Midnite Baby Box as a disconnect

[Surfpath]

Hi,
I am helping a friend install six 250 watt (30v) grid tied panels in one string, using a Midnite classic 250 (I am about to order).

Panel Specs: VMP 31.32, VOC 37.2, IMP 7.98, ISC 8.45

NEC does not apply to this installation

However, I believe it'd be important for the array to have a 'disconnect'.  I am thinking of recommending a Baby Box with one appropriately sized breaker.  #10 AWG will be used in the wire run from the panels.

Sounds OK to use the Baby box in this application??  Which Midnite breaker would be best.
Thanks!

Oh, and is there room to mount a Midnite 300DC SPD on the Baby?  That would be neat.

[Doug]

Hi Surfpath,

The Baby Box is a good general use box and should be quite adequate for this.
MNEPV DinRail breakers work with this box. This link is to the product page and shows some breaker choices. http://www.midnitesolar.com/productPhoto.php?product_ID=79&productCatName=Small Breaker Boxes&productCat_ID=10&sortOrder=1&act=pc
The SPD is not intended to be used with this box. There is a flush mount kit for the MNSPD or you could use a MNPV3 Combiner as a disconnect if used with breakers (Never fuses for a disconnect!). The MNSPD can mount on a MNPV3 and you could add more strings later if you choose. http://www.midnitesolar.com/productPhoto.php?product_ID=78&productCatName=Combiners&productCat_ID=9&sortOrder=4&act=pc

Doug

[Surfpath]

Thanks.  Perhaps they will mount the SPD stand alone (or get the MNPV3 box like you suggest)

According to the Midnite string calculator, the combined voltage from these six 30 volt panels will be 223volts (and 7.98 amps)

My friend lives in a warm climate: 20 degree Centigrade historical minimums.

Which breaker?  Would it be the 60 amp 300 VDC MNEDC60-300?

http://www.midnitesolar.com/productPhoto.php?product_ID=271&productCatName=Breakers&productCat_ID=16&sortOrder=16&act=p

[Surfpath]

One last check.  The Big Baby Box seems to be able to handle one of the above 300v breakers and an SPD. Not so?

I think this user installed one like this in his RV...
http://forum.solar-electric.com/showthread.php?25043-Wiring-the-SPD

[Doug]

The breaker in your link is a panel mount breaker. For the Baby or Big Baby you will want DinRail breakers such as the MNEPV 300 http://www.midnitesolar.com/productPhoto.php?product_ID=217&productCatName=Breakers&productCat_ID=16&sortOrder=20&act=pc This breaker takes up two positions on the rail. I will defer to Ryan as to whether you can use a MNSPD with a Big Baby. I suspect the wiring would be tight. Ryan?

Doug

[Halfcrazy]

Doug, All
Yeah you can "Technically" add the SPD there. it really depends on the guy wiring it. if he has enough room and adequate connection points I see no reason you couldn't but again I am not there wiring it so use your own judgment.

[Surfpath]

OK.  There will be nothing else in the Big Baby, but the one breaker and the SPD. Hopefully it will be OK.

I will try to pass this by the local guy here who will likely wire it.  Thankfully Midnite has good drawings and documentation so that he can approximate the spacing.
Thanks for the feedback, Doug and Ryan.
SP

[Surfpath]

Doug,
Thanks for setting me straight on the din rail type breaker.

With the current coming from the string being 7.98 and VOC about 223, I presume I need to get the MNEPV7-300??

Wait...I also see that there is a MidNite Solar MNEPV10 10A 300VDC Din Rail Mount Breaker.  This seems to be the next "size up" from the proposed array's ISC.

I'd guess this would be the right breaker.

[Halfcrazy]

There are 2 ways to size that breaker:

A- take ISC 7.98 amps and multiply by 1.25 = 9.975 and round up to the next breaker (10 amps)

B- look at the data sheet for the module it will have a MAX series fuse rating (Probably 15 amps) so you can use that size breaker as the Maximum size