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Old 05-22-2016, 08:34 PM   #1
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Ground on Solar panels

I had chosen green 8 gauge cable for grounding my solar panels and now wonder if I have made the correct choice. Thoughts? I used the recommended UV rated solar panel cabling obtained from the solar panel supplier to bring the positive and negative to the fused combiner box and then used 8 gauge marine cable to the MPPT controller and to the batteries.


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Old 05-22-2016, 09:23 PM   #2
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How many watts of panels do you have and what is their voltage? No one can answer your question without that info.


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Old 05-22-2016, 09:48 PM   #3
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You also need the length of cable run. Use a voltage drop calculator such as the one in this link
Voltage Drop Calculator Australia, 12V, 12 volt, metric

General consensus is to use panels in parallel to minimise losses from shading, even minor shading from antenna shadows. But if you have a long wire run you could put some in series, and have a series-parallel arrangement to get higher voltage feeding the MPTT. That helps keep manageable cable sizes with low voltage drop.

As David says, provide more info to get specific advice. Panel and controller specs and cable length.

I'm about to relocate 2 of my panels to reduce shading on them. I cannot emphasize enough how important it is to avoid shading if you want good output. I lower VHF antennas when anchored to avoid shading.
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Old 05-23-2016, 02:19 AM   #4
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Ground on Solar panels

It's not the gauge I'm concerned about but wire colour. Sorry I wasn't clear. Is green the proper colour for ground or is that reserved for bonding wire?

The electrician and the solar panel electrical engineer,were ok with the gauge. 3 panels totalling 435 watts. The cable run is 15' for each panel to the combiner box on the 10 gauge and 30 feet to the batteries with the controller in between.

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Old 05-23-2016, 02:39 AM   #5
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Green is the common usage colour for the negative or ground wire in most things, with black for neg, and red for pos, so I don't think anyone is going to spit the dummy over it if you have used green for the ground. My solar panels don't have a ground actually. They are flexible Uni-Solars, and just come with ready provided cable with pos and neg. Red and black.
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Old 05-23-2016, 06:36 AM   #6
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Jim:


We can check the voltage drop in your wiring if you will give us the panel specs: the Vmpp and the Impp.


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Old 05-23-2016, 07:09 AM   #7
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I think all he is discussing is bonding the solar panel cases.

Green is fine....not sure of the need...haven't read the marine recommendations for solar panel grounding.
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Old 05-23-2016, 07:11 AM   #8
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Jim, just to be clear, we are talking about the THIRD, non-power carrying, safety ground wire that connects to the frame of the panels, right? If that's the case then I think green is the right color and is what's used for typical safety grounds and bonding.
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Old 05-23-2016, 10:56 AM   #9
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Jim, just to be clear, we are talking about the THIRD, non-power carrying, safety ground wire that connects to the frame of the panels, right? If that's the case then I think green is the right color and is what's used for typical safety grounds and bonding.
That's correct Peter, it's the grounding wire, but to follow up on David's request:
VMP: 18.5 volts
IMP: 7.83 amps


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Old 05-23-2016, 11:52 AM   #10
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Jim:


The voltage drop on each #10 from the panel to the "combiner" (I assume that is a junction box) is about a 1/4 volt. The voltage drop from the combiner to the solar controller (which I assume is about 15 feet) is about .45 volt.


So the net voltage to the MPPT controller will be approximately 18.5 -.25-.45 = 17.8 which is fine for the controller and represents a 4% loss to the controller.


The current from the controller to the batteries will be maybe 15% more than the input, because the voltage is lower, so the voltage drop will be about .55 volts. That is significant and I would consider increasing the wire gauge to the batteries. Or you can relocate the controller closer to the batteries.


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Old 05-23-2016, 12:08 PM   #11
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Thanks David. The run between the MPPT to the batteries is about 3' to a buss bar and then 2/0 to the batteries. I got 30' of black and red 8 gauge. Probably 25' was used to the MPPT controller.


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Old 05-23-2016, 02:21 PM   #12
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Three feet from the controller to a 2/0 buss connection should be fine. I like to keep the controller voltage drop to the batteries to a few tenths of a volt or less. Otherwise the batteries will not see the same charging voltage that the controller is putting out. The controller will think that the batteries are full when they are not and will drop to float.
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Old 05-23-2016, 10:04 PM   #13
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I called Morning Star about grounding the casing of the controller. They said in a boat system it was not necessary. The negative bus is tied to the ground/bonding bus.
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Old 05-24-2016, 12:38 AM   #14
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Quote:
Originally Posted by JDCAVE View Post
It's not the gauge I'm concerned about but wire colour. Sorry I wasn't clear. Is green the proper colour for ground or is that reserved for bonding wire?

The electrician and the solar panel electrical engineer,were ok with the gauge. 3 panels totalling 435 watts. The cable run is 15' for each panel to the combiner box on the 10 gauge and 30 feet to the batteries with the controller in between.
Hello Jim.

I would be concerned about the gauge more than the color. I have 445 watts on a regular Morningstar30 solar controller.

I found when the amps in topped 20 my 8 gauge wires were getting warm -- too warm. I called Morningstar asking how large a wire I could fit into the slots. They said 6 gauge.

Side Note: It was 5' from the buss bars to the controller and 6' to the batteries. 8 Gauge was not sufficient.

I upgraded and now the wires are the same temperature.

Like you I have 10 gauge to a buss bar. From there to the controller is now 6 gauge. And 6 gauge out to the batteries. I would definitely upgrade. Theoretically I could be pushing 27 amps down those wires. Bigger is better.
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Old 05-24-2016, 01:48 AM   #15
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Hello Jim.



I would be concerned about the gauge more than the color. I have 445 watts on a regular Morningstar30 solar controller.



I found when the amps in topped 20 my 8 gauge wires were getting warm -- too warm. I called Morningstar asking how large a wire I could fit into the slots. They said 6 gauge.



Side Note: It was 5' from the buss bars to the controller and 6' to the batteries. 8 Gauge was not sufficient.



I upgraded and now the wires are the same temperature.



Like you I have 10 gauge to a buss bar. From there to the controller is now 6 gauge. And 6 gauge out to the batteries. I would definitely upgrade. Theoretically I could be pushing 27 amps down those wires. Bigger is better.

Just to clarify,10 gauge from each panel to the combiner box, 8 gauge to the controller, <1' of 8 gauge to 35 amp breaker and another 2' to a buss bar and 2/0 the rest of the way to the batteries. I'm leaving it as it is for now. The electrician had difficulty working with 8 gauge inside the MPPT box. I think putting 6 gauge in there would have been near impossible. I could run 6 gauge from the breaker to the buss bar.


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Old 05-24-2016, 01:59 AM   #16
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Where are you grounding to ???
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Old 05-24-2016, 08:28 AM   #17
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Jim, did you consider wiring the panels in series rather than parallel? I doubt tearing your system apart and changing it is high on your priority list, but it's worth keep in the back of your mind. In series you get higher voltage and lower current, so can use smaller wires and have less loss. And it requires a charge controller cable of stepping down the voltage, but most MPPT controllers can already do that as part of the MPPT function.
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Old 05-24-2016, 09:44 AM   #18
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Where are you grounding to ???
Not sure where the electrician attached the ground, I'll have to check, but all cabling went into the engine room.
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Jim, did you consider wiring the panels in series rather than parallel? I doubt tearing your system apart and changing it is high on your priority list, but it's worth keep in the back of your mind. In series you get higher voltage and lower current, so can use smaller wires and have less loss. And it requires a charge controller cable of stepping down the voltage, but most MPPT controllers can already do that as part of the MPPT function.
That is still an option, as I think the combiner box allows for that. I still need to connect the panels to the combiner box. However, the electrical engineer at the Canadian Renewable energy, said there is an issue in very cold weather condition as the voltage rises and can exceed the rated maximum.

I'm going back to CRE and will discuss this further.


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Old 05-24-2016, 04:38 PM   #19
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Quote:
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Just to clarify,10 gauge from each panel to the combiner box, 8 gauge to the controller, <1' of 8 gauge to 35 amp breaker and another 2' to a buss bar and 2/0 the rest of the way to the batteries. I'm leaving it as it is for now. The electrician had difficulty working with 8 gauge inside the MPPT box. I think putting 6 gauge in there would have been near impossible. I could run 6 gauge from the breaker to the buss bar.
Thanks Jim. I was concerned. Your wire runs are shorter than mine. And you're right, shoving the 6 gauge in those slots was NOT EASY. Separating the positive and ground wires was difficult especially when one or two strands wouldn't go in properly. Argh.

Why on earth Morningstar doesn't have slots for terminal rings I do not know. It is a design flaw in my view. Then again, I prefer terminal rings. They seem more secure.

I checked with Morningstar to see how big a wire would fit in the ProStar-30. Technical support stated 6 gauge so that is what I used.

Your runs are short. And you can always test the wires. I would definitely monitor the temps of the wires as they exit the controller. For me I was seeing much warmer on the way out versus in from the solar panels with 8 gauge.

With 6 gauge the heat issue is gone.

Being in the cold puts a whole 'nother spin on the problem. Morningstar and Canadian Renewable Energy will have a solution. Good luck.
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Old 05-24-2016, 05:14 PM   #20
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The rated max voltage from the panels is at 70F I think, and max sun light. The colder they get, the higher the voltage. I haven't done the calculations in a while, but as I recall you adjust for the lowest temp you think you will even encounter (not average, but lowest), then provide a safety margin like 10-15%. NEC in the US spells it all out, and I expect the CN rules are the same or very close.

At our place in VT I designed for either -20F or maybe even -40F. -20F definitely happens, even during sun light. -40F during sun light would be very, very rare.

In your case you have two mitigating factors. First, in the PNW the winter temps are actually quite mild. Some compensation will be required, but nothing like inland and at elevations. Also, I presume your panels are flat on the roof? In the winter the sun will be very low on the horizon even at mid day. Probably no more than 20 deg in your area. So there is a huge angle between the panels and sun significantly reducing output. In contrast, my panels in Vermont get tilted to be almost completely vertical in the winter.

So I'd run the calculations, but be sure to use realistic temps, and you can probably de-rate for light incident angle.

OK, rather than be lazy I went and checked. I used 125% of the panel's VOC as the design max. So you can use that to figure out how many panels you can wire in series before you exceed the input voltage of the charge controller. My charge controller's limit is 150V and I ended up with 4 panels in series for a 125% VOC of 110V. Electrically, 5 panels would have been possible, but I didn't have physical space to mount groups of 5, just groups of 4.
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