AMETEK SGI Series User Manual
Page 34
Installation
Sorensen SGI Series
2-12
M550221-01 Rev AA
When determining the optimum cable specification for your power applications,
the same engineering rules apply whether at the 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 instruments
and corresponding loads.
When specifying wire gauge, consider derating due to 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 quality 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.
–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)).