Fuses vs Circuit Breakers for 12v Protection?

[dbj216]

I'm installing a new converter in a 69 Globetrotter. The old one had the 12v fuses built right in it for the 3 12v circuits. The new one does not.

So I was wondering the difference in circuit protection between a 12v fuse and a 12v circuit breaker. I understand a circuit breaker will interrupt current flow when it gets hot, and reset itself when it cools down. It would be easier to use just the circuit breakers.

My 66 Trade Wind has both fuses and circuit breakers as delivered from the factory, see photo below.

Can I use just circuit breakers and forget the fuses?

David

[idroba]

When a fault developed, a fuse blows and cuts the power off completely until it is replaced (and the fault is found). The automatic reseting circuit breakers I think you are referring to keep trying to reset themselves and in doing so, keep sending power to the fault, over and over and over. Eventually something fails, like the wire insulation and then you have a potential fire.

Automatic reseting 12 volt circuit breakers are not a good solution at all for the circuits. There are a very few situations that they are useful, and even then, one can question that they be used.

I cannot recommend them.

[HiJoeSilver]

Couldn't agree with idroba more! 12v auto resetting circuit breakers are a disaster in the making.

On a separate note my I phone spell checks idroba with "odor a" made me wonder if anybody ever came up with a user name based on spell check suggestion being something funny. Just a thought.

[Al and Missy]

While auto-resetting circuit breakers are probably not good for general use, there is nothing wrong with manual resetting ones. You'll never be wishing you had one more fuse.

Marine suppliers like Defender Industries and West Marine have a wide variety of fuse and circuit breaker panels.

Al

[idroba]

Originally Posted by HiJoeSilver

Couldn't agree with idroba more! 12v auto resetting circuit breakers are a disaster in the making.

On a separate note my I phone spell checks idroba with "odor a" made me wonder if anybody ever came up with a user name based on spell check suggestion being something funny. Just a thought.

I have been known to have intestinal issues, so maybe spell check is working just right.

[Kent M]

"I was wondering the difference in circuit protection between a 12v fuse and a 12v circuit breaker. I understand a circuit breaker will interrupt current flow when it gets hot, and reset itself when it cools down. It would be easier to use just the circuit breakers.
.....
Can I use just circuit breakers and forget the fuses?".

-----------------------------------------------------------

David:

Certainly you can.

Fuses are short-circuit protection, NOT overload protection, and are usually sized (depending on the purpose/designer) 4-10 times the full load current. Breakers are for overload protection FIRST, and short circuit as a secondary facet. Usually, they have "long time characteristics" for overload, and "short time characteristics" for short circuits. In house circuits, a 20 amp breaker is NOT loaded to 20 amps, it's normal upper loading is 16 amps; between 16 and 20 amps, the "trip element" begins to heat, and will eventually trip because of the buildup of heat. Seventeen amps may take an hour (for instance) and 19 amps might go in five minutes. If there's a short in the operating circuit, a low level short (say, 25 amps) it might trip in two or three cycles, while a 30 amp short might trip in a half cycle. All this depends on a bunch of things, but it's typical.

Fuses have the advantage that they FORCE you to hunt for the cause. Their disadvantages start with "I don't have a spare".

Auto reset breakers do NOT normally respond with getting hotter and hotter each time they operate, only to eventually burn up, or even to harm the conductors. If chosen properly, they'll safely continue to operate through many operations. Consider relay contacts ---- same making and breaking. The auto resets have one of the same characteristics of fuses: they don't force you find the problem as quickly. Same's true for breakers in general, in fact.

But about the third time a breaker trips, you don't have to consider replacing it like a fuse. Just size it correctly, and remember it's for DC, and NOT AC.

General question: Why do vehicles almost exclusively use fuses?

Kent
Registered Professional E.E., Texas

[Kent M]

Just dawned on me (as I hit the send button) that I should have made a clear distinction about auto reset versus manual reset breakers.

Use the manual reset types.....

[dznf0g]

The breakers in my 2007 are not self resetting. They have a little black reset button on the end of them.

[TG Twinkie]

I will stick with fuses, especially the modern blade type. They are simple, cheap and easy to check to see if they are blown. Anything mechanical like circuit breakers can become problematic. I am referring to the 12 volt system specifically.

[lewster]

The only place RVIA specifies auto re-set circuit breakers for a DC circuit is on the 12VDC feed going to your trailer brakes. The reasoning should be obvious.

If you look at the 12VDC positive bus bar at the front of all newer Airstream trailers (at least from 2000 on), you will see 4 auto re-set circuit breakers connected to a copper bus. One is where the house battery connects. The second is where the 12VDC disconnect solenoid is connected which then runs to your 12VDC fuse panel and the other 2 are used for loads not controlled by the disconnect solenoid, like CO detectors (parasitic loads).

This bus bar is usually located in locations that are rather difficult to access. Ever wonder why????

[dznf0g]

Likewise with autos....headlights have self resetting breakers for obvious reasons.

[dznf0g]

Originally Posted by lewster

The only place RVIA specifies auto re-set circuit breakers for a DC circuit is on the 12VDC feed going to your trailer brakes. The reasoning should be obvious.

If you look at the 12VDC positive bus bar at the front of all newer Airstream trailers (at least from 2000 on), you will see 4 auto re-set circuit breakers connected to a copper bus. One is where the house battery connects. The second is where the 12VDC disconnect solenoid is connected which then runs to your 12VDC fuse panel and the other 2 are used for loads not controlled by the disconnect solenoid, like CO detectors (parasitic loads).

This bus bar is usually located in locations that are rather difficult to access. Ever wonder why????

Mine has manual resets at the buss and all circuits in the "fuse" panel.

[mrfixit51]

Hi
I did an overhaul of my 71 Travelux electrical. Not quite the same as airstream ,but the same principle. I used an automotive fuse block with the connectors for each circuit. I also used an electrical rail with snap in connector blocks , for those wires that needed to be connected. I was in the process of fixing it , so please excuse the mess when i took the picture . You probably will have to zoom in to see what i mean. hope this helps. PS- i agree with not using auto circuit breakers, they can sometimes heat up from trying to reset themselves and pit the contacts inside, and stick

[mrfixit51]

Just learned to add a photo on the forum thks

Originally Posted by mrfixit51

Hi
I did an overhaul of my 71 Travelux electrical. Not quite the same as airstream ,but the same principle. I used an automotive fuse block with the connectors for each circuit. I also used an electrical rail with snap in connector blocks , for those wires that needed to be connected. I was in the process of fixing it , so please excuse the mess when i took the picture . You probably will have to zoom in to see what i mean. hope this helps. PS- i agree with not using auto circuit breakers, they can sometimes heat up from trying to reset themselves and pit the contacts inside, and stick

[dbj216]

Thank you all for the great advice. I'll use automotive blade type fuses like I did on my 66 Trade Wind. I understand that a blown fuse means find the cause. And it might be Airstream thought both fuses and resetting circuit breakers were safer, belts and suspenders so to speak.

My thread was not visible to me for some reason. I just read your replies now. I wasn't ignoring you.

David

[guskmg]

Lewster and Idroba are right. One night a few years ago I pinched and shorted a pigtail while backing up in a near jackknife position trying to turn around at a closed park entrance. In the dark of night I repaired the pigtail and replaced the truck clearance light fuses. The next day going down a long mountain grade I noticed smoke coming from under the hood. As I pulled over to the shoulder, a tow truck driver going in the opposite direction saw me and did a U turn, and came back to me. He jumped out of his truck with a cable cutter, I released the hood and he raised it. He cut the main battery cable. He then towed me to a friends house were the kind people let me park a couple of days while I got everything repaired. He came by the next day and towed my truck to a GM dealer.
There was apparently a low grade short that became worse as I had driven after the original pigtail damage. The trailer circuit breakers were "type one" auto resetting. They were not only burned up, but a large portion of the truck battery to pigtail wiring was destroyed. A mobile RV repairman and a GM dealer replaced the damage wiring. Irony rained when all this happened, while rolling to a stop on the Interstate I noticed a loss of all electrical power in the truck. My fist though as I came to a stop, "how are my wife , mother-in-law and I going to open the electric door locks? Then as the panic subsided I notice the manual lock knobs. About that time the tow truck driver was at the side window motioning to me to release the hood. Oh well, another towing adventure.
guskmg

[ROBERTSUNRUS]

Hi, I replaced the fuse on my tongue jack with a circuit breaker; It's not just a 12 volt circuit breaker but the amp rating must match too. Don't replace a 10 amp fuse with a 20 amp circuit breaker.

[twinklerai]

I will prefer using circuit breakers in comparison with fuses.
You can find air circuit breakers and vacuum circuit breakers online.

[Aerowood]

I also plan on using manual resetting circuit breakers for all of the 12VDC

[lewster]

One can purchase ready made DC marine fuse blocks by Blue Sea Systems for reasonable prices from outfits like Defender Marine.

They at all arranged into a good looking panel that's easy to mount and wire.

All you need to do is specify the amperage rating of the breakers.


Lew Farber
RVIA/RVDA Nationally Certified Master Tech
ABYC Certified Master Marine Electrician
Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center*AMS Lithium Batteries
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541-490-6357