Fuse or circuit breaker?

[tljones7879]

In process of my van build and wondering if I should use a fuse or a circuit breaker between my battery bank and my 1200 watt inverter. Is is correct to use a 100 amp fuse or circuit breaker? I’m told that 12v divided by 1200watts equals 100, and I should use a 100 amp fuse or circuit breaker. I have seen folks use and fuse and a circuit breaker between the battery and the inverter. Thank you in advance!

 

[John Frum]

1000 watts / .85 conversion factor / 12 = 98.039215686 dc amps
98.039215686 dc amps * 1.25 fuse factor = 122.549019608 fuse amps
You can use a fuse or a breaker.
Fuses are cheaper.
Circuit breakers are more convenient and make it easier to manually isolate things for troubleshooting or maintenance.
Whichever you choose get the good ones.
Cheap "amazon" circuit breakers open too low if you are lucky and weld closed if you are unlucky.

187-Series Circuit Breaker - Surface Mount 120A - Blue Sea Systems

Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.

www.bluesea.com

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.

www.bluesea.com

MRBF Terminal Fuse - 125A - Blue Sea Systems

Space-saving ignition protected fuse for 30 to 300 Amp loads. Must use with Terminal Fuse Block.

www.bluesea.com

 

[RickP]

I had similar questions in my build, and came to much the same conclusion as @smoothJoey states above... either works, don’t go cheap.

I went the breaker route on mine, all from Blue Sea except one, which was a Cooper/Bussman. One thing I have learned is that Blue Sea Systems, a company I had never heard of prior to my solar project, builds some top notch gear. Every item I have purchased from breakers to bus bars to fuse blocks to panels has been a clear cut above in materials and workmanship. For these items, I now specifically search for their products first.

Back to your question, my decision for breakers was a reliability in the field thing. Unless the breaker fails mechanically, which is unlikely with a high quality unit, getting back to operational status is simple and requires no additional parts. Fuses are more cost effective up front, but are a one-and-done option, necessitating carrying spares. I wanted the most sure path to reliable protection, and for me that was breakers.

 

[ghostwriter66]

Although the answers above about circuit breakers are 100% correct -- anything over 60A I go with physical fuses ... the reasoning is that fuses have no mechanical parts - they are typically made to extreme tolerances and those tolerances are easy to replicate by the manufacture ... so a 200A physical fuse will normally blow at 200A ... For Circuit Breakers i have seen 60A blow anywhere between 52 and 66 -- at 52 it was a nuisance -- at 66 you start smelling the cable .... NOT saying that they are all that way -- stricter tolerance manufacturers have higher tolerances -- but in this day and age of everybody getting there stuff manufacturers in China is it worth the risk??

NOW with that said - I often use those push button circuit breakers for when i need an FUSE and ON/OFF switch capability ...

Once again -- just my opinion ...

If your application allows for wider tolerances then circuit breaker types are fine ... but if you want it to blow right at 200A then I would go with solid fuses

 

[Bob142]

In process of my van build and wondering if I should use a fuse or a circuit breaker between my battery bank and my 1200 watt inverter.

1000 watts / .85 conversion factor / 12 = 98.039215686 dc amps
98.039215686 dc amps * 1.25 fuse factor = 122.549019608 fuse amps

You need to adjust SJ's math to account for your 1200 watts vs the 1000 watts he put in his reply. You'll see you're in need of a 150A fuse or breaker.

 

[tljones7879]

You need to adjust SJ's math to account for your 1200 watts vs the 1000 watts he put in his reply. You'll see you're in need of a 150A fuse or breaker.

Awesome! thank you! Last question. Which is better circuit breaker? I know that a circuit breaker gives me a disconnect, in case I want to work on batteries. Thoughts? Again thank you!

 

[tljones7879]

1000 watts / .85 conversion factor / 12 = 98.039215686 dc amps
98.039215686 dc amps * 1.25 fuse factor = 122.549019608 fuse amps
You can use a fuse or a breaker.
Fuses are cheaper.
Circuit breakers are more convenient and make it easier to manually isolate things for troubleshooting or maintenance.
Whichever you choose get the good ones.
Cheap "amazon" circuit breakers open too low if you are lucky and weld closed if you are unlucky.

187-Series Circuit Breaker - Surface Mount 120A - Blue Sea Systems

Thermal circuit breakers provide heavy duty circuit protection for 25 to 200 Amp loads when switching and circuit protection are both required.

www.bluesea.com

MRBF Terminal Fuse Block - 30 to 300A - Blue Sea Systems

Easily and economically satisfies ABYC 7 circuit protection rule by mounting on a 3/8 battery post, battery switch or bus bar.

www.bluesea.com

MRBF Terminal Fuse - 125A - Blue Sea Systems

Space-saving ignition protected fuse for 30 to 300 Amp loads. Must use with Terminal Fuse Block.

www.bluesea.com

Thank you so very much! I will get a high quality circuit breaker.

 

[Ampster]

NOW with that said - I often use those push button circuit breakers for when i need an FUSE and ON/OFF switch capability ...

That is what I have done. My inverter has a 125 Amp circuit breaker. That is sized to the capacity of the inverter. My cables to the inverter are 4/0. In my battery cabinet I have a Blue Sea disconnect and a 200 Amp fuse. It is way overkill but makes for easy maintenance. YMMV

 

[tljones7879]

I had similar questions in my build, and came to much the same conclusion as @smoothJoey states above... either works, don’t go cheap.

I went the breaker route on mine, all from Blue Sea except one, which was a Cooper/Bussman. One thing I have learned is that Blue Sea Systems, a company I had never heard of prior to my solar project, builds some top notch gear. Every item I have purchased from breakers to bus bars to fuse blocks to panels has been a clear cut above in materials and workmanship. For these items, I now specifically search for their products first.

Back to your question, my decision for breakers was a reliability in the field thing. Unless the breaker fails mechanically, which is unlikely with a high quality unit, getting back to operational status is simple and requires no additional parts. Fuses are more cost effective up front, but are a one-and-done option, necessitating carrying spares. I wanted the most sure path to reliable protection, and for me that was breakers.

When I bought my cargo van, it came from the factory, Chevrolet, with no passenger seat. I bought a passenger seat and modified a way to properly bolt it to the floor. Also installed was a bulk head and mounted on the bulkhead right behind the “ passenger“ seat was a 1200 watt inverter. The inverter was wired to the vehicles alternator with a 150 amp breaker close to the vehicles battery in the engine compartment. There was no battery isolator or continuous duty solenoid, so I assumed the company that previously owned this van kept the engine running while operating the inverter. I am a mechanic by trade but was confused when I researched and found folks using fuses, battery disconnects and circuit breakers between the battery and inverter. One guy used all three! After your response and the formula smoothjay sent through, I took a look at the 150 amp circuit breaker name brand and it is a Truck Star brand. The best I can tell by my few min research it is not a cheap brand circuit breaker. So I will go with it. I will use solar and not my alternator to charge my batteries. I will also gave the option to charge batteries with shore power. Thank you for your input! Terry. The van is 2014 extended Chevy express 3500 with 6.0 71,000 and I only pd $13,500.

 

[tljones7879]

That is what I have done. My inverter has a 125 Amp circuit breaker. That is sized to the capacity of the inverter. My cables to the inverter are 4/0. In my battery cabinet I have a Blue Sea disconnect and a 200 Amp fuse. It is way overkill but makes for easy maintenance. YMMV

Wow 4 aught wire is huge! You must have a 1000 watt inverter if you are using 125 amp circuit breaker. May I ask what size fuse you are using with the 125a circuit breaker? Thx!

 

[tljones7879]

Wow 4 aught wire is huge! You must have a 1000 watt inverter if you are using 125 amp circuit breaker. May I ask what size fuse you are using with the 125a circuit breaker? Thx!

Sorry, I see you are using a 200 amp fuse. Do you have 1000 watt inverter?

 

[Zil]

I have a 2000W sine wave inverter. It draws 150 amps when microwave is on high. I have 4 feet of 2/0 cable. With a 250 amp fuse as the wire can safely carry 280 to 300 amps depending on temperature. Fuses and circuit breakers are sized to protect the wire. Larger fuses have lower voltage drop.

 

[Zil]

Worth repeating, Fuses protect the wire, not the device.

 

[Ampster]

Do you have 1000 watt inverter?

I have a 5000 Watt inverter at 48 volts.

 

[tljones7879]

I acquired free about 10 foot of red and 10 foot of black 4 aught wire. I also went and bought the 3/8 hole connectors for 4/0 wire. I was thinking of using the 4/0 to connect my two AGM batteries then using 2/0 to go from battery bank to my 1200 watt inverter. Smooth Joey gave me the formula to determine breaker size and I should use a high quality 150 amp breaker. Should I use a fuse close to the battery before the breaker or is that overkill? If so, what amp fuse should I use? Thank all of you for your great help thus far!

 

[John Frum]

I acquired free about 10 foot of red and 10 foot of black 4 aught wire. I also went and bought the 3/8 hole connectors for 4/0 wire. I was thinking of using the 4/0 to connect my two AGM batteries then using 2/0 to go from battery bank to my 1200 watt inverter. Smooth Joey gave me the formula to determine breaker size and I should use a high quality 150 amp breaker. Should I use a fuse close to the battery before the breaker or is that overkill? If so, what amp fuse should I use? Thank all of you for your great help thus far!

Just put the breaker as close to the positive terminal as possible. Under 12 inches is acceptable.

 

[tljones7879]

Just put the breaker as close to the positive terminal as possible. Under 12 inches is acceptable.

Awesome! Thank you!

 

[Ampster]

Should I use a fuse close to the battery before the breaker or is that overkill?

I also use a fuse as close to the battery as I can. It may be over kill but it gives me a second line of defense if the circuit breaker is slow yo trip. I have a 125 Amp circuit breaker and 200 Amp fuse. Also 4/0 cable.

 

[eric108]

I was watching a YouTube video and the guy was why a fuse was better than circuit breaker. He was using a small gauge wire and taking the amps over the rating of the circuit breaker, it would fry the wire before it would trip the breaker. He said if you are going to use a breaker to use a quick trip breaker. But I do like the idea of using a breaker and a fuse.

 

[John Frum]

I was watching a YouTube video and the guy was why a fuse was better than circuit breaker. He was using a small gauge wire and taking the amps over the rating of the circuit breaker, it would fry the wire before it would trip the breaker. He said if you are going to use a breaker to use a quick trip breaker. But I do like the idea of using a breaker and a fuse.

With a quality properly rated breaker the wire should not be damaged.
That is the hole point of their existence.

This link has an ampacity table for pure copper at 105 celcius.
As long as you use a quality thermal breaker like these https://www.bluesea.com/products/category/14/30/Circuit_Breakers/187-Series
That is within the spec of the wire.
The wire should not exceed its rated temperature.