Anyone else using their EV charge point to top up a motorhome via shore power hookup?

Bit of an unusual one here. I've got a 7kW Ohme home charger fitted primarily for the car, but I've been experimenting with running a 16A blue commando socket off the same circuit to give the motorhome a proper shore power feed when it's parked up on the drive. The idea being the Victron MultiPlus 2000 onboard handles the AC input and bulk-charges the 200Ah Fogstar lithium bank overnight.

The snag I keep running into is the Ohme's load balancing logic occasionally decides to throttle the output when it thinks the house is drawing too much, which plays havoc with the Victron's absorption phase. I've got the MultiPlus set to limit input current to 10A, but it still seems to confuse the Ohme's CT clamp readings. Getting some odd behaviour where the charger drops to 6A and the Victron starts hunting.

Has anyone wired this sort of dual-use setup properly, or found a way to either isolate the motorhome circuit from the Ohme's CT clamp monitoring, or just accepted that a dumb 3.6kW feed is more sensible for overnight leisure battery charging? Wondering whether a separate dedicated 16A circuit with a basic Mastervolt or similar unit onboard would just be cleaner overall.

Hey @SomersetVanLifer, interesting setup! One thing worth flagging - if your Ohme and the commando socket are sharing the same circuit, you'll want to make sure they can't draw simultaneously, otherwise you're potentially asking for more than the circuit's rated for. A simple interlock or even just a robust "one or the other" switching arrangement would sort that. Also worth checking your DNO agreement - some 7kW installs have specific conditions attached. That said, loads of people run motorhome hookups from a dedicated 16A radial without issue, so the concept is sound. What's the actual cable run length to where you park the van? Voltage drop could be worth calculating if it's more than about 20 metres.

Wardy16 | Posts: 847

@SomersetVanLifer interesting setup! One thing worth flagging - your Ohme and the motorhome hookup sharing the same circuit could cause headaches depending on how it's wired. If both are drawing simultaneously you'll likely trip the breaker sharpish, and most DNO connections for 7kW chargers are on a dedicated circuit specifically to avoid that scenario.

Worth checking with whoever installed the Ohme whether the supply was uprated, as some installs piggyback the existing consumer unit without boosting the incoming capacity.

The smarter approach might be using the Ohme's load balancing/scheduling feature to ensure the car isn't charging when the motorhome is hooked up. Do you have anything controlling that currently or is it manual switching?

Also worth a quick chat with an electrician about whether your current arrangement is fully compliant - blue commando installs have their own regs to consider.

Has anyone actually had issues with the RCBO tripping when both are drawing simultaneously? I've got a similar dilemma at my cabin — I use a 16A commando for emergency backup hookup when the solar isn't keeping up in winter, but mine's on a dedicated circuit rather than sharing with an EV charger.

Curious whether the Ohme's load-balancing would actually pull back the car charging automatically if the motorhome hookup starts pulling hard — does it see that additional load or only what the car is drawing? I'd have thought if it's monitoring via CT clamp it should compensate, but only if the clamp is upstream of both loads.

What's your consumer unit setup like @SomersetVanLifer? Are both feeds coming off the same MCB or separate breakers sharing the same incoming phase?

@GemmaStewart yes, had exactly this at my static caravan setup. RCBO nuisance tripped repeatedly when the motorhome fridge compressor kicked in at the same time as another load. Wasn't an overload issue — it was the inrush current from the compressor causing a false trip.

Ended up fitting a Type B RCBO rather than the standard Type A, which handles DC-pulsed and inrush currents far better. Sorted it immediately.

Worth checking what type yours is before assuming there's a fault. Most domestic installs default to Type A, which can be a bit twitchy with motor loads and inverter-based kit. If you've got anything Victron or similar on board with a battery charger running, that makes it worse.

Get an electrician to confirm your RCD discrimination is set up correctly too if you're sharing the circuit like @SomersetVanLifer describes.

StuCampbell | Posts: 2,341

@GemmaStewart the RCBO tripping issue is worth taking seriously beyond just nuisance trips. On my narrowboat I learned the hard way that cumulative earth leakage across multiple appliances on the same circuit stacks up — your motorhome fridge compressor starting, the Ohme doing its thing, maybe a battery charger humming away — each individually fine but collectively nudging past the 30mA threshold.

Worth checking whether your RCBO is Type A or Type B. EV chargers can produce pulsed DC residual current that a Type A simply isn't rated to handle correctly — this is actually a legal requirement for dedicated EV circuits to use Type F or Type B RCDs under the 18th Edition Amendment 2 regs.

If you're sharing that circuit between EV and hook-up, you potentially have a compliance headache sitting there regardless of the tripping annoyance.

@OldSailor79 this is really relevant to my boat setup actually — I've got a similar arrangement where I'm sharing a circuit between shore power and my Victron MultiPlus. What sorted it for me was fitting a proper load balancing relay so the two loads can't both pull simultaneously at full demand. Cost about £40 from a marine supplier.

The other thing worth checking — are you using a decent RCD or a cheaper unit? I replaced a budget RCBO with a Hager unit and the nuisance tripping basically stopped overnight. Cheap ones can be hypersensitive to the kind of switching noise that inverter chargers generate.

Not saying that's definitely your problem but it's worth ruling out before you start rewiring anything significant.

DebbieKelly | Posts: 847

@LindaPrice87 interesting you mention the boat angle — the marine environment adds another layer of complication with salt air and corrosion on connections, which can make earth leakage worse over time and trigger those RCBOs even more readily.

@SomersetVanLifer to your original question, I've been doing something similar but I keep the motorhome and car on completely separate MCBs fed from the same consumer unit rather than sharing a circuit. Means any issues with the motorhome don't risk interrupting the car charging overnight. Might be worth considering if you're doing this regularly — the marginal extra cost during installation is well worth the peace of mind.

ExBrickie94 | Posts: 612

Built a similar bodge myself — Victron MultiPlus on the van side means it'll happily take whatever trickle makes it down the cable without throwing a tantrum about voltage drop. 🧱⚡

OllieRoss74 | Posts: 234

My shepherd's hut runs off a similar shared-circuit arrangement — single 32A feed from the house doing double duty. The key thing nobody's mentioned is interlocking. You really don't want both loads drawing hard simultaneously, especially on a cold morning when the EV's pre-conditioning and your motorhome's heating kicks in.

I fitted a simple mechanical interlock between the two circuits — nothing fancy, just prevents both being live together. Saved me a very awkward conversation with the DNO about my meter spinning like a Catherine wheel.

@ExBrickie94 the Victron angle is interesting — does the MultiPlus handle the supply quality gracefully when the Ohme's doing its demand-response thing?

DevonCruiser | Posts: 234

@ExBrickie94 the Victron angle is worth expanding on — the MultiPlus is brilliant for exactly this reason. The input current limit setting is your friend here. If the car charger happens to kick in while you're on hookup, you can set the MultiPlus to throttle back its draw automatically rather than tripping the breaker. I've got mine set to 6A input limit as a conservative buffer on a shared circuit. Not a perfect long-term solution, but it works a treat for overnight top-ups. Just make sure your commando socket installation is signed off properly — a notifiable job under Part P.

ShortCircuit56 | Posts: 1,203

Worth flagging for @LindaPrice87 and anyone on a marine setup — if you're sharing a circuit between an EV charger and shore power hookup, check how your earth fault protection is arranged. Boats and motorhomes both have their own PME exclusion requirements, and you really don't want the EV charger's earthing arrangement conflicting with a floating or TT earth on the vessel or van side. @ExBrickie94 the Victron MultiPlus helps enormously here since it provides galvanic isolation. An isolation transformer on the boat connection specifically would be my strong recommendation before going any further with that Linda.