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3.0 Installation
DC Wiring (continued)
DC Disconnect and Over-current Protection
NOTE: for Table 3-3:
*The NEC allows rounding
to the next standard fuse
size from the cable rating
(i.e.,150 amp cable size
rounds u to a standard
175 amp size.)
C
a
b
e l
S
z i
e
R
e
q
i u
e r
d
#
2
A
W
G
#
2
0 /
A
W
G
#
4
0 /
A
W
G
©2002 Xantrex Technology Inc. All Rights Reserved.
P/N 975-0026-01-01 Rev A 06/2002
For safety and compliance with regulations, battery over-current protection is
required. Fuses and disconnects must be sized to protect the wiring in the
system and are required to open before the wire reaches its maximum current
carrying capability.
The National Electrical Code (NEC) requires both over-current protection and a
disconnect switch for residential and commercial electrical systems. These items
are not supplied as part of the inverter. However, Xantrex offers a DC circuit
breaker disconnect module specifically designed to meet NEC compliance. Two
amperage ratings are available: a DC250 (250 amps) and a DC175 (175 amps).
When sizing the DC disconnect, the expected continuous load on the inverter
should be used to determine the DC current. Efficiency loss through the inverter
increase the DC current draw and must be accounted for. Divide the maximum
continuous current draw by the inverter's efficiency. Add a 25% safety margin to
comply with code requirements.
The term "free air" is defined by the NEC as cabling that is not enclosed in a
conduit or a raceway. Cables enclosed in conduit or raceways have substantially
lower continuous current carrying ability due to heating factors.
Some installations may not require conduit or a disconnect device, although
over-current protection is still required. Xantrex offers a fuse block (TFB)
providing the code required inverter over-current protection for these
applications. These fuses are available in 110, 200, 300, 350 and 400 amp sizes.
See Table 3-3 below for battery cable to maximum breaker/fuse size.
M
a
i x
R
t a
n i
g
n i
B
e r
C
o
n
d
u
t i
S
1
1
5
a
m
p
s
m
a
. x
N
1
7
5
a
m
p
s
m
a
. x
D
C
2
5
0
a
m
p
s
m
a
. x
D
C
Table 3-3
Battery Cable to Maximum Breaker/Fuse Size
m
u
m
a
k
r e
R
t a
n i
g
n i
"
F
e r
z i
e
A /
1
7
0
a
m
p
s
1
7
5
2
6
5
a
m
p
s
m
2
5
0
3
6
0
a
m
p
s
m
M
a
i x
m
u
m
e
i a
" r
F
u
s
e
S
z i
e
m
a
x
* .
T
F
B
2
0
0
a
x
* .
T
F
B
3
0
0
a
x
* .
T
F
B
4
0
0
35
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