Protective or equipotential bonding
conductor
The connection of the protective conductor terminal is to be made over the
power cable in the protective conductor into the terminal box of the MKE motor.
An additional connection of a protective or equipotential bonding conductor is
prescribed for MKE motors according to EN 50014: 1992. All MKE motors have
to be grounded over the additional connection part (protective conductor clamp
on the motor flange). Protective conductor cross-section see fig. 8-2 " Additional
protective conductor" on page 66.
8.4 Dimensioning Power Cable
The cables' cross-sections specified and calculated in this Bosch Rexroth doc‐
umentation base upon RMS currents and the assumption of a "rotating motor".
The basis for this calculation are the continuous currents at standstill which are
given as crest values in the technical data chapter of this documentation.
The relevant electric currents are related as follows:
Speed n ≥ 0.01 Hz "rotating motor"
I
(cable)
relevant electric current for the dimensioning of the cable
I
dN(motor)
Constant current at standstill of the motor (crest value)
Fig.8-6: RMS and peak values ("rotating motor")
In general, it suffices to dimension according to the RMS current for a "rotating
motor".
Speed n ≤ 0.01 Hz "rotating motor"
I
(cable)
relevant electric current for the dimensioning of the cable
I
dN(motor)
Constant current at standstill of the motor (crest value)
Fig.8-7: RMS and peak values ("motor at stillstand")
In individual cases, for applications of longer time intervals (guide values see
Fig.:8-8) which require the continuous torque at standstill at speed = 0 min
-1
, it
is recommended to realise the cable dimensioning according to the crest values
("motor at standstill") given in the Technical Data.
Motor type Period of time
MKE037 10 min
MKE047, -098, -118 15 min
Fig.8-8: Longer-term operation
The recommended minimum cross-sections specified are to be
checked by the machine / system manufacturer for the machine- /
system-specific conditions and, if necessary, corrected.
8.5 Cable – Handling and Installation Recommendations
General
The maximum operating time of cables largely depends on the mode of instal‐
lation and environmental factors at the place of installation. Since there is a
great variety of operating conditions, the following recommendations can only
be a help in order to provide for a faultless operation of the lines (cables) as
long as possible.
Project Planning Manual | Rexroth MKE Synchronous Motors Electric Drives
and Controls
| Bosch Rexroth AG 69/131
Connection Technique
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