Short answer: for most campervan and motorhome solar systems, fitting a dedicated DC isolator between the solar panels and the MPPT charge controller is a sensible safety choice. It gives you a clear, accessible way to disconnect the panels for testing, fault-finding or replacement.

However, the device must be designed for solar PV direct current, sized for the highest voltage and current the array can produce, wired in the manufacturer’s approved configuration and installed correctly. A poorly selected isolator can introduce heat and fire risk instead of reducing it.

Safety note: solar panels generate voltage whenever light reaches them. Switching an isolator off does not make the cable between the panels and the isolator dead. If you are unsure about the design, ratings, wiring or test procedure, ask a competent auto-electrician or electrical installer with off-grid PV experience.

What does a campervan solar DC isolator do?

A DC isolator—more precisely, a PV-rated switch-disconnector—opens the circuit between the solar array and the charge controller. It allows the controller side of the circuit to be separated from the panels for maintenance.

This is useful when you need to:

• replace or inspect an MPPT solar charge controller;
• test the solar array or wiring;
• respond to a fault, damaged cable or water ingress;
• work on nearby electrical equipment; or
• follow the charge controller manufacturer’s shutdown sequence.

An isolator is not automatically an overcurrent protective device. A fuse or circuit-breaker may still be required, depending on the array design, cable capacity and equipment instructions. A correctly specified DC circuit-breaker can sometimes provide both functions, but only when it is explicitly rated for isolation and for the PV circuit concerned.

Is a DC isolator legally required for campervan solar panels?

There is no simple yes-or-no rule that covers every campervan solar installation.

Section 712 of BS 7671 deals with solar photovoltaic power-supply systems. The current UK edition, BS 7671:2018+A4:2026, requires a means of isolating an inverter from both its AC and DC sides. Campervan systems commonly use an MPPT charge controller feeding a battery rather than a grid-connected PV inverter, so the wording does not map neatly onto every off-grid vehicle installation.

Standards and codes written for building-mounted PV can still provide valuable safety principles, but shore-power connection does not by itself turn a campervan’s battery-charging solar array into a grid-connected PV system. The complete design, the equipment manufacturer’s instructions and the rules applicable to the vehicle all need to be considered.

For a small single string, suitable plug-and-socket connectors may sometimes provide a means of isolation when they are correctly located and used as intended. In practice, roof-mounted connectors are often difficult to reach, and standard PV connectors should not be unplugged while current is flowing unless their manufacturer explicitly permits load breaking. An accessible PV-rated isolator is therefore normally the clearer and safer arrangement.

When should you fit a solar DC isolator?

A dedicated isolator is particularly useful when:

• the panel connectors are on the roof or otherwise hard to reach;
• you have more than one solar string or panels connected in parallel;
• the charge controller has no suitable built-in PV isolation;
• the controller or wiring may need regular inspection or replacement;
• the vehicle is exposed to vibration, moisture and frequent movement; or
• the equipment instructions require a defined means of disconnection.

If an inverter, controller or combiner box already includes an appropriate DC switch-disconnector, another external device may not be necessary. Confirm what the built-in switch actually isolates and whether its ratings cover the array.

How to choose the right DC isolator

Do not select a device from panel wattage alone. The designer must check the worst-case voltage and current of the whole array.

1. Use a genuine PV-rated DC device

An AC isolator must not be assumed suitable for DC. Alternating current crosses zero regularly, which helps extinguish an arc. Direct current does not, so a DC switch must control a more persistent arc.

For a switch-disconnector, look for conformity with BS EN IEC 60947-3 and an appropriate PV utilisation category. DC-PV0 is intended for operation when no current is flowing. DC-PV1 can be suitable for PV circuits where significant overcurrent cannot occur, while DC-PV2 is intended for circuits where significant overcurrent and reverse current may occur, such as parallel strings. The exact choice belongs to the system designer.

2. Calculate maximum open-circuit voltage

Add the open-circuit voltage (Voc) of panels connected in series, then apply the correction required for the lowest expected panel temperature. Cold panels can produce a higher voltage than the figure shown at standard test conditions. The isolator’s DC voltage rating must be at least the calculated maximum for the chosen pole configuration.

3. Calculate maximum circuit current

Use the panel short-circuit current (Isc), the number of strings connected in parallel and the appropriate design factor. Parallel strings increase current, even though panels connected in series do not.

Check the manufacturer’s ratings at the calculated voltage. A switch may carry less current safely at a higher DC voltage, so a headline current rating is not enough on its own.

4. Check poles and wiring configuration

Many campervan PV inputs are unearthed, so isolation normally needs to disconnect both conductors. Some two-pole and four-pole devices require specific series or parallel links to achieve their published rating. Follow the diagram supplied with that exact model; do not copy the arrangement from a different isolator.

5. Match the installation environment

Choose an enclosure and cable entries suited to moisture, dust, heat and vibration. Keep the switch accessible, protected from accidental operation and close enough to the charge controller to make the isolation point obvious. Avoid locations where direct sun or nearby heat sources could raise the enclosure temperature beyond its rating.

Installation details that prevent overheating

Most failures occur at connections rather than along an intact length of cable. Good installation matters as much as the switch rating.

• Use the conductor type and size accepted by the terminals.
• For fine-stranded flexible cable, use bootlace ferrules only when the terminal or manufacturer specifies or accepts them.
• Strip insulation without cutting or losing strands.
• Tighten terminals to the stated torque using a suitable torque tool.
• Provide strain relief so vibration is not transferred to the terminals.
• Use compatible connectors from the same manufacturer and product family.
• Label the isolator clearly and show the ON and OFF positions.

After installation, test polarity, continuity, insulation and operation using an appropriate safe procedure. Include the isolator in routine inspections for looseness, discolouration, heat damage, water ingress and mechanical deterioration.

How should you shut down a campervan solar system?

Always follow the instructions for your charge controller and battery system. The order matters because many controllers need to detect battery voltage before the PV input is connected.

A common sequence is to isolate the PV input before disconnecting the controller from the battery, then reconnect the battery before restoring the PV input. This is not universal. Treat the manufacturer’s sequence as the authority for your equipment.

Remember that the panel-side terminals and cables may remain live in daylight after the switch has opened. Prove isolation at the intended work point with suitable test equipment before touching conductors.

Common mistakes to avoid

• Using an AC-only switch: its contacts may not interrupt a DC arc safely.
• Choosing by watts: isolator selection depends on corrected voltage, corrected current and pole configuration.
• Unplugging PV connectors under load: this can create an arc and damage the connector.
• Assuming OFF means every cable is dead: panels continue generating whenever illuminated.
• Treating isolation as fusing: the two functions are different unless a suitably rated device provides both.
• Ignoring torque and cable preparation: loose or damaged terminations create resistance and heat.
• Hiding the switch: an isolator is most useful when it is clearly labelled and readily accessible.

Frequently asked questions

Can I use an MC4 connector as a solar isolator?

A suitable connector can sometimes provide disconnection for a small string, but it must be accessible and used within its rating. Standard PV connectors should not be separated under load unless the manufacturer states that they can break current. A dedicated switch-disconnector is normally easier and safer to operate.

Can I use a fuse instead of a DC isolator?

Not automatically. A fuse protects against overcurrent; it is not normally a convenient switching device. Use a component specifically rated to provide isolation, or a PV-rated circuit-breaker that is approved for both protection and isolation.

Should the isolator disconnect positive and negative?

In an unearthed PV circuit, both live conductors normally need to be isolated. Confirm the earthing arrangement and the switch manufacturer’s approved wiring configuration before installation.

Where should the isolator be fitted?

Place it in a readily accessible, protected position, commonly near the charge controller. The final location must suit the enclosure rating, cable route, heat conditions and manufacturer’s instructions.

Does switching off the isolator make the solar panels safe?

No. It separates parts of the circuit, but illuminated panels and the wiring between the panels and isolator can still be live. Covering panels is not a substitute for a verified safe-isolation procedure.

The practical answer

For most campervan solar installations, a correctly designed and installed DC isolator is worth fitting. It makes maintenance simpler, gives users a clear control point and avoids relying on inaccessible connectors.

The important word is correctly. Use a PV-rated switch-disconnector, calculate worst-case array voltage and current, follow its pole-configuration diagram, prepare and torque the cables properly, and follow the charge controller’s shutdown sequence. If any of those details are uncertain, have the design checked by a competent professional.

Technical references

• IET: BS 7671, 18th Edition and Amendment 4:2026
• IET Wiring Matters: Solar PV DC switch-disconnector selection and configuration