Question about breaker polarity wiring - Greatest power potential

[kauaisolarman]

thanks vic

so basically if the panels have a series fuse rating of 15A then a 15A breaker should be used in the combiner box to combine any series/individual panels together.

[Vic]

Hi kauaisolarman,

YES,  you are correct,  you can just use the Max rating stated on the PM module sticker,  on the back of each PV,  and it is usually on the Data Sheet as well.

Long ago,  when the Max Fuse/breaker rating was less often stated,  one would multiply the Isc rating of the PV by 1.56 (this value is 1.25  1.25),  and then round up to the next standard breaker size.

These days,  the max fuse sizes are usually standard breaker sizes,  and most of us usually just use that breaker rating as stated by the PV manufacturer.

Have Fun,   Vic

[CDN-VT]

Only the CBI din rail breakers are polarity sensitive. They have a + emblem on then and that is the side with the greatest potential.

This is easy on the PV side. The PV is the potential so the + emblem goes towards the PV panel.

On the battery side it is not so easy. Common sense tells us the charge controller is the source so it is the potential. But out research shows the real issue is when a charge controller fails it shorts thus the breaker is working off the battery at that point. So we want the + emblem to point towards the battery not the charge controller.

Thats How I took all of this DC breaker stuff, Since 2015NEC  regs , all must be marked +/ - so most know the line or load . LINE is the greater power / AMPS !! as I read it .

VT

[CDN-VT]

thanks vic

so basically if the panels have a series fuse rating of 15A then a 15A breaker should be used in the combiner box to combine any series/individual panels together.

Adding series amps is NOT the way , VOLTAGE Yes . SO above is not correct !!
read this and see ,copy of  from another forum :


SO Rules first !!
2 stings of same value , No need for any breakers ( not wise due to adding or checking a string against another) , Three strings , then the rules kick in due to back feeding of two OR more strings into one that is the MAJOR .

Kid (nice girl & boys ) wack a ball & it hits a roof , but your panels are in the way , crack & a short between cells length so the (im picking on yours !! 36 cell) gets shorted to 8cells but are fused so all power is going from 2 strings into one1 shorted string @ 8 cell broken & it starts to overheat on one panel .

YOUR imp is 8.xx (never see that in TX ) but your breaker is 15 amps
Series adds voltage / per panel , but AMPS are the same !!!
SO now we have 2 series strings feeding a shorted panel 16 Amps , went the max currant out of each string is 8,xx (in a perfect world) times 2 , so just under (losses) 15 amps , breaker holds & roof is on fire !!


OCB's /Breakers / Fuses/ Cut-outs are ONLY to protect the WIRE , NOT the appliance or supply ..



VT

My panels are 8amp max in a string of 2 or 3 on different systems , my breakers are 10A 150Vdc on each string .

[Vic]

thanks vic

so basically if the panels have a series fuse rating of 15A then a 15A breaker should be used in the combiner box to combine any series/individual panels together.

Adding series amps is NOT the way , VOLTAGE Yes . SO above is not correct !!
read this and see :
SO Rules first !!
2 stings of same value , No need for any breakers ( not wise due to adding or checking a string against another) , Three strings , then the rules kick in due to back feeding of two OR more strings into one that is the MAJOR .

Kid (nice girl & boys ) wack a ball & it hits a roof , but your panels are in the way , crack & a short between cells length so the (im picking on yours !! 36 cell) gets shorted to 8cells but are fused so all power is going from 2 strings into one1 shorted string @ 8 cell broken & it starts to overheat on one panel .

YOUR imp is 8.xx (never see that in TX ) but your breaker is 15 amps
Series adds voltage / per panel , but AMPS are the same !!!
SO now we have 2 series strings feeding a shorted panel 16 Amps , went the max currant out of each string is 8,xx (in a perfect world) times 2 , so just under (losses) 15 amps , breaker holds & roof is on fire !!


OCB's /Breakers / Fuses/ Cut-outs are ONLY to protect the WIRE , NOT the appliance or supply ..

I know many ways to read that NEC2015 code book & the outcome can be taken in a few ways .
I too have read a line or two & it can be taken a few different ways.
I myself have been caught up on the "Wording" with Solar Installs as has many other .
That Code book is written to confuse I Swear.
When the Solar NEC courses were put on buy a few Suppliers , on every course , i heard the strangest questions from the folks taking the course's . Between the main suppliers putting on the course John & Mike (didn't learn the Sir names) to get back to us ..

Learn save first !

VT

OK,  there are probably some semantics involved in what kauaisolarman said ...

There have been several ways of stating the Rating of the Fuse to use on PV strings;

Early on,  the max fuse rating was frequently not specified,  and the 1.56 X Isc,  with rounding was used.

Some manufacturers seemed to use "Series Fuse Rating",  or similar.  The Sanyo HIT 190s have used this.  See Spec sheet:
http://pdf.wholesalesolar.com/module%20pdf%20folder/Sanyo190BA3.pdf?_ga=1.235928966.685482414.1344465168

Believe that this term of Series Fuse Rating that Kauai..  used came directly from this reference.  The Series Fuse Rating for the Sanyo HITs IS 15 A.  This 15 A rating is far above 1.56 X Isc for that PV.

Then there were several terms,  like "Maximum Fuse Rating",  or similar,  and now,  is the fairly common reference to Maximum Reverse Current.

Believe that we are all on the same page regarding when fuses/breakers & an official Combiner are REQUIRED,  verses a convenient and inexpensive feature of having breakers when not absolutely REQUIRED.

FWIW,   Vic

[TomW]

Back when the air and water were clean ans sex was "dirty" and dinosaurs roamed The Earth we were taught that polarity was based on "most positive [or negative] potential".

Not sure t applies to DC stuff as "most positive" will be changing based on the system status. Charging, discharging or static.

Just in case it was  not confusing enough.

Most of these guys are more current than I am so do NOT take my advice as gospel.

Tom

[Vic]

thanks vic

so basically if the panels have a series fuse rating of 15A then a 15A breaker should be used in the combiner box to combine any series/individual panels together.

Adding series amps is NOT the way , VOLTAGE Yes . SO above is not correct !!
read this and see ,copy of  from another forum :


SO Rules first !!
2 stings of same value , No need for any breakers ( not wise due to adding or checking a string against another) , Three strings , then the rules kick in due to back feeding of two OR more strings into one that is the MAJOR .

Kid (nice girl & boys ) wack a ball & it hits a roof , but your panels are in the way , crack & a short between cells length so the (im picking on yours !! 36 cell) gets shorted to 8cells but are fused so all power is going from 2 strings into one1 shorted string @ 8 cell broken & it starts to overheat on one panel .

YOUR imp is 8.xx (never see that in TX ) but your breaker is 15 amps
Series adds voltage / per panel , but AMPS are the same !!!
SO now we have 2 series strings feeding a shorted panel 16 Amps , went the max currant out of each string is 8,xx (in a perfect world) times 2 , so just under (losses) 15 amps , breaker holds & roof is on fire !!


OCB's /Breakers / Fuses/ Cut-outs are ONLY to protect the WIRE , NOT the appliance or supply .

VT

My panels are 8amp max in a string of 2 or 3 on different systems , my breakers are 10A 150Vdc on each string .

Not quite certain just how to read some of the above ...

kauaisolarman's HIT 190 PVs have an Isc rating of 3.75 A,  and a stated Maximum Series Fuse rating of 15 A.

As I read it,  a 15 A DC breaker would be safe,  and the minimum size would be 6 A (3.75 X 1.56, and rounded up).  MNEPV breakers are available in a 6 A rating,  and that size breaker should not be subject to nuisance tripping.

SO,  IMO,  Sanyo is saying that  15 amp DC Combiner breakers are safe,  but breakers between 6 and 15 amps would be safe and should work well.

But,  that's just my take.    Vic