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What cable for running accessories?

If you used the second run that is free I think we can safely discount any grouping factor. The only circuits to consider would be the rear demist and the wiper, all others are negligible loads or intermittent/short time loads. I think we can ignore those if you keep your cable separate. 6mm is the minimum size really. You are unlikely to run thecair compressor for 30 minutes or more so this can be discounted for loading.

As Moggy said the accessory sockets can be a concern, Best avoid these or fuse them down appropriately. In other words hard wire the compressor or use a dedicated plug. Cigar lighter sockets are awful things for anything more than a few amps as they can get hot and melt over time. Hence also aim to hard wire your fridge in. Consider using Anderson connectors of 20A or more for disconnecting if you really need to. No reason to avoid cigar lighter sockets for occasional use of chargers etc though but keep fusing to 7 to 10A.

6mm, in the unused Channel will in all practicality be perfectly adequate for your current and future planned loads as listed.
 
@StarCruiser Your help has been amazing (as has the help of others). Thank you very much sir, it's greatly appreciated.

The compressor will be via a suitably rated DIN socket/plug. I was thinking about suitable fridge connectors last night and I was leaning towards something like this:
https://hobbyking.com/en_us/hxt-4mm-gold-connector-w-protector-10pcs-set.html
You could do but these https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.co.uk/ulk/itm/140906405729 are very widely used, can link together to form multiples and are the smaller cousin to those used on fork lifts, race cars, uninterruptible power supplies etc. They just work and are under Constant Spring pressure which means they aren’t susceptible to vibration or loosening. They can safely be hidden away though it’s always best to maintain access to such things for the future.
 
If your fridge has a cut out voltage then voltage drop can be a problem for that and you may find it cuts out much sooner than you expect.
 
It’s a good point Jon. Where motor starting is concerned the voltage drop for a short period can be considerable but I would be surprised if the Fridge was quick enough to sense it (it may do) and would almost certainly restart after depending on the battery voltage at the time. Even without power the fridges stay cold for a considerable time but of course it depends on what the ambient temperature is. Depending on the Fridge the cut out voltage is often adjustable.
 
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If your fridge has a cut out voltage then voltage drop can be a problem for that and you may find it cuts out much sooner than you expect.

That's a good point. I'm probably only looking at a 0.1v drop. Also ,the fridge voltage drop cutoff is adjustable, so I can compensate.
 
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@StarCruiser - Last Q I promise!

When I wire up my fridge. Should it have a local fuse or do I rely on the fuse in the fridge itself?

i.e. should it be scenario A or B (in lieu of diagrams)?

A - Battery positive > 40A midi fuse > 6.0mm cable > local fuse box (rear of car) > 7.5A fuse > cabling and connector to fridge > fridge's own fuse.

OR

B - Battery positive > 40A midi fuse > 6.0mm cable > buss bar (rear of car) > cabling and connector to fridge > fridge's own fuse.

I'm inclined to go with A as it gives more protection and is more flexible.
 
Answer is…A

To boil it down, generally when the cable gets smaller fuse it at source to protect the smaller cable. Ideally, and for convenience, the nearest fuse to the fault between it and the battery should be the one to blow sonyou would for example have one in the fridge at 7.5A then one feeding its supply cable at 15A then the 40 A feeding the whole lot. If the fridge has a fault the 7.5A should blow, if the feed cable gets damaged, the 15A should blow, if the main feed gets damaged or too many things are switched on the 40 A should blow. You get the picture. Or, if you want, you can omit the fuse at the Fridge, put a dedicated supply in for it via a non fused socket and fuse at the fuse box at 7.5A, thereby simplifying things a little and keeping all the fuses in one place.
 
Answer is…A

To boil it down, generally when the cable gets smaller fuse it at source to protect the smaller cable. Ideally, and for convenience, the nearest fuse to the fault between it and the battery should be the one to blow sonyou would for example have one in the fridge at 7.5A then one feeding its supply cable at 15A then the 40 A feeding the whole lot. If the fridge has a fault the 7.5A should blow, if the feed cable gets damaged, the 15A should blow, if the main feed gets damaged or too many things are switched on the 40 A should blow. You get the picture. Or, if you want, you can omit the fuse at the Fridge, put a dedicated supply in for it via a non fused socket and fuse at the fuse box at 7.5A, thereby simplifying things a little and keeping all the fuses in one place.

Thank you. I'll be going with A.
 
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