Rockwell Automation 8720MC High Performance Drives Installation Manual - Manual (Page 70)

Publication 8720MC-IN001D-EN-P — December 2002
3-8 Connecting Your 8720MC
Grounded Distribution
Systems The AC input drives are designed for use with conventional
three-phase supplies that are symmetrical with respect to ground.
Surge suppression devices are included to protect the drive from
lightning-induced over voltage between line and ground. For this
reason, use a neutral grounded system. The drive works with a
grounded phase, but you may want to use an isolation transformer to
provide a supply balanced with respect to ground.
Figure 3.3
Recommended 8720MC Grounding
Ungrounded Distribution
Systems All 8720MC AC input drives are equipped with a metal oxide varistor
(MOV). The MOV provides voltage surge protection, phase-to-phase
as well as phase-to-ground, which is designed to meet IEEE 587. The
MOV circuit is designed for surge suppression only (transient line
protection), not continuous operation.
With ungrounded distribution systems, the phase-to-ground MOV
connection could become a continuous current path to ground. MOV
line-to-line and line-to-ground voltages should not exceed the input
voltage rating shown in Appendix A. Exceeding these values may
cause physical damage to the MOV.
R (L1)
S (L2)
T (L3)
PE
Ground Rod/Grid
or Building Structure Steel
Conduit/4-Wire Cable
U (T1)
V (T2)
W (T3)
PE/Gnd TE
Shield
Motor Frame
PE
Ground per
Local Codes
PE
8720 MC
HIGH PERFORMANCE DRIVE