off grid setup questions related to grounding and awg

[arnold_ky]

Does anyone have recommendations on a 6amp breaker for the AC side?

[Mike90250]

Many times, an RV uses the chassis as a "ground" and "- battery return". Which is sort of OK when you just have a couple 10 w lights. But if you start putting any power currents through the poor electrical connections in the chassis, with all the rubber buffers and isolators, you get problems. So you always have to run hard wires for all your added on stuff + & -.

[claydbal]

a good read here. so, how would all this grounding, or not grounding, or floating be accomplished on a rv? which way would be better?
thanks

[sensij]

The DC side. Being under 50 volts there is no requirement to ground the system. By SYSTEM I mean bonding one of the circuits conductors like the Negative Battery to ground. Chassis either way require Bonding. Look at the two methods. One is FLOATING where you see both polarities of the battery with fuses, and the Grounded System has the Negative Battery Polarity bonded to ground. See that?

Floating systems are safer and more reliable, but cost more to implement because you have to have over current protection on both polarities, where as Ground Systems only require one polarity with over current protection. But there is a CATCH you will need to check. With an Ohm Meter and with the Inverter and Charge Controller in your hands disconnected from everything, measure between the Negative Battery Input Terminal and the Chassis Ground Terminal for continuity. If you see Continiuty you have no choice other than a Grounded System. Manufactures are notorious for doing that.

or just read the charge controller manual. Page 10 clearly states all of the negatives are connected, and that DC grounding is required. It also indicates that positive ground models of the charge controller exist, so if you do Sunking's test and find no continuity on negative, if you check for continuity between the solar + and the battery + you will probably find it there.

[Sunking]

Sunking, sorry I missed that. On the "Personally I would not ground the system.", are you referring to just the DC side (controller, inverter, and panels) and is the reason cost, safety or something else.

Thanks.

The DC side. Being under 50 volts there is no requirement to ground the system. By SYSTEM I mean bonding one of the circuits conductors like the Negative Battery to ground. Chassis either way require Bonding. Look at the two methods. One is FLOATING where you see both polarities of the battery with fuses, and the Grounded System has the Negative Battery Polarity bonded to ground. See that?

Floating systems are safer and more reliable, but cost more to implement because you have to have over current protection on both polarities, where as Ground Systems only require one polarity with over current protection. But there is a CATCH you will need to check. With an Ohm Meter and with the Inverter and Charge Controller in your hands disconnected from everything, measure between the Negative Battery Input Terminal and the Chassis Ground Terminal for continuity. If you see Continiuty you have no choice other than a Grounded System. Manufactures are notorious for doing that.

[arnold_ky]

Sunking, sorry I missed that. On the "Personally I would not ground the system.", are you referring to just the DC side (controller, inverter, and panels) and is the reason cost, safety or something else.

Thanks.

[Sunking]

I see what you are saying with the battery cables. I will go with the terminal fuses.

As far as not doing this setup, was that do to the size of the invertor or the dc breaker box?


Also on the ground. I read quite a few places online where you should terminate the dc and ac grounds to the same grounding rod with a separate wire for each, but seems to be hard to find a definite answer.


Here is the updated drawing.

Arnold I drew that up for you a couple of pages ago. Both AC and Dc must share a common ground. Personally I would not ground the system.

[arnold_ky]

Thanks sensij. Definitely appreciate all the help so far. I will get some pictures once I get back out there.

[sensij]

Yes, one ground rod. If you have more than one, they should probably be bonded together anyway.

[arnold_ky]

Thanks Amy. That picture helps a lot. When you show the earth ground coming from the big baby box and the ground coming out of the AC box, can they be going to the same grounding rod?

[Amy@altE]

grounding panels

You need to get a grounding lug like a Lay-in-Lug or Grounding Split bolt to ground the frames. There is likely a hole in the frame to install it, look for the ground symbol.

[Amy@altE]

corrected schematic

2PV par BBB SS300_bonded.pdf Nice catch, remind me not to draw schematics with only 1 cup of coffee. Bonded negative to ground in Big Baby Box.

[arnold_ky]

The solar panels are from Renogy. They don't have a ground as far as I can tell. They came with there own connectors, but nothing related to the ground.

[sensij]

[ATTACH]5231[/ATTACH] Not sure if this worked. I threw together a schematic for you.

Amy

Your drawing shows EGC's, but not the GEC. Per Morningstar (step 9 on page 10 of the manual), the DC voltage must be ground referenced.

[Amy@altE]

Schematic attached

2PV par BBB SS300.pdf Not sure if this worked. I threw together a schematic for you.

Amy