RCD & MCB Consumer Units

RCD & MCB Consumer Units for Campervans: 240V Safety Guide

The 240V AC side of a campervan electrical system requires proper circuit protection. An RCD (Residual Current Device) protects people from electric shock. An MCB (Miniature Circuit Breaker) protects cables from overcurrent. They are not optional — and they are a legal requirement for any mains-voltage installation in a vehicle.

This guide covers the 240V consumer unit, how to wire it, and the UK regulations that apply to campervan AC installations.

What You Need

Every campervan with 240V AC must have:

RCD vs MCB vs RCBO

RCD (Residual Current Device)

Detects when current is leaking to earth (through a person's body, for example). If the difference between live and neutral exceeds 30mA, the RCD trips in 40ms — fast enough to prevent fatal electric shock.

For campervans: You need a 30mA RCD. No exceptions.

MCB (Miniature Circuit Breaker)

Protects the cable from overcurrent (too many appliances on one circuit). The MCB's rating must match the cable's current capacity.

RCBO (Residual Current Breaker with Overcurrent)

A combined RCD + MCB in one unit. Saves space in a small consumer unit. Each RCBO protects a single circuit with both earth leakage and overcurrent protection.

Best for campervans: A single RCBO is often the simplest solution for a van with one 240V circuit. It provides both RCD and MCB protection in one module.

Consumer Unit Types

The Standard Setup

For most campervans with a single inverter and shore power inlet:

Shore Power Inlet (16A blue plug)
    │
    ├── 16A RCBO (protects all 240V sockets)
    │
    └── 240V Sockets (1–3, wired in a radial circuit with 2.5mm² cable)

Larger Setup (Inverter + Shore Power + Transfer Switch)

If you have a Victron MultiPlus or similar inverter/charger with a transfer switch:

Shore Power Inlet
    │
    ├── 16A RCBO (shore power protection)
    │
    ├── MultiPlus Inverter/Charger (receives shore power, passes through)
    │
    └── 16A RCBO (MultiPlus output)
        │
        └── 240V Sockets

Wiring Regulations (UK)

The UK wiring regulations (BS 7671, the IET Wiring Regulations) apply to campervan 240V installations. The key requirements are:

Do I Need a Qualified Electrician?

For the 12V DC side: No — you can DIY.

For the 240V AC side: Technically, you can DIY under the "competent person" exception for your own vehicle. However:

• Your insurance may require installation by a qualified electrician
• If you sell the van, the buyer may ask for evidence of professional installation
• If the installation causes a fire, your insurance may investigate the installer's competence

Recommendation: Have a qualified electrician check your 240V wiring before energising it. Most charge £50–100 for an inspection.

Earthing and Bonding

This is the most misunderstood aspect of campervan 240V wiring.

The Earth Connection

In a house, the earth wire connects to the ground via a ground rod or the utility provider's earth terminal. In a van, there is no connection to actual ground. The "earth" is the van chassis.

For shore power: The earth wire from the shore power cable connects to the van chassis. If a fault occurs, the current flows through the earth wire to the shore power's earth, which trips the RCD.

For inverter power: The inverter's earth terminal must connect to the van chassis. The inverter's internal design determines whether the neutral is bonded to earth (some are, some have a relay that bonds when in inverter mode).

Neutral-to-Earth Bonding

The issue: In a house, neutral and earth are bonded at the consumer unit. In a van on inverter power, the neutral is typically floating (not bonded to earth). This means the RCD cannot detect earth leakage — there is no path for current to flow.

The solution:

• Victron MultiPlus and similar high-end inverter/chargers have an internal relay that bonds neutral to earth when in inverter mode and disconnects when on shore power
• For basic inverters, you may need an external neutral-to-earth bonding relay
• Without correct bonding, the RCD does not work in inverter mode

Check your inverter manual. If it does not handle neutral-to-earth bonding automatically, fit a dedicated bonding relay (Grundfos PM2 or similar, £30–50).

Installation Steps

What You Need

Step-by-Step

1. Mount the consumer unit: In a dry, accessible location. Not in a gas locker, not in the bathroom, not where it can be splashed.
2. Mount the shore power inlet: On the exterior of the van (driver's side, rear quarter — protected from spray). Use silicon sealant around the cut-out.
3. Run the cable: 2.5mm² three-core from the shore power inlet to the consumer unit input. Secure every 30cm. Avoid running alongside 12V cables (20cm separation).
4. Wire the consumer unit: Live (brown) to MCB input. Neutral (blue) to neutral bar. Earth (green/yellow) to earth bar.
5. Earth bonding: Connect the earth bar to the van chassis with 6mm² green/yellow cable. Clean the chassis point to bare metal. Use a star washer.
6. Run socket cables: 2.5mm² three-core from the MCB output to each socket.
7. Wire sockets: Live to L terminal, neutral to N, earth to E or ⏚.
8. Label: Label the consumer unit with the circuit description.

Testing

1. Continuity test: With a multimeter, check continuity between shore power earth pin and van chassis — should read 0 ohms.
2. Polarity test: Live connects to L, neutral to N, earth to E. No reverse polarity.
3. RCD test: Press the test button on the RCD. It should trip immediately.
4. Load test: Plug in a 1,000W load (heater or kettle). Check the MCB does not trip (unless the load exceeds the rating).

Common Mistakes

1. No RCD: The most common and most dangerous mistake. An RCD saves lives. Fit one.
2. Undersized cable: 2.5mm² for a 16A circuit is the minimum. 1.5mm² heats up at 16A.
3. No earth bonding: The chassis must be bonded to the earth busbar. Without this, the RCD cannot detect a fault.
4. Reverse polarity: Live and neutral swapped. This is dangerous — the RCD may not trip, and appliances have live metalwork even when switched off.
5. Cables too long without support: 240V cables must be secured every 30cm. Unsupported cables chafe on metal edges over time.
6. Cable run with 12V cables: Inductive coupling causes interference. Keep 240V and 12V cables 20cm apart.

FAQ

Q: Do I need an RCD if I only use an inverter? A: Yes. The inverter produces 240V AC, which can kill. An RCD between the inverter and the sockets protects you.

Q: What is the difference between an RCD and an MCB? A: An RCD protects people (detects earth leakage). An MCB protects cables (detects overcurrent). A campervan needs both.

Q: Can I use a standard household consumer unit in my van? A: Yes, a small garage or shed consumer unit works. It must have a 30mA RCD protection. Metal-clad units are preferred for mounting durability.

Q: Is it legal to wire 240V in a campervan myself? A: There is no specific law against it for your own vehicle. However, insurance policies may require professional installation. The IET Wiring Regulations (BS 7671) apply as best practice.

Q: How many 240V sockets can I have in my van? A: As many as the MCB rating allows. A 16A circuit running 2.5mm² cable can support multiple sockets in a radial or ring configuration. The limiting factor is the shore power supply (usually 10A or 16A on UK campsites).

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