40 | SAMLEX AMERICA INC.
SAMLEX AMERICA INC. | 41
Table 8.1 Battery Cable Resistance per Foot
WIRE SIZE,
AWG
RESISTANCE IN OHM (Ω)
PER FOOT AT 25°C / 77°F
AWG#2
0.000159 Ω per Foot
AWG#1/0
0.000096 Ω per Foot
AWG#2/0
0.000077 Ω per Foot
AWG#4/0
0.000050 Ω per Foot
Conductors are protected with insulating material rated for specific temperature e.g.
105˚C/221˚F. As current flow produces heat that affects insulation, there is a maximum
permissible value of current (called “Ampacity”) for each size of conductor based on
temperature rating of its insulation. The insulating material of the cables will also be
affected by the elevated operating temperature of the terminals to which these are con-
nected. Ampacity of cables is based on UL-458 and the National Electrical Code (NEC)-
2014. Please see details given under “Notes for Table 8.2”.
The DC input circuit is required to handle very large DC currents and hence, the size of
the wires and connectors should be selected to ensure minimum voltage drop between
the battery and the inverter. Thinner wires and loose connections will result in poor
inverter performance and will produce abnormal heating leading to risk of insulation
melt down and fire. Normally, the thickness of the wire should be such that the voltage
drop due to the current & the resistance of the length of the wire should be less than
2%. Use oil resistant, multi- stranded copper wire wires rated at 90ºC minimum. Do not
use aluminum wire as it has higher resistance per unit length. Wires can be bought at a
marine / welding supply store.
Effects of low voltage on common electrical loads are given below:
- Lighting circuits - Incandescent and Quartz Halogen: A 5% voltage drop causes an
approximate 10% loss in light output. This is because the bulb not only receives less
power, but the cooler filament drops from white-hot towards red-hot, emitting much
less visible light.
- Lighting circuits - Fluorescent: Voltage drop causes a nearly proportional drop in
light output.
- AC induction motors: These are commonly found in power tools, appliances, well
pumps etc. They exhibit very high surge demands when starting. Significant voltage
drop in these circuits may cause failure to start and possible motor damage.
- PV battery charging circuits: These are critical because voltage drop can cause a dis-
proportionate loss of charge current to charge a battery. A voltage drop greater than
5% can reduce charge current to the battery by a much greater percentage.
8.4.4 Fuse Protection In Battery Circuits
A battery is an unlimited source of current. Under short circuit conditions, a battery can
supply thousands of Amperes of current. If there is a short circuit along the length of the
SECTION 8 |
Installation
