Why use fuses instead of breakers?

2manyquestions · Aug 25, 2021

Hello, everyone.

I have seen a lot of people use fuses between the battery and another item (ie, inverter) to protect the inverter, or another appliance. My question is this:

Why use a fuse which would need to be replaced if it does its job, when you can use a breaker and simply reset it?

circus · Aug 25, 2021

sketchy breakers

wattmatters · Aug 25, 2021

2manyquestions said:
Why use a fuse which would need to be replaced if it does its job, when you can use a breaker and simply reset it?

Breakers can fail. When a fuse fails it's done its job. When a breaker fails you go up in smoke.

Just keep a spare fuse handy to replace it. Provided of course you know what caused it to blow in the first place.

Also breaking a DC circuit can be hard to do safely, especially when it's under load. AC is a relative doddle in comparison.

MrSigmaDelta · Aug 25, 2021

A fuse is probably there, so you know it was tripped. The breaker is user friendly. Anyone can reset it.

Just John · Aug 25, 2021

2manyquestions said:
Hello, everyone.

I have seen a lot of people use fuses between the battery and another item (ie, inverter) to protect the inverter, or another appliance. My question is this:

Why use a fuse which would need to be replaced if it does its job, when you can use a breaker and simply reset it?

Using the correct fuse has the ability to stop a lot more current, a genuine concern for lithium chemistry batteries.
Breakers (especially the cheap ones) will only last so many trips. Personally I use class T fuse, and a quality breaker (Eaton Bussmann). The breaker makes it very easy to disconnect the battery, the class T fuse makes things much safer.

Shop around, class T fuses and quality breakers are not that expensive.

Two places I've done business with:

Class T Fuse Kits & Fuses | DonRowe.com

Fast-acting Class T fuse kits and fuses provide over-current protection for your batteries and cables, while helping to ensure safe inverter operation.

www.donrowe.com

Fuses & Circuit Protection | Powerwerx

Fuse and protect your power distribution with a fuse block, available in multiple sizes with or without a ground bus. Add fuse protection with an inline fuse holder. Blade style fuses in ATC/ATO, Mini/ATM and Maxi sizes. Resettable mountable circuit breakers and manual resettable ATC blade fuses.

powerwerx.com

wattmatters · Aug 25, 2021

No problem having a (properly spec'd) breaker, but make sure you also have a fuse.

time2roll · Aug 25, 2021

Fuses are sized to never open during normal use. Circuit breaker is used more when the load is unknown or shared and such is more likely to trip. And yes I believe for DC circuits the fuses are more consistent and reliable vs the breakers. That is my perception for better or worse.

2manyquestions · Aug 25, 2021

Many thanks for all the replies! Consensus seems to be that a quality fuse is the way to go for safety, and that is my primary concern.

Rocketman · Aug 25, 2021

There are places where the breakers are great. I have one installed between my solar panels and my solar charge controller. This way I can turn off the sun. That makes it easy to work on that section of the system and if I want to see battery voltage during the day - turn off the sun.

chrisski · Aug 25, 2021

2manyquestions said:
Many thanks for all the replies! Consensus seems to be that a quality fuse is the way to go for safety, and that is my primary concern.

I suggestyou start reading stuff like the NEC code in the resources and perhapsdownloaf the ABYC electric code to start start understanding “how it should be done/“

Hedges · Aug 25, 2021

Fuse ratings matter. (breaker too). There's a lot more than just "Amps"

https://www.littelfuse.com/~/media/electronics/product_catalogs/littelfuse_fuseology_selection_guide.pdf.pdf

Selection is an exercise in electrical engineering.

DerpsyDoodler · Aug 25, 2021

Just John said:
Using the correct fuse has the ability to stop a lot more current, a genuine concern for lithium chemistry batteries.
Breakers (especially the cheap ones) will only last so many trips. Personally I use class T fuse, and a quality breaker (Eaton Bussmann). The breaker makes it very easy to disconnect the battery, the class T fuse makes things much safer.

Shop around, class T fuses and quality breakers are not that expensive.

Two places I've done business with:

Class T Fuse Kits & Fuses | DonRowe.com

Fast-acting Class T fuse kits and fuses provide over-current protection for your batteries and cables, while helping to ensure safe inverter operation.

www.donrowe.com

Fuses & Circuit Protection | Powerwerx

Fuse and protect your power distribution with a fuse block, available in multiple sizes with or without a ground bus. Add fuse protection with an inline fuse holder. Blade style fuses in ATC/ATO, Mini/ATM and Maxi sizes. Resettable mountable circuit breakers and manual resettable ATC blade fuses.

powerwerx.com

You could also look into contactors for the secondary purpose. I have a class t fuse for each paralleled battery and one for the inverter, i have a manual disconnect that severs all batteries from the system, and both batteries' BMS' control contactors, which I can also manually enable or disable through each BMS (as well as by simply pulling a plug).

2manyquestions · Aug 25, 2021

chrisski said:
I suggestyou start reading stuff like the VNEC code in the resources and perhapsdownloaf the ABYCC electric code to start start understanding “how it should be done/“

Will do. I don't know what the VNEC code is, but I did find the NEC code. Is there a difference? Same with ABYC which I will look at, is ABYCC different?

Pierre · Aug 26, 2021

Fuses are much cheaper and if your system is designed properly you will only blow a fuse when something is really wrong. You can always incorporate a double pole isolator at an easily accessible location as to isolate parts of the system for maintenance etc.

chrisski · Aug 26, 2021

2manyquestions said:
Will do. I don't know what the VNEC code is, but I did find the NEC code. Is there a difference? Same with ABYC which I will look at, is ABYCC different?

You are correct. NEC and ABYC. Parts of the NEC code are available on the resource section and an old copy of the ABYC code is available.

kenryan · Aug 26, 2021

2manyquestions said:
Why use a fuse which would need to be replaced if it does its job, when you can use a breaker and simply reset it?

This is true, but you should never blow a fuse. Certainly not twice.

circus · Aug 26, 2021

Yesterday while using a lot of power the breaker on the battery started farting, not quite open. The charge controller didn't like that. It started beeping then quit but rebooted after a couple seconds, thank heaven. Today I spliced in a fuse, just for the CC, bypassing the breaker.
So I guess the answer is use both. Use fuses where a malfunctioning breaker might damage something.

chrisski · Aug 26, 2021

If your breaker is “farting” throw it away

DerpsyDoodler · Aug 26, 2021

I'd never keep a farting breaker around, myself. Methane is a fire risk.

circus · Aug 26, 2021

chrisski said:
If your breaker is “farting” throw it away

When I bought it I thought 125a was way oversized. Didn't take long to realize it's way undersized.
Safer with a 60a fuse going to the CC anyway. Gotta be good, stole it from a Toyota.

Why use fuses instead of breakers?

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