It's like a jigsaw puzzle that could kill me (setting up my bus bar) - my thoughts make sense?

[AlaskanNoob]

Does anybody know how these covers for the fuse blocks and bus bars work with the Blue Sea products? Do I bend these plastic tabs so cables can attach or should I just cut them off?

 

[FilterGuy]

It certainly looks like the protective tabs are designed to be removed. I have never played with one but I suspect if you bend it, it will snap at the line.



If you try to bend it and it doesn't snap. cut it at the line.

 

[629658]

The disappointing thing about Lynx is that it uses Mega Fuses with a very low AIC. If you need Tclass, it has to be external to the Lynx and that takes the nice clean design of the Lynx system and adds ugly warts to it.

Victron is usually pretty good about addressing the needs of people but this is one area they have failed to address. This surprises me because even the Victron Ambassadors tell me LiFePO4 needs more than Meag Fuse

Perhaps but I’m confident about my setup. If 4 sets of redundancy isn’t enough then a 5th isn’t going to make any difference.

 

[HRTKD]

On one of my covers, I tried to break it where the plastic was scored and it didn't work out so well. After that, I used a Dremel with a cutoff wheel.

 

[SamDeleted]

A) I measure my positive cable length as 18" for the two Quattro positive cables, and 19" for the two MPPT positive cables. Should I go with those numbers to keep it as short as possible, or round it up to 24" to give me some wiggle room? I could also move the bus bars closer to the devices and shorten the lengths if needed a bit.

I just put the cable in place and cut it where looks about right ,

 

[rhino]

For your system, it would be perfectly fine to have a single 300A fuse and terminate two sets of cables on it (preferrably with an extra bus rather than double-lugging).

Doing this will make for cleaner easier to maintain system. How would you even know if only one of the fuses blew since the inverter would still have power.

 

[HRTKD]

How would you even know if only one of the fuses blew since the inverter would still have power.

That's question that I had. But only after I had installed the twin fuses.

 

[AlaskanNoob]

Doing this will make for cleaner easier to maintain system. How would you even know if only one of the fuses blew since the inverter would still have power.

I guess I'll know once the second fuse blows because it demands too much power through the only remaining cable.

 

[AlaskanNoob]

Continuous is the correct sizing. I won't ever pull as much as the Victron manual specified for the fusing, which was 400 amps. But I went with their requirement anyhow.

The consultant we hired said:

There is a lot of confusion about overcurrent protection on forums etc
Overcurrent protection (fuse or breaker) is to protect wires only, not equipment.
Thus, overcurrent protection is sized based on wire size. In this case, 300A is perfectly suitable for 4/0 cables.
You could certainly downsize the fuses, but there's no advantage that I can see in doing that and you risk nuisance tripping of the fuse.

 

[Ampster]

The consultant we hired said:

There is a lot of confusion about overcurrent protection on forums etc​

Overcurrent protection (fuse or breaker) is to protect wires only, not equipment.​

That was the point I made earlier to the comment from @Shimmy

 

[rhino]

I guess I'll know once the second fuse blows because it demands too much power through the only remaining cable.

That won't be guaranteed to happen. If something damages the one cable it's possible the fault clears before the 2nd fuse can blow (rodent chewing it). In any event you'd then be replacing two expensive fuses every time a "single" fault happens when you could just have one. You're also slightly increasing the total resistance of the battery->inverter cabling by having two fuses instead of one. Maybe someone can enlighten me but I don't see what advantage you get with that arrangement.

 

[Shimmy]

I have never understood the logic of protecting an inverter? What could go wrong if the DC inputs to an inverter are shorted? A fuse at the pack would protect the wire. If the short was internal to the inverter the inverter is probably fried anyway and further damage to the cables is prevented by the breaker or the fuse..

The inverter issue is that the IGBTs have an extremely low reverse current capability so an AC input (or output in some conditions) transient will cause them to blow. This can start a fire. For large pump VFDs you sometimes need to add a suplemental snubber circuit to ensure the system is sufficiently robust.

 

[629658]

The consultant we hired said:

100% correct. I’m expecting someone on here to suggest we hire someone to sit in our battery rooms 24/7 to watch them!!!!

I’m all for safety but how many redundancies is enough? 2,6,or 8.

 

[Ampster]

The inverter issue is that the IGBTs have an extremely low reverse current capability so an AC input (or output in some conditions) transient will cause them to blow.

Most inverters have circuit breakers on the AC side anyway. I thought the above discussion was about the DC fuse and that was what my question was about. How does a fuse at the inverter protect the inverter if the DC inputs are shorted? Do you agree that the purpose of fuses and circuit breakers is to protect the wires?

 

[629658]

So I have to ask the obvious question is it worth spending $500+ to protect $150 worth of wire worst case?

 

[Ampster]

So I have to ask the obvious question is it worth spending $500+ to protect $150 worth of wire worst case?

The wire is not the the ultimate risk. When the wire gets hot from overcurrent it could cause a fire. A fire could burn down a home. I did not spend $500 to purchase a Class T fuse. My 225 Amp Blue Seas Class T fuse cost $40. I bought it to ultimately protect my home.

I’m all for safety but how many redundancies is enough? 2,6,or 8.

Just one in the right location would work. I put mine at the largest current source which is my 42kWh pack which would be capable of releasing over a thousand Amps on a direct short.

 

[Shimmy]

Do you agree that the purpose of fuses and circuit breakers is to protect the wires?

Primarily, but not exclusively. The NEC focus (for consistency) is on the wires. But, what you are protecting the DC wires from is not overload but a short sourced by the batteries (highest source of fault current).

Most of the DC circuit breakers I have seen in inverters are not actually rated for fault load-break; they are just isolation switches functionally.

 

[629658]

The wire is not the the ultimate risk. When the wire gets hot from overcurrent it could cause a fire. A fire could burn down a home. I did not spend $500 to purchase a Class T fuse. My 225 Amp Blue Seas Class T fuse cost $40.

Just one in the right location would work. I put mine at the largest current source which is my 42kWh pack which would be capable of releasing over a thousand Amps on a direct short.

I know I’m just poking the bear. But some on here are putting in many class T fuses. One correctly sized is sufficient. But by the time you buy the fuse, holder, case and lugs you’re looking at least $100 maybe $120. If I took them seriously I’d be looking at over $1k (8 batteries and two from the inverter). They are advocating 1 for each pack into the buss. I did fuse my packs at the buss using Mega’s (I know they don’t have the arc stopping capability of class T but if I have an arc it’s not going to be at the buss anyway. Hopefully, the Mega’s would blow way before we get to arc time and then we have the DC breakers on the batts themselves and of course the BMS itself and then the DC breakers on the inverter and lastly the class T feeding the buss. Add to that the central smoke detector over the bank and the temp alarms.

This stuff will drive you crazy if you let it. I’m a safety first guy and I think it’s as safe as possible. But it kills me looking at pictures of the crap some hang on their walls with batteries and wires running everywhere. Now that would scare the hell out of me.

 

[AlaskanNoob]

The wire is not the the ultimate risk. When the wire gets hot from overcurrent it could cause a fire. A fire could burn down a home. I did not spend $500 to purchase a Class T fuse. My 225 Amp Blue Seas Class T fuse cost $40.

Just one in the right location would work. I put mine at the largest current source which is my 42kWh pack which would be capable of releasing over a thousand Amps on a direct short.

Yeah, the fire potential is my concern.
On the inverter side, it can pull 520A surge, and 250A continuous.

Anybody think I have a greater fire risk if I size my t-fuse based on the surge rather than the continuous number? Unless there is a safety issue I'll stick with the fuses I got.

 

[time2roll]

If the previous poster is correct that I should have sized my t-fuses for the max continuous inverter draw (250A) rather than what I did, which was sizing for max surge (520A) then I'm going to have to get smaller t-fuses anyway for the cables to the inverter. Maybe I'll put fuses on both ends of the cables.

200% goes to about 50 seconds. Easily 10 seconds.

https://www.bluesea.com/products/5112/Fuse_A3T___Class_T_110_Amp

 

[HRTKD]

Hopefully not a dumb questions, but is the time spent over the rated amps cumulative? I don't know what goes on inside one of these Class T fuses.

 

[rhino]

Hopefully not a dumb questions, but is the time spent over the rated amps cumulative? I don't know what goes on inside one of these Class T fuses.

They aren't like MOVs which degrade after each surge they protect against. There is no aging factor. There's just a piece of metal inside connecting the two ends like you normally see in a fuse but with "sand" surrounding it to help extinguish any arcing when the metal breaks/melts.

 

[Bluedog225]

I thought fuses did age/deteriorate.

 

[Shimmy]

Hopefully not a dumb questions, but is the time spent over the rated amps cumulative? I don't know what goes on inside one of these Class T fuses.

Not so much on Class T fuses, but some of the fuses have a series of parallel ribbons where you can see one starting to melt. This typically happens on low-level faults rather than overload; these segments are designed for high fault current instantaneous protection.

 

[Ampster]

Anybody think I have a greater fire risk if I size my t-fuse based on the surge rather than the continuous number?

Yes it is a greater fire risk if you size the fuse for the surge and your wire size is smaller. If you ignore the conscept of the fuse is to protect the wire then you are on your own and have learned nothing from your consultant or this thread. Sorry to be so blunt.
EDIT: The OP subsequently clarified that the fuse was correctly sized to protect the wire in the above question.