Xantrex Technology SW Series - Manual (Page 31)

INSTALLATION
 2001 Xantrex Technology, Inc.
5916 - 195th Street N. E.
Arlington, WA 98223
Telephone: 360/435-8826
Fax: 360/435-2229
www.traceengineering.com
SW Series Inverter/Charger
Part No. 2031-5
Rev. C: February 2001
Page
23
DC DISCONNECT AND OVERCURRENT PROTECTION
For safety and to comply with regulations, battery over-current protection is required. Fuses and
disconnects must be sized to protect the wiring in the system. The fuse or disconnect is required to open
before the wire reaches its maximum current carrying capability.
For residential and commercial electrical systems, the National Electrical Code requires both overcurrent
protection and a disconnect switch. These installation parts are not supplied as part of the inverter.
However, Xantrex offers a DC rated, UL listed, circuit breaker disconnect specifically designed for use
with Trace™ inverters for applications requiring NEC compliance. Two amperage ratings are available - a
DC250 (250 amps) and a DC175 (175 amps). These disconnects are available in a single or double pole
configuration to handle either one or two inverters. The DC disconnect enclosure will accommodate up to
four smaller breakers for use as DC load disconnects, PV array disconnects, etc. and the top is designed
to allow direct connection of up to two Xantrex charge controllers. The Trace™ DC disconnect is not
designed to accept doubled (paralleled) cables which may be required for long cable runs. Also, the plastic
red and black covers on the end of the inverter is not designed to accommodate dual cables. If dual
cables are used, the optional conduit box (SWCB) should be used.
When sizing the DC disconnect, the expected continuous load on the inverter is used to determine the DC
current involved. You must account for the efficiency loss through the inverter (see the POWER VS.
EFFICIENCY section on page 59 in this manual) which increases the DC current draw. Divide the
maximum continuous current draw by the lowest efficiency to determine the DC current, a 25% safety
margin should be included to comply with the code requirements. When a breaker has been selected as
the overcurrent device, tighter sizing may be acceptable since the breaker is more easily reset when
compared to a high current, bolt-in type fuse.
Marine and RV installations typically do not require conduit or a means of disconnection, although
overcurrent protection (fuse) is required. Xantrex offers a fuseblock (TFB) that provides the code required
inverter overcurrent protection for residential, commercial, RV and Marine applications.
TFB’s include a fast acting, current limiting class-T fuse to protect your battery, inverter and high
amperage cables from damage by short circuits and overloads. This fuse provides extremely fast
protection when a short circuit occurs. When properly selected, it also has a time delay that allows the
inverter to surge to full power without blowing the fuse. A slide off cover prevents accidental contact with
the fuse’s live terminals. For maximum protection, install the fuseblock within 18 inches (45 cm) of the
battery. The fuses are available in 110, 200, 300, and 400 amp sizes.
Use Table 3 below, to determine the proper size disconnect (breaker) or fuse for the battery cables you
are using. These recommendations may not meet all local code or the NEC requirements, consult your
applicable electrical code for more information regarding acceptable fuse and cable sizes.
Table 3, Battery Cable To Maximum Breaker/Fuse Size
CABLE SIZE
REQUIRED
RATING IN
CONDUIT
MAXIMUM
BREAKER SIZE
RATING IN
“FREE AIR”
MAXIMUM
FUSE SIZE
# 2 AWG 115 amps 125 amps* 170 amps 175 amps*
00 AWG 175 amps 175 amps 265 amps 300 amps*
0000 AWG 250 amps 250 amps 360 amps 400 amps*
*The NEC allows rounding up to the next standard fuse size from the cable rating, i.e. 150-amp cable size
rounds up to a standard 175-amp fuse or breaker size. The term "free air" is defined by the NEC as cabling that
is not enclosed in conduit or a raceway. Cables enclosed in raceways or conduits have substantially lower
continuous current carrying ability due to heating factors.
Contact your Xantrex dealer to order the inverter disconnects/fuses or see the OTHER PRODUCTS
section in this manual on page 129 for more information.