NEC 690.16 - How can I combine three 450V strings with overcurrent & disconnect?

[Aladdin]

I'm designing a residential PV system with battery backup. I've got 7 strings of 7 Sanyo HIT 225N modules each. I'm using the new Outback 600 volt charge controllers of which I need 3. So 2 strings to one Outback, 2 strings to another Outback and 3 strings to the third Outback. The two arrays of 2 strings do not need series fuses so that's straightforward. The array with 3 strings requires a combiner with overcurrent protection and the 2011 NEC 690.16 requires a disconnecting means for fuse servicing. Is there a Midnite Solar solution that handles 3 strings with ability to disconnect 600V circuits?

[Halfcrazy]

What Outback 600 volt charge controller? Never heard of such a thing?

[Vic]

Half,

You folks are in much better position to know the scuttlebutt about who is working on what.

For me,  google does not seem to know of this OB CC.  OB's site only lists the two we all know about -- the FM 60 & 80.

SSOOooo,  It must be the newish X/Schneider XW MPPT 600 80, unless Aladdin has an inside track.

The XW 600 V CC is about $1300 ea shipped ... they are HUGE,  and weigh about 50 Lbs in the box,  BUT a 49 panel array and racks is no small amount of change,  either.

EDIT:  However,  in googling around more,  50 of those panels are about $35K,  so never mind what I said about the CC cost,  it is in the noise.

Am just gussing,  I know nothing.  Good luck with that big array.   Vic

[Aladdin]

Yes, the Outback charge controller is new and just came out. 80 amps, 600 volts, up to 4800 watts of PV. But we are off the track... how about help with my question? How can I combine three high voltage strings and satisfy NEC 690.16? Is there a MidNite solution that doesn't get too out-of-hand? Can't use solutions with 150V or 300V breakers. Do I have to use three separate 600V fused disconnects?

[Halfcrazy]

Yes, the Outback charge controller is new and just came out. 80 amps, 600 volts, up to 4800 watts of PV. But we are off the track... how about help with my question? How can I combine three high voltage strings and satisfy NEC 690.16? Is there a MidNite solution that doesn't get too out-of-hand? Can't use solutions with 150V or 300V breakers. Do I have to use three separate 600V fused disconnects?

Ok hot off the press I just called Outback and there is no 600 volt controller. They make the 2 FM controllers that go up to 150vdc.

But at your request I will answer the question anyhow use a MNPV combiner with fuses and then our MNPV6 Disco as a 600 volt disconnect.

[Aladdin]

Sorry, that was three Schneider/Xantrex XW-MPPT-80-600 on this project, not Outbacks -- but they ARE 600 volts. Working on too many projects at a time, I guess. (Been working with Outback (yes, 150 volt) on another project. My mind said Xantrex and my fingers typed Outback!).

[Aladdin]

But at your request I will answer the question anyhow use a MNPV combiner with fuses and then our MNPV6 Disco as a 600 volt disconnect.

Halfcrazy, thanks for overlooking my misspelling of "Xantrex" when I typed the letters O-ut-b-a-c-k and for getting back to my question.
My understanding of 690.16 is that the disconnect must de-energize both sides of the series fuses so they are safe to remove and replace without arcing. Placing the disconnect after the combiner only protects the inverter side of the fuse. Seems to me we need to put a separate disconnect on every string to de-energize the PV side of the fuses if the string voltage is over 300V. Unless somebody makes a disconnecting combiner box with breakers rated for 600V. Or if there's a 600VDC disconnect that can switch off several independent strings before the combiner. If voltage is 300 or less we could use the MidNite disconnecting combiner with breakers.

[niel]

i'm confused why you would design around such a high voltage as necessitating several costly 600v controllers (371v oc) when it could be done so much cheaper using lower voltages and midnite does offer a few options ranging from 150v up to 250v? the only motivation i can see for such a high voltage would be because you wish to tap an existing gt system. if i'm wrong about the gt system then i might suggest reworking the design for lower voltages.

to my knowledge there aren't any breakers for 600v and you would need to use fuses. if the breakers were available you'd think you could get them from schneider electric who actually makes the controller in question.

[Vic]

Aladdin,

I know nothing of doing 400 VDC (or so) PV arrays.

But appears that the Midnite PV Combiners will accommodate "Touch Safe" Fuse Holders rated for 600 VDC:

http://www.midnitesolar.com/pdfs/MNTS_USM1.pdf

Re the Disconnect,  Square D (A Schneider company - now) has a Disconnect rated for 600 VDC.

Would seem to me that one disconnect on the output of the Combiner,  plus the TS Fuseholders should meet your needs.  I am a real chicken about HV DC arrays,  and would be a bit timid about touching any part that is not grounded that has 400-ish VDC floating around inside it.  Guess that is why they inveted night-time.

I know nothing,  think that this is HC's or Robin's territory.

niel,  think that this is a "cost is NO object" type system.  I had considered the X/S XW MPPT 600 80 as a CC for my system under construction,  as it would save a LOT of labor,  and wire/giblets,  etc.  BUT,  this CC does not quite have enough current capability for my system,  so two would have been requierd.  THat,  plus the need to BUY two additional thingies,  and string them into the system (the SCP,  and Firmware Implanter "Tool"),  that was the real deal breaker.  ...  I dunno WHY a high-end manufacturer requires all of these doo-dads.  Why not just design the product with a real front panel and display,  and put the ingelligence INTO the CC where it belongs.  This flaw is a deal killer for stand-alone apps.  ...   Brain-Dead!!

Good Luck Al  with the BIG new system.  Vic

[Aladdin]

Yep, I was trying see what I could do to reduce the number of strings, wire costs, and devices but it looks like a bad plan at over 300 volts because of a bunch of specialized fuse/combiners/disconnects required to do it proper. Looks like it makes more sense to go back to 12 strings of 4 modules each, two arrays (one of 7 and one of 5 strings) and two Midnite Classic 250s. Puts my temperature corrected string VOC at just under 250 volts. The MNPV6-250 Disco disconnecting combiners can take up to three of these strings each so the way my arrays lay out, I'll still need 5 of those (three for the south facing array and two for the west facing array). Can you really put 6300 watts of PV into one Midnite Classic 250? (One of my arrays is 7 strings, 49.5 ISC, 244 temp corrected VOC).

[Vic]

Aladdin,

NO,  you are asking the CL 250 to put out almost twice the amount of its rated output current current:

http://www.midnitesolar.com/images/classicFrontPage/graphs.php

About 43 A MAX at 180 V nominal string voltage -- about 3700 watts MAX nominal is the MAX I see from the chart.  And it is not good to ask the CC to run at/near its MAX ratings for hour,  after hour (IMHO).  So,  wyou will need more CCs.  The X/S(chneider)  XW MPPT 600 80  ( wonder if they could have come up with an even-longer part number??),  is rated at 4800 watts max,  and you were looking at three of those.

Expect you will get some sage advice from HC or boB on the max sustained power available from the CL 200 & 250.  For my new system,  had planned to try to run the CL 150 very near its MAX,  but was counciled to perhaps not be THAT aggressive in my demands.

EDIT:  This is that thread.  Post #8 from boB,  states that I am basically being too aggressive:
http://midnitesolar.com/smf_forum/index.php?topic=252.0

Think that there is another post made,  that I cannot yet see,  so some this may be a bit redundant. VB

Good Luck with the system design,  Vic

[Aladdin]

Vic: I appreciated your interpreting that chart as to the maximum PV wattage for the Classic 250. I never could make much sense out of those three Power Graphs and how to relate them to the PV source. Other manufacturer just state it directly, the max PV wattage for various battery voltages. The Classic 250 label (in the installation manual) says "Max PV Operating Current = 62A", "Max PV Short Circuit Current = 62A" and "Max PV VOC = 250 Volts + Battery Voltage" whatever " + Battery Voltage" means. How are those "Current" values useful if they don't apply to sizing of the PV? So you're saying the graph says my maximum PV input is about 3700 watts and I should keep it to some percentage less -- like 80% or 90% ... or ?

[Vic]

Aladdin,

First,  I am no expert on this,  BUt reading the chart,  the 43A is what I read,  for 180 volt strings.

Regarding the Classic 250 label stating 62A,  think that this for the ETL rating agency.  They need to see something.  It is my guess that this is the Absolute Maximum current one would ever see from this CC.  It may be very near a Fault current or similar.

Have you tried to run your strings through the Midnite Classic Simulator?
Should be here:
http://www.midnitesolar.com/classic/classicCP.php

Some may feel that it is a bit tedious,  but it should give fairly accurate answers.  I have not run it for your array.

The MN Tech folks must be very busy,  as they should have something to say about just where the comfortable limit is for this CC.

The power/current ratings for CCs can be a bit of a sensitive point,  as the NUMBERS are always compared twix CCs,  and they are a in a competitive field.  Almost every company wants to beat the competition by at least a biy.  Whatta I know?

More later,  Have Fun,  Vic

[Robin]

Max power for the Classic 250 is somewhere between 3000 and 3500 watts depending on your system configuration. I just did a quick calculation. 62 amps times 48 volts is about 3000 watts. You will actually be charging at about 57 volts though. That would be about 3500 watts. The charge controller may be tapering off by the time it reaches 57 volts though. I would not put more than 3000 watts on the Classic 250 myself. It will just run hot. That is never a good idea to run the controller flat out at its maximun day after day. The Schneider 600V controller requires a special set of circumstances to justify its use for sure. IT is the only 600V controller out there at the moment though, so if you need it, go for it.
Remember that by using our power graphs, you will be able to see the difference in max output power based on PV voltage and battery voltage. Essentually, the lower, the more power.

[Vic]

Hi Robin,

Thanks for the guidance.   Keeping the electronics and batteries COOL is a good thing.  Have A/C in the power room,  here,  and it takes priority over the A/C in the dwelling.  Altho,  for the new system/location,  still do not quite have the new arrays on the roof,  so not enuf power to run A/C,  yet.

Vic