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Technical description
6.10
Shock-hazard protection
6.10.1
Leakage current
Leakage current via the PE conductor results from the combination of equipment and
cable leakage currents. The leakage current frequency pattern comprises a number of
frequencies, whereby the residual-current circuit breakers definitively evaluate the 50Hz
current. 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:
At other mains voltage ratings, the leakage current varies in proportion to the voltage.
Example:
Since the leakage current to PE is more than 3.5 mA, in compliance with IEC
61800-5-1 the PE connection must either be doubled or a connecting cable with a
cross-section >10mm² must be used. Use the PE terminals and the PE bolt in order
to fulfil this requirement.
The following measures can be used to minimize leakage currents.
— Reduce the length of the engine cable, use low-capacity cables (see p.53)
— Remove external EMC filters (radio-interference suppressors are integrated)
6.10.2
Residual current protective device (RCD)
In conformity with IEC 60364-4-41 – Regulations for installation and IEC 60204 – Electri-
cal equipment of machinery, residual current protective devices (called RCD below) can
be used provided the requisite regulations are complied with. The S700 is a 3-phase sys-
tem with a B6 bridge. Therefore, RCDs which are sensitive to all currents must be
used in order to detect any D.C. fault current.
Rated residual currents in the RCD
10 - 30 mA
50 - 300 mA Protection against "indirect contact" for stationary equipment
Recommendation: In order to protect against direct contact (with motor cables
shorter than 5 m) we recommend that each servo amplifier be protected
individually using a 30mA RCD which is sensitive to all currents.
If you use a selective RCD, the more intelligent evaluation process will prevent spurious
tripping of the RCD.
6.10.3
Isolating transformers
When protection against indirect contact is absolutely essential despite a higher leakage
current, or when an alternative form of shock-hazard protection is sought, the S700 can
also be operated via an isolating transformer (schematic connection see p.58). A
ground-leakage monitor can be used to monitor for short circuits.
Be advised to keep the length of wiring between the transformer and the servo
amplifier as short as possible.
44
I
= n x 20mA + L x 1mA/m at 8kHz clock frequency at the output stage
leak
I
= n x 20mA + L x 2mA/m at a 16kHz clock frequency at the output stage
leak
(where Ileak=leakage current, n=number of amplifiers, L=length of motor cable)
2 x servo amplifiers + a 25m motor cable at a clock frequency of 8kHz:
2 x 20mA + 25m x 1mA/m = 65mA leakage current.
Protection against "indirect contact" for stationary and mobile equipment,
as well as for "direct contact".
S701...S724 (single channel STO) Instruction Manual
12/2010a
Kollmorgen
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