1-306 ACH550-UH User’s Manual
Technical data
Note: ACH550-UH drives are shipped with the screw removed (but included in the
conduit box).
EM3 (an M4x16 screw) makes an internal ground connection
that reduces electro-magnetic emission. Where EMC (electro-
magnetic compatibility) is a concern, and the network is
symmetrically grounded, EM3 may be installed. For
reference, the diagram at right illustrates a symmetrically
grounded network.
Floating networks
WARNING! Do not attempt to install or remove EM1, EM3, F1 or F2 screws while
power is applied to the drive’s input terminals.
For floating networks (also known as IT, ungrounded, or impedance/resistance
grounded networks):
• Disconnect the ground connection to the internal RFI filters:
– Frame sizes R1…R4: Remove the EM1 screw (unit is shipped with EM3
removed, see Connection diagrams on page 1-20).
– Frame sizes R5…R6: Remove both the F1 and F2 screws (see page 1-21).
• Where EMC requirements exist, check for excessive emission propagated to
neighboring low voltage networks. In some cases, the natural suppression in
transformers and cables is sufficient. If in doubt, use a supply transformer with
static screening between the primary and secondary windings.
• Do NOT install an external RFI/EMC filter, such as one of the kits listed in
EN 61800-3 compliant motor cables on page 1-312. Using an RFI filter grounds
the input power through the filter capacitors, which could be dangerous and could
damage the unit.
Unsymmetrically Grounded Networks – EM3 Must Be Out
Grounded at the
corner of the
delta
Grounded at the
mid point of a
delta leg
Single phase,
grounded at an
end point
Three phase
“Variac” without
solidly grounded
neutral
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