ABB MU 80, Product Manual

Page: 64 / 102

3.6 Insulation in arc welding stations
Galvanic insulation from the weld circuit
If using the motor unit or gear unit in an arc welding cell, the return currents must
be properly taken care of. The SMB box must always be insulated from the weld
circuit.
Gear units
The rotary units (MTD) and the station interchange units (MID) have the motor
galvanically insulated from the weld circuit, that is, there is no connection between
the weld circuit and protective earth.
SMB box
The SMB box is connected to protective earth and must always be mounted
galvanically insulated from the weld circuit.
Motor units
The motor units are connected to protective earth. When using the motor units in
work piece positioners or other equipment connected to the weld circuit there will
be a connection between the weld circuit and protective earth.
To avoid malfunction:
• Verify that good contact is established between the welding power source
and work piece positioner.
• Never disconnect the weld return cable.
• Verify that the current collector, if used, is working properly and has a low
voltage drop.
Hazardous scenario
The following graphic shows a hazardous scenario with two faults causing the weld
current to flow in protective earth.
• The weld return cable is disconnected from the work piece positioner.
• The weld return cable has contact with protective earth, in this case a cable
channel made of metal.
Continues on next page
64 Product manual - Motor Units and Gear Units
3HAC040148-001 Revision: K
© Copyright 2011 -2018 ABB. All rights reserved.
3 Installation
3.6 Insulation in arc welding stations