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©
2017 Sensata Technologies
Installation
2.4.1
DC Wire Sizing
It is important to use the correct DC wire to achieve maximum ef
fi
ciency from the system and
reduce
fi
re hazards associated with overheating. Always keep your wire runs as short as practical
to help prevent low voltage shutdowns and keep the DC breaker from nuisance tripping (or open
fuses) because of increased current draw. See Table 2-1 to select the required minimum DC wire
size (and corresponding overcurrent device) based on your inverter model. The cable sizes listed in
Table 2-1 for your inverter model are required to reduce stress on the inverter, minimize voltage
drops, increase system ef
fi
ciency, and ensure the inverter’s ability to surge heavy loads.
If the distance from the inverter to the battery bank is greater than 5 feet (1.5m), the DC wire
size will need to be increased. Longer distances cause an increase in resistance, which affects the
performance of the inverter. Use the overcurrent device previously determined from Table 2-1
and then refer to Table 2-2 to determine the minimum DC wire size needed for various distances.
2.4.2
DC Overcurrent Protection
DC overcurrent protection is not included in the inverter—for safety reasons and to comply with
electrical code regulations—it 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 or a circuit
breaker, and it 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. If a circuit breaker is used as the overcurrent protection device, it can also
be used as the required DC disconnect.
If a fuse is used as an overcurrent device, a Class-T type or equivalent is recommended. This fuse
type is rated for DC operation, can handle the high short-circuit currents, and has a time delay
that allows for momentary current surges from the inverter without opening the fuse. However,
because the fuse can be energized from both directions, the NEC requires that it be installed in
such a manner that the power must be disconnected on both ends of the fuse before servicing.
Use Table 2-1 to select the DC overcurrent device needed based on the recommended minimum
wire size for your particular inverter model (may not meet all local code or NEC requirements).
Table 2-1, Recommended DC Wire/Overcurrent Device for Rated Use
Maximum
Continuous
Current
1
In Free Air
DC Grounding
Electrode Wire
Size
4
Minimum DC Wire
Size (rating)
2
Maximum DC
Fuse Size
3
ME2012
267 amps
#2/0 AWG (67.4 mm
2
)
300 amps
300 amps with
time delay
#6 AWG
(13.3 mm
2
)
ME2512
333 amps
#4/0 AWG (107.16 mm
2
)
400 amps
400 amps with
time delay
#6 AWG
(13.3 mm
2
)
ME3112
413 amps
#4/0 AWG (107.16 mm
2
)
400 amps
400 amps with
time delay
5
#6 AWG
(13.3 mm
2
)
Note
1
– Maximum continuous current is based on the inverter’s continuous power rating at the lowest
input voltage with an inverter inef
fi
ciency factored in.
Note
2
– Copper wire rated with 90°C (194°F) insulation at an ambient temperature of 30°C (86°F),
with a multiple cable
fi
ll factor (0.8) de-rating (if needed).
Note
3
– The next larger standard size overcurrent device may be used if the de-rated cable ampacity
falls between the standard overcurrent devices found in the NEC.
Note
4
– Per the NEC, the DC grounding electrode conductor can be a #6 AWG (33.6 mm
2
) conductor
if that is the only connection to the grounding electrode and that grounding electrode is a rod, pipe,
or plate electrode.
