Technical information

•all the components in the system must be approved

•it is sufficient for there to be a single branch circuit protector up line from the

rectifier the size/calibration of which must be no larg er than the smallest v alue

of the following two:

a) the size required for the larger of the motors in the group plus the sum of

the full load currents of the remaining motors (in the same way as required

in point c) for the group installation); or

b) the maximum size allowed by the rectifier,in the instructions or in the

markings.

1.6 Three-phase, two-speed or Dahlander motor

The motors with multiple winding and those with Dahlander starting have

multiple power supply terminal strips, each characterised by its own current

characteristics. Every power entrance must be protected as if it were a single

motor on the basis of the rules defined above.

The only exception allowed is the use of a single protection from the BCP short-

circuit that however must be scaled in such a way as to meet the regulations for

all the windings connected downline.

1.7 Reversal of direction

The reversal of direction requires an interlock between the two contactors that

command the direction of turning.

The interlock can be mechanical or electrical, but there is an exception in the

case of Industrial Machinery: in the USA the NFPA 79 standard (and UL508A in

the relative section) require the use of both types of interlock.

1.8 – VFD Inverter and Softstarter

Inverter and softstarter demand that the branch circuit protection, against short-

circuits, is made according to the indications of the instruction manual (as

established in the UL 508A § 31.3.2 ).

Without this datum, it is allowed to size the protection as if it were a motor by

multiplying the feed current of the drive, indicated in the manual, by the

coefficient indicated in the relevant tables.

BRANCH CIRCUIT