Magnum Energy MS-G Series - Manual (Page 24)

Page 16
©
2015 Sensata Technologies
Installation
2.4.1 DC Wire Sizing
It is important to use the correct sized DC wire to achieve maximum effi ciency from the system
and to reduce fi re hazards associated with overheating. Always keep your wire runs as short as
practical to prevent low voltage shutdowns and to keep the DC breaker from nuisance tripping (or
open fuses) because of increased current draw. See Table 2-1 to select the minimum DC wire size
(and corresponding overcurrent device) required based on your inverter model. The cable sizes
listed in Table 2-1 are required in order to reduce stress on the inverter, minimize voltage drops,
increase system effi ciency, and ensure the inverter’s ability to surge heavy loads.
If the distance from the inverter to the battery bank is >5 feet (1.5 m), the DC wire needs 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 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. In a residential or commercial electrical installation, 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 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 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
Inverter
Model
Maximum
Continuous
Current 1
Using Conduit In Free Air
DC
Grounding
Electrode
Wire Size 4
Minimum DC
Wire Size
(rating) 2
Recommended
DC Breaker
Size
Minimum DC
Wire Size
(rating) 2
Maximum DC
Fuse Size 3
MS2000-G 267 amps
#4/0 AWG
(107.2 mm 2 )
[260 amps]
250 amps 5
#2/0 AWG
(67.4 mm 2 )
[300 amps]
300 amps with
time delay
#6 AWG
(13.3 mm 2 )
MS2012-G 267 amps
#4/0 AWG
(107.2 mm 2 )
[260 amps]
250 amps 5
#2/0 AWG
(67.4 mm 2 )
[300 amps]
300 amps with
time delay
#6 AWG
(13.3 mm 2 )
MS2812-G 373 amps
#4/0 AWG
(107.2 mm 2 )
[260 amps]
250 amps 5
#4/0 AWG
(107.2 mm 2 )
[405 amps]
400 amps with
time delay
#6 AWG
(13.3 mm 2 )
MS4024-G 267 amps
#4/0 AWG
(107.2 mm 2 )
[260 amps]
250 amps 5
#2/0 AWG
(67.4 mm 2 )
[300 amps]
300 amps with
time delay
#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 ineffi 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 derated 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 conductor if that is the only
connection to the grounding electrode and that grounding electrode is a rod, pipe, or plate electrode.
Note 5 – May not allow continuous operation at full rated power as defi ned by the NEC.