T D App endix D - Tehnial data
D.1 Supp orted earthing systems
International standard IEC 60364 resp. DIN VDE0100 distinguishes three families of earthing arrangements,
using the two-letter codes TN, TT, and IT.
• Within a TN system one point is directly connected with earth, usually the star point in a three-phase
system. The body of the electrical device is connected with earth via this earth connection at the trans-
former.
• Within a TT system the protective ear th connection of the consumer is provided by a local connection
to earth, independent of any earth connection at the generator.
• Within a IT system there is no direct connection between active wires (L1, L2, L3, N) and grounded
parts (PE). The body of the electric device is connected to earth. Separation is accomplished by the use
of an isolating transformer or an independent power source (generator, battery).
Within TN or TT systems a sufficient low impedant earth fault will trigger an overcurrent circuit-breaker or
fuse. A higher impedant earth fault however won’t trigger the fuse, so an RCD is usually employed.
In IT systems, a single insulation fault is unlikely to cause dangerous currents to flow through a human body
in contact with earth, because no low-impedance circuit exists for such a current to flow. However, a first
insulation fault can effectively turn a n IT system into a TN system, and then a second insulation fault can
lead to dangerous body currents. Worse, in a multi-phase system, if one of the live conductors made contact
with earth, it would cause the other phase cores to r ise to the phase-phase voltage relative to earth rather than
the phase-neutral voltage.
NOTE
Operation of b maXX® BM3400 devices is generally possible at TT and TN sy stems.
The earthing systems commonly used in the USA c learly distinguish from systems used in eu-
ropean networks. Other than in the IEC there is a corner grounded delta system besides the
center grounded system (Solidly Grounded Wye), which is similar to the TN-S system.
Operation on a gr ounded delta system is only allowed for single-phase devices, because in this
case the necessary air and creepage path will be complied with.
With a triple-phase device operation on a grounded delta system is b a sically only allowed for
devices, which have a type key like BM34XXX-L4XXX-XXXXX- X.
Operation with DC link connection bar and attendance of an inverter with energetic recov-
ery system is strictly forbidden, because in this operation mode the Y capacitors will be over-
loaded by voltage.
170
Instrution Manual
b maXX
®
BM3400
from 206 Doument No.: 5.07013.03
Baumueller Kamenz GmbH
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