IanD

You're assuming that a cheap possibly shoddily-built inverter has an internal fuse... Yes a "zero-ohm" dead short will blow a 400A fuse pretty quickly (or a 150A one), but not all faults are dead shorts, especially if the return current path for the short isn't through the heavy-current cable. Drawing 1000A or so for tens of seconds through a 400A fuse isn't going to do the cables or the batteries any good. There's still no good reason to put a 2x rated fuse in -- no advantages, only disadvantages. Why do you think it's a good idea?

Because if the inverter goes wrong (e.g. both output stage switches on at the same time, or a MOSFET failure) it doesn't appear as a dead short but a small resistance -- in this case you want the fuse to blow as quickly as possible to avoid the inverter bursting into flames as it dissipates several kW internally instead of the hundred watts or so it's designed to dissipate. There's still no good reason to double the fuse rating...

Fuses should be chosen to match the continuous power draw of a circuit -- at 2x the rated current a fuse this size won't blow for about a minute, so if you use a 350A-400A fuse it will pass something like 800A for plenty long enough to set the inverter on fire or damage the rest of your system. Suggest you use a 150A fuse for a 1500W inverter. Here's an example of the trip curve for a 150A fuse: https://www.bluesea.com/products/5114/Fuse_A3T___Class_T_150_Amp At 300A it won't break for at least 1 minute, and is guaranteed to break in about 5 minutes -- the difference is due to manufacturing tolerances. If inverter manufacturers recommend a fuse at 2x the inverter rating, they don't understand how fuses work... ?

We did exactly the route you're doing (in the same boay, possibly) a couple of years ago, and turned with no problem just above Newlay Top Lock -- this is shown on Pearson's but not Nicholson's.

It also has the advantages of showing where you are, and being easily zoomable in and out so you can see lots of detail or an overall route.

If you have a phone with data, opencanalmap is good too.