How to Route Solar Cables Through Your Van Roof

Getting solar panels onto your campervan roof is only half the job. You also need to get the cables from those panels down into your electrical system without creating a leak point that haunts you for years. A poorly sealed roof entry is one of the most common causes of water damage in self-built campervans.

This guide is part of our complete campervan solar setup guide. If you have not yet decided on your panel setup, start there first. Once you know your panel configuration, you can work out how many cable entries you need and where to place them. Our free calculator will help you size your solar system and determine cable requirements.

Size your solar system first

Before drilling any holes, make sure your panel configuration is finalised. Our free calculator sizes your solar array, battery, and charge controller based on your actual daily usage.

Open Calculator

Why the Roof Entry Matters

Your campervan roof is constantly exposed to rain, UV, temperature extremes, and vibration from driving. A cable entry that seems watertight on day one can fail within months if the wrong method or sealant is used. The consequences range from annoying damp patches to serious structural corrosion in the roof panel.

There are three main approaches to getting solar cables through the roof:

Cable glands — purpose-built waterproof fittings
ABS cable entry boxes — flat-profile junction boxes
Direct sealant — cables pushed through a hole and sealed

Each has its place, but for most campervan builds, a combination of a cable gland or ABS entry box with proper sealant is the recommended approach.

Cable Glands (IP68 Rated)

Cable glands are threaded waterproof fittings commonly used in marine and industrial applications. They consist of a body that threads through the roof, a rubber compression seal that grips the cable, and a locknut underneath.

Advantages

Excellent waterproof seal when properly installed
Removable — you can withdraw and replace cables
Compact and low-profile
Rated to IP68 when correctly tightened
Inexpensive: £2–£5 each

Choosing the Right Size

Cable glands are sized by the cable diameter they accept. For standard 4mm² solar cable (roughly 6mm outer diameter), you typically need a PG7 or PG9 gland. For 6mm² solar cable, a PG9 or PG11 is usually correct.

Gland Size	Cable Range	Common Use
PG7	3–6.5mm	2.5–4mm² solar cable
PG9	4–8mm	4–6mm² solar cable
PG11	5–10mm	6–10mm² solar cable
PG13.5	6–12mm	Larger or double cables

Use nylon glands, not brass

Brass cable glands can cause galvanic corrosion when in contact with aluminium or steel van roofs. Nylon (polyamide) glands are UV-resistant, non-conductive, and will not corrode against any roof material. They cost less too.

Installation Steps

Choose your location — as close to the panels as practical, avoiding any internal ribs or structural members underneath
Drill a pilot hole from the outside using a small bit (3–4mm)
Step up to the correct diameter using a step drill bit — PG7 needs a 12.5mm hole, PG9 needs 15.2mm, PG11 needs 18.6mm
Deburr the hole thoroughly with a deburring tool or fine file
Apply rust-preventive paint to the bare metal edges if your van has a steel roof
Thread the gland body through from outside, with the rubber washer between the gland flange and the roof
Apply a ring of Sikaflex 522 or Dicor self-levelling sealant around the base of the gland
Tighten the locknut from inside to compress the washer and pull the gland snug
Feed your solar cables through the gland
Tighten the compression cap until the rubber seal grips the cable firmly

Never drill without checking underneath

Before drilling any hole in your van roof, check from inside to confirm there are no wiring looms, structural ribs, or cross-members at that point. Use a magnet on the outside to identify where the double-skinned sections are on panel vans. Drilling into a structural member weakens the roof and is almost impossible to seal properly.

ABS Cable Entry Boxes

ABS cable entry boxes are flat, rectangular housings that sit on the roof surface. The cables enter from the side (under the box) and exit downwards through the roof. They are popular because they provide a large bonding surface and protect the cable entry point from direct water flow.

When to Use an ABS Box

When running multiple cables through a single entry point (positive and negative from each panel)
When you want maximum weather protection over the entry point
When mounting on a curved roof where a cable gland might sit at an angle
Typically supplied with solar panel mounting kits

Installation

Position the box and mark its outline with masking tape
Drill the cable hole inside the marked area — a 10–15mm hole is usually sufficient
Deburr and treat the hole as above
Feed cables through the hole and up through the box
Apply Sikaflex 252 or 522 generously to the base of the box
Press down firmly and weight or tape the box while the adhesive cures (24–48 hours)
Fill inside the box with additional sealant once cables are connected, then snap the lid on

Most ABS entry boxes include a rubber gasket. This is a secondary seal — the Sikaflex bond is your primary waterproofing.

Sealant Selection

The sealant you use is arguably more important than the entry method. Using the wrong product is the number one cause of roof leaks in campervan solar installations.

Recommended Sealants

Product	Type	Best For	Cure Time	Price
Sikaflex 522	Adhesive sealant	Cable glands, ABS boxes, general sealing	24–48 hrs	£12–£18
Sikaflex 252	Structural adhesive	Permanent bonds, mounting brackets	24–72 hrs	£14–£20
Dicor 501LSW	Self-levelling sealant	Flat roof surfaces, lap joints	24 hrs	£15–£22
CT1	Hybrid polymer	All-purpose, fast tack	12–24 hrs	£10–£15

Never use standard silicone

Bathroom silicone and general-purpose silicone sealants do not bond well to painted metal, degrade rapidly in UV light, and can release acetic acid that corrodes aluminium. They are completely unsuitable for roof-mounted solar installations. Always use a polyurethane or hybrid polymer sealant.

Application Tips

Clean the roof surface with isopropyl alcohol (IPA) before applying any sealant
Apply sealant in a continuous bead — gaps invite water
Use Sika Aktivator 205 primer on the roof surface for maximum adhesion
Avoid applying in temperatures below 5°C — the sealant will not cure properly
More is better — you can always trim excess once cured

Cable Routing on the Roof

Before your cables enter the roof, they need to get from the panels to the entry point. Exposed cables flapping in the wind at 70mph will abrade, fatigue, and eventually fail.

Securing Cables to the Roof

Cable clips with Sikaflex — self-adhesive cable clips bonded to the roof with additional sealant
Under panel frames — route cables along the underside of the panel frame where possible
Trunking — small self-adhesive cable trunking for longer runs across the roof
UV-resistant cable ties — through adhesive mounts bonded to the roof

Leave a drip loop

Before cables enter any roof fitting, create a small downward loop (a drip loop). This prevents water from tracking along the cable and into the entry point. The loop should hang lower than the entry fitting so gravity diverts water away.

Cable Routing Inside the Van

Once cables are through the roof, you need to get them to your charge controller, which is usually mounted near the batteries.

Common Internal Routes

Down a wall cavity — feed cables behind wall panels, using the gap between the van body and your insulation or cladding
Through ceiling panels — run cables along the ceiling and drop down at the battery location
Through a purpose-built conduit — corrugated split conduit (available from any electrical supplier) protects cables from chafing

Always use conduit or protective sleeving where cables pass through metal holes or sharp edges. A single point of abrasion can wear through insulation over months of vibration.

Cable Length Considerations

Keep cable runs as short as practical. Longer cables mean more voltage drop, which reduces charging efficiency. For a typical campervan with panels on the roof and batteries under a rear bench, expect a cable run of 4–6 metres.

Use our calculator to check voltage drop for your specific cable length and gauge. If voltage drop exceeds 3%, consider upping the cable size by one gauge.

Single Entry vs Multiple Entries

If you have two or more solar panels, you need to decide whether to bring all cables through a single entry point or use separate entries for each panel.

Single Entry

Fewer holes in the roof
Easier to seal and maintain
Requires a larger gland or ABS box
Cables may need to cross the roof to reach the entry point

Multiple Entries

Shorter cable runs from each panel
Smaller, easier-to-seal glands
More holes to maintain
Better if panels are widely spaced

For most builds with two panels, a single ABS entry box positioned centrally between the panels is the simplest and most reliable option.

Common Mistakes

Using Too Much Force on Cable Glands

Over-tightening the compression cap on a cable gland can crush the cable insulation, potentially causing a short circuit. Tighten until the cable resists a firm tug — no more.

Skipping the Primer

Sealant manufacturers recommend primer for a reason. On painted metal and aluminium, a primer like Sika Aktivator 205 can double the bond strength. The few minutes it takes to apply is worth it.

Forgetting the Internal Seal

Water that gets past the external seal can run down the cable and drip inside. Apply a small amount of sealant around the cable where it emerges inside the van as a secondary barrier.

Drilling into Structural Ribs

Panel vans have double-skinned areas and structural ribs in the roof. Drilling into these is extremely difficult to seal and can compromise structural integrity. Always check from inside first.

Frequently Asked Questions

Can I use a single hole for both positive and negative cables?

Yes, but use a gland or entry box rated for multiple cables. A PG13.5 gland can accept two standard 4mm² solar cables side by side. Alternatively, an ABS entry box is designed for multiple cables and provides more space.

Do I need to seal inside the van as well as outside?

It is good practice. The external seal is your primary barrier, but a secondary seal inside prevents any water that does get past from dripping onto your electrics. A small blob of Sikaflex around the cable entry on the inside is sufficient.

How do I route cables on a ribbed roof?

Vans like the Fiat Ducato and Mercedes Sprinter have corrugated roof panels. Route cables along the valleys (lower sections) rather than over the ridges. Use adhesive-backed cable clips in the valleys to keep cables secure and protected.

Can I route cables through an existing roof vent or fan?

Some builders route cables alongside a MaxxFan or roof vent installation. This can work but you must ensure the cables do not interfere with the fan operation and that the existing seal is not compromised. It is generally easier and more reliable to use a dedicated cable entry.

What if I need to add more panels later?

If you think you might add panels in the future, install a slightly larger cable entry now, or add a spare entry point sealed with a blanking cap. It is much easier to do this while you have the sealant out than to add one later.

Is it safe to route solar cables near gas pipes or plumbing?

Keep solar cables at least 50mm away from gas lines and avoid running them alongside water pipes where a leak could reach electrical connections. Use separate routing channels where possible.