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BECKHOFF
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:
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 EN50178
the PE connection must either be doubled or a connecting cable with a
cross-section >10mm² must be used.
The following measures can be used to minimise leakage currents.
— Reduce the length of the engine cable
— Use low-capacity cables (see p.41)
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 AX2040/2070 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
50 -300 mA
Recommendation: In order to protect against direct contact (with motor cables
<5m) 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.
AX2040/2070 Product Manual
Ileak = n x 20mA + L x 1mA/m at 8kHz clock frequency at the output stage
Ileak = n x 20mA + L x 2mA/m at a 16kHz clock frequency at the output stage
(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" (personal fire protection) for stationary and mo-
bile equipment, as well as for "direct contact".
Protection against "indirect contact" (personal fire protection) for stationary equip-
ment
06/2007
Technical description
31
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