Class T is better in a DC system and more is better in a circuit when it comes to fuse protection. DC current can arc across and open ANL element that has burned in half due to a short. Even open, if you have enough current it can jump across with DC. Take a look at an arc welder for proof. The class T has elements inside that are surrounded by material (silica sand, I believe) that absorbs that arcing. And some class T fuses I've seen are rated up to 200,000 amps, against arcing current. For personal protection and property protection class T is much better.
Class T vs ANL fuse
- Thread starter MarvRVHam
- Start date
I want to say you should size according the weakest link and that would probably be the wire. If you have wired using 2/0 then at least 175 amp. 3/0 would be 200 amp etc. Now if your circuit has other weakness' such as terminals etc that are less, then you want to size to their max ability to conduct amperage. And when I say max, I mean before they heat up. Better yet is to size even less than the weakest link if possible. Since you are not pushing the inverter, you might want to consider less ampacity in a fuse. However, remember if you exceed the max size with current in an instant or 2 you may have to replace the fuse. So it's a fine balance. One never knows the actual ampacity of a crimped lug for instance due to the nature of such a mechanical connection. You may have everything sized according to ampacity charts and still not have enough at a crimp. So if you size according to what the weakest link is (on paper) you should still check the entire system with a temperature probe periodically and inspect for discoloration or other signs of an issue.
By the way I've seen class T fuses rated as high as 200,000 amp disconnect capable. That's positive open with no arcing across the burned element(s) inside. Perhaps there are those with only a 20,000 amp rating as well. But better to check the rating on any being used to be sure.
In any circuit the 'deciding factor' is the weakest link in the circuit. That could be the inverter, the wire, the connectors, etc. Crimped connectors would be the weakest link due to deviations in continuity within the crimp. Checking for resistance with a temperature probe after putting a system in operation and rechecking often is a great idea no matter what you decide to do.
Better to have one class T before you split and go to the two inverters.
Well, there are different parameters for each chemistry. Knowing what they are for your type is critical to avoid overcharging for instance as well as over-discharging.LCO is what a lot of people maybe imply with
“Lithium Ion”
LiFePO4 = Lithium Ion Subtype
LiCoO2 = LCO = Lithium Ion Subtype
this isn’t something that should be painful.
LMO LTO LFP LYP NCA NMC LCO are all Lithium Ion chemistries. There is no more to it than thisif it uses lithium ions then it’s a lithium ion cell.
Roswell Bob
Solar Enthusiast
I used a class T to clear under short circuit. I put a breaker in series with a lower value to protect the wire. The only way the class T will ever clear is with a short circuit. That is just another way to do it with maybe a little more margin before the expensive fuse clears.
As long as you do not exceed the volt rating, it's the ampacity rating that matters.
Class T is more about protecting you. A breaker can allow arcing even when open depending on the amount of amperage available in a DC circuit. A regular breaker is okay in an AC circuit but in DC you're dealing with another phenom. And that's arcing. Arcing can cross over an open set of contacts in a breaker or other current protection devices and fry you. Watch an arc welder for a demonstration of that. Class T has the ability to absorb the arc when it opens. So if you are touching it you don't end up in the hospital or worse. Now of course nothing is going to protect the fellow who drops a screwdriver on the battery bank but he is less likely to be holding it when and if it shorts the contacts on the batteries. Get the point? If not don't mess with this stuff.
Roswell Bob
Solar Enthusiast
I have DC rated breakers that should clear anything but a short. The arcing is taken into account when the breaker is designed. The class T will clear a short circuit before the transistors blow into fragments. I've designed large 3 phase industrial inverters for a long time. I get the point.
Hedges
I See Electromagnetic Fields!
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Class T fuses are rated 200,000 AIC for AC, 20,000 AIC for DC.
They are called "current limiting"; what they actually do is limit time current flows by blowing so fast at 200,000A (for AC) that anything the current goes through doesn't need to be rated over 20,000A fault current. (I guess that means current^2 x resistance x time, the deposited energy.)
In DC application, although they interrupt 20,000A, they don't do it fast enough to protect anything rated lower. Which is unfortunate, because we'd like it to protect breakers downstream. (looks like up to 30A rating they are 50,000 AIC.)
Last 2 pages show the "current limiting" let-through.
Possibly something like Ferraz Shawmut "Amp Trap" fuses are fast enough to protect other lesser rated DC components.
Has anyone looked into other types of fuses? Such as the BS88 style fuses: Eaton-Bussman 100LET (~$13) for example. Very detailed datasheet gives many charts for calculating total clearing I^2*t and max let-through current.
Ratings:
Volts: — 240Vac/150Vdc
Amps: — 6-900A
IR: — 200kA RMS Sym.
It appears they could be bolted directly to battery lugs and the cable bolted to the other side of the fuse which seems safer to me than having a separate fuse block because the fuse is closer to the battery. Then, it's less likely that a short would happen between the battery and the fuse.
Ratings:
Volts: — 240Vac/150Vdc
Amps: — 6-900A
IR: — 200kA RMS Sym.
It appears they could be bolted directly to battery lugs and the cable bolted to the other side of the fuse which seems safer to me than having a separate fuse block because the fuse is closer to the battery. Then, it's less likely that a short would happen between the battery and the fuse.
There are a lot of fuses able to interrupt 20kA. Bussmann 100FE is the one I'll be using for my 48V battery. 22USD for 3 pieces a couple of months ago. About half a year ago I used a 2USD fuse 32A 10x38mm fuse with 50kA breaking capacity.
There are cheaper options. It is not only the class T fuse that can do that job.
The one in the attached image is common in Europe and is pretty cheap. This type of fuse goes to over 500A and is way cheaper compared to the class T stuff. Breaking capacity is usually 120kA.
There are cheaper options. It is not only the class T fuse that can do that job.
The one in the attached image is common in Europe and is pretty cheap. This type of fuse goes to over 500A and is way cheaper compared to the class T stuff. Breaking capacity is usually 120kA.
Attachments
curiouscarbon
Science Penguin
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only for systems at 14V. drops to 5,000 A @ 32V and 2,000 A @ 48.
that said, they seem fantastic for 12V systems, and i am using one and plan on using more for 12V systems. for 24V systems i might use them for each battery with an upstream fuse equivalent of class T.
quick reference table for the different ampere interrupt rating vs voltage:
Post in thread 'MRBF or class T'
https://diysolarforum.com/threads/mrbf-or-class-t.47659/post-606422
kind regards?
You might want to add these Bussman BS88 style fuses that I mentioned to your table. I think they blow all the others out of the water in terms of AIC per $. NH style fuses also seem to be about $10, DC rated and 120kA.
I'm just a little confused why Class T fuses became the defacto standard for DIY Solar. Maybe they used to be cheaper or there is some marine or industrial standard that requires Class T. I see a lot of people complaining that Class T fuses are expensive but they make is sound like there is no other acceptable option.
I'm just a little confused why Class T fuses became the defacto standard for DIY Solar. Maybe they used to be cheaper or there is some marine or industrial standard that requires Class T. I see a lot of people complaining that Class T fuses are expensive but they make is sound like there is no other acceptable option.
curiouscarbon
Science Penguin
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thank you for mentioning! will try to integrate those. much appreciated.
class-T is simply able to support very high AIC even with 48VDC batteries, so i think that is why there has been a convergence in this community.
thanks again for bringing those types to attention! ?
tigerwillow1
Solar Enthusiast
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Can somebody decode the BS 88 spec sheet? Translate it from British specs to more common terms like AIC? One of the specs says "IR: — 200kA RMS Sym." which I'd guess might be the equivalent of AIC, but 200kA? That couldn't be right for a DC spec, and I couldn't find anything that looks like an AIC spec for DC.
I found "Technical Data Sheet" at Eaton that has the DC Breaking Capacity rating: 50 kA at 500 V d.c.
Because some marine spec defined them as standard or requirement. And for people, it is usually easier to stick to what is known to be good instead of checking the specs and trying to justify the price.
The NH style will probably require a custom mounting solution. The standard holder is designed for high voltage where minor voltage drop is not an issue. But in a 12V system, everything should be bolt-on and properly crimped to reduce voltage losses. And they are a lot bigger compared to cylindrical fuses.
