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I have an RV with both 12V and 230V systems. The 12V uses internal battery, while 230V is supplied from outside via plug. Should I connect these systems to metal frame of vehicle (minus of 12V or earth from 230V)?

The vehicle stands on rubber tyres and can touch ground via metal steps and metal vertical stabilizers.

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  • \$\begingroup\$ Can you provide details of which part of the world you are based in, and the nature of the supplies you are using? \$\endgroup\$
    – colintd
    Oct 26, 2023 at 11:57
  • \$\begingroup\$ EU - so 230V Schuko plug - IEC60309 adapter cable. It has neutral, phase and ground. So far it is only connected to 12V charger (victronenergy.com/chargers/blue-smart-ip67-charger-waterproof) \$\endgroup\$
    – Ri Di
    Oct 26, 2023 at 13:29

2 Answers 2

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Grounding of RVs is a complex question, and the correct approach is dependent on the details of the supply earthing system.

Based on the reference to 230V I'm going to assume you're in the UK, in which case the relevant standard is section 708 of BS7671:2018.

This standard explicitly states in subsection 708.411.4, that a PME ("Protective Multiple Earthing") earth should not be connected to any metal work in a caravan, and in 708.553.1.14 that sockets for supplying caravans should not have an earth conductor connected to PME earthing.

This is because in environments such as building sites, caravan parks and farms, you can't be certain of establishing and maintaining the equipotential zone that is required to safely use PME.

The bonding is required because if the neutral conductor goes open circuit, the PME "earthed" metal work can potentially rise to full line voltage. Only by ensuring that this happens to all metalwork in the zone simultaneously, can the shock risk be minimized.

enter image description here

(Diagram from the Voltimum article linked above.)

Given that most domestic supplies will be PME, this means that you should avoid just using extension cables from a house socket, as the earth wire will extend the house's PME earth outside the equipotential bonding zone.

Instead, supplies to caravans should be via a dedicated 30mA RCD protected supply, with TT ("Terra-Terra") earthing connecting to a dedicated earth electrode (not the PME terminal). This setup is mandated for commercial sites, and strongly recommended for long term domestic settings.

Standards in other countries may vary, but the reasoning for the UK guidance remains valid - you don't want to be able to grab a PME earth while in contact with true ground...

It is up to you to ensure that the supplies which you use meet the no-PME requirement, but if that condition is met, then grounding of the metalwork is safe and in fact required (to avoid the chassis becoming live in the event of a L-chassis short).

For the 12V system, connecting the negative terminal to the RV body is perfectly natural and safe.

(Note, when using PME earthing for a building and TT outside, you need to ensure that there is sufficient separation so that you can't simultaneously touch grounded objects in the two separate zones.)

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  • \$\begingroup\$ I am using standard caravan IEC 60309 plug with three pins - phase, neutral and earth. "you should avoid just using extension cables from a house socket" - you mean the ones without earth (two wire)? \$\endgroup\$
    – Ri Di
    Oct 24, 2023 at 13:39
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    \$\begingroup\$ It isn't the cable that is the issue, more that by plugging into a typical 3 pin socket on a long extension cable, you exporting the house's PME equipotential zone to a location that can't be reliably bonded and will likely expose access to objects at true earth as well. Most garden tools get round this issue by being double insulated (so no exposed PME earthed metal work). Caravan parks follow the BS standards and offer sockets with individual RCDs and earth from dedicated earth rods. If this is a long term setup, you should aim to have a dedicated feed with its own RCD and TT earthing. \$\endgroup\$
    – colintd
    Oct 24, 2023 at 15:32
  • \$\begingroup\$ Fyi there are similar restrictions on earthing farms, pool, building sites, etc, all of which generally avoid use of PME as you can't reliably ensure equipotential zones. For additional safety building sites also typically use 110V supplies fed via isolating transformers, center tapped to local earth with 55V each side. \$\endgroup\$
    – colintd
    Oct 24, 2023 at 15:40
  • \$\begingroup\$ I've updated my answer to clarify the above points. \$\endgroup\$
    – colintd
    Oct 24, 2023 at 15:47
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    \$\begingroup\$ Already up-voted, but I feel like a couple of diagrams would help a lot to illustrate the separate 'zones'. \$\endgroup\$
    – brhans
    Oct 24, 2023 at 16:02
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This is a good question, however it's impossible to answer without knowing what country you live in! The top-voted answer is specific to the UK.

On the off-chance that you live in NZ or Oz, then ... perhaps you're unaware that a registered electrician must sign off on the installation before you'll get a WOEF ("Warrant of Electrical Fitness") for your RV? See https://www.nzmca.org.nz/electrical-inspections. Increasingly often, I'm asked about my WOEF when I roll into a caravan park in NZ and ask for a powered site. So... I'd suggest you look for a sparky who would inspect and then (hopefully!) sign off on whatever you wired up... and that you'd take their advice on how to hook up PE on your RV's 230VAC sockets, rather than taking advice that's relevant to some other country's electrical-safety regulations!

An RV in Australia or New Zealand -- unless it has an onboard inverter -- will I think normally be wired as in https://www.caravansplus.com.au/guides/traditional-electrical-installation-guide-a-56.html.

If you have an inverter on-board, then things get much more complicated. The Victron Multiplus in my e-NV200 is (somehow!) able to supply a PE -- even when it is not connected to "shore power" -- which is sufficient to persuade an IC-CPD (aka "granny charger") not to throw a fault when I use it for a roadside topup (either for my e-NV200 or to some stranded EV). I think this is done with a grounding relay internal to the Victron Multiplus, and with a bonding of the chassis of the Multiplus to the chassis of my RV. See https://community.victronenergy.com/questions/21965/rcd-grounding-multiplus-grounding-negative.html

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