Xantrex Technology SW Series DC Disconnect and Overcurrent Protection, Cable Size Required

INSTALLATION

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.

CABLE SIZE

REQUIRED

#2 AWG

00 AWG

0000 AWG

Table 3, Battery Cable To Maximum Breaker/Fuse Size

RATING IN	MAXIMUM	RATING IN
CONDUIT	BREAKER SIZE	“FREE AIR”
115 amps	125 amps*	170 amps
175 amps	175 amps	265 amps
250 amps	250 amps	360 amps

MAXIMUM FUSE SIZE

175amps*

300amps*

400amps*

*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.

 2001 Xantrex Technology, Inc.	Telephone: 360/435-8826	SW Series Inverter/Charger
5916 - 195th Street N. E.	Fax: 360/435-2229	Part No. 2031-5
Arlington, WA 98223	www.traceengineering.com	Rev. C: February 2001

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