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6.9 Shock-hazard protection
6.9.1 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. 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
=nx20mA+Lx1mA/m at 8kHz clock frequency at the output stage
I
leak
=nx20mA+Lx2mA/m at a 16kHz clock frequency at the output stage
(where I
leak
=leakage current, n=number of amplifiers, L=length of motor cable)
At other mains voltage ratings, the leakage current varies in proportion to the voltage.
Example: 2 x servo amplifiers + a 25m motor cable at a clock frequency of 8kHz:
2 x 20mA + 25m x 1mA/m = 65mA leakage current.
Since the leakage current to PE is more than 3.5 mA, in compliance with EN50178
the PE connection must either be doubled or a connecting cable with a
cross-section >10mm² must be used. Use the PE terminals (X0A and X0B) or the PE
bolt in order to fulfil this requirement.
The following measures can be used to minimise leakage currents.
— Reduce the length of the engine cable
— Use low-capacity cables (see p.42)
— Avoid mains asymmetries (with an isolating transformer)
6.9.2 Residual-current circuit breakers (FI)
In conformity with DIN IEC 60364-4-41 – Regulations for installation and EN 60204 – Electrical
equipment of machinery, residual-current circuit-breakers (called FI below) can be used provided
the requisite regulations are complied with.
The SERVOSTAR 600 is a 3-phase system with a B6 bridge. Therefore, FIs which are sensitive
to all currents must be used in order to detect any d.c. fault current. Refer to chapter 6.9.1 for the
rule of thumb for determining the leakage current.
Rated residual currents in the FI
10 -30 mA
Protection against "indirect contact" (personal fire protection) for stationary and mo
-
bile equipment, as well as for "direct contact".
50 -300 mA
Protection against "indirect contact" (personal fire protection) for stationary equip
-
ment
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 residual-current circuit-breaker which is sensitive to all
currents.
If you use a selective FI circuit-breaker, the more intelligent evaluation process will prevent spurious
tripping of the circuit-breakers.
32 SERVOSTAR
®
601...620 Product Manual
Technical description
07/2007 Danaher Motion