Auto inverter changeover relay

First picture is a selection of relays from RS components. The one on the right is my choice as it is 10 amp rated through the normally closed contact set which will be used for the inverter when off hook up.
The normally open contact set is 30 amp rated and will be used to power a skt/skts as normal when on hook up
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I've mounted the relay in a "really useful box" and fitted a 25mm thread stuffing gland big enough to grip 3x1.5mm flexes all together
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Power IN flex lugged up to go on the N/O contacts and the 230volt relay coil
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Power out connected to the common pair of terminals and inverter feed connected to the N/C terminals
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All that remains is to customise the flexes to required lengths
fit a 13 amp plug top to the inverter feed but with a 10amp fuse!!!
Fit two pairs of 10 amp rated connectors being careful to fit the female halves to the ends that will be live i.e. the flex from the 10 amp breaker that you are going to cut that normally feeds the skt and the power out lead from the changeover.
The male ends go on the feed in to the relay box and the other part of the flex cut earlier that continues on to the socket.
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Now I just need an inverter, probably a 1.8K for my needs but I'll see what's on special.

I've already been using this setup with the other relay in the first picture but with a 350watt pure sine inverter for the entertainment and gizmo charging area "lounge"

The modus operandus is
The socket radial circuit is now routed through the normally open contacts of the relay, as soon as the hook up is made this makes those contacts close to feed the socket as normal.
Without hook up you just switch the inverter on and the socket is now fed through the normally closed contacts of the relay.

PART II location of the unit will vary from van to van
MARK II enclosure used which is an 80p container from ASDA
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Side locker floor removed and there is the flex from the mains board coming up through the floor and on its way to the nearside kitchen sockets
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I managed to obtain spare length by re routing the converters choice of cable run.
Fit the 10amp through connector Female to mains side male to socket side
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unit plugged in between the open ends
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No holes to drill in my case, feed from inverter flex passed through gap into vicinity of batteries.
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Plugged into my 350watt inverter just to test
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Microwave lights on :-)
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Kitchen sockets live
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When my new inverter arrives it has 2 sockets so the 350watt could be redundant.