Class T fuse or DC circuit breaker

[EPicTony]

I recently posted asking about cheap car fuses vs. class t fuses for my 48v 30kwh battery bank.
I now understand why you want a high quality fuse. I also came across this DC CB. The CB cost will be less than the fuse / fuse block costs and it's resettable.
Any reason to not go with the CB ? Thanks for any advise.

 

[Supervstech]

If you need a disconnect, the breaker is a good investment,but you still need the class t fuse.

 

[Aussie Collie]

Battery CB needs to be able to handle a short and/or over current in both directions. You need a non polarised CB. I'm not sure that the one in the picture is.
I would stick with the Class T and good quality switch.

 

[timselectric]

I always prefer a breaker.
Just make sure that it's properly rated for the use.

 

[Shimmy]

A fuse provides better protection than a circuit breaker: it limits fault current and is extremely reliable when used within its rating. The current limiting effect can help to minimize damage to equipment, but it isn't going to be enough to save your inverter.

A circuit breaker is great as a disconnect that provides protection, but the more you use it as a disconnect the shorter its life will be; the arcing will wear out the breaker contacts.

• You need a disconnect to change a fuse though, so your battery bank is going to need circuit breakers for each parallel string.
• You don't need a disconnect on the common bus out of your battery though, so that is a good place for a Class T fuse.
• You branch off that common bus to go to indivdual pieces of equipment-- an inverter/charger, solar charge controller, etc. Each piece of equipment needs a disconnect (with overcurrent protection) , so you use a circuit breaker.
• Your PV likely exceeds 60V, so it needs both conductors to be disconnected at the same time, so you use a 2-pole circuit breaker upstream of the solar charge controller.

The places where fuses are a pain are on AC branch circuits; you don't want to have to hunt for a fuse when the lights go out.

 

[Lilikoi_Heavy_Industries]

So where are the specs on the fuse showing that it's better than the circuit breaker? I've seen people call out the 20000AIC DC spec on the T Class fuses as the reason that they're the only acceptable option for a LiFePO4 bank.

And then I pull apart a 20 year old DC breaker box from an old install and find that the Eaton Heinemann GJ1P DC Circuit Breaker I just pulled has the same Amp interrupting capacity as the T Class fuses I just bought.

And now there's somebody posting and telling us that the circuit breaker is going to wear out right away. And we all know that isn't the truth so...

 

[niktak11]

I'm going with with these when I redo my current wiring setup. 50k AIC.

Product - MidNite Solar

MidNite Solar Product Page.

www.midnitesolar.com

 

[Shimmy]

So where are the specs on the fuse showing that it's better than the circuit breaker? I've seen people call out the 20000AIC DC spec on the T Class fuses as the reason that they're the only acceptable option for a LiFePO4 bank.

And then I pull apart a 20 year old DC breaker box from an old install and find that the Eaton Heinemann GJ1P DC Circuit Breaker I just pulled has the same Amp interrupting capacity as the T Class fuses I just bought.

And now there's somebody posting and telling us that the circuit breaker is going to wear out right away. And we all know that isn't the truth so...

Refer to page 6 and 7: https://www.littelfuse.com/media?re...871-38e7378ac8f3&filename=jlln-fuse-datasheet

(Pick a specific circuit breaker with datasheet if you want a detailed comparison.)

Fault clearing time is about 0.01s vs 0.1s.

Fault energy is I^2*t; even a 20% reduction in peak fault current and a 90% reduction in clearing time will mean your total let-through energy is about 6% of what a circuit breaker will allow.

Most DC faults in inverter systems are dead shorts, so you should be in the instantaneous range. Overloads the difference is less significant.

 

[Lilikoi_Heavy_Industries]

Refer to page 6 and 7: https://www.littelfuse.com/media?re...871-38e7378ac8f3&filename=jlln-fuse-datasheet

(Pick a specific circuit breaker with datasheet if you want a detailed comparison.)

Fault clearing time is about 0.01s vs 0.1s.

Fault energy is I^2*t; even a 20% reduction in peak fault current and a 90% reduction in clearing time will mean your total let-through energy is about 6% of what a circuit breaker will allow.

Most DC faults in inverter systems are dead shorts, so you should be in the instantaneous range. Overloads the difference is less significant.

Interesting, I did read my datasheet and trying to piece together comparable details.

Circuit breaker from before midnite solar existed (I have a GJ1 but I would need to go check if I have curve 1, 2 or 3):

https://www.eaton.com/content/dam/eaton/products/electrical-circuit-protection/hydraulic-magnetic-circuit-breakers/heinemann-series-gj-circuit-breakers.pdf

but I believe a comparison against Midnite's breaker would be more useful, I have no idea how long it's been since they made this one I'm looking at.

That old GJ1 breaker is currently being used on a lead acid bank since I do have Littelfuse JLLN 125A T Class fuses for my LiFePO4 batteries. It was originally from a permitted Trace SW2512 installation, but the Trace had died before I moved here (there was no AC electricity until I replaced it).

 

[Shimmy]

Interesting, I did read my datasheet and trying to piece together comparable details.

If you can find actual DC circuit breaker clearing times vs operating times, that is what is important. You don't get the zero crossing of an AC system that simplifies the process, so actual data is critical.

 

[shot428]

This would be the proper/correct breaker

JGL37125D81 - Circuit breaker, PowerPact J, 125A, 3 pole, 500VDC, 20kA, lugs, thermal magnetic, 80% | Schneider Electric USA

Schneider Electric USA. JGL37125D81 - Circuit breaker, PowerPact J, 125A, 3 pole, 500VDC, 20kA, lugs, thermal magnetic, 80%.

www.se.com

Which is why I shared links for cheap british version t fuses here,

Battery to inverter fuse type

I'm building my system and need to fuse the battery bank. 30kwh 48v Class t fuses are super expensive, what do you think about these ? Way cheaper and I won't cry if I blow a fuse. thanks for your help ! InstallGear 0/2/4 Gauge Ga ANL Fuse Holder + 300 Amp ANL Fuses (2 Pack)

diysolarforum.com

 

[rhino]

Wouldn't this also work? https://ntsecostore.com/products/noark-160a-500v-dc-circuit-breaker-2-pole-nrk-n28901

 

[Paul_R]

Midnite Solar has great breakers, I've had several.

Midnite Solar Breakers

 

[rhino]

Does someone know what the actual trip curves are of the 100A and up DC breakers for Midnite? The data sheet has different trip curves but it isn't obvious which curves each breaker adheres to. cc: @SpongeboB Sinewave

 

[Paul_R]

Does someone know what the actual trip curves are of the 100A and up DC breakers for Midnite? The data sheet has different trip curves but it isn't obvious which curves each breaker adheres to. cc: @SpongeboB Sinewave

Midnite has great phone support, call 'em and ask.

 

[niktak11]

Does someone know what the actual trip curves are of the 100A and up DC breakers for Midnite? The data sheet has different trip curves but it isn't obvious which curves each breaker adheres to. cc: @SpongeboB Sinewave

I was wondering the same thing. I couldn't find which of the three trip curves applied. I'm guessing not the instantaneous ones.

 

[rhino]

I was wondering the same thing. I couldn't find which of the three trip curves applied. I'm guessing not the instantaneous ones.

I looked again at this since I'm trying to decide about using a breaker for parallel batteries and found the info.. It was "hidden" in the drawing document (Delay, 14 for the 175A and 16 for the 250A breaker, then use chart below):

(other docs on page say it is an F series and the manufacture's page looks like them as well)


The AIC for these breakers is also 50kA which is much higher than the Class-T fuses of this amperage.

Compared to the JLLN Class T Fuse chart below (reference) it looks like for 175A the Midnite 175A circuit breaker is similar. For example, 400% of the 175A (700A) will trip the breaker in 0.5 to 3.0 seconds. For the T Fuse it would be approximately 15s. For something closer to a short circuit such as 800% (1400A) the breaker is 0.01 to 0.28 and T fuse appears to be instantaneous. Breaker would be close to instantaneous if short circuit was over 1700A.

So based on this it appears you could use one of the Midnite breakers for a cutoff/battery switch and circuit protection and not need class T fuse at all.