Ask any installer "what does BOS mean?" and they'll say: everything that isn't the solar panel or the inverter. From the string combiner box on the roof, all the way to the AC output that goes into your home — that's Balance of Systems, and skipping it is the #1 reason cheap solar plants fail early.
1. What does "BOS" stand for?
BOS = Balance Of Systems. It covers every electrical and mechanical component between your PV modules and the inverter (DC side), and between the inverter and your load/grid (AC side). A well-engineered BOS means a 25-year plant; a bad one means nuisance trips, fire risk and warranty claims.
2. The DC-side family
🔌 Array Junction Box (AJB / Combiner Box)
The AJB sits on the roof, just after the string of modules. It brings 4–8 strings together, fuses each one, adds a Surge Protection Device (SPD), an isolation switch, and MC4 connectors for the output cable. An IP-65 polycarbonate enclosure is mandatory for outdoor use.
- DC string protection — one bad string doesn't kill the plant
- Lightning surge protection — SPD Type-2, 40kA minimum
- DC isolator / MCB for firemen and maintenance safety
⚡ DC Distribution Box (DCDB)
Located just before the inverter. Houses the DC MCB, fuse holders, SPD, terminals and PG glands. For larger plants this is where you isolate and protect multiple AJB outputs and combine them safely into the inverter.
3. The AC-side family
🏠 AC Distribution Box (ACDB)
The ACDB sits between the inverter output and your home/main panel. Contains the AC MCB, MCCB, SPD and metering CTs. It's the last line of protection between the inverter and your appliances — and where your DISCOM net-meter lands in.
- AC MCB / MCCB rated for inverter max output current
- AC SPD Type-2 for 230/415V — protects against grid surges
- Metering CTs for kWh export/import logging
4. Cables, connectors, earthing
Solar plants run 25+ years. Cable and connectors are the most common failure point on cheap installs.
🔗 Solar DC cable (TUV/EN 50618)
Specialized double-insulated, UV-resistant, halogen-free cable in 4 mm² or 6 mm² sizes. Never use PVC household wire — it cracks in sun and burns easily.
🔗 MC4 connectors (IP67)
Industry-standard plug-and-play DC connectors. Genuine Stäubli MC4 (originally Multi-Contact) last 25 years; counterfeit MC4s are a known fire cause — buy from authorized stockists only.
⚙️ GI Earthing & Lightning
Every panel structure needs a GI earth rod (50mm dia × 3m) + chemical backfill. The plant must have an equipotential bonding ring connecting the panel frames, the structure, the ACDB enclosure and the lightning arrestor earthing. Earthing = the difference between a 25-year plant and a fire.
5. What Arsiga Solar stocks
As authorised North-India distributor we keep the entire BOS range in ready stock across our 5 warehouses — with factory-tested panels, datasheets and BIS/ISI marking for every component. Same-day dispatch from Lucknow, Delhi, Jaipur, Sonipat, or Varanasi.
- AJB / ACDB / DCDB in 1-in-1-out to 8-in-1-out configurations
- TUV DC cables 4/6 sq mm in 100m rolls
- Stäubli / genuine MC4 connectors in pairs (M+F)
- Lightning arrestors + Earthing kit with chemical backfill
Need a full BOS quotation?
Send us your project size (kWp), module quantity & inverter make — we'll send a complete, sized BOM within an hour.
Request BOS QuoteTags: BOS, AJB, ACDB, DCDB, MC4, lightning arrestor, GI earthing, solar PV balance of system