Electrical installation material
Electrical installation material is the cabling, protection and enclosure hardware that connects a photovoltaic array to the grid safely and keeps it compliant: solar DC cable, AC conductors, string fuses, DC isolators, surge protection devices, RCDs, distribution boxes, earthing and bonding components, cable management and MC4 crimping tools. Choose by side of the system, DC between the modules and the inverter, AC between the inverter and the consumer unit, then by cross section, voltage rating and IP class. Pairs with connectors, mounting systems and accessories. Guide
Related installation categories
DC cable, AC cable and the protection devices between them
A photovoltaic installation has two electrically different halves. On the DC side the array delivers a high, non-zero voltage whenever there is light, so it needs H1Z2Z2-K solar cable rated 1.5 kV DC, gPV string fuses, a load-break DC isolator and DC-rated surge protection. On the AC side the usual rules of a low-voltage installation apply: correct conductor cross section, a circuit breaker matched to the inverter output, the right RCD type and AC surge protection at the consumer unit.
This category covers both halves plus the parts that hold them together: distribution boxes and enclosures with an IP rating suited to the location, earthing and equipotential bonding conductors for frames and rails, UV-stabilised cable management, and the crimping tools that make an MC4 termination reliable. Sizing follows IEC 60364-7-712 for the PV part and the local wiring rules for everything downstream of the inverter.
FROM THE FIELD
"The failures we get called out to are almost never the panels. They are terminations and cable routing. Standard natural nylon ties on a south-facing roof go brittle in two summers, the cable drops onto the tiles and chafes through the sheath. Use UV-stabilised black PA66 or stainless steel ties and clip the cable to the rail, never to the roof covering."
Ladislav Proc · Photovoltaics specialist, ONSA Plus
How to choose electrical installation material
Work from the array outwards. First the DC cable that leaves the roof, then the DC protection and isolation at the inverter, then the AC feed to the consumer unit, and finally the enclosures, earthing and cable management that keep all of it in place for twenty-five years.
Two numbers drive most of the decisions: the maximum system voltage, which is the string open-circuit voltage at the lowest expected ambient temperature, and the maximum current, which is derived from the module short-circuit current. Every fuse, isolator, surge arrester and cable has to be rated above both.
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Solar DC cable: H1Z2Z2-K in 4 and 6 mm²
H1Z2Z2-K is the harmonised solar cable type defined by EN 50618. It uses flexible class 5 tinned copper stranding with cross-linked, halogen-free insulation and a separate cross-linked outer sheath, so the cable is double insulated and can be treated as class II. It is rated 1.5 kV DC between conductors, carries a conductor temperature rating of 90 °C continuous with short-term tolerance to 120 °C, works down to about −40 °C, and is tested for UV, ozone and weather exposure with a design life of 25 years.
- 4 mm² is the default for string runs on residential roofs. In free air it carries well above any single string current, so the limiting factor is voltage drop, not heating.
- 6 mm² is used for long runs, for parallel strings combined before the inverter, and wherever the calculated DC voltage drop would otherwise exceed roughly 1 %.
- Colour is a convention only, not insulation: red or black for positive, blue or black for negative. Label both ends, because both cores are live.
- Never substitute H07RN-F, NYY or ordinary building cable on the DC side. They are rated for AC service voltage and are not qualified for continuous UV and 1.5 kV DC.
AC cabling and sizing for voltage drop
The AC cable between the inverter and the distribution board is sized on three checks: continuous current including the derating factors for grouping, insulation and ambient temperature, the disconnection time of the protective device on a fault, and voltage drop. In practice voltage drop is the one that forces a larger cross section, because a long run at low drop keeps the inverter from raising its terminal voltage and tripping on over-voltage.
- Target roughly 1 % drop on the DC side and 1 % on the AC side, with a total across the generator circuit normally kept under 3 %.
- Single phase inverters up to about 5 kW usually take 3G4 or 3G6; three-phase units at 10 kW and above typically start at 5G6 and go up with run length.
- Grid over-voltage trips are frequently a cabling problem, not a grid problem. Recheck the cross section before blaming the network operator.
DC protection: string fuses, isolators and surge arresters
Fuses on the DC side are there to stop reverse current flowing back into a faulted string from the other strings in parallel. With one or two strings per input the possible reverse current cannot exceed the module reverse-current rating, so fuses are generally not required. From three parallel strings upwards they are.
- String fuses must be gPV type to IEC 60269-6, rated for the full DC system voltage. The rating sits above about 1.5 times the module short-circuit current and below the module maximum series fuse rating printed on the label.
- DC isolators must be DC rated and load-break capable, tested to IEC 60947-3 with a PV utilisation category. An AC switch of the same nominal current will not extinguish a DC arc.
- Type 2 DC surge protection belongs close to the inverter DC input and handles induced surges. Use PV-specific arresters with a continuous operating voltage above the array maximum voltage.
- Type 1 or Type 1+2 is required where the building has an external lightning protection system or the array is exposed, because only Type 1 devices are tested with the 10/350 µs impulse.
Tip from practice
Keep the positive and negative conductors of each string running side by side along the whole route. A large separation creates a big induction loop, and that loop is what couples a nearby lightning strike into your inverter. Routing discipline costs nothing and does more than an extra surge arrester.
AC protection and RCD selection
The inverter feed gets its own circuit breaker sized to the inverter maximum output current, and Type 2 AC surge protection sits at the main distribution board. The residual current device needs more thought, because transformerless inverters can inject a smooth DC residual current that blinds a standard Type AC or Type A device.
- Type A is acceptable where the inverter documentation confirms it has integrated DC residual current monitoring and no RCD or only Type A is required.
- Type B or Type A combined with a 6 mA DC detection module is the choice where smooth DC fault current is possible, and it is the normal requirement for a wallbox circuit.
- 30 mA is the standard sensitivity for additional protection; 300 mA selective devices are used upstream for fire protection on larger boards.
- Selectivity matters: a single 30 mA device covering the whole house plus the inverter will nuisance trip on accumulated leakage current.
Enclosures, IP rating, earthing and bonding
DC combiner boxes and AC connection boxes on an outside wall need at least IP65, with UV-stabilised polycarbonate and a suitable impact rating. Cable entries have to be sealed with correctly sized glands, because an unused knockout turns an IP65 box into an IP20 box. Indoor boards in a dry plant room can drop to IP40.
- Equipotential bonding of module frames and mounting rails is normally done with 6 mm² copper, using stainless steel bonding clips or toothed washers that bite through the anodised layer.
- 16 mm² copper or the equivalent is used where the array is connected to an external lightning protection system or forms part of the down-conductor path.
- Continuity must be measured and recorded, not assumed. Rail clamps and anodising are the two usual reasons a bond reads open.
- Enclosure labelling with DC warning signs and a single-line diagram inside the door is part of the handover, not an optional extra.
Cable management, MC4 connectors and crimping
Every DC cable on the roof should be clipped to the mounting rail or to the module frame, never left resting on the roof covering and never routed over a sharp edge. Terminations are made with a proper ratchet crimping tool and the die that matches the conductor cross section, then the contact is pushed into the housing until it clicks and the gland is tightened.
- Crimp, do not solder. A soldered MC4 contact goes stiff, cracks with thermal cycling and creates the hot joint you were trying to avoid.
- Do not cross-mate connector brands. Male and female parts from different manufacturers may fit mechanically but are not type tested as a pair, which voids compliance.
- UV-resistant ties in black PA66 or stainless steel are the only acceptable option outdoors. Natural nylon fails within a couple of seasons.
- Leave a drip loop before each connector so water runs off rather than into the housing.
Quick selection table
| Component | What to check | What it affects |
|---|---|---|
| DC solar cable | H1Z2Z2-K, 4 or 6 mm², 1.5 kV DC, UV rated | Voltage drop, service life on the roof, compliance |
| AC cable | Cross section against run length and inverter current | Voltage drop, inverter over-voltage trips, heating |
| DC protection | gPV fuses, DC-rated load-break isolator, PV surge arrester | Reverse current, safe isolation, surge survival |
| AC protection | Breaker rating, RCD type A or B, Type 2 SPD | Fault clearance, shock protection, nuisance tripping |
| Enclosures and bonding | IP65 outdoors, sealed glands, 6 or 16 mm² earth | Water ingress, corrosion, touch safety, inspection |
Swipe the table to the left
Frequently asked questions about electrical installation material
What cable is used between solar panels and the inverter?
H1Z2Z2-K solar cable to EN 50618, typically 4 or 6 mm². It is double insulated, halogen-free, rated 1.5 kV DC, tested for UV and weather exposure, and rated to 90 °C conductor temperature with a 25 year design life outdoors.
Should I use 4 mm² or 6 mm² solar cable?
Use 4 mm² for normal residential string runs and 6 mm² for long runs, combined parallel strings or wherever the calculated DC voltage drop would exceed about 1 %. Current capacity is rarely the limit on the DC side; voltage drop is.
Can I use ordinary building cable on the DC side?
No. Cables such as NYY or H07RN-F are rated for AC service voltage and are not qualified for continuous UV exposure or a 1.5 kV DC system. Using them on the array side breaches IEC 60364-7-712 and usually voids the installation certificate.
Do I need string fuses in my PV array?
Only when three or more strings are connected in parallel. With one or two strings the possible reverse current stays below the module rating. Where fuses are needed they must be gPV type to IEC 60269-6, rated for the full DC system voltage.
Is a separate DC isolator required if the inverter has one built in?
Many inverters include an integrated DC switch that satisfies the requirement, but local rules or roof access conditions often call for an additional isolator near the array. Any added device must be DC rated and load-break capable; an AC switch will not extinguish a DC arc.
Do I need Type 1 or Type 2 surge protection?
Type 2 covers induced surges and is the normal minimum on both the DC and AC sides. Type 1, or a combined Type 1+2, is required where the building has an external lightning protection system, because only Type 1 devices are tested with the 10/350 µs impulse.
Which RCD type do I need for a solar inverter?
Type A is acceptable only if the inverter documentation confirms integrated DC residual current monitoring. Otherwise use Type B, or Type A with a 6 mA DC detection module. Transformerless inverters can produce smooth DC residual current that blinds a Type AC or plain Type A device.
How much voltage drop is acceptable in a PV installation?
Aim for roughly 1 % on the DC side and 1 % on the AC side, keeping the total across the generator circuit under about 3 %. Excess AC drop is a common cause of inverters tripping on grid over-voltage, especially on long runs.
Do module frames and mounting rails have to be earthed?
Yes, equipotential bonding of frames and rails is standard practice, normally in 6 mm² copper, or 16 mm² where an external lightning protection system is involved. Use stainless clips or toothed washers that cut through anodising, then measure and record continuity.
Can I fit MC4 connectors with ordinary pliers?
No. Use a ratchet crimping tool with the die matching the conductor cross section, then push the contact into the housing until it clicks and tighten the gland. Never solder the contact. Poor crimps are the most common cause of hot joints and burnt connectors.
Cable cross-sections, protection device ratings and earthing arrangements must follow the applicable national wiring rules and the design for the specific installation.
About ONSA Plus
Why installers across Europe buy installation material from us
ONSA Plus is a European B2B distributor of photovoltaics, battery storage, heat pumps and EV charging stations. In our own EU warehouses we keep over 1,500 products from 25+ brands, including Huawei, Solis, SolaX and Dyness.
We are not just a trading company. We design and service energy systems ourselves, so we answer questions on cable sizing, DC protection and surge protection from engineering practice, not from a catalogue. You handle a warranty claim directly with us and you buy per job.
