Coffee van mains and inverter help

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CupofCoffee

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Hi,

I've recently purchased a small coffee van that is in need of a fairly comprehensive overhaul. As purchased I wasn't comfortable with the on-board electrical setup: caravan style hookup -> 4 way consumer unit/RCD/16A MCBs > coffee machine socket (2000W element), "sockets" to grinder/fridge, 12v water pump via a DC transformer and 2x 230V rated flourescents).

There was provision for an inverter to be used by way of a length of flex with a 13A plug on each end going from the inverter to a double socket used as an inlet and then into the same RCD input as the mains......... Allegedly this was as the van was fitted out by a professional conversion company and supplied with a basic cert... To add amusement to the mix, the inverter supplied was rated 300W and the connectors were a pair of jump leads which sat next to the van's own tiny battery (and they wondered why they had trouble starting it?).

As both the coffee machine and fridge are dual fuel (LPG), the coffee van can be run "off-grid", however the grinder cannot.

I would like to re-incorporate a battery/inverter system with a leisure battery being charged when hooked up to the mains supply using a smart charger (van won't be driven more than 5 or so miles for a split-charge setup to be worthwhile and I anticipate mains access 75% of the time). With the current setup it would be a snake swallowing it's own tail with the charge system on the same circuit as the inverter, additionally the coffee machine's electrical side isn't suited to the inverter (1500W) I've got.

What I had in mind was the feed from the caravan hookup to a junction box with one side feeding a 2 way garage type consumer unit to covering the charger and the coffee machine and the other split going to a switching relay that'd detect whether mains or inverter were active to supply a 4 way consumer unit covering lighting, coffee grinder, fridge and water pump.

Probably best explained with a couple of pictures, original (with no inverter) and planned. Would really appreciate some feedback as to whether this is workable or if there's a better way forward?
 

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Original
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Proposed

 
This needs careful thought due to the multiple permutations of operating conditions and faults which could occur.

My initial thoughts are that an RCD needs to be at the external power input  to protect all the vehicle installation.

Second thought concerns the idea of a changeover switch. I think I would be more inclined to use two sockets and a plug on a short flying lead. One of these sockets would be from the invertor output and I think should also have an RCD.  (Is the invertor output neutral grounded?)

Finally I think there are regulations concerning mobile installations, but I don't have these and I don't know what's in them.

The complete vehicle presumably constitutes a workplace, with the regulations that implies.

Time for someone else to advise!

 
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