18 FXMP25 User Guide
www.controltechniques.com Issue Number: 3
4.5 Cable and fuse size ratings
Maximum continuous input currents are given in section 2.1 Ratings on page 9 to aid
the selection of fuses and cabling.
The cable sizing selected when installing the FXMP25 must comply with local wiring
regulations. The information provided in this section is for guidance purposes only.
The power terminals on the FXMP25 are designed to accommodate a maximum cable
size of 5.26 mm
2
(10 AWG).
The actual size depends on a number of factors including:
• Actual maximum continuous current
• Ambient temperature
• Cable support, method and grouping
• Cable voltage drop
Where continuous field current is reduced, the cable sizing selected can be appropriate
for the reduced current. The field controller parameters should be programmed with the
correct values.
Table 4-2 gives examples of the cable sizes based on IEC 60364-5-52 and UL508C/
NEC. The example cable sizes below assume three current-carrying conductors per
cable or raceway and 40 °C ambient temperature.
Control of current below 250 mA (thyristor holding currents) should be avoided. If
control at this level is required then line reactors must be installed to reduce the effect
of dv/dt as thyristors turn off.
The selection of the correct fuse is essential to ensure the safety of the installation.
The AC supply inputs in the FXMP25 controller are fitted with auxiliary fuses for
protection against short circuits in the FXMP25 controller and field-winding of the
motor. These fuses will not protect the supply cables to the FXMP25 controller. There
are other fuses are suggested to install in branch circuits. The branch circuit fuses will
protect the supply cables to the FXMP25 controller. This section shows recommended
cable sizes and fuse ratings for a number of current levels. Failure to observe this
recommendation will cause a risk of fire.
Wiring must be in accordance with local regulations and codes of practice. The table
shows typical cable sizes for power input and output wiring. In the event of a conflict,
local regulations prevail.
When using reduced cable sizes, the branch circuit protection fuse rating needs to be
reduced in line with the cable size selected.
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