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Wiring and breakers for 300 Amps


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So I have a 8000 watt split phase inverter, I want to wire it and limit it to only pull 300 amps.  The inline breakers and fuses I find online for 300 amps only fit up to a 0/1 wire, I have 0/4 wire for my inverter.  Am I missing something and I don't need 0/4 or do the manufactures knowing something I missed when I figured my setup at 300 amps.  At 300 amps it suggests I use 500 kcmil, which I haven't heard of anyone using for a smaller solar set up like this.  

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Not about your wire query, but a 300A breaker / fuse won't actually limit the current to 300A.  Now before the thread explodes into a NO NO!!! IT WILL!! style of flow, the specs for the fuse need to be checked.  There are different standards.  Long ago the standard in the USA was that a fuse rated at 300A will eventually blow at 300A.  Say that to the rest of the world and they'll look at your quizzically because as far as the rest of the world is concerned a 300A fuse will carry 300A indefinitely at standard conditions.  So please before posting here, check the specs for the particular fuse.

A 300A break in most cases will absolutely not trip at 300A in standard conditions.  It will eventually trip at 310A but it can take a long time for the thermal strip to heat before it will trip.

Every decent fuse and breaker has a trip curve.  It will tell you how long it will take to trip at a given current at given environmental conditions.  If you really want 300A tripping you may need to move to a lower rated device or if you want a tight 300A limit an electronic fuse (breaker that has sensing circuit to monitor the current).

 

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Posted (edited)

I have been looking into fuses instead of breakers too, I have been noticing that 300A isn't a perfect always 300A break and some amount of sway is alright.  My biggest question though is the wiring, following the AWG charts I would needs some extremely expensive and thick wire to handle 300 amps, yet the fuses and breakers don't go above 0/1 wire fitting.  So whose wrong in this situation?  I am starting to think all of it is wrong.

Edited by Aaron
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I personally recommend breakers, simply because no matter what happens, you can fix/clear the issue, and then re-use 'em.  Fuses...if they blow, you're down until you get a replacement.  Or worse yet, you're tempted to bypass the fuse to get going again.

As far as wiring is concerned, any wiring you do will be properly rated--when compared to what's inside the PJ inverter.  An 8kw PJ inverter has 4 lengths of 8AWG wire from the negative terminal to the PCB, and 2 lengths of 6AWG wire from the positive terminal to the heatsink (or 3 if you're lucky).

Yup, that's all.  Don't plan on getting 8kw out of it; consider yourself fortunate to get 2-3kw continuous.

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It's split for 4kw on 110v and 4kw on 220v, so are you saying I should be able to get 2-3kw on each side or all together because if its 2 - 3kw combined how can it be rated 8000 watts?

I have 0/2 and 0/4 wire I planed on using, should I scrap that and just go for the 4 8awg and 2 6awg wires instead?

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1 hour ago, Aaron said:

It's split for 4kw on 110v and 4kw on 220v, so are you saying I should be able to get 2-3kw on each side or all together because if its 2 - 3kw combined how can it be rated 8000 watts?

Ha.  Welcome to China, where you can put whatever numbers you feel like on a case and sell it...and people believe it.

I saw some power banks rated at 3,000,000mAh on eBay a few days ago, a steal at $15.  Let's not forget the 9,900mAh 18650 cells that you can buy, a hundred for $80.  How about some H11 LED car headlight replacements, rated at 3,420W and 453,000LM?  (How many amps at 12v again??  Most car headlights are on the fusebox for 20A max!)

  • I've never bought one of those power banks, though the listing does have a poorly worded disclaimer to indicate that their numbers might not be quite right.  Can guarantee you that they won't be much more than 3,000mAh.
  • My brother has bought some of those 9,900mAh 18650 cells.  They tested at........let's see...900mAh, or 1/10th of the rated number
  • I personally bought a set of ridiculously over-rated headlights for my car (not those exact ones though).  Expected them to fall far short of the rating--and so in the end they did meet my expectations.  They use far less power than the 60W halogen originals...and are a tad brighter than the originals. 
  • I have personally bought a 9kw PJ--that's my first PJ.  Overheated at 3kw continuous (transformer >180F).  The transformer in your "8kw" inverter is a smaller size.  (Eventually got a rewound tranny from someone else--WOW what a difference a properly rated tranny makes!  Fans don't even come on under 2kw load.)
  • U-Power rebrands the exact same inverter that you have, as a 15kw unit.  With no internal changes whatsoever.

There are no standards that these products must meet in order to be sold.  What ends up happening, is that company "A" decides to stretch the truth just a little on their product's abilities.  Clueless customers decide that because of the bigger number, it must be better--so they start buying it up like crazy.  So company "B" stretches the truth on theirs a good bit more--and they get the business back.  Back and forth they go--and then we end up with a never-ending spiral of insane and completely useless specifications in the Chinese market.

 

1 hour ago, Aaron said:

I have 0/2 and 0/4 wire I planed on using, should I scrap that and just go for the 4 8awg and 2 6awg wires instead?

Go ahead and use the properly rated wire--if you end up needing to replace the inverter with one that is actually designed to do what the label says, the wiring infrastructure is already in place.

I don't recommend doubling up wires like that--I was just noting what's internal to the inverter (4x 8AWG on negative, 2x 6AWG on positive), for comparison to your properly rated 0/2 and 0/4 wire.  Remember, no chain is stronger than it's weakest link.

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This is very disheartening, I know about how sellers blatantly put false claims and I even got on ebay about allowing it, battery banks and solar panels are probably some of the worst for that.  I have been trying to find good quality inverters for even a somewhat reasonable price but its impossible.  If you buy American you are paying 10X the amount for the same exact product you can get from china minus the companies name on it.  I am finding this whole solar market to be full of blatant lies and just people trying to take advantage of unknowing customers. Where are ethics and morals in marketing anymore, it's so frustrating because I have bought and returned so many different pieces of equipment trying to find good equipment, not to mention all the equipment I couldn't return and now am stuck with.  Granted I came into this not knowing all that much but I do my research but even the research is different especially when it comes to wiring sizing, you can find all kinds of different values on the same gauge wires depending on what source you go to.  

What would it cost for a split phase 8000 watt inverter from you guys?

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There is no such thing as good AND cheap power electronics. You either pay high prices for reputable names, or build it yourself. Cheap charge controllers on eBay can be hacked into decent operation, but it doesn't come out of the box worth diddly and it isn't plug 'n' play.

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21 minutes ago, Aaron said:

I have been trying to find good quality inverters for even a somewhat reasonable price but its impossible.  If you buy American you are paying 10X the amount for the same exact product you can get from china minus the companies name on it. 

Unfortunately, this is very true...me personally, I tend to try to "go around the middleman" and get the actual product.  Paying for labeling is about as practical as putting a 60,000W inverter label on a little 12v car lighter socket inverter that's only good for 100W...the insides haven't changed, just the cost and the hype has.

 

22 minutes ago, Aaron said:

it's so frustrating because I have bought and returned so many different pieces of equipment trying to find good equipment, not to mention all the equipment I couldn't return and now am stuck with.

Not doubting you one bit there.  Unfortunately, the "too good to be true" often holds true.  Curious what kind of setup you've come up with thus far?

 

22 minutes ago, Aaron said:

but even the research is different especially when it comes to wiring sizing, you can find all kinds of different values on the same gauge wires depending on what source you go to.  

Largely has to do with the wire ratings--is it 60C wire, 80C wire, 100C wire?  But yes, it can be a gamble at best.

 

18 minutes ago, Aaron said:

What would it cost for a split phase 8000 watt inverter from you guys?

We sell a split-phase 6kw inverter for right around $1k.  Similar in price point to Aims, Sigineer, Sungold Power (which I believe are all rebranded Chinese units made by Yiyen), but we have a MOUNTAIN of features by comparison.  Pretty much any setting can be adjusted--and if not, I can provide a firmware update to adjust it.

Genetry Solar inverters are NOT rebranded Chinese units--the inverter design is completely our responsibility, and they are manufactured exclusively for us.  Tested to run 6kw continuous, internal temps stable around 130F.  (A 12kw inverter is in the pike...currently awaiting some design changes.)

If you already have the PJ 8kw inverter, I'd suggest you give it a try, and see if it meets your needs.  But if you're counting on getting 8kw out of it...well...'fraid to say that's not going to happen.

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I am building a portable solar generator, a large one.  I need it to be able to run my house and my shop whenever power goes out.  I am going to hook it up to the fuse box with a typical generator setup.  

My problem is the "too good to be true" is an inverter capable of doing what it says it can do.  I am not looking for gold plated inverters able to power the star ship enterprise.  I am looking for an inverter that can power more than a walkman.  All these so called reputable dealers here in America claim their equipment is the best thing since sliced bread is just a chinese made device that they slapped their sticker on.  I can go direct to the factories and buy the same thing for a fraction of the price.  Anyways that's where I have been looking until I found the powerjack inverter and I always thought they were a good company, my thinking is changing again.

 

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30 minutes ago, InPhase said:

table 310.15(B)(16) of the NEC

This is the one I have been looking at and for the 300 amps my setup should be able to pull it is saying I need 350 kcmil wiring @ 75C.  This is where I am confused a bit because none of the breakers or fuses for 300 amps take larger than a 0/1 wire.  I never heard of anyone using this size wire for any DC application, not even welding, I am not in the loop but through my research this size is never mentioned.  

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Posted (edited)

Plenty of smaller wires can indeed handle 300 amps for short periods. But to be in compliance with the standards of permanent electrical wiring, the NEC size is it. Most fuse holders of that size will have a bolt stud connection, meaning you use a ring terminal or mechanical box lug of the appropriate size. 

 

I personally would size the wire to the maximum continuous load likely to exist. Size it for that load and to minimize excessive voltage drop at temporary peak loads. For example, if your long term load is 150 amps, you could use 1/0. But at 300 amps, the voltage drop might be excessive, so you might use 2/0 or 3/0 instead.

Edited by InPhase
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Thanks for the information InPhase, after looking at this for some time it seems like the guidelines are under par and using them and your best guess is the way to go.  I am putting 300 amp breakers or fuses in the system to keep the amps where they can be controlled so I think with my setup my 0/2 should be more than enough, especially after hearing that the inverter will never even do enough to get close to pushing the amps up. 

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  • 1 month later...
On 5/14/2021 at 1:09 PM, Aaron said:

Thanks for the information InPhase, after looking at this for some time it seems like the guidelines are under par and using them and your best guess is the way to go.  I am putting 300 amp breakers or fuses in the system to keep the amps where they can be controlled so I think with my setup my 0/2 should be more than enough, especially after hearing that the inverter will never even do enough to get close to pushing the amps up. 

The challenge becomes trying to use any chart including the NEC one for something like power delivery in a DC system at short distances since the chart doesn't include cable with higher temp ratings like 105C, 125C and 200C rated cable(or at least I can't find an NEC chart with the higher temp rated cable in my code book).  How you install or use the cable also makes a big difference on its allowed ampacity.  Its always a good idea to go over board on the cable in stationary battery systems to limit voltage drop.  I know from personal experience winding my own transformers that I can get around 200 amps through 12AWG wire for about 5-10 seconds before it begins acting more as a slow blow fuse.  

The 2/0 cable you are using should be more than sufficient.

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  • 2 months later...

i use class t fuses in a class T fuse holder. i use 4/0 wire and a 400 amp class t fuse between the inverter and the 24 volt LiFePo4 battery on the 8000 watt lf sp psw powerjack inverter. i have not put it to the limit test so no where near 4000 watts at this time.

i like the class T fuses and have had zero problems with them.

i also have 300 amp class t fuses on a 6000 watt powerjack lf psw sp inverter hooked up to a different lifepo4 24-volt battery. possibly a smaller 1/0 cable there and still nowhere near the possible 3000 watt potential output.

the wire size between the inverter and the battery should be sixed as large as you expect to pull and the fuse should be 1.25 times larger than the largest amp draw you expect to use. that a rough rule of thumb for fuse sizing. 

i crimp the lugs hydraulically ti match the bolts in the class t fuse holder.  I think as many other do >>> it is best to use as heavy gauge pure copper wire as you can dso it does not overheat and become the fuse.

you can buy lugs with walmost any sixe hole to match you cable and bolt down needs. 

bolt down class T fuses are the overcurrent protection i like the best. 😎

there is a guy on youTube who talks about the fuses with the handle of Lithium Solar. Check out his videos.

many circuit breakers are not reliable on the DC side of things and are sold by many snake oil salesman as more capable than they are.

 

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i would look at the nec table. 300 amps is a lot and does require a larger cable. 

perhaps if you use battery cable also known as welding cable with 105 degree C rating 2/0 will have a 300 amp capacity rating. 

you really need to look at a battery cable table or a welding cable table to get the corrrect ampacity rating. 

southwire royal excelene 2/0 welding cable is rated at 300 amps for 75 feet. 

of course you do not want your inverter cables anywhere this long. 

most people try to limit the inverter cable to battery length to 6 feet or less. some say up to 10 feet but the shorter is likely better.

longer cables have more resistance and larger voltage drop.

there is a voltage drop calculator you can get online also. i will see if i can find it again.

http://nooutage.com/vdrop.htm 

2/0 will easily work for 300 amp for you inverter cables. the battery cables or welding cable should be pure copper of a high strand count.

hydraulically crimped ends that bolt onto your fuse or properly sized Dc breaker if you go that route. i large dc breake capable of 300 amps will likely cost 200 dollars or more where as a class t fuse can be bought for 20-30 dollars or less.

https://www.directwire.com/resources/welding-cable-ampacity-chart/#jumptoampacitychart

 

 

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as an example:

I use 5 feet of 2/0 royal excelene welding cable the voltage drop is 1.13 percent so on a 27.2 volt LiFePO4 battery to inverter the voltage drop thru the 10 feet of cable (5 feet of positive and 5 feet of negative cable) is calculated to be .3536 volts.

therefore the 27.2 volts from the battery to the inverter is decreased by .3536 volts due to resistance and voltage drop 27.2 minus .3536 volts = 26.8464 volts. this is still  enough voltage for most all inverters to be able to utilize to output the desired 120 volt AC current. 

hope this helps!!!!!! 😎

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