HEIDENHAIN TNC 410 M Technical Manual page 177

TN network
TT and IT networks
January 2008
TN networks provide a low-impedance galvanic connection between the
reference ground potentials of the power source and the grounding conductor
potential of the electric consuming device (VDE 0100 Part 300). This means
that direct connection of the inverter system is possible (without fault-current
circuit breaker and isolating transformer) and, in the event of an error, proper
electrical separation can be ensured by means of standard measures (e.g.
fuse).
Should you want for a specific reason to use a fault-current circuit breaker, you
must use an AC/DC-universal fault-current circuit breaker Type B with a fault
current of 300 mA. When using a fault-current circuit breaker, you must
ensure that the grounding conductor of the inverter system is properly
grounded and has a large enough cross section (min. 10 mm²).
If a low-impedance reference ground potential cannot be guaranteed by the
power supply company, the inverter system must be connected in the same
way as in a TT or IT network. This is due to the resulting asymmetries between
the external lines and the star point, and makes the use of an isolating
transformer absolutely necessary.
Warning
Type A and type AC fault-current circuit breakers may not be used.
For TT and IT networks, power supply companies require the inverters to be
connected via fault-current circuit breakers or isolating transformers because
a ground connection at the generator is not always provided (VDE 0100 Part
300). This is necessary because the line power must be quickly disconnected
and all of the system's parts must be free of hazardous voltage when an error
occurs (IEC 61800-5-1). This can only be ensured if appropriate measures are
taken.
Appropriate protective measures are AC/DC-universal fault-current circuit
breakers (Type B, switching threshold 300 mA, with frequency evaluation,
available up to a rated current of 63 A) or an isolating transformer. In addition,
the machine must have its own connection to ground (central grounding
point).
The network requirements allow the use of a fault-current circuit breaker for
the HEIDENHAIN compact inverters and the modular inverter systems up to
30 kW (e.g. UVR 120 D, UVR 130D; VDE 0100 Part 300). When using a fault-
current circuit breaker, you must ensure that the grounding conductor of the
inverter system is properly grounded and has a large enough cross section
(min. 10 mm²).
If, however, the inverter systems for 45 kW and higher (e.g. UVR 140D at max.
load, UVR 150D, UVR 160D(W)) are used, the rated current of 63 A of the
fault-current circuit breaker is exceeded. In this case an isolating transformer
must be used. For connection and dimensions, see "Isolating transformer" on
page 4 – 8.
Warning
Type A and type AC fault-current circuit breakers may not be used.
General
4 – 7