AMETEK SGA Series - Manual (Page 32)

Installation Sorensen SGA Series
2-12 M550129-01 Rev AG
When determining the optimum cable specification for your power
applications, the same engineering rules apply whether at input or output of
an electrical device. Thus, this guide applies equally to the AC input cable
and DC output cable for this power supply and application loads.
Power cables must be able to safely carry maximum load current without
overheating or causing insulation degradation. It is important to power supply
performance to minimize IR (voltage drop) loss within the cable. These
losses have a direct effect on the quality of power delivered to and from the
power supply and corresponding loads.
When specifying wire gauge, consider derating due to the operating
temperature at the wire location. Wire gauge current capability and insulation
performance drops with the increased temperature developed within a cable
bundle and with increased environmental temperature. Thus, short cables
with generously derated gauge and insulation properties are recommended
for power source applications.
Be careful when using published commercial utility wiring codes. These
codes are designed for the internal wiring of homes and buildings and
accommodate the safety factors of wiring loss, heat, breakdown insulation,
aging, etc. However, these codes consider that up to 5% voltage drop is
acceptable. Such a loss directly detracts from the performance specifications
of this SG power supply. Also, consider how the wiring codes apply to
bundles of wire within a cable arrangement.
In high performance applications requiring high inrush/ transient currents,
additional consideration is required. The cable wire gauge must
accommodate peak currents developed at peak voltages, which might be up
to ten times the average current values. An underrated wire gauge adds
losses, which alter the inrush characteristics of the application and thus the
expected performance.
Table 2 –9 presents wire resistance and resulting cable voltage drop at
maximum rated current, with the wire at 20°C. Copper wire has a temperature
coefficient
of α = 0.00393Ω/°C at t1 = 20°C, so that at an elevated
temperature, t2, the resistance would be R2 = R1 (1 + α (t2 - t1)).