Solar BOS Solutions
Solar String Monitoring Box 12 String | 1500V DC | IP65
A string monitoring box (SMB) for utility-scale PV plants that combines 12 fused solar strings, protects them against surges, and sends real-time string data to your monitoring system over a built-in wireless unit.
- 1500V DC
- 12 Strings
- IP65 + IK10
- Wireless Monitoring
What Is SMB in Solar?
An SMB (String Monitoring Box) is a DC enclosure in a solar PV plant that combines the output of several PV strings, protects each string with a fuse, and measures string-level data so operators can see how every string is performing.
It sits between the PV strings and the inverter. Because it reports string data individually, an SMB lets the O&M team locate an underperforming or faulty string without testing the field manually. An SMB is essentially a solar combiner box with monitoring added.
Product Walkthrough
Inside the String Monitoring Box
A closer look at how the 12-string, 1500V DC SMB is built: the FRP enclosure, the fused string inputs, the switch disconnector with its DC output, and the monitoring board that reports string data.
- 12 fused string inputs with a 50 A fuse on each string
- Switch disconnector for safe isolation during maintenance
- Wireless monitoring unit for real-time string data and alerts
How Does a String Monitoring Box Work?
Solar string monitoring follows the DC power path from the array to the inverter.
- 1
PV strings connect
Up to 12 solar PV strings, each carrying up to 40 A, terminate inside the box.
- 2
Each string is fused
A 50 A fuse on every string isolates a faulted string from the rest of the array.
- 3
String data is measured
The monitoring unit reads string-level data so deviations between strings become visible.
- 4
Surges are diverted
A built-in DC surge protection device guards against lightning and transient overvoltages.
- 5
Output is combined
Strings combine onto the DC output through a switch disconnector rated up to 500 A.
- 6
Data goes remote
The wireless remote monitoring unit sends real-time data and alerts to the plant monitoring system.
Key Functions of the String Monitoring Box
String Monitoring
Individual visibility across all 12 strings for faster performance comparison.
Fuse Protection
50 A fuse per string, with total system current up to 430 A DC.
Surge Protection
Integrated DC SPD against lightning-induced and transient overvoltages.
Safe Isolation
Switch disconnector (max 500 A) for safe isolation during maintenance.
Wireless Remote Monitoring
Built-in unit for real-time data and alerts, with no data cabling to the box.
Rugged Enclosure
FRP housing rated IP65 for dust and water, and IK10 for impact.
Why String Monitoring Matters in Solar Plants
- String-level visibility: see each string, not just inverter totals.
- Faster fault location: alerts point the team to the right box and string.
- Easier troubleshooting: fewer manual checks across large arrays.
- Better maintenance planning: data helps prioritise field work.
- Scales with the plant: one SMB per 12 strings across the field.
Where Is an SMB Used?
- Utility-scale solar PV plants
- 1500V DC ground-mount projects
- Solar EPC projects
- Solar O&M operations
- Large commercial & industrial solar
Pole or wall mounted, to suit diverse site layouts.
SMB vs Solar Combiner Box
Both enclosures combine and protect PV strings. The difference is visibility.
| Feature | Combiner Box | String Monitoring Box (SMB) |
|---|---|---|
| Combines PV strings | Yes | Yes |
| String fuse protection | Yes | Yes |
| DC surge protection | Usually | Yes |
| Per-string monitoring | No | Yes |
| Remote alerts to SCADA / monitoring | No | Yes (wireless) |
| Fault location | Manual field testing | Pinpointed by string data |
| Best suited for | Small or budget arrays | Utility-scale and large C&I plants |
String Monitoring Box Specifications
| Electrical | |
|---|---|
| Number of strings | 12 |
| Max. system voltage | 1500 VDC |
| Max. current per string | 40 A |
| Fuse rating per string | 50 A |
| Max. system current | 430 A DC |
| Mechanical | |
| Enclosure type | Wall cabinet (pole / wall mounting) |
| Closure | Metal snap latch |
| Dimensions (W × H × D) | 802 × 650 × 307 mm |
| Material | Fiberglass reinforced polyester (FRP) |
| Ingress protection (IEC 60529) | IP65 |
| Impact resistance (IEC 62262) | IK10 |
| Colour | Grey (RAL 7035) |
| Vents | Yes, for condensation control |
| Components | |
| Surge protection device | Yes (DC SPD) |
| Switch disconnector | Max. 500 A |
| Wireless remote monitoring unit | Yes |
| Environment & Standards | |
| Ambient conditions | −10 °C to +70 °C, < 95% RH |
| Standards | Designed to relevant IEC standards. |
Why F.Robin Technologies
A Chennai-headquartered electronics engineering company, part of the F.Robin Group, with teams in Chennai, Bengaluru and Madurai.
Electronics Engineering
In-house PCB design and manufacturing capability behind the monitoring electronics.
Product Engineering
Mechanical and electrical engineering teams that understand enclosure, protection and field conditions.
Project Support
Engineers who discuss string counts, site layout and monitoring needs for your plant.
Frequently Asked Questions
SMB stands for String Monitoring Box. It is a DC enclosure that combines several solar PV strings, protects each one with a fuse, and monitors string-level data so operators can spot underperforming strings quickly.
An SMB connector (SubMiniature version B) is a small snap-on coaxial RF connector used in electronics and radio equipment. It is unrelated to a solar SMB, which means String Monitoring Box. In solar, PV strings connect to an SMB through cable glands and terminals.
A string monitoring box combines PV strings, protects them with fuses and surge protection, provides a disconnector for safe isolation, and reports string data to the plant monitoring system. F.Robin's SMB does this for 12 strings at 1500V DC with wireless reporting.
String monitoring is tracking the output of each PV string individually instead of only the inverter total. Comparing strings reveals faults such as blown fuses, damaged cables or soiled modules, so the O&M team knows exactly where to look.
A combiner box joins and protects PV strings. An SMB does the same and adds string-level monitoring and communication, so it also tells you how each string is performing.
This SMB accepts 12 strings at up to 40 A each, with a 50 A fuse per string and a maximum system current of 430 A DC at 1500V DC.
Yes. It has a built-in wireless remote monitoring unit that sends real-time data and alerts to the monitoring system.
It is installed in the PV array field between the strings and the inverter. This model can be pole or wall mounted, and its IP65, IK10 FRP enclosure suits outdoor sites from −10 °C to +70 °C.
Find F.Robin Technologies
Share your string count, system voltage and site layout, and our engineering team will respond with the right configuration.
KOSMO ONE, Tower B, 4th Floor, Sai Nagar Plot 14, 3rd Main Rd, Ambattur Industrial Estate, Chennai, Tamil Nadu 600058