Another DC Breaker/ Fuse Question.

CV350

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I am in the process of sizing the breaker/ fuse between my Growatt SPF5000 TL HVM inverter and my 48v Lifepo4 280AH 16s battery box.

The system will be initially set up as a UPS only but later I will add PV panels and then at a final stage (after I expand the property) another bank of batteries and another Growatt in parallel. So initially I am oversizing on a few things with a view to the end plan (e.g. I am running 2/0 AWG wire between the battery and my BMS has a peak capacity up to 200A). This is a remote property constantly impacted by grid outages of 3 to 4 hours max and consumption on site is generally very stable at <6kwh per day.

There are just the two leads coming from the battery direct to the inverter and it is my intent to insert a Class T Fuse on the battery positive as well as a VDC breaker.

The two items I am considering are:

T Fuse = Eaton Bussmann 250A 300Vac IR200Ka


Schneider VDC breaker = LV438670 160A 240Vac SP

I went with this breaker because it has external posts on the back of it which can accommodate larger lugs/ wire. One prob I see with 2/0AWG wire is that the lugs are big and not necessarily accommodated on all breaker types.

I guess some people will ask why a fuse as well as a breaker. Well according to what I have read on this forum the T Fuse is very safe and I also wanted a disconnect switch so I went with a breaker in lieu of a switch so as to give me double protection. The T Fuse will be as close to the positive side of the battery as possible.

Do these specs look OK? If possible I want to stay with Schneider brand as it is available here in Thailand.

Thanks for any advice.
 

CV350

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Forgot to mention that the Growatt manual specifies a 150a/ 60VDC breaker between the battery and inverter.

My question above is not so much about what size breaker I need but whether the particular breaker I have chosen is OK and whether there are any considerations from running a breaker at 150a and a T Fuse at 250a. I'm viewing the T Fuse as a last resort protection.
 
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HRTKD

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My worry about circuit breakers that say AC/DC but provide mostly AC data is that they really aren't a good fit for a DC environment. I made the mistake of buying a breaker that was designed for an AC environment and had to subsequently replace it with a DC-only breaker.

Take a look at the Midnite Solar breakers. Be aware that many of them are polarized and are not to be used between a battery and both loads/chargers.
 

Alphacarina

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My question above is not so much about what size breaker I need but whether the particular breaker I have chosen is OK and whether there are any considerations from running a breaker at 150a and a T Fuse at 250a. I'm viewing the T Fuse as a last resort protection.
Fuses and breakers are sized to protect the wire, not the load, so if your wire is rated for 200 amps, that's the fuse size I would use. I agree with HRTKD that I would use a DC rated breaker

Don
 

CV350

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Thank you HRTKD and Alphacarina for you responses.

Please don't take this as being disrespectful (as I am only trying to learn) but why would the Schneider AC/ DC breaker not work properly? Is it an issue in that it won't disconnect properly, wears out quicker over time or something else?

I am not an expert by any test but I did consult directly with Schneider giving them the detail on my system/ application (same as I Iisted above) and this is what they came back with as their recommendation. And I went with Schneider as Schneider brand is a good and reliable brand and distributed here locally with local warranty. While Midnight Solar is also a very well renowned and specialist provider within the solar industry it is not cheap to bring it into Thailand as in addition to the price I have to also add freight and tax. Warranty is also difficult to manage if a return is required with me having to pay freight both ways and wait weeks for replacement.

In terms of specs being aligned to AC is it that you feel the VAC of 250VDC is to high for DC? Or is it something else? Your experience would be appreciated. I am aware and have looked at the various warnings of using an AC breaker in a DC system but this breaker is actually dual rated for AC/ DC.

Again please don't take this the wrong way as I am highly appreciative that you did respond to my question and am simply only trying to learn.
 

Short_Shot

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Thank you HRTKD and Alphacarina for you responses.

Please don't take this as being disrespectful (as I am only trying to learn) but why would the Schneider AC/ DC breaker not work properly? Is it an issue in that it won't disconnect properly, wears out quicker over time or something else?

I am not an expert by any test but I did consult directly with Schneider giving them the detail on my system/ application (same as I Iisted above) and this is what they came back with as their recommendation. And I went with Schneider as Schneider brand is a good and reliable brand and distributed here locally with local warranty. While Midnight Solar is also a very well renowned and specialist provider within the solar industry it is not cheap to bring it into Thailand as in addition to the price I have to also add freight and tax. Warranty is also difficult to manage if a return is required with me having to pay freight both ways and wait weeks for replacement.

In terms of specs being aligned to AC is it that you feel the VAC of 250VDC is to high for DC? Or is it something else? Your experience would be appreciated. I am aware and have looked at the various warnings of using an AC breaker in a DC system but this breaker is actually dual rated for AC/ DC.

Again please don't take this the wrong way as I am highly appreciative that you did respond to my question and am simply only trying to learn.
Dc and ac breakers have to be built very differently to safely protect a DC circuit.

As I recall, they need special arc prevention components.

An AC breaker can "work" on a dc circuit but it'll never be "right". So if a breaker is advertised as both you need to ensure you stay within its specs, and you may find a difference between ac and dc specs.

If Schneider says it's fine for dc, then it's fine in my book. I've never had an issue with Schneider components and I've got literally thousands of them around this facility I'm sitting in.
 

pierre

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I agree. Not all cct breakers are equal. An AC/DC breaker from a reputable manufacturer ( Schneider etc ) can be trusted. If it was my system I would use a decent quality fuse and for a quick disconnect I will use a suitably rated isolator ( 1 or 2pole ) without overload protection. Too many horror stories of bad quality breakers out there for DC systems.
 

HRTKD

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Thank you HRTKD and Alphacarina for you responses.

Please don't take this as being disrespectful (as I am only trying to learn) but why would the Schneider AC/ DC breaker not work properly? Is it an issue in that it won't disconnect properly, wears out quicker over time or something else?

No problem. Questions are good. I'm no electrician, electrical engineer or otherwise qualified professional. So I have to go by what I read/see here on the forum and elsewhere. What @Short_Shot wrote is darn close to what I would have written, so I'm not going to repeat it.

This video is probably what pushed me over the edge to fix my incorrect install. The caveat to that test is that most of us aren't dealing with DC volts in that range. Could you get by with an AC, or even AC/DC, rated breaker at lower voltages? Probably. But I'm not going to risk my property and family on "probably".

 

CV350

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Thanks for your response HRTKD and I understand your point totally. The problem I have here in Thailand is that we don’t have access to many things that are available elsewhere in the world. Safety is paramount to me and that’s why I asked for advice from Schneider and didn’t go the China route on AliExpress I can still import form US, Europe or Australia but it just adds to the end cost at every step. But again I get your point and appreciate your advice.

if anyone knows a dedicated Schneider DC only breaker SP and panel mount rated to 150A then that would solve my problem perfectly.
 

Hedges

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When I saw "18 kA at 240 VAC" I was concerned this breaker could trip and burn at some current less than my estimate of 20kA from a lithium battery, perhaps with voltage drop and current flow/power dissipation such that class T fuse doesn't blow for a while.

When a circuit is protected by a fuse/breaker such as class T with 20kA AIC rating, we want the rest of the circuit to hold together long enough for fuse to blow. For instance, my AC disconnect switches are rated to carry 200kA (long enough for suitably rated fuses to interrupt the current.) Anything which opens into the high current before fuse could be a problem.

But, I see this Schneider breaker has an even higher DC interrupt capability:

"
[Icu] rated ultimate short-circuit breaking capacity36 kA Icu at 250 V DC 1P conforming to IEC 60947-2
36 kA Icu at 125 V DC 1P conforming to IEC 60947-2
18 kA Icu at 220/240 V AC 50/60 Hz conforming to IEC 60947-2
"

Remaining part of the puzzle is trip speed - which goes first, fuse or breaker?
Breaker data sheet says 160A rating and 1250A magnetic trip:


Page 354 show conditions for fast trip < 10 milliseconds. Could be either fuse or breaker goes first,


It appears the breaker is pretty good for the battery/application.
Fuse right at battery protects against shorted wiring as well, and breaker can be mounted where accessible.
 

CV350

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When I saw "18 kA at 240 VAC" I was concerned this breaker could trip and burn at some current less than my estimate of 20kA from a lithium battery, perhaps with voltage drop and current flow/power dissipation such that class T fuse doesn't blow for a while.

When a circuit is protected by a fuse/breaker such as class T with 20kA AIC rating, we want the rest of the circuit to hold together long enough for fuse to blow. For instance, my AC disconnect switches are rated to carry 200kA (long enough for suitably rated fuses to interrupt the current.) Anything which opens into the high current before fuse could be a problem.

But, I see this Schneider breaker has an even higher DC interrupt capability:

"
[Icu] rated ultimate short-circuit breaking capacity36 kA Icu at 250 V DC 1P conforming to IEC 60947-2
36 kA Icu at 125 V DC 1P conforming to IEC 60947-2
18 kA Icu at 220/240 V AC 50/60 Hz conforming to IEC 60947-2
"

Remaining part of the puzzle is trip speed - which goes first, fuse or breaker?
Breaker data sheet says 160A rating and 1250A magnetic trip:


Page 354 show conditions for fast trip < 10 milliseconds. Could be either fuse or breaker goes first,


It appears the breaker is pretty good for the battery/application.
Fuse right at battery protects against shorted wiring as well, and breaker can be mounted where accessible.
Thank you Hedges. That’s the technical input that I was seeking and I appreciate greatly the effort you have put into the research. This is all beyond lme when it gets to this level of detail and it’s great to be able to seek input from this forum.

And thanks also to the inputs from others.
 

RayfromTX

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This is a nice breaker for my system as well. I would use it near the terminal block where batteries are combined in parallel. This would allow the disconnected cable to be dead. If I put it at the battery then the disconnected cable would have the full unfused potential of the combined packs to be live on the disconnected cable. I'm thinking a fuse in the battery and this breaker between the bus and the cable. Is this the same reason that you are considering using both devices?
 

CV350

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This is a nice breaker for my system as well. I would use it near the terminal block where batteries are combined in parallel. This would allow the disconnected cable to be dead. If I put it at the battery then the disconnected cable would have the full unfused potential of the combined packs to be live on the disconnected cable. I'm thinking a fuse in the battery and this breaker between the bus and the cable. Is this the same reason that you are considering using both devices?
Yes RayformTX. I was thinking of it as a disconnect switch (eventually on each pack) with the added benefit that if I did have a short that it might actually trip before I blew the fuse but as Hedges said I am uncertain on that part. Lastly its just another point of protection.
 
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