ABB ACS 600 Hardware Manual page 11

Relay Contacts
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ACS/ACC/ACP 604/607 Frequency Converters
When used with inductive loads (relays, contactors, motors), the relay
contacts of ACx 600 must be protected with varistors or RC networks
(AC) or diodes (DC) against voltage transients. The protective
components should not be installed at the NIOC board terminal block.
The ACx 600 and adjoining equipment must be properly earthed.
The ACx 600 and the motor must be earthed at the installation site to
ensure personnel safety in all circumstances and in addition to reduce
electromagnetic emission and pick-up. Make sure that earthing
(grounding) conductors are adequately sized as required by safety
regulations.
In CE compliant installations and in other installations where EMC
emissions must be minimized, 360° high frequency earthing
(grounding) of cable entries is done in order to suppress
electromagnetic disturbances. In addition, cable screens have to be
connected to protective earth (PE) in order to meet safety regulations.
Power cable screens are suitable for use as equipment earthing
(grounding) conductors only when the screen conductors are
adequately sized as required by safety regulations.
The ACx 600 earth (ground) terminals should not be connected in
series in case of a multiple installation. Incorrect earthing can cause
physical injury, death or equipment malfunction and increase
electromagnetic interference.
ACx = ACS/ACC/ACP
Safety Instructions
ix