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2017 Sensata Technologies
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 2-2 for the fuse size (coordinated with the DC wire
size) recommended for your CSW inverter.
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, to reduce
the possibility for electric shock. For most 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. The grounding conductor for the DC system
shall meet the sizing requirements speci
fi
ed in the NEC for the application,
but must be no smaller than 8 AWG copper.
Example: An inverter used in a marine application under ABYC guidelines
requires the size of the DC grounding conductor to be of an ampacity equal
to or one size less than that of the DC positive conductor.
See Table 2-2 for the minimum ground wire size recommended for your
inverter.
Info:
If the inverter is installed in a vehicle, connect the battery
negative cable directly to the inverter’s negative terminal. DO NOT
connect the negative battery cable meant for the inverter to the
vehicle’s frame/safety ground.
2.4.4 DC Cable Connections
Do not put anything between the battery cable ring lug and the battery
post (see Figure 2-7), or the
fl
at metal part of the inverter’s DC terminal
(see Figure 2-8). 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.
See Table 2-1 for the torque requirements.
