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Balance of System
Shop solar BOS components — PV wire, combiner boxes, DC disconnects, breakers, fuses, surge protection, and conduit. Wholesale pricing on NEC-compliant balance of system hardware for professional installers.
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10/3 SEOOW Portable Cord, 600V UL/CSA, Power CablesSKU: SEOOW-CORD
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125VDC Panel Mount Breaker - Width 1 inch (25.4mm) - 1/4 studsSKU: MNEDCRT
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150VDC din rail mount breaker - non polarizedSKU: MNEPVxx-150-1PNP
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2/0 Busbar, Insulator And Cover with 5 Wire LocationsSKU: MNTBB2
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2/0 Busbar, insulator and cover with 9 wire locationsSKU: MNTBB2-9
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300VDC Din Rail Mount Breaker, Single Pole, PolarizedSKU: MNEPV##-300-1PP
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400amp Copper Bus Bar - 4x M10 Positive and 4x M10 NegativeSKU: BUSBAR400AMP8XM10RB
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50 amp 300VDC ground fault protector din rail mountSKU: MNDC-GFP50-300
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63 amp 150VDC din rail mount DC ground fault protectorSKU: MNDC-GFP63
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80 amp 150VDC panel mount DC ground fault protectorSKU: MNDC-GFP80
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Busbar, insulator and cover with 15 wire locationsSKU: MNTBB2-15
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Bussmann Fusetron Dual-Element Class Rk5 FusesSKU: BUSSMANNXXXAMPXXXVAC
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Communication Cable for Tigo, Sol-ark, CAT 5e, 600v 90c USE-2 Sunlight Resistant UL-444SKU: CAT5E600V
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Midnite Solar MNEDC175RT Remote Trip 175 Amp 125VDC Panel Mount BreakerSKU: MIDMNEDC125RT
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RS-485 Shielded 2 Pair 24AWG Communication cable for Tigo, Sol-ark, Modbus, Canbus - UL 1685SKU: RS485COMS
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Solar Cable made with Stäubli Original MC4 connectorsSKU: SOLARCABLE-
Balance of System (BOS) Buying Guide
Balance of system components are everything between the panels and the inverter output — wire, overcurrent protection, disconnects, combiners, and surge protection. Properly specified BOS hardware protects the system, satisfies code, and passes inspection the first time.
Combiner Boxes
A DC combiner box serves as the central hub when a system has more than two or three panel strings. Each string connects through its own overcurrent protection device (fuse or breaker) before feeding into a common busbar. This isolates a faulted string and prevents backfeed from the remaining strings. Key internal components include string fuses or breakers, positive and negative busbars, a DC disconnect or isolator switch, a surge protection device (SPD), and a grounding bar. For residential systems a 2–4 string combiner is typical; commercial arrays may use 12–24 string boxes with integrated string-level monitoring.
Wire, Conduit & Connectors
PV wire (USE-2 / PV Wire) is rated for direct sunlight exposure and higher temperatures than standard building wire. Size conductors to keep voltage drop under 3 % over the full run from combiner to inverter — the three factors are amperage, voltage, and distance. Module-level connections use MC4 or equivalent locking connectors rated for the system voltage. All exposed wiring on rooftops must be secured in conduit or approved cable management per NEC Article 690. Use copper conductors for all DC circuits; aluminum is acceptable on the AC side for larger feeders where cost savings justify the larger conduit size.
Fuses, Breakers & Disconnects
Overcurrent protection devices must be DC-rated — standard AC breakers cannot safely interrupt a DC arc. Size string fuses at 1.56 times the panel short-circuit current (two NEC 1.25x multipliers stacked). DC disconnects are required between the array and the inverter and between the inverter and the grid, giving firefighters and technicians visible isolation points. Use fuses where cost matters and replacement is simple; use breakers where frequent resets are expected, such as on commercial arrays where nuisance trips during commissioning are common.
Surge Protection & Grounding
A Type 2 DC surge protection device (SPD) at the combiner box protects against lightning-induced transients and switching surges. SPDs should be installed with the shortest possible lead length to the grounding bar — long leads reduce clamping effectiveness. Equipment grounding connects all metallic racking, enclosures, and frames to the grounding electrode system per NEC 250. Verify that all BOS components carry the appropriate listings: UL 248-19 for PV fuses, UL 489B for DC breakers, and UL 1449 for SPDs.
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