Why not use circuit breaker on inverter & load?

[zachj]

I'm following Will's 400watt guide but purchased a 180 Amp circuit breaker instead of 50. What is the reasoning behind a 50 Amp for a 40A MPPT? Why not put the inverter and DC fusebox on the circuit breaker as well so that you can shut everything off when disconnecting/connecting the battery?

 

[sunshine_eggo]

Fuses and breakers are sized for the wire: 1.25X

Each circuit must be protected.

 

[zachj]

So seeing as my wire is big enough for both circuit breaker and fuse I can just ditch the fuse and hook it all on the breaker?

 

[zachj]

Why do you think Will decided to use both, he must have a good reason

 

[sunshine_eggo]

Why do you think Will decided to use both, he must have a good reason

Sketch it and post. When you're building the sketch, remember that each individual circuit needs protection.

 

[zachj]

Sketch it and post. When you're building the sketch, remember that each individual circuit needs protection.

 

[12vDC]

Why do you think Will decided to use both, he must have a good reason

maintenance. you cant turn off a fuse.

you dont have to do anything really. but whichever safety measures you choose not to implement increase your risk for hazard ~ like welding a wrench to your system and incinerating personal property.

 

[sunshine_eggo]

What 5awg cable can handle 180A without catching fire?

 

[crossy]

What 5awg cable can handle 180A without catching fire?

Isn't 5AWG a bit small for a 1500W inverter at 12V too?

 

[zachj]

What 5awg cable can handle 180A without catching fire?

Ah right so I need a 120 Amp circuit breaker or thicker wire. So the inverter came with 5 AWG wire to connect it to a battery as it uses around 125 Amps absolute max, but running more DC loads through that would set it ablaze.

 

[zachj]

maintenance. you cant turn off a fuse.

you dont have to do anything really. but whichever safety measures you choose not to implement increase your risk for hazard ~ like welding a wrench to your system and incinerating personal property.

Yea this is why I want to use the circuit breaker for everything instead of the fuse - so I won't have to replace a fuse but mainly so that when I disconnect/reconnect battery I don't get a spark charging up inverter capacitors

 

[zachj]

Isn't 5AWG a bit small for a 1500W inverter at 12V too?

It's actually 16mm squared which is actually a bit under 5AWG as well. It does get a bit warm after using anything high-draw, but never too hot to hold

 

[crossy]

It's actually 16mm squared which is actually a bit under 5AWG as well. It does get a bit warm after using anything high-draw, but never too hot to hold

Yeah, we're in the metric world so I converted to 16mm2. Bangkok Cable puts their 16mm2 at 95A in free air.

It's not going to explode everywhere but if you are running constantly anywhere near 90A I'd be looking at bigger cable.

 

[zachj]

Yeah, we're in the metric world so I converted to 16mm2. Bangkok Cable puts their 16mm2 at 95A in free air.

It's not going to explode everywhere but if you are running constantly anywhere near 90A I'd be looking at bigger cable.

Is it safe enough to use two, three 5AWG cables in parallel instead of one large 1 or 2AWG? $160 AUD for 25 feet of 1AWG!

 

[crossy]

Is it safe enough to use two, three 5AWG cables in parallel instead of one large 1 or 2AWG? $160 AUD for 25 feet of 1AWG!

Using several smaller conductors instead of one fat one is common in the power distribution industry, we use it all the time in the rail traction-power systems (4 x 500mm2 is much easier to manage than 1 x 2000mm2) but we are talking about currents in the kA range.

It is essential that, in order to ensure proper current sharing, that all the parallel conductors are exactly the same length/resistance. In reality, at our sort of level expect 3 parallel wires to carry about 2x what one wire does, you can check how well the current is shared with your trusty DC clamp-meter.

 

[mikefitz]

What is the reasoning behind a 50 Amp for a 40A MPPT?

The connectors and internal wiring of the controller are designed for 40 amps. An internal fault would flow current only limited by a fuse or breaker in the path between controler and battery.
Your 180 or 120 breaker may alow a fire within the faulty controller.
Overcurrent protection is need for the cable rating and whatever current rated device is on the end of that cable.
You have a similar issue with the fuse box, it will have a maximum current rating.

 

[zachj]

The connectors and internal wiring of the controller are designed for 40 amps. An internal fault would flow current only limited by a fuse or breaker in the path between controler and battery.
Your 180 or 120 breaker may alow a fire within the faulty controller.
Overcurrent protection is need for the cable rating and whatever current rated device is on the end of that cable.
You have a similar issue with the fuse box, it will have a maximum current rating.

Alright so you go about 10 Amps over what's rated for that equipment so that if something goes wrong, it will only go around 10 amps over and not more? If I had a 80A MPPT for example I would get a 90A circuit breaker/fuse? Assuming it's not safe to trust the device itself as Will has included this in his systems