Circuit breaker vs fuse

[VanKitten]

I am looking at using circuit breakers instead of fuses in these situations....

Between MPPT and house battery.  60amp breaker.  (690 w solar panels)
Between isolator and house battery. 50 amp breaker
Between house battery and power bus 60 amp breaker
Between house battery and inverter/charger 150 amp breaker.

I think I can also use the breaker on the inverter as a switch to shut it off and isolate the battery to prevent the inverter from drawing current when not in use...true?

Does this make sense?

 

[Trebor English]

Why?

Fuses are simple and cheap.  Breakers are more expensive and more complicated.  Google "Federal Pacific Electric" to see why I don't like breakers  It costs $1000 - $2000 to replace an FPE house panel because breakers fail to trip.  The laundromat I use just replaced their FPE breaker panels.  It cost them 7 kilobucks and a full day of business.

You listed the fuse between the MPPT controller and the battery.  If you have a fuse that is working I suggest leaving it.  If you put in a breaker and it trips your MPPT will be connected to a panel and no battery.  That fries some controllers.  Did yours come with instructions that said to connect first to the battery then the panel?  Breakers contain switch contacts held together with spring pressure.  Vibration could momentarily affect that.

Breakers make sense when fuses regularly blow and become expensive.  It makes more sense to me to upgrade the circuit so that it is capable of supplying the necessary load.

Breakers make sense if you can't trust the user to replace a blown fuse with the correct size fuse.

Breakers aren't designed for repetitive switching.  If you need a switch, get one.  Inverters have substantial input capacitors.  If there is any load to avoid using a breaker as a swith for it's an inverter.  Get a switch rated for at least double the inverter max load.  Did you ever notice a spark when connecting an inverter?

Fuses and breakers have specifications.  They specify things like, for example, how long it takes to blow or trip with twice the rated current and accuracy of max current and all kinds of stuff.  Surely you can find breakers that will do what you need according to their spec.  I see a fuse as a very simple mechanism, wire too hot, it melts before protected circuit starts a fire.

So again, why change?

 

[Optimistic Paranoid]

I'm not sure I would recommend a circuit breaker on the inverter.  Circuit breakers are inherently slow-blow devices, and electronic circuits are better protected by fast-blow fuses.

Also, understand that circuit breakers aren't usable indefinitely.  Every time you throw one, the contacts inside arc, and eventually you damage them enough that they need replacing with a new one.

Finally, if you haven't done your calculations quite right, it will be a lot cheaper to replace one size fuse with a slightly bigger one - WITHOUT EXCEEDING THE SAFE FUSE SIZE FOR THE SIZE WIRE INVOLVED - than it would be to buy a bigger circuit breaker.

See this article:

http://bdfuses.com/breaker.php

 

[Weight]

Breakers are fine on smaller load DC circuits. I don't recommend over 20 amps. The problem with heavy amps such as in a short to ground, the breaker can weld its contacts and not interrupt the circuit. Please use a "catastrophic" fuse as the first fuse off the battery. The fuse will interrupt the circuit if there is a heavy current flow as in a short.

 

[SternWake]

I can see the appeal for a lever type of circuit breaker on some DC circuits.  Pushing a button to disconnect and moving the lever back to reconnect is quick, easy and convenient, and good fuses are expensive if having to be replaced often.

BUT, How many manual switching cycles are they good for?  I Don't know, I could not find any info on this on the Cooper/bussman site.

http://www.cooperindustries.com/con...ucts/circuit_protection/circuit_breakers.html

By the way do not cheap out on any wire protection methods, whether fuses or circuit breakers.  

I recently had my cheapo absolut brand 140 amp lever type circuit breaker, trip after 5 minutes of 70 to 90 amps, then a few seconds at 110 amps and it tripped.  It could have taken out my alternator.  It cost 2/3 that of bussman brand, but could have cost me the alternator.  False economy.

I used a 30 amp circuit breaker of this type on My solar:
https://www.amazon.com/Circuit-Breaker-Inline-System-Protection/dp/B00HNOWWTI

I highly regret it.  My IR temp gun indicates it gets a few degrees warmer than the surrounding wiring, My voltmeter indicates it drops a few hundredths of a volt, and my clampmeter also reads slightly less amperage on one side than the other.  It also has the much despised clamp stranded wire under a set screw.  This might be convenient but makes for a poor electrical connection which degrades quickly as the exposed copper stranding oxidizes rapidly, introducing more resistance.

Will a fuse drop the same amount of juice on the line? I highly suspect NOT.

Anyway, I will repeat, do not use bargain wire protection devices.



Putting a switch on the inverter + cable seems a bit overkill.  There is always an initial spark when hooking up an inverter as the capacitors fill, perhaps this makes some believe there is always a parasitic draw even with the inverter turned off.  If My 400psw or 800msw inverters have parasitic draws when completely Off, It is below the threshold of my Ammeters. Seems an additional switch is just another source of electrical resistance.  Also it is pretty easy to unhook the ground cable from the inverter, or pull its fuse, but I have never bothered doing so, unless relocating things.


I plan on getting rid of both my existing circuit breakers.  the solar controller one will get a 30 amp maxi fuse, the alternator direct feed will get a cooper bussman circuit breaker replacing the POS absolut brand which tripped well below its rating.  Not sure which amperage rating on the alternator feed, as I will upgrade the cabling further to a thicker unknown gauge, at some point.

This is the maxi fuse holder I desire for my solar controller.  When installed the 30 amp POS circuit breaker will be dissected for science.

https://www.amazon.com/Blue-Sea-Sys...8-1-fkmr0&keywords=blue+seas+maxi+fuse+holder

 

[SternWake]

Here is why one should not buy cables from auto parts stores. ****** steel ring terminals amd undersized SAE gauge wire:

Here is why one should not cheap out of fuses/ circuit breaker/ wire protection methods:

the load was no more than 22 amps:

Amd the following photo exposes the weaknesses of 12v ciggy plugs. This one failed after a few months of use passing mostly 40 to 50 watts, and occassionally upto 90.

One does not save money buying or using cheap devices related to wiring as at some point it will have to be redone, at best, at worst it takes out the RV or one of its appliances.
Save money elsewhere.

 

[galladanb]

I was going to ask a two part question, but you guys are so great, you already answered one part for me.

The EverStart cables at Wallie world are? Not good? Too cheap? Etc....

And then a little tuffer one...

Can I use 4AWG throughout my install of the battery systems?

Again, 200w solar, 2 230ah, 6v egc-2's, 30 amp charger-inverter-transfer combo switch,
With light loads, led lighting, engel fridge, laptop...

Such Fun!!!

 

[galladanb]

The reason I was asking about the 4awg throughout is because there is a local auto sound dealer that can make me custom 4awg cables on the spot, so no waiting...

That way, I can get the exact lengths I need for a really clean looking non spaghetti look...

He has spooled 4awg, but has to order in other sizes.
So I might as well go with the genuine deal guys for the same turn around times...

 

[Optimistic Paranoid]

4 AWG should be good for carrying 60 amps over any reasonable distance.

 

[galladanb]

60 amps? How do I know what my system is?

Also, I have not yet measured what lengths I actually need, but I'm guessing
Maybe Around 25 feet or so?

Do I need to worry down to total length, doubled for pos and neg?
Or in general, or in other words, linear length?

Gawd, I'm such a newbbbbb!
Lol!

Such Fun!!!

 

[VanKitten]

I looked a while at inline fuse holders. They look a lot like the burned out pictures above.

If there a reliable inline fuse holder that is decent? No one needs melting equipment or fires.

 

[Optimistic Paranoid]

Stick to a good brand like Blue Sea Marine.  You can use Maxi Fuses for your 50 and 60 amp circuits.  Probably need something like an AMG fuse for the inverter.

https://www.bluesea.com/products/category/3/Fuses_and_Fuse_Blocks

 

[Optimistic Paranoid]

60 amps? How do I know what my system is?

You listed a bunch of stuff, none of which was more than 30 amps . . .

Actually, I've just taken a look at the owners manual for your Triplite.  While it's a 30 amp battery charger, it says it can draw up to 125 amps while operating as an inverter.  It says you should use the shortest, fattest battery cables possible, and it mentions specifically that 2/0 gauge cable is the biggest cable that will fit the dc input terminals.

4 gauge should be fine for your solar controller to battery connection, and should be adequate as a main power feed to a fuse box that you'll hook your lights, refrigerator, etc. up to.  But I'd wire that inverter with 2/0 if this were my project . . .

 

[galladanb]

Ok, so in summary...
4awg from alternator/isolator to 60 amp fuse to cutoff switch to house battery positive buss.
2awg from tripplite charger to 60 amp fuse to cutoff to house battery positive buss.
2awg from house battery positive buss to positive terminal on battery.
4awg from house battery positive buss to 60 amp? fuse to cutoff to dc input on power distribution panel.
4awg from solar controller to fuse ( I actually have other questions on installing the included wires from the kit, is this where the blade type fuse goes?) to house battery positive buss.

Repeat using same wire sizes for grounds or return side, but with out fuses.
And put the meter shunt after the ground buss but before ground to frame.

Is that about right? Not sure on fuse amp sizes...

The solar kit came with an inline fuse AND a blade fuse an holder...?

So, you think the controller will accept 4awg wires?

 

[BradKW]

I used Blue Sea Systems 285-Series Circuit Breaker between panels and MPPT and really like the convenience of being able to shut off the power feed with it...

[img=400x400]https://images-na.ssl-images-amazon.com/images/I/812gpitxMPL._SL1500_.jpg[/img]

 

[akrvbob]

Be aware that 2/0 is a much thicker wire than 2 awg. Two very different animals. For a big inverter 2 awg will NOT do, you want 2/0.

 

[VanKitten]

Brad,

Why do you need a breaker between panels and mppt? And why would you need to shut the power off there?

I understood the need for a large fuse between mppt and battery. ... I thought 60 was large enough??

 

[Optimistic Paranoid]

2awg from tripplite charger to 60 amp fuse to cutoff to house battery positive buss.
2awg from house battery positive buss to positive terminal on battery.

Dan, the Triplite manual says it can draw 125 amps at full power.  A 60 amp fuse is NOT going to cut it.

Bob is right there is a difference between 2 gauge and 2/0 gauge (aka 00).  The Triplite manual says that 2/0 is the maximum size that will fit.  I don't know how physically close you plan to locate the Triplite to the battery.  If they are very close, you might be ok with 1/0 or even 1 gauge.  2/0 is just me playing it safe.

 

[Optimistic Paranoid]

The solar kit came with an inline fuse AND a blade fuse an holder...?

So, you think the controller will accept 4awg wires?

One fuse holder between the panels and the controller and one between the controller and the battery.  As for the 4 awg, what does your controller's manual say?  If it doesn't say, you'll have to get a scrap of 4 awg and try it.

 

[BradKW]

Brad,

 Why do you need a breaker between panels and mppt?   And why would you need to shut the power off there?

I understood the need for a large fuse between mppt and battery. ... I thought 60 was large enough??

I always wondered why you needed one there too...maybe I knew and forgot, but probably I decided to just do what everyone else does and put it there.

The link to the Amazon 150 amp is one of those where all amp/sizes are in same link...not sure what amp I used for my 1kw panels, but at the time I knew the answer  

I really like being able to turn off the power feed to the MPPT not only when I'm working on wiring, but when the vehicle is sitting unattended for days, sometimes weeks. I don't know if doing so actually improves safety or saves wear on the MPPT, but I do feel better about it