Rockwell Automation 825 Smart Motor Manager User Manual - Manual (Page 31)

Equipment Description 2-11
Publication 825-UM001B-EN-P January 2001
Core Balance Current Transformer
Table 2.H Recommended Data for Core Balance Current Transformer
A core balance current transformer, current ratio = 100:1, is available, and might suit most
applications. (Max. earth (ground) fault current = 30 A.
Short-Circuit Protection
Choosing a Circuit Breaker or Fuse and Associated Contactor
The branch circuit short-circuit protective device series (circuit breaker or fuse) must assure
that the motor can start while interrupting short-circuit currents rapidly enough to prevent
damage to the installation. To aid in the latter, the fuse rating should be as low as possible.
The lowest possible fuse rating depends on the starting current of the motor and the tripping
time set on the Smart Motor Manager.
The Short-Circuit Coordination of the Starter Must Always be Taken into Account
The contactor receives its tripping signal when the Smart Motor Manager basic unit trips. The
basic unit interrupts all current up to the point of intersection with the time/current
characteristics of the circuit breaker or fuse.
When starting large motors, the main contacts on the contactor are subjected to high thermal
loads. If the motor starting time exceeds a certain limit, the maximum permissible current has
to be reduced.
The rating of the fuse or contactor must also allow for the prospective short-circuit current.
The Bulletin 825 converter modules are short-circuit proof.
The coordination (grading) diagrams for contactors are available on request.
Nominal ratio K
n
=
minimum detectable earth (ground) fault
Pickup current of basic unit earth (ground) fault protection
Burden: Measuring circuit 825-M…
Power consumption at max. rated current
0.4 VA
Continuous thermal current 0.5 A
Thermal current, 1 s duration 25 A
Frequency of input current 50/60 Hz