Weidmüller Stringbox 7770019121 – PV Next String Combiner Box (12 strings / 6 MPPT, with Fireman Switch)
The Weidmüller PV Next String Combiner Box 7770019121 makes your DC side neat, safe and maintenance-friendly.
This PV Next string box is intended for mounting in the DC connection between PV modules and inverter(s).
It allows you to conveniently combine up to 12 PV strings on 6 electrically separate MPPTs.
Which version is this exactly?
- Order number: 7770019121
- Type (according to type overview): PVNCM6I12S1FXV101TXPX10
- Capacity: maximum 12 strings on 6 MPPTs (2 strings per MPPT)
- Note: this variant is without string fuses (fuse holders are only on 7770019118 and 7770019119)
Main advantages
- Fireman switch: contactors can switch off locally and remotely. An activated fireman switch is normally released with a key.
- DC power contactors per MPPT: the installation can be completely disconnected on the DC side.
- Overvoltage protection per MPPT: each MPPT has a replaceable SPD (type I/II or type II – depending on version/design).
- Quick installation: PV connectors at the bottom reduce installation time and make service easy.
- IP65 enclosure: suitable for protected outdoor use, with transparent polycarbonate cover for quick inspection.
Technical specifications (core)
- Max. DC input voltage: 1000 V DC
- Max. current per string input (Inc): 15 A DC
- Max. current per PV connector: 30 A DC
- Ambient temperature (operation): -40°C to +40°C
- Protection rating: IP65
- Enclosure: GFRP base (glass fibre reinforced polyester) + transparent polycarbonate cover
- Connectors: WM4C PV connectors, suitable for 4-6 mm²
- Remote signalling contact (SPD): 24 V / max. 100 mA; 48 V / max. 200 mA
- Contactor coil voltage: 230 VAC (operating voltage range approx. 195-253 VAC)
Dimensions and mounting
- Housing (7770019121): approx. 720 (W) × 540 (H) × 202 (D) mm
- Mounting: wall-mounted, preferably vertically with connectors/cable glands facing downwards
- Free space: maintain at least 250 mm all round (preferably 400 mm) for cooling and maintenance
Installation tips from practice
- Protected location: preferably out of direct sun and driving rain (prolonged UV/weather exposure shortens lifespan).
- Never drill additional holes: IP class remains intact only if the enclosure remains undamaged.
- Seal unused feedthroughs/connectors: use sealing/blinding materials and protective caps on free PV connectors.
- Pay attention to polarity & string matching: only connect strings with identical open-clamp voltage together per input to avoid equalisation currents.
Application
This string box is a fine choice for larger residential and business PV systems with multiple MPPTs,
where you want above all: safe switching, surge protection, and a tight, service-friendly DC design.
Safety (short but important)
Preferably work without voltage and follow the correct switch-off sequence: first switch off the inverter, then the DC switch/load breaker,
only then disconnect the strings. DC can be dangerous up to 1000 V – use suitable PPE and always measure without voltage.