Dc Overcurrent Protection; Dc Grounding; Dc Cable Connections - Magnum CSW1012 Owner's Manual

2.0 Installation
2.4.2

DC Overcurrent Protection

For safety reasons and to comply with electrical code regulations, DC
overcurrent protection must be provided as part of the installation. The DC
overcurrent protection device must be installed in the positive DC cable line,
it can be a fuse (with a disconnect switch) or a circuit breaker and must
be DC-rated. It must be correctly sized according to the size of DC cables
being used, which means it is required to open before the cable reaches its
maximum current carrying capability, thereby preventing a fi re. The NEC
requires both overcurrent protection and a disconnect switch.
Because batteries can deliver thousands of amps in an instant during a
short, you are required to install a DC-rated fuse (or circuit breaker) that
has a interrupt current rating (known as Amps Interrupting Current or AIC)
that can withstand the short-circuit current without explosion or damage.
If a fuse is used as an overcurrent device, a Class-T type or equivalent is
highly recommended when used with inverters. A Class-T fuse is rated for
DC operation, can handle very high short-circuit currents (up to 100,000
amps), and has a time delay that allows for momentary current surges from
the inverter without opening the fuse. In some installations, if the combined
short-circuit current of all the batteries in the bank is determined to be
2,700 amps or less, then an ANL type of fuse may be used—if in doubt, use
a Class-T fuse. See Table 2-1 for the fuse size (coordinated with the DC wire
size) recommended for the CSW1012.
2.4.3

DC Grounding

The inverter should always be connected to a permanent, grounded wiring
system. The idea is to connect the metallic chassis of the various enclosures
together to have them at the same voltage potential, which reduces the
possibility for electric shock. For the majority of installations, the inverter
chassis and the negative battery conductor are connected to the system's
ground bond via a safety grounding conductor (bare wire or green insulated
wire) at only one point in the system. Per the NEC, the DC grounding
conductor is required to be no less than the wire size of the DC positive/
negative cables. Use a ring terminal or box lug to connect the DC ground
wire to the DC ground screw (Figure 1-2, item 12). If the inverter is in a
vehicle, DO NOT connect the battery negative (-) cable to the vehicle's frame/
safety ground—only connect to the inverter's negative battery terminal.
See Table 2-1 for the ground wire size (coordinated with the DC wire size)
recommended for the CSW1012.
2.4.4

DC Cable Connections

Do not put anything between the battery cable ring lug and the battery post
(see Figure 2-4), or the fl at metal part of the inverter's DC terminal (see
Figure 2-5). When connecting the battery cable, it should be placed directly
against the battery post or inverter terminal. Incorrectly installed hardware
causes a high resistance connection which could lead to poor inverter
performance, and may melt the cable and terminal connections.
Use an insulated 10mm wrench or socket to tighten the M6-1.0 Hex nuts to
79 to 96 lbf-in (8.9 to 10.9 N-m) for each inverter input terminal.
Info: The DC terminal and Hex nuts are made of stainless steel,
which have a high likelihood of galling or thread seizing while being
tightened. To reduce the risk of the bolt and nut seizing—causing
the bolts to strip or to snap/break off—use an anti-seize lubricant,
tighten the fasteners slowly (at low rpms) without interruption, and
apply only light pressure.
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