Download Ultra Start 4265 series Specifications

UBS Wiring Harness Handbook
Trailer Wiring Data
HOW TO SELECT SIZE OF ELECTRICAL CABLE
Wire is used to carry current from the battery through the vehicle to
various electrical components: lights, instruments, etc.
In automotive use, the grounded return system is used almost
exclusively. In this system, a single wire is run from the battery
through switches to the load and the vehicle itself provides the
ground or return to the battery.
It is important to note that all electric components have a good
ground. In a combination of vehicles (tractor-trailer) it is important
that a good and adequate size ground wire be provided between the
two vehicles to carry the current.
Wire has certain resistance to current flow. The smaller the wire,
the greater the resistance.
Also, as the amount of current (amps) increases, the resistance
(ohms) increases.
For a 12-volt system there are two factors to be considered:
1) Voltage drop is the primary consideration in selecting the proper
electrical wire size. The length of wire in a circuit is the major
contributing factor to voltage drop.
2) The current carrying capacity of the wire. The heavy load in an
undersize wire may increase the temperature of the PVC
insulation above a safe level of 180° F.
The Wire Size charts shown below are provided for easy
selection of wire sizes. These charts, however, neglect losses due to
connections or switches.
To use either of these charts:
a) Determine the total wire length from the power source to the
most distant point in the circuit.
b) Determine the total electrical load on the circuit.
c) Find the load along one edge of the chart. (6v or 12v) depending on
the vehicle voltage in question, taking the next higher load if the
indicated load falls between two points on the chart.
d) Find the cable length required along the edge of the chart, taking
the next higher length (if the exact length is not cited).
e) At the intersection of the length and load column, read the
minimum size wire required for that particular circuit.
Example
WIRE SIZE CHART
For A
For A
12-Volt 6-Volt
System System
10'
Load in Load in
Amps
Amps
Wire
Gauge
TEMPERATURE CHART
Length of Wire (Most Distant Light)
20'
30'
40'
50'
60'
70'
80'
Add 2 feet for connections
and slack to reach around
On a 12-volt system,
obstacles.
operating at an ambient
POWER
SOURCE
temperature of 125° F,
3’
determine the wire size
Most Distant
8’
Light
required for a clearance
light circuit having eleven
lights using No. 97 bulbs.
45’
Wire
8’
a) Find the total ampere
Length
load in the circuit. There Calculation:
are 11 No. 97 bulbs.
3
45
From the bulb chart on
4
pages 50 and 51, you
4’
8
8
determine that each bulb
+ 2
is rated at 0.69 amps.
70 Feet
The total load is 0.69
amps x 11 = 7.59 amps.
b) Find the distance from the power source to the most distant
light. Total distance = 3 + 45 + 4 + 8 + 8 + 2 = 70 ft.
c) In the “Wire Size Chart” below, find the column with the
“Length of Wire” that matches the example. Your most distant
light is 70 ft. Next, find the row with the ampere load that
matches the example. Hint: The next highest value above 7.59
amps is 8.0 amps. At the intersection of this row and column,
you’ll find a 12 gauge wire indicated. This is the correct wire
size to use.
d) Check to see if it’s safe to use a 12-gauge wire at an ambient
temperature of 125° F. In the “Temperature Chart” below, find
the temperature column that matches the example. Your ambient
temperature is 125° F. Next, find the row with the wire gauge
that matches the example. Your wire is 12 gauge. At the
intersection of this row and column, you’ll find that the current
carrying capacity of a 12-gauge wire at 125° F is 32 amps.
That’s well in excess of your 8-amp load, so you’re okay.
90'
100'
Wire
Wire
Wire
Wire
Wire
Wire
Wire
Wire
Wire
Gauge Gauge Gauge Gauge Gauge Gauge Gauge Gauge Gauge
1.0
0.5
18
18
18
18
18
18
18
18
18
18
1.5
0.75
18
18
18
18
18
18
18
18
18
18
2.0
1.0
18
18
18
18
18
18
18
16
16
16
3.0
1.5
18
18
18
18
18
16
16
16
14
14
4.0
2.0
18
18
18
16
16
16
14
14
14
12
5.0
2.5
18
18
18
16
14
14
14
12
12
12
6.0
3.0
18
18
16
16
14
14
12
12
12
12
7.0
3.5
18
18
16
14
14
12
12
12
12
10
8.0
4.0
18
16
16
14
12
12
12
10
10
10
10.0
5.0
18
16
14
12
12
12
10
10
10
10
11.0
5.5
18
16
14
12
12
10
10
10
10
8
12.0
6.0
18
16
14
12
12
10
10
10
8
8
15.0
7.5
18
14
12
12
10
10
10
8
8
8
18.0
9.0
16
14
12
10
10
8
8
8
8
8
20.0
10.0
16
16
12
12
10
10
8
8
8
8
– 54 –
Maximum Current Carrying Capacity
Cable Size
(For 12 Volts at Listed Temperatures)
120° F
125° F
150° F
20 Gauge
15 Amps
13 Amps
9 Amps
18 Gauge
18 Amps
15 Amps
11 Amps
16 Gauge
22 Amps
19 Amps
14 Amps
14 Gauge
27 Amps
23 Amps
17 Amps
12 Gauge
40 Amps
32 Amps
24 Amps
10 Gauge
50 Amps
42 Amps
31 Amps