AKD Installation | 7 Technical description and data
7.17 Shock-hazard Protection
7.17.1 Leakage current
Leakage current via the PE conductor results from the combination of equipment and cable
leakage currents. The leakage current frequency pattern includes a number of frequencies,
whereby the residual-current circuit breakers definitively evaluate the 50 Hz current. For this
reason, the leakage current cannot be measured using a conventional multimeter. As a rule of
thumb, the following assumption can be made for leakage current on our low-capacity cables
at a mains voltage of 400 V, depending on the clock frequency of the output stage:
I
leak
=
n x 20 mA + L x 1 mA/m
at 8 kHz clock frequency at the output stage
I
leak
=
n x 20 mA + L x 2 mA/m
at a 16 kHz clock frequency at the output stage
(where Ileak=leakage current, n=number of drives, L=length of motor cable)
At other mains voltage ratings, the leakage current varies in proportion to the voltage.
Example:
2 x a 25m motor cable at a clock frequency of 8 kHz:
2 x 20 mA + 25 m x 1 mA/m = 65 mA leakage current.
Since the leakage current to PE is more than 3.5 mA, in compliance with IEC61800-5-1 the
PE connection must either be doubled or a connecting cable with a cross-section >10 mm²
must be used. Use the PE terminal and the PE connection screws in order to fulfill this
requirement.
The following measures can be used to minimize leakage currents:
Reduce the length of the engine cable.
Use low-capacity cables (
7.17.2 Residual current protective device (RCD)
In conformity with IEC 60364-4-41 – Regulations for installation and IEC 60204 – Electrical
equipment of machinery, residual current protective devices (RCDs) can be used provided
the requisite regulations are complied with. The AKD is a 3-phase system with a B6 bridge.
Therefore, RCDs which are sensitive to all currents must be used in order to detect any DC
fault current. Refer to the chapter above for the rule of thumb for determining the leakage cur-
rent. Rated residual currents in the RCDs:
10 to 30 mA
Protection against "indirect contact" (personal fire protection) for stationary
and mobile equipment, as well as for "direct contact".
50 to 300 mA
Protection against "indirect contact" (personal fire protection) for stationary
equipment
Recommendation: In order to protect against direct contact (with motor cables shorter than
5 m) Kollmorgen recommends that each drive be protected individually using a 30 mA RCD
which is sensitive to all currents.
If you use a selective RCD, the more intelligent evaluation process will prevent spurious trip-
ping of the RCD.
7.17.3 Isolating transformers
When protection against indirect contact is absolutely essential despite a higher leakage cur-
rent, or when an alternative form of shock-hazard protection is sought, the AKD can also be
operated via an isolating transformer (schematic connection (
# 103). A ground-leakage
monitor can be used to monitor for short circuits.
Keep the length of wiring between the transformer and the drive as short as possible.
66
Kollmorgen | kdn.kollmorgen.com | October 2017
