Installation
GUPS 2400A
–107 Operation Manual
2-7
The following notes apply to Table 2
–2 and to the power cable definition:
1. The above figures are based upon insulated copper conductors at 25°C (77°F), two current
carrying conductors in the cable plus a safety (chassis) ground.
Columns 3 and 4 refer to "one way" ohms and IR drop of current carrying conductors
(e.g., a 50-foot cable contains 100 feet of current carrying conductor).
2. Determine which wire gauge for the application by knowing the expected peak load current
(I
peak
), the maximum tolerated voltage loss (V
loss
) within the cable, and the one way cable
length. The formula below determines which ohms/100 feet entry is required from Column
3. Read the corresponding wire gauge from Column 1.
(Column 3 value) = V
loss
/[I
peak
x 0.02 x (cable length)]
Where:
Column 3 value = Entry of the table above.
Cable length = One way cable length in feet.
V
loss
= Maximum loss, in volts, permitted within cable.
SPECIAL CASE:
Should the V
loss
requirement be very loose, I
peak
may exceed the maximum amperes
(Column 2). In this case, the correct wire gauge is selected directly from the first two
columns of the table.
EXAMPLE:
A 20 ampere (I
peak
) circuit which may have a maximum 0.5 volt drop (V
loss
) along its 15-
foot cable (one way cable length) requires (by formula) a Column 3 resistance value of
0.083. This corresponds to wire gauge size 8 AWG.
If the cable length was 10 feet, the Column 3 value would be 0.125 and the
corresponding wire gauge would be 10 AWG.
3. Aluminum wire is not recommended due to soft metal migration at the terminals which may
cause long term (on the order of years) poor connections and oxidation. If used, increase the
wire gauge by two sizes (e.g., specify 10 gauge aluminum instead of 14 gauge aluminum).
4. Derate the above wire gauge (use a heavier gauge) for higher environmental temperatures
since conductor resistance increases with temperature.
Temperature
Current
°C
°F
Capability
40
104
80%
