Question on wiring for an RV with Solar

[Vic]

Hi Ozz

OK,  just downloaded the spec sheet for the SW-315s.   They will accept an unusually large Reverse Current -- 25 Amps.

Because the maximum Short Circuit current,  Isc is 9.35 A,  even with the safety factor of 125%,  two PVs forcing current into one other PV  would still be below 25 A.   As long as the connectors and the cables connecting the PVs can accept the 23.3 A max current,  there SHOULD not be a fire hazard.  Believe that those paralleling connectors that you are using have a Max current rating of 22 A,  but that is probably OK.

So,  it appears that I was WRONG about those Siamese connectors being a bad idea ...  at least this is the way that I now read it.

Never mind!  Sorry for distracting you,  and hopefully not others.

Have Fun,   Vic

[Ozz]

Vic,
You are a gentleman and a person of character. You were just trying to help a feller out, no way that could be wrong. None of us have all the answers all the time, I am stumped on a regular basis in my work.
Thanks.
Ozz

[zoneblue]

Ozz. The guys helping you here are experienced, and worth listening to. Your "latching connecters" (multibranch MC4s), are suitable for certain scenarios. And no one is wrong. Always go back to first principles. The rule is, (i believe) this: string fusing is required when Isc * (n-1) > module fuse rating., where n is the number of strings. For the average panel the fuse rating is 15A, and the Isc 8ish, thus 3 or more strings gets a fuse. But thats the general case. Some panels do have greater string fuse ratings, and 3 strings you may get away with out string fusing.

A combiner does have other uses and most folk eventually put one in. However your big baby is kind of an array disconnect, so that should work out fine. Hopefully someone at midnite (Ryan?) can advise on correct use of SPDs in mobile applications. As Vic mentioned disipating surges to the chasis is an attempt to keep said surges away from your gear. MIght help, dunno. But the issue is that lightening is trying to find planet earth, and it appears to me that there is very little you can do to help it on a vehicle that has no earth stake.

OTOH, the SPD will try to prevent high voltage transients from forming.  It does this by shunting the current effectively betweent POS and GRD, which is effectively NEG in this situation (IF your DC system is correctly NEG-GND bonded). MOVs are basically just a resistor whose resistance is initially very high but which radically breaks down on high voltages. See http://en.wikipedia.org/wiki/Varistor

DC GFI might complicate this even some more!

Shore power then complicates it again, as then you have ( or should have)  an earth connection.

[vtmaps]

Well from a safety stand point it would normally be 2. You need to divide the series fuse rating by the short circuit current of the number in parallel to see if it is ok.

Basically the issue is if a single module or string should short out then it can handle say 15 amps all day long no issue. But if we had say 3 strings in series then we may feed it 17-18 amps and then that shorted string catches on fire...

I think you meant 3 strings in "parallel", not "series"   --vtMaps

[Ozz]

Thanks for the additional info, I appreciate it.