How can I protect a 12VDC power source from high-resistance shorts?

[pugai]

Hello guys, first topic in ck5, please be kind. I have a pickup truck with a 3kw AIMS inverter-charger. It is wired with 4/0 welding cable (for both positive and dedicated neutral back to the alternator), and I installed a block with a 300A fuse in the engine bay as close to the alternator as possible. My concern is that most of the conceivable events causing a short circuit would have a current path with resistance such that the short would be much less than 300A and therefore not blow the fuse.

What is the recommended practice for wiring such systems? I did a search for "DC ground fault protection" but none of the products that came up appeared to be appropriate for my application. If a 300A 12VDC GFCI device was available I would gladly purchase it. Thanks in advance.

Edit: I am talking about a live-to-ground short, not live-to-neutral. Suppose the insulation surrounding the live wire to the inverter (which is routed along the truck's frame) is somehow sliced open and the bare wire makes a weak short against the frame. This is the event I want to be protected from. To be clear, answers pertaining to the physical protection of the live wire are not appropriate here; I have already taken steps to make sure it is as far out of harm's way as possible.

Edit 2: These are the events I foresee possibly occurring as a result of a live-to-ground short (and want to prevent): 1) batteries being drained, 2) batteries exploding due to a short of up to 300A, 3) a fire being started due to the resistive heating from a short of up to 300A through components of the body or frame.

Edit 3: I emphasize that the inverter has a dedicated neutral that connects directly to the alternator housing. Therefore, ALL return current must pass through this wire unless there is a live-to-ground fault somewhere. In such an event there will be a difference in current between the live and neutral wires, which is the condition upon which I want my mystery device to trip and disconnect the live wire.

Edit 4: Here is a concrete example of a situation I want to prevent from which the fuse offers no protection. Imagine that the vehicle is involved in a collision and the body of the truck pierces the 12V wire insulation. The 12V wire will now have a weak (the body of the truck is painted and likely dirty) short against the truck body, resulting in finite current that could quite possibly be way less than 300A but still sufficient to cause a fire due to resistive heating and/or battery explosion (or even just drain the battery and make the truck unusable).
Thanks all advice!

 

[Blue85]

This is similar to wiring a winch or even the starter motor.

I think you've already pointed to the solution you want. The dedicated "neutral" (not sure how that term applies, it's really the power return) should have the same current as the power line. As long as they are routed side-by-side somewhere, you just run them through a hall effect current sensing device. That device could drive a relay that interrupts a continuous-duty solenoid coil on the inverter supply.

Also "high resistance" and "short" are kind of opposites. Anything with high resistance doesn't really matter and will be quite hard to detect. In the case of a frayed wire dumping 100A into the frame, that's 0.12 Ohms.

 

[Truckman4life]

Welcome to CK5. I am assuming you have household electrical experience with your use of the terms "ground" and "neutral". I am used to only power and ground and no such thing as a neutral in a 12 volt system. I have issues crossing over into the household electrical world because of my background in vehicles.
All of our winches and inverters(3,000 watt Pure Sine Wave) on the utility trucks I work on are just protected by a 300 amp fuse as close to the batteries as possible. We do run high amp continuous duty solenoids on the inverters to only allow them to be connected to the trucks main batteries when the key is in the "on" position. The winches run a similar solenoid that is wired in a "normally closed" position with the key on and there is an emergency stop button right at the winch that will open the main power to the winch if pressed. Aside from that I can only recommend that you route your cables and secure them and insulate them as best as you can.
I have worked on semis for over 12 yrs and done a ton of battery cables and aftermarket add-ons and never ran into any issues to get too worried about. Some semis run 2-3 4/0 cables to the starter at a length of 6-10' and no circuit protection at all and a bank of 4-1000 CCA or larger batteries.