Thread: Fuse or Circuit Breaker

I'll be interested in the advice you get to this too. For interest, in a recent youtube video MOST PEOPLE GET THIS WRONG - YouTube, Ronny Dahl essentially said to preference fuses in engine bay due to heat, and circuit breakers elsewhere. I have no idea if the advice is based on any expertise.

Originally Posted by d2dave

I have an auxiliary battery mounted at the rear of my D2.

From this battery I am going to run 6B&S cable to an Anderson plug at the rear bumper to charge the house batteries in my Tvan.

What is better to use, Maxi fuse or circuit breaker and the reason for your choice.

Also opinions as to size. I was thinking 100 amp.

I would use fuses myself for 2 reasons. Firstly is the heat issue under the bonnet. Circuit breakers rely on a thermal circuit that heats up as load increases and excess heat can cause early tripping. The other reason is vibration - eventually this will cause the breaker to nuisance trip - it’s one of the reasons we run HRC fuses in our gensets on pretty much all circuits, even low voltage, low current DC.

What Gav said.

As for rating, the cable you are using is rated to a max of 120. I'd prefer a little more margin than 24% but it's probably ample given good cable performs better than it's stated rating.

Originally Posted by Homestar

it’s one of the reasons we run HRC fuses in our gensets on pretty much all circuits, even low voltage, low current DC.

On another note,we have HRC fuses on many jobs as well,they are often near impossible to get hold of these days,particularly if they are needed urgently.

My two cents on what the OP asked,fuses any day.

Originally Posted by Homestar

I would use fuses myself for 2 reasons. Firstly is the heat issue under the bonnet. Circuit breakers rely on a thermal circuit that heats up as load increases and excess heat can cause early tripping. The other reason is vibration - eventually this will cause the breaker to nuisance trip - it’s one of the reasons we run HRC fuses in our gensets on pretty much all circuits, even low voltage, low current DC.

Gav. Heat is not an issue here as the wiring is going from my battery in the rear of the vehicle to rear bumper.

However, in response to your heat concern with circuit breakers, I have one of Tim's Traxide isolators.

He told me that due to my battery being in the rear that I need a circuit breaker at each battery in case of a short between the two.

He sold me two 50 amp auto reset breakers with the isolator. They have been in use now for 10 plus years without a problem, one under the bonnet, one at the rear.

And when it comes to this stuff Tim is the man.

Originally Posted by d2dave

I have an auxiliary battery mounted at the rear of my D2.

From this battery I am going to run 6B&S cable to an Anderson plug at the rear bumper to charge the house batteries in my Tvan.

What is better to use, Maxi fuse or circuit breaker and the reason for your choice.

Also opinions as to size. I was thinking 100 amp.

Hi Dave and you can use circuit breakers or fuses and don’t take any notice of the idiot misinformation in that video.

I near burst out laughing when I heard him say “You should not use circuit breakers under the bonnet because of the heat, but fuses will work”.

Yes, in extreme heat situations, circuit breakers will go open circuit at lower currents.

BUT GUESS WHAT, fuses will act in the exact same manner. He has no idea what he is talking about.

Dave, if you use 6B&S cabling, while 6B&S is rated at a continuous current 140 amps in “OPEN AIR”.

But in the confines of a motor vehicle, 6B&S is derated to a continuous current rating of 105 amps.

Any fuse or circuit breaker use to protect a circuit must have a maximum current rate of at least 20% less than the cables continuous current rating, so an 80 amp fuse or circuit breaker would be perfect.

Originally Posted by Homestar

I would use fuses myself for 2 reasons. Firstly is the heat issue under the bonnet. Circuit breakers rely on a thermal circuit that heats up as load increases and excess heat can cause early tripping. The other reason is vibration - eventually this will cause the breaker to nuisance trip - it’s one of the reasons we run HRC fuses in our gensets on pretty much all circuits, even low voltage, low current DC.

Yep, fuses are far more tolerant to vibration.

Originally Posted by towe0609

I'll be interested in the advice you get to this too. For interest, in a recent youtube video MOST PEOPLE GET THIS WRONG - YouTube, Ronny Dahl essentially said to preference fuses in engine bay due to heat, and circuit breakers elsewhere. I have no idea if the advice is based on any expertise.

Hi towe0609, and sorry mate but that guy is nothing more than a keyboard cowboy.

There are so many erroneous statements in that video that people would be far better off ignoring just about everything he rants on about.

The most common bit of B/S that shows he knows nothing about batteries, is his claim that taking AGMs below 50% SoC can damage them.

Why would battery manufacturers specifically state that their AGM batteries can be discharged down to 20% SoC and some of the newer AGMs can be safely discharged down to 0% SoC?

Again, he calls the AUXILIARY battery a house battery.

For the forty plus years I have worked in the field, the second battery in any vehicle has always been called the Auxiliary battery and House batteries are found in Camper Trailers, Caravans and Motorhomes.

He as done a little bit of googling and is now making out he is some sort of expert in a field he actually hasn't got a clue about.

Again, he states the second battery under the bonnet should be a Deep Cycle battery and he claims it can used to jump start and assist when winching.

First off, most Deep Cycle batteries do not like under bonnet heat and they do not tolerate any form of ultra high current discharging.

There are heaps of other errors in his video.