Solar Combiner Boxes Explained

A solar string combiner box connects multiple PV string cables at a single point, provides string-level fusing or disconnect capability, and typically integrates DC surge protection — protecting the inverter's DC inputs from both overcurrent and overvoltage events.

On any solar PV installation with more than one string, a combiner box sits between the panel strings and the inverter's DC input. It provides a safe, organised point to bring multiple strings together, protects each string individually, and protects the whole DC circuit against surge events. Without a combiner box, string connections at the inverter become unwieldy and the DC circuit lacks proper individual protection.

What a solar combiner box contains

Component	Function
String fuses (or DC MCBs)	Protect each individual string cable against overcurrent — typically 10–15A per string
DC disconnect switch	Allows safe isolation of the DC circuit for inverter maintenance without disconnecting panels individually
DC surge protection device (SPD)	Protects inverter DC inputs against lightning-induced surges in string cables
IP65 polycarbonate enclosure	Weatherproof housing for outdoor installation between panels and inverter

WCED solar combiner box range

The WCED WMPV and WPPV series provides 1-string and 2-string solar combiner boxes with integrated DC SPD protection. These are designed for standard residential and small commercial PV installations and include everything needed for a compliant DC circuit — string fusing, DC disconnect, and Type 2 DC surge protection — in a weatherproof IP65 enclosure.

Part code	Strings	String fuses	SPD voltage	Application
WMPV1S1000	1 string	15A per string	1000V DC Type 2	Single string residential PV
WMPV2S1000	2 strings	15A per string	1000V DC Type 2	Two-string residential PV
WPPV1S1000	1 string	15A per string	1000V DC Type 2	Single string — IP65 polycarbonate
WPPV2S1000	2 strings	15A per string	1000V DC Type 2	Two-string — IP65 polycarbonate

Where a combiner box is installed

The combiner box is installed between the PV panel strings and the solar inverter's DC input terminals. It is typically located in the roof space, loft, or on the exterior wall near the inverter position — as close as practical to the inverter to minimise the DC cable run from the combiner to the inverter. All WCED combiner boxes are IP65 rated and suitable for outdoor or indoor installation.

1-string and 2-string configurations

DC Type 2 SPD — 1000V rated

15A string fuses included

DC disconnect switch

IP65 — suitable for outdoor installation

Compatible with all standard string inverters

Shop WCED Solar Combiner Boxes

1-string and 2-string combiner boxes with DC SPD, string fusing, and DC disconnect. IP65. In stock.

View solar combiner boxes →

Frequently Asked Questions

Do I need a combiner box for a single-string installation?

Not strictly — a single string can connect directly to the inverter's DC input with a single string fuse. However, a single-string combiner box adds DC surge protection and a DC disconnect point, both of which are best practice on any PV installation. Given the low cost of a 1-string combiner box relative to the inverter it protects, most installers specify one as standard.

Can I use one combiner box for more than two strings?

The WCED range covers up to 2 strings per combiner box. For installations with 3 or more strings, multiple combiner boxes can be used, or a larger custom combiner arrangement may be required. For large commercial systems, speak to us directly about multi-string combiner solutions.

Does a combiner box replace the need for AC surge protection?

No — DC and AC surge protection serve different purposes and protect different parts of the system. The combiner box DC SPD protects against surges arriving via the string cables (DC side). An AC SPD at the consumer unit protects the inverter's AC output connections and the rest of the installation (AC side). Both are needed for complete protection.

Further reading:
DC surge protection (1000V) explained
Surge protection for solar and heat pumps
IP40 vs IP65 enclosures explained
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