Danfoss VLT Training Manual page 22

VLT Installation
4) Installation Checks
Fuses must be installed, if not part of VLT
4) Installation Checks
a. Fuses
To comply with UL / cUL, fuses must be wired on the incoming power side of the
drive. The types of fuses needed for each VLT are shown in the technical data
section of the instruction manual. Most VLT units do not include fuses and it is the
responsibility of the installer to ensure the proper fusing in order to comply with
local electrical codes and satisfy UL requirements. Some of the larger power
(>75HP) VLTs can be supplied with fuses built in from the factory, verify this before
installing additional external fuses. In the example above fuses and a disconnect
switch are diagramed. To comply with UL never wire the drive to circuit breakers
because they do not trip as fast as fuses.
All Danfoss drives come with DC Chokes which greatly reduces the harmonics going
back to the supply transformer. The reduction of Harmonics is equivalent to the use
of a 3% Input Line Reactor without the associated loss in power. There is no
advantage of placing a 3% Line Reactor on the incoming power of a Danfoss VLT.
Rev.02
a. Fuses
• Check your VLT Instruction Manual - use the index in
the back to find the page reference for "Fuses"
Input Line Reactor not required
• Since the VLT comes with DC Chokes (Coils) it
automatically reduces the harmonics to the same level
as if you were using a 3% input line reactor.
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