Installation
2-6
GUPS 2400A
–104 Operation Manual
2.6
Wire Gauge Selection
The following guidelines assist in determining the optimum cable specification for the user's
power applications. These guidelines are equally applicable to both DC and low frequency AC
(up to 450 Hz) power cabling. The same engineering rules apply whether going into or out of an
electrical device. Thus, this guide applies equally to the input cable and output cable for this
Elgar instrument and application loads.
Power cables must be able to safely carry maximum load current without overheating or causing
insulation destruction. It is important to everyday 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, the operating temperature needs to be considered. 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.
Avoid 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 instrument.
Frequently, these codes do not consider bundles of wire within a cable arrangement.
In high performance applications, as in motor start-up and associated inrush/ transient currents,
additional consideration is required. The cable wire gauge must consider peak voltages and
currents which may be up to ten times the average values. An underrated wire gauge adds
losses which alter the inrush characteristics of the application and thus the expected
performance.
Table 2
–2 identifies popular ratings for DC and AC power source cable wire gauges.
Column 1
Size
(AWG)
Column 2
Amperes
(Maximum)
Column 3
Ohms/100 Feet
(One Way)
Column 4
IR Drop/100 Feet
(Col. 2 x Col. 3)
14
15
0.257
3.85
12
20
0.162
3.24
10
30
0.102
3.06
8
40
0.064
2.56
6
55
0.043
2.36
4
70
0.025
1.75
2
95
0.015
1.42
1/0
125
0.010
1.25
3/0
165
0.006
1.04
Table 2
–2. Recommended Wire Gauge Selection Guide
Summary of Contents for GUPS 2400A-104
Page 2: ......
