Do we still need T-Class Fuses?

[priorityelec]

I have a few EG4 batteries and an LV6548 all in one. The batteries come with a built in circuit breaker/fuse and I'm pretty sure I read the LV6548 has built in fuses. They all connect to the same bus bars. Do i need a T Class fuse for each battery too? Do I not need any more fuses? Am I safe or what am I missing?

 

[12VoltInstalls]

I have a few EG4 batteries and an LV6548 all in one. The batteries come with a built in circuit breaker/fuse and I'm pretty sure I read the LV6548 has built in fuses. They all connect to the same bus bars. Do i need a T Class fuse for each battery too? Do I not need any more fuses? Am I safe or what am I missing?

Sub’d. Interested in this discussion.
I’ve seen too many answers either way.

 

[DIYrich]

It is the interrupt current. During a short, the breaker may be held closed by too much current (10,000 amps).
Also, the Class T fuse protects the wire from the fuse to the Inverter. If the short happens prior to the inverter, you are not protected by the inverter breaker. Hence the advice to put the Class T as close to the battery as possible.

 

[OzSolar]

I have a few EG4 batteries and an LV6548 all in one. The batteries come with a built in circuit breaker/fuse and I'm pretty sure I read the LV6548 has built in fuses. They all connect to the same bus bars. Do i need a T Class fuse for each battery too? Do I not need any more fuses? Am I safe or what am I missing?

It's been mentioned that the BMS is capable of shutting off the battery in a dead fault situation therefore no need for a Class T fuse.

I seem recall a thread where that was tested and shown to be correct.

Anyone who's struggled with the BMS shutting down while pre-charging their inverter has seen how fast a BMS can activate.

Still it's best to follow the battery manufacturer's instructions. Most of the ones I've seen still suggest a Class T fuse as close the battery positive as possible.

 

[12VoltInstalls]

If the short happens prior to the inverter, you are not protected by the inverter breaker. Hence the advice to put the Class T as close to the battery as possible.

batteries come with a built in circuit breaker/fuse

During a short, the breaker may be held closed by too much current (10,000 amps).

So the breakers on the batteries are merely disconnects, not properly rated over current devices?

 

[Zwy]

I have a few EG4 batteries and an LV6548 all in one. The batteries come with a built in circuit breaker/fuse and I'm pretty sure I read the LV6548 has built in fuses. They all connect to the same bus bars. Do i need a T Class fuse for each battery too? Do I not need any more fuses? Am I safe or what am I missing?

I run a Class T between each battery and the busbar, shown here with the cover off during assembly. The reason is simple, if there was a short on any battery in the bank, the other batteries would feed into that short.

 

[Supervstech]

It is all insurance. Spend more on the battery build, or get better fire insurance.

Seems an easy choice to me.

 

[timselectric]

With breakers on each battery and a fuse in the AIO (needs to be confirmed).
You are actually covered all the way around. (As long as you size your conductors correctly)

 

[Zwy]

It is all insurance. Spend more on the battery build, or get better fire insurance.

Seems an easy choice to me.

I mentioned the deal on Don Rowe's website in this post from January 24, 2024. At $59.99 each it was a deal. They were out of stock at the time but they called me and said these might be in stock within 30 days. I received the six 175A T fuses and holders last week which was mid February.

 

[12VoltInstalls]

it's best to follow the battery manufacturer's instructions. Most of the ones I've seen still suggest a Class T fuse as close the battery positive as possible.

It is all insurance. Spend more on the battery build, or get better fire insurance.

Seems an easy choice to me.

This battery:
…does not include any indication of adding a fuse. Distributor said it wasn’t needed.
Wall mount 5kWh Battery has electronic over current and a built in breaker.
These are (I believe) voltronic batteries sold under various labeling - MPP, Rich Solar for two examples; talks to 6548 - and I don’t know what to think. Of course I can’t speak to other batteries I haven’t seen but if the instructions do not indicate a need for additional fusing and there are no means (or instructions of how) to accommodate external fusing…. other than the default “to have insurance“ would not one be correct in believing the battery breakers are sufficient as Tim says?

With breakers on each battery and a fuse in the AIO (needs to be confirmed).
You are actually covered all the way around. (As long as you size your conductors correctly)

 

[Kornbread]

It is the interrupt current.

^This.

 

[12VoltInstalls]

I

It is the interrupt current

This

So the batteries come with breakers that are not 10,000A (or whatever) rated?

 

[DIYrich]

So the batteries come with breakers that are not 10,000A (or whatever) rated?

Breakers are designed to work under normal conditions. Class T is designed for the extreme conditions.

In the recent Shunt Fire thread, a breaker at the AIO does not do any good.

 

[upnorthandpersonal]

Something can always go wrong, especially with high currents. Contacts can fuse, FETs may fail, etc. Personally, I trust a class T fuse much more in these situations compared to a breaker or the BMS ability to shut it all off.

 

[Kornbread]

Something can always go wrong, especially with high currents. Contacts can fuse, FETs may fail, etc. Personally, I trust a class T fuse much more in these situations compared to a breaker or the BMS ability to shut it all off.

As I always like to tell my riding buddies, dress for the fall, not the ride.

 

[740GLE]

I still would love to see tests of these “breaker” and dead shorts. Theoretical fault current is one thing but tested fault current through all various connections is another

Also a test of various other fuses other than class T. See if people are going way overboard in the name of safety when a cheaper fuse is “just as good”.

 

[upnorthandpersonal]

Also a test of various other fuses other than class T. See if people are going way overboard in the name of safety when a cheaper fuse is “just as good”.

I'm using BS88 type fuses instead of Class T as well - especially when Class T is hard to find.

 

[tinyt]

Accidentally blew a class T fuse. Replaced it with ANL, accidentally blew it also, nothing spectacular. So, I am now using ANLs.

 

[NapalmFist]

I was just about to ask this same question. I noticed in Will's old videos he strongly emphasized using T class fuses and explained why. Then I go watch his videos on the 6000xp setup and I see he didn't use any T class fuses and I thought this was very strange since the breaker on the inverter is obviously not the same as a T class fuse and doesn't provide the same protection as what he explained was necessary in his old videos where he would install both breakers and fuses in his setup.

 

[Sennen]

I used MRBF for my build. Though, I like the idea of a fuse on each connector... I do have a bunch of extra 100A ANL fuses since it was cheaper to buy 10 than 3 when I did the inverter in my van.