SamplexPower PST-1500-12 Mode D'emploi page 32

SECTION 8 |
Table 8.1 Wiring Resistance per Foot
WIRE SIZE,
AWG
AWG#2
AWG#1/0
AWG#2/0
AWG#4/0
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
cables and connectors should be selected to ensure minimum voltage drop between the
battery and the inverter. Thinner cables 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 cable should be such that the voltage drop due to
the current & the resistance of the length of the cable should be less than 2% to 5%. Use
oil resistant, multi-stranded copper wire cables rated at 105ºC / 221°F minimum. Do not use
aluminum cable as it has higher resistance per unit length. Cables 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 approxi-
mate 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 volt-
age 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
disproportionate 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 the Battery Circuit
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 cables that connects the battery to the inverter, thousands of Amperes of current
can flow from the battery to the point of shorting and that section of the cable will
32 | SAMLEX AMERICA INC.
Installation
RESISTANCE IN OHM (Ω)
PER FOOT AT 25°C / 77°F
0.000159 Ω per Foot
0.000096 Ω per Foot
0.000077 Ω per Foot
0.000050 Ω per Foot