ZENER 8000-V Installation Manual
IM00165
11
ZENER 8000-V Power wiring
AC line overcurrent protection device
An overcurrent protection device is required in the AC supply to the ZENER 8000-V. The purpose of this device
is twofold:
To provide thermal protection for the cables etc between the location of the overcurrent
protective device (usually at the origin of the relevant supply sub
‑
circuit) and the ZENER 8000-V. This is
predominantly a measure to prevent injury and property damage from melting and fire.
To limit the energy available at the location of a short circuit or near short circuit in the
unlikely, but possible, event of a major arcing fault in wiring or within the ZENER 8000-V enclosure. This
measure is to control the risk of personal injury and property damage due to arc flash,
conductor erosion, explosion and the like.
The first requirement is relatively slow and normally provided by fuses or the timed (traditionally
referred to as thermal) characteristic of a circuit breaker. Note that the protection offered by this device on the
AC line side of the ZENER 8000-V does not extend to the output (motor) side because the AC line side current
may be considerably less than the ZENER 8000-V output current when operating at less than full speed. This is a
consequence of the high efficiency of the ZENER 8000-V and the power required by the load being a
product of torque and speed, the AC input power (and current) reduce with speed, even if the load torque
remains high. The ZENER 8000-V itself provides both timed overcurrent (I
2
t) and instantaneous overcurrent
protection for the output wiring and motor.
The second requirement may be met with either the instantaneous trip function of a circuit breaker or a fuse.
The total amount of energy let through in the event of a short circuit or near short circuit event is usually the
critical factor in determining the injury risk, extent of physical damage and consequently the time and expense
involved in repair. The let through energy may be accessed in terms of the I
2
t (time integral of current squared)
let through the protective device in the process of interrupting the fault current. In order to minimise the I
2
t let
through and the associated risks of injury, property damage and downtime, we recommend the use of
appropriately rated current limiting
2
type fuses. In some circumstances, the user’s protection needs may be
met by a suitably selected circuit breaker however, we strongly recommend that any such selection be based on
detailed engineering evaluation and not simply a catalogue selection.
Coordination of supply circuit protection and switchgear
Either fuses or a circuit breaker must be connected as shown. The protective elements used and any upstream
switchgear (contactors, isolation switches etc) must be selected with due regard for the prospective short
circuit currents of the electrical supply and the requirements of your local electrical code. The selection should
provide for “type II” (no damage) coordination as per IEC 60947 or Australian Standard AS 3947.
Cable sizes
Power cables between the various system components are the responsibility of the installer and the
size and type to be used should be selected to suit the application and on the basis of the continuous current
rating of the ZENER 8000-V and a minimum temperature rating of 70C. Cables sizes should be selected
according to local wiring rules using the currents given in the table on page 51. Note that the power
terminals of the ZENER 8000-V enclosure and the input/output line reactors are intended for use with
cables terminated in crimp lugs with a single hole to match the diameter of the hole or bolt provided.
2
“Current limiting” describes the ability of an overcurrent protective device (fuse or circuit breaker) to reduce the peak
current that flows in a circuit, by opening and clearing the fault in a sub half-cycle time frame.
