Samlexpower PST-15S-12E Owner's manual - Section 8 |
32 | SAMLEX AMERICA INC.
SAMLEX AMERICA INC. | 33
seCtIOn 8 |
Installation
8.4.3 connection from Batteries to the Dc input Side – Sizing of cables
and Fuses
!
cAUtion!
The input section of the inverter has large value capacitors connected across the
input terminals. As soon as the DC input connection loop (Battery (+) terminal
"
External fuse
"
Positive input terminal
"
Negative input terminal
"
battery
(–) terminal) is completed, these capacitors will start charging and the unit will
momentarily draw very heavy current to charge these capacitors that will produce
sparking on the last contact in the input loop even when the unit is in Off condi-
tion. Ensure that the fuse is inserted only after all the connections in the loop have
been completed so that sparking is limited to the fuse area.
flow of electric current in a conductor is opposed by the resistance of the conductor.
The resistance of the conductor is directly proportional to the length of the conductor
and inversely proportional to its cross-section (thickness). The resistance in the conduc-
tor produces undesirable effects of voltage drop and heating. The size (thickness /
cross-section) of the conductors is specified in mm
2
or in AWG (American Wire Gauge).
Conductors thicker than AWG #4/0 are sized in MCM/kcmil. Table 8.1 below gives Resist-
ance in Ohm (Ω) per foot at 25°C / 77°f for the wire sizing recommended for use with
this inverter.
table 8.1 Wiring Resistance per Foot
WiRe SiZe,
AWG
ReSiStAnce in oHM (Ω)
PeR Foot At 25°c / 77°F
50 mm
2
/ AWG#1/0
0.000100 Ω per foot
120 mm
2
/ AWG#4/0
0.000049 Ω per foot
185 mm
2
/ MCM 350
0.00003 Ω per foot
Conductors are protected with insulating material rated for specific temperature e.g.
90˚C/194˚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 guidelines 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