both motors.
Use an insulated coupling to link the motors.
4.7.4 Operation with insulated coupling (EX)
If you connect two motors in series in "tandem operation", fit a coupling between the
motors; this coupling should satisfy the ATEX Directive or the regulations that apply
in the country where the equipment is installed.
Explosion-protected machines
56100000002002, 01/2016
④
Insulated bearings
⑤
Insulated tachometer fitting
⑥
Insulated coupling
Preparing for use
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