battery bank wiring

[wolfe]

http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QO-QOB%20Circuit%20Breakers/0730CT9801R108.pdf

presuming the link works, page 4 under "voltage rating":

48vdc (10-70a for 1 and 2 pole circuit breakers, 10-60a for 3 pole circuit breakers).

then on page 5, there is a chart that seems to say the same thing.  to me, that says 70a is the limit, but i could be misunderstanding it.

you could do what chris did, with a 100amp 2pole breaker...with a 40 amp breaker...

it appears from your link the larger breakers are no longer dc rated, but if you were to go with 2 runs of either 8 or 6 awg in parallel from battery to breaker to inverter, each leg would carry 40 amps, for a total of 80 amps protected

that is how chris ran 200 amps thru a 100 amp breaker

[birdhouse]

defed-
i understand now your frustration.  the breakers i was speaking of above are "DIN" rail mounted breakers.  sqaure d's stop at 60A for DC ratings.  you're trying to keep a NEC or CODE set-up, and trying to keep things neat and inspection passable. 

chris is running a 100amp two pole breaker with DC.  i'm sure this will work just fine, but an inspector may have an issue with it, since the higher amperage breakers are not rated for DC.  you may be able to get away from this by just telling the inspector "oh yea, the "QO" series are ratd for DC".  he may just buy it. 

otherwise...  i'd buy one of the breakers you linked to.  do some very serious, very professional alterations to a standard AC fused disconnect, and thread in a specialty DC breaker, and make it look like it was factory.  an inspector would buy that any day, and if he doesn't, tell him you bought it at some solar specialty store.  make sure to keep the UL sticker in plain view.

option two- can you divide your solar into two parts, and say feed them through (2) 40amp standard DIN mounted square d breakers? 

just trying to help.  i deal with inspectors all the time, and sometimes can be very easy to trick them. 

[ChrisOlson]

This right here is the breaker I used, guys:
http://ecatalog.squared.com/fulldetail.cfm?partnumber=QO2100

When I talked to the engineer at Schneider Electric about it, he had no problem with me using this breaker on a DC system.  The only problem he had was with the fact that I was running 100 amps thru each pole instead of 100 amps in total.  He told me the breaker will work fine doing it the way I was, and that it will not hurt it, but that the enclosure the breaker came in was not rated for more than 100 amps, and neither was the breaker.

He told me the proper way to hook it up was to jumper the poles and run 100 amps total thru it.

I argued with him a little bit and told him if that breaker was being used on a AC 240 volt split phase circuit that each pole in it would be carrying 100 amps of the load.  So why can't I do that on DC - run 100 amps thru each pole?  He said you can, but it is not UL Listed for that and therefore he did not recommend it.

I don't know if their specs have changed, but like I said, at the time when I talked to this guy he had no problems with the fact that I was using that breaker for a DC application.  And I never had any problems with it either and I even tested it by using the carbon pile on my Sun AVR to trip it and see what it would take.  IIRC I could pull like 250 amps on it for a few seconds before it would trip but it would handle slightly over 200 without a problem and without tripping.

If you need high amp capacity you could do like someone else suggested and use several smaller breakers in parallel.  If you use three 60 amp single pole breakers, for instance, you can deliver 180 amps to the load by paralleling them.  But I'm sure that wouldn't meet inspection either unless they were common trip.
--
Chris

[birdhouse]

chris-
i mean no ill words, but yes, i think an inspector might fail your current set up.  it WILL handle what you're trying to do with it, BUT, what works, and what an inspector will approve are two different things. 

defed is trying to to build a system, and keep within NEC. 

you can run a 30amp hot water heater on 12/2, and it works fine for years, but no building inspector is going to approve it. 

adam

[ChrisOlson]

Actually, I am no longer using that setup.  When we switched our system to 24 volt and 120/240 split phase and put in the Xantrex inverters we installed dual Xantrex DC250 disconnects - one on each inverter.

--
Chris

[defed]

i really appreciate the discussion we have going here.  alot of good info.

adam is right.  i personally don't have a problem w/ the way you did yours, chris, but the inspector might.  altho, come to think of it, when i was talking to him about sizing certain wiring, he said use X awg wire, and then i would ask, well doesn't the code say i have to use a bigger wire because of this or that?  he was like, not that i know of...when i'm nearly certain that's what the code says!  so...MY inspector might NOT notice anything.

i narrowed it down to 2 options...a panel mount breaker or a marine type switch w/ separate in-line fuse.  i talked to the experts at my local electrical supply place about an outdoor enclosure for panel mount breakers.  he said it is probably possible, but not that easy, so the only way i could do it (easily) was indoor.  i wanted the batt disconnect outside on the battery box.  so i decided to try the marine type disconnect.  they are UL listed as a battery switch, rated at 48v @ 300amps.  not sure that the UL rating applies to residential use, but the fact that it's listed as a battery switch should mean something.  i will mount it in an enclosure.

[defed]

this 75amp line is really being a pain in my butt...now i can't find a fuse block for class r fuses.  class t is all over the place, but the min on them seems to be 110amp.  i did find some, but they don't state DC....they do state that they can use FRN-R fuses, which are AC/DC rated...so not sure that covers that.  either way, i can't see there being a problem using a fuse block on DC as long as the current is cut off before trying to install or remove one.

[rossw]

I argued with him a little bit and told him if that breaker was being used on a AC 240 volt split phase circuit that each pole in it would be carrying 100 amps of the load.  So why can't I do that on DC - run 100 amps thru each pole?  He said you can, but it is not UL Listed for that and therefore he did not recommend it.

I could pull like 250 amps on it for a few seconds before it would trip but it would handle slightly over 200 without a problem and without tripping.

Seriously guys, part of the problem has been overlooked here.
If you'd said "isolators" I wouldn't butt in. But we're talking about BREAKERS.

Its easy to say "amps are amps", but DC is a very different animal to AC.
And "interrupting capacity" is hugely different to "carrying capacity".

Breaking a 240V AC circuit carrying 100A is a pretty decent job - but at least an AC arc is SELF QUENCHING. That is, at 50 or 60Hz, the arc actually extinguishes 100 or 120 times a second. As soon as the contacts get far enough apart, the arc goes out and stays out.

Breaking a 80-100V *DC* circuit carrying 100A is a very different animal. The arc doesn't extinguish. There is a HUGE amount of heat generated. It will quickly melt contacts, ruin spring material, burn breaker bodies, switchboards, cables and if you're not lucky - the whole installation.

DC rated breakers use various techniques to "pull" the arc into a quench chamber where it can be handled (and extinguished) quickly. Frequently this is assisted with magnets, and/or electromagnets (coils) within the breaker. Polarity becomes important as you will draw the arc into the quench chamber one way - or push it out into the breaker body the other.

Any decent, knowledgable engineer who knows his switchgear would be advising you to use the breakers within their design/test/certified range.

[rossw]

i can't see there being a problem using a fuse block on DC as long as the current is cut off before trying to install or remove one.

It's a fuse.
It's there to protect things if sh!t happens.
If it can't *safely* interrupt the current when it needs to, what's the point in having it there at all?

[defed]

It's a fuse.
It's there to protect things if sh!t happens.
If it can't *safely* interrupt the current when it needs to, what's the point in having it there at all?

the fuse would be ac/dc (FRN-R).

i've seen bussman H600/R600 listed as ac/dc...i've also seen them listed as dc only.  H250/R250, i've only seen listed as ac...but then referenced for use with 12/24v inverters.  in your previous post about quenching the dc arc...i can't see that being a problem on a 6" long fuse block, whether it is rated ac or ac/dc.  i do understand that dc requires special fuses/breakers, which is why i am going thru all this trouble in the 1st place.

[rossw]

i've seen bussman H600/R600 listed as ac/dc...i've also seen them listed as dc only.

The fuses I use on my batteries (which are 200A HRC) are available as AC fuses, AND AC/DC fuses.
The ones rated for DC are more expensive, and have a different internal construction, including a whole lot (I believe) of arc-quenching balls of something.

If your application is only 12V, or 24V, it's probably not such an issue.
If you are running 48V or above (could easily see 60V), OR IF YOU THINK YOU MIGHT UPGRADE AND DON'T WANT TO REPLACE EVERYTHING LATER - you probably do need to pay great care to it now. (As you are doing, and kudos to you for it).

[defed]

i made a typo in the portion that you quoted....it should have said "i've also seen them listed as AC only".

i have some NON-60 fuses.  i've seen them as ac and ac/dc (FRN-R 60).  you say the fuses you use can be found either way...how is the fuse block that you are using listed?  seems like class T fuses have tons of nice blocks w/ covers...not finding as much for class R.

i'm currently at 24v, and am trying to at least design things so that if i change voltage (or inverter upgrade), the equipment changes would be minimal.  the battery switches/fuse and the wires/switch/fuse to the inverter are mostly what would need changing in an upgrade.  the wires for those areas will be 10' or less and the fusing would have to be changed regardless.

trying to balance cost vs future compatibility.

[defed]

here is an example...

fuse block, doesn't specify ac/dc:

http://www.altestore.com/store/Enclosures-Electrical-Safety/Overcurrent-Devices-Fuses-Breakers/Fuse-Fuseblocks/61-100-Amp-1-Pole-Class-R-Fuse-Block/p4130/

fuse, says ac/dc:

http://www.altestore.com/store/Enclosures-Electrical-Safety/Overcurrent-Devices-Fuses-Breakers/Fuse-Fuseblocks/80-Amp-250-VAC-125-VDC-Class-R-Fuse/p4127/?nav=detail-addon

when used together, does this equate to a dc OCPD?

[rossw]

when used together, does this equate to a dc OCPD?

I'm not the insurance company who'll try to duck a claim if you ever needed one, nor the inspector who's going to tell you to replace if it he doesn't like the colour it's painted, but from the outward appearance (and logic) I'd say it should meet all safety and code requirements. My reason being that in the event the fuse needs to operate, it's rated to 125V DC, and that the arc would be entirely within the fuse cartridge, so the holder (in this case) plays no part.

The first two parties may or may not agree with my reasoning

[defed]

I'm not the insurance company who'll try to duck a claim if you ever needed one, nor the inspector who's going to tell you to replace if it he doesn't like the colour it's painted, but from the outward appearance (and logic) I'd say it should meet all safety and code requirements. My reason being that in the event the fuse needs to operate, it's rated to 125V DC, and that the arc would be entirely within the fuse cartridge, so the holder (in this case) plays no part.

The first two parties may or may not agree with my reasoning

i agree on both parts....yes it SHOULD be correct, and yes they may NOT see it that way!

i'm 99% sure my inspector would approve it, but i guess that still doesn't mean the insurance co would after the fact.

[defed]

but i have seen them listed in mfg's literature as AC (no mention of DC) and AC/DC...i don't know how they expect anyone to know what's going on.