Question on wiring for an RV with Solar

[Ozz]

Hi,
I have the Baby box breaker box, three panels, 3 wires coming from the roof.
How do I wire in the protection device? (Midnight solar)
One wire; green/ground and Neutral? to frame ground, and one wire; line, to hot on breaker?
Instructions are geared to power grid applications as far as I could see.
Thanks!
Ozz

[Vic]

Hi Ozz,

OK,  so you are making your own Combiner Box,  using the MN Baby Box  (I would guess).

So,  you have three PVs on an RV,  so would guess that you have a 12 V system (?).   If the three PVs are in parallel,  each needs a circuit breaker or fuse,  and these protective devices would normally be in a Combiner.  Here is the manual for a small-ish MidNite combiner series,  page 6 has wiring diagrams:
http://www.midnitesolar.com/pdfs/MNPV2-3-4-6_manual.pdf

The advantage of using a formal Combiner for three PVs (or strings) in parallel,  is that it will have a busbar for the combined output to the CC,  and a Negative bus for the negative wires from each PV.  The Baby Box is a nice little box,  but it is quite small inside,  and there is not a  lot of room for these busses.  You could probably get by with using Wire Nuts to combine the output side of each breaker,  and also for the negative wires from the PVs ....    although,  you might have a single string of three PVs ...

A bit more info on your system configuration would help,  so less incorrect guessing would be done by folks like me.

What is the battery voltage?  (looks like it is still 12V)
How many strings of PVs will this system have? (dgd had advised on three PVs in parallel  ...  still the case?)
Do you have a separate box for the circuit breakers for the input and output of the Charge Controller  (CC)?
Which CC are you using?

EDIT:  OH,   had thought that you were asking about the wiring of circuit breakers (a circuit Protective device).   Since this is in the SPD Topic,  perhaps you are asking about the  wiring of the SPD (?).   Still the Baby Box is quite petite.  Is the ONLY function of this Baby Box for an SPD??

Your CC should really have a breaker on its input,  its output,  and one breaker for each PV "string" (even if it is only a string of one PV) ...   the baby box cannot provide all of these functions,  let alone accommodating the SPD ...   really do need more info on the layout of your power system ...

On an RV,  the PVs are not a great lightning exposure,  IMO.   But  the RV frame is really your only ground.

And so on.  Thanks!    Vic

[Ozz]

Hi,
Thanks for the great info on your reply. Sorry, I should have given more info.
3 Solar World 315 Mono Panels with MC4 Latching Cables, wired with  to one lead coming down the Big Baby Box with 1 40 amp breaker, Midnight Solar Classic 96 amp MPPT Controller (100 amp breaker from converter to Batteries) and 6each 6 volt Trojan T-125 240 AH batteries and a Magnum MS 2012 Inverter.
I mis-spoke...(Typed)  that I had 3 wires coming down. :0
Yes, I was just asking about wiring the SPD, I have a Surge protection device on my line voltage, a 2 pole Intermatic  IG1240RC3.
Also, I am not getting email notification of posts on my thread, I will go and insure I have that mode checked.
Thanks again
Ozz

[Vic]

Hi Ozz,

Sorry for the reply delay and for the added info.

So,  a couple more questions;

1.  Are your PVs wired in Parallel?  If so,  do you have a Fuse or breaker for each string (this would probably have to be on the roof   ...  ?).

2. OR are the three PVs wired in series?  This would NOT be a good configuration for these PVs,  especially on a 12 V system,  as well as for Voc considerations - IMO.

3. Is the Baby Box ONLY for the SPD?

4.  Where are the breakers for the Classic located in your plan?    And be certain to have a large breaker,   and cables for the Inverter wiring.

You probably want to stay with 12 V,  as this is an RV,  BUT having three strings of batteries can be a real issue with string balance,  and keeping the strings balanced as the batteries age (differently).   Al Clamp-On DC Ammeter will be essential for you to monitor balance of string currents.   There are fairly good,  and inexpensive DC CO meters available now.

Glad that you have chosen the Classic CC.  More later,  thanks for any added detail on your system ...  have you used the Classic String Sizing Tool,  yet(?):
http://www.midnitesolar.com/sizingTool/displaySizing.php

...   FWIW - Vic

[Vic]

Hi Ozz,  you appear to be on-line here,  now,  so will add this as a Reply;

Here is some info on wiring parallel strings of batteries:
http://www.smartgauge.co.uk/batt_con.html

Good Luck,    Vic

[Ozz]

Hi Vic,
The panels are wired Parallel
Three panels connected together with PV-AZB4 and PV-AZS4 Latching branch connectors  and extender cables with MC4 Extension cables . 2 wires coming down.
As I stated, I have a 40 amp breaker for the one line coming into the Box.
I have my batteries wired correctly.

I have all this covered, Dan with NAWS designed my system, I just want to know about wiring the SPD on the DC Breaker box.
Thanks, Ozz

[Vic]

Ozz,

Will poke around on the wind-sun Forum ...

BUT,  you simply MUST use fuses or breakers for each PV  where they are combined.  Without these correctly rated (for current) protective devices,   there is a risk of FIRE   ...  perhaps those connecting devices have built-in,  correctly-rated fuses  (but,  guessing,  not too likely).

Sorry to make so many guesses on this,  too many of which were incorrect,   but felt like was starting in the middle of some thing that was not too well defined.  And your question has been sitting,  unanswered,  for a couple of days.

Good Luck,    Vic

[Ozz]

I guess I am not going to get my original and continuing question answered.

[Vic]

Hi Ozz,

Just came from the W-S Forum ...   read 28 of your posts ...

OK,  so you have the MN Big Baby Box -- this is larger than the Baby Box,  by two additional breaker spaces inside a larger box.  Larger is often better.

You appear to have NO Combiner box for the three parallel PVs.  You will want/need one!  The risk of fire from having simple parallel strings without a combiner could be larger than your risk of fire from lightning ...  impossible to tell.

You are going to a lot of trouble to try to get info on how to correctly install your PV Solar power system.  Using a combiner is part of this correct installation.

Regarding your perennial question on how to wire the SPD,  I am not the best person to answer,  it is not even clear the model number of this SPD,  but it may te the 115 V(AC) model.   These questions get into GROUNDING.   Grounding is very,  very specific to the exact details of the structure and the wiring.  Personally,  I would run the PV frame grounds separately,  in its own conduit,  to the RV frame.   Would run the SPD green wire to the frame.   How this wire relates to the bonding of the CC,  inverter and battery depends on how these cables are run.

How is that for an ambiguous answer ...  it all depends on things that depend on the exactness of other things,  and so on.   FWIW,  YMMV,  All the Best!   Vic

[Ozz]

Thanks Vic,
I don't think NAWS would sell me the system they sold me and have it wrong. I bought the best, there were no short-cuts for my system,  Dan Hanselman  drew up the schematic, put the list together according to options we discussed and I am wiring it accordingly.
I am about 90% on what I think the wiring for the SPD, but wanted to double check with Midnite Solar

All my questions and research on the NAWS Forum was prior to me buying the system and conferencing with Dan. The latching connectors combine the PV panels, they design them that way and sell hundreds.. maybe thousands of them.
You are a pro at this, so I am not saying otherwise. I own and operate a HVAC business and rely on my suppliers and factory reps for correct information. If I have a Fire, or short, or problems, I will send a letter to Dan
Thanks again for your help.
Ozz

[Vic]

OK,  Fine Ozz,

[Although,  have never seen those MC-4 Paralleling connectors at Wind-Sun ...  and would be surprised if they had them ....  just looked again,  did not see them]

Beating this poor old horse a bit more ...   When running two PVs in parallel,  no circuit breakers or fuses are required,  as a short circuit in one PV  could only have the current of one other PV being forced into it.   BUT,  with three or more PVs (or strings of PVs) in parallel,  there could be two,  or more PVs forcing current into one shorted PV,  and that is what could cause the fire.

Here is a nice Combiner,  that you will not be buying ...  it can accommodate up to 6 strings of PVs,  allowing you to perhaps expand the system later:
http://www.solar-electric.com/installation-parts-and-equipment/midnite/pvarco.html

There is a three PV combiner,  also,  for a little bit le$$ cash.

No need to reply,  believe that we are each done on the Combiner thing,  will let others address this or the SPD.   Have fun in your travels.      Non-professional Vic.

[Ozz]

Here are examples of the latching connectors:

http://www.solar-electric.com/what-are-mc-cables-connectors.html

http://www.solar-electric.com/installation-parts-and-equipment/wiring-cables-and-connectors/hardware-wire/incaforsoelp.html

[Vic]

Hi Ozz,

Have seen these connectors in the past,  just have never seen them on Wind_Sun,  previously.   So thanks for that info.   A surprising that there is no mention of the maximum number of strings that these connectors should be used on,  in  a single system.

FWIW.    Vic

[Ozz]

Yea, that Max number is above my pay-grade They are sweet connectors.

[Halfcrazy]

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...