Grounding your Electrical System - Vans, Boats, Campers, Caravans...

Grounding or earthing your Electrical System is a crucial step whether it is for a van conversion, camper, caravan, boat or in your shed at home. There is a lot of conflicting information on how to establish the ground for electrics. In this article, we'll cover everything in detail. We'll explore the types of ground, which appliances need grounding, and how we connect grounds.

What is Ground?

The term ground (or earth) frequently holds various meanings for different individuals, leading to confusion, particularly in the context of off-grid installations. For example, to an electrician, ground might signify something different than it does to an electronics engineer.

Proper grounding is a vital safety measure in the field of electrics. We ground electrical equipment to prevent wiring failures from increasing the voltage to hazardous levels. Grounding provides an alternative route for electricity in the event of a fault in your system. Instead of flowing through your electrical system at dangerous voltages, electricity is directed to the ground to protect your wires and appliances, and ideally prevent a fire.

A circuit must be complete for current to flow:

We can use ground as an alternative circuit return path in case something goes wrong in our main circuit:

In a vehicle, the metal chassis is the common return path for all return current to the battery:

In the world of van, camper, caravan or boat conversions, ground is simply a connection from the negative terminal of your leisure battery to the chassis of your vehicle.

BS 7671 Guidelines for Grounding in Vehicles

Adequate grounding in your campervan's electrical system is crucial for ensuring safety and meeting compliance standards. Outlined below are the main regulations from BS 7671 (UK) that specifically pertain to grounding in vehicles.

BS 7671 - UK Wiring Regulations

Section 721.411.3.1: Protective Earthing and Bonding in Caravans and Motor Caravans

• All exposed conductive parts, such as metal appliances or components, must be properly earthed. The chassis of the vehicle serves as the DC ground for the 12V system, providing a return path for current.

• For the AC system (shore power), a separate AC earth must be connected to the vehicle chassis, and it must be isolated from the DC ground. This prevents any crossover between the AC and DC earthing systems, ensuring the systems remain safe and separate.

Regulation 543.2.7: Earthing Conductors and Connections

• Ground connections in campervans must be both permanent and accessible. For instance, your main ground point should not be hidden behind cladding or insulation to allow for inspection and maintenance.

• Use a suitable earthing conductor that is sized appropriately. The minimum cross-sectional area for a DC grounding cable must be at least as large as the main DC positive cable, and for AC grounding, the green/yellow cable must comply with the minimum sizing set out in Regulation 543.1.

Regulation 411.3.2.1: Protective Earthing of Electrical Installations

• Any connection to shore power (AC) must have a protective earthing connection, which bonds the AC system to the vehicle chassis. The earthing conductor should run directly from the consumer unit to a dedicated AC ground point on the chassis.

• It is crucial that RCDs (Residual Current Devices) are installed in the AC system to ensure safety, as they detect faults and disconnect power if a ground fault is detected.

Regulation 411.4.2: Earthing Systems for TN-S and TN-C-S Installations

• If your campervan is connected to a TN-S or TN-C-S earthing system via shore power, ensure the earthing conductor from the electrical installation is connected directly to the main earth terminal at the vehicle's consumer unit. The system must include protection against faults that may occur due to a disconnection or interruption in the supply earth.

Key Takeaways for Grounding in Off-Grid Installations

DC Ground: Connect the negative terminal of your leisure battery and all 12V components to the chassis. Utilise a negative bus bar to gather connections, and connect the bus bar back to the vehicles factory-installed chassis ground point or establish a new one by firmly bolting into bare metal.

AC Ground: AC systems (such as shore power) must be grounded separately to avoid cross-currents with the DC system. Use a dedicated AC ground point on the chassis for appliances like the inverter and consumer unit.

Ground Fault Protection: Install RCDs (UK) to protect the AC system from ground faults. These devices disconnect power in the event of a fault, safeguarding the system from electrical hazards.

Accessible Ground Point: Ensure that your ground point is accessible for inspection and maintenance. Use green/yellow cables for AC ground and appropriately sized cables for DC ground, per the BS 7671 guidelines.

AC Ground vs. DC Ground

The main difference between AC and DC ground is that no current should flow into AC ground during normal operation, while all current should flow into DC ground. Why?

DC appliances don't have a "ground" per se, because the negative battery terminal (which people sometimes call "ground") is itself at the same electrical potential as the chassis. The negative terminal of your leisure battery is ground for the appliances.

Which Appliances Should I Ground in my off-grid installation?

Certain elements must be grounded in a vehicle:

• Starter battery (should be grounded already)

• Negative DC busbar - this grounds your leisure battery and the other DC components in the electrical system

• Shore power (EHU) consumer unit (must be grounded per BS 7671:2018 – Section 721 regulations to a separate AC ground)

Others might need grounding depending on their construction. Consult the manufacturer’s guidelines:

• MPPT

• Battery chargers and split chargers (separate AC ground)

• Inverter and inverter consumer unit (separate AC ground)

  
  

It is particularly important that you check the manufacturer’s guidelines as it relates to grounding your inverter (and the related consumer unit, if required), as grounding advice frequently changes with the manufacturer and how the inverter is built. As a general rule of thumb, each component in your electrical system should be grounded, unless the manufacturer’s instructions say otherwise.

It is important that all your grounds are connected together (ie. to a single ground point) to avoid ground loops. A ground loop is a closed conductive loop that will slowly but surely drain your batteries.

Note: The DC ground and AC ground should run to separate ground points - with no crossover between the two. This means that the inverter and shore power consumer unit run to a dedicated AC chassis ground.

How to Install Ground in a Vehicle Off-Grid Installation

Every vehicle comes with ground points integrated into the chassis. A simple Google search for your vehicle's ground points should reveal their locations. According to BS7671 regulations, the ground point should be kept in an accessible location, meaning it should not be hidden behind cladding, insulation, or furniture.

Sometimes, you may want to make your own ground point if existing points are in an awkward place:

1. Sand down the paint on the chassis of the vehicle on an interior part of the chassis. This gives a clean connection point against the bare metal.

2. Drill a hole into that point.

3. Rub some dielectric grease/Vaseline on the connection point to prevent corrosion and improve the electrical connection.

4. Screw a bolt into the hole, followed by a nut and an external tooth lock washer. This is your new ground bolt.

The correct color for a dedicated ground wire is green and yellow:

Wire Size

According to the guidelines, the chassis ground cable must be at least one size smaller than the largest wire in the system. This means you should use a cable approximately the same size as your battery cable for the ground connection.

Negative Busbar as Common DC Ground

Rather than connecting each appliance directly to the ground point, we usually employ a negative busbar as a common ground for all DC components requiring grounding. All DC grounds connect to the negative busbar, which in turn connects to the ground point.

Avoid connecting the AC ground to your negative DC busbar. If you need to connect the AC ground to a busbar, it should be directed to a new dedicated busbar called the 'earth busbar'. The negative DC busbar should connect back to the vehicle manufacturer-assigned negative point on the chassis. The earth busbar should connect to a newly established mains ground point on the chassis.

Ground Fault Protection

Ground Fault Protection safeguards your system from potentially dangerous electrical faults, where current unintentionally flows to ground through the chassis or a person.

Install Ground Fault Circuit Interrupters (GFCIs) in your AC system, particularly near outlets or wet areas. GFCIs monitor the current flow and instantly disconnect power if they detect a ground fault (a mismatch between incoming and outgoing current).

For DC systems, fuses and circuit breakers provide essential protection by preventing overcurrents in the event of a fault.

Conclusion

Grounding is an essential safety component of any electrical system. If you're uncertain about your installation or how to best approach grounding, consult a professional electrician. It's best not to play around with your electrical system unless you're 100% sure of what you're doing.