New to solar. questions on fuses, breakers, and grounding

[njp6x6]

As I stated in the title I am new to solar energy systems. I have several questions regarding circuit protections. I will be living out of small travel trailer for the summer and as of now I have a single 100 watt panel, a Xantrex C40 (40 amp) charge controller, and a 1000 watt power inverter. I don't anticipate every going over 500 watts of panels. This will be a 12 volt system. Most videos i have watched don't talk about fuses or grounding on small scale systems like this. I planned on placing appropriately sized fuses between the panel and the controller, controller and batteries, and between the batteries and inverter. However, the instructions that came with the charge controller show a ground fault protection breaker and something called a shunt between the controller and the batteries. Is that necessary or do they just have to put that in the instructions because ground fault protection is required by electrical code? ( These breakers cost about 10x more than a fuse) What is the purpose of this shunt and is it necessary? And lastly, do i need to drive a 8 foot long ground rod to ground the panel, controller, and inverter? I am thinking the answer is yes on the grounding question. Thank you in advance for any help

[Raj]

Hi njp6x6,

Most small RV type solar power systems require a chases ground, not a ground rod. Check the literature for your inverter for grounding requirements. 500 watts would be about the max amps that your controller can handle, but the PV panel wattage needs to balanced with the size of the battery bank.

Example: PV is 400 watts divide by 12V (battery voltage) equal 33 amps. So FLA (flooded lead acid) batteries need about a 10 percent charge rate so 33 divided by .1 (10%) = 330 amp hour battery bank at 12 volts. If using AGM batteries you can use a 15% charge rate. In this case 220 amp hour. However battery bank size is really determined by your power use as loads in kilowatt hours. Then size PV accordingly.

PV panels need to be fused if you have more than 2 in parallel. Breakers are better for PV to CC and CC to battery and also battery to inverter because they can be used as switches for maintenance and emergency shutoff.

The shunt is just a resistor that can be used to get a very accurate measurement of battery voltage and amps used.

This enclosure ...http://www.solar-electric.com/instal...nedc-quad.html

With this type breaker ...http://www.solar-electric.com/instal...amodccibr.html

These would work well on a small system. Size your wiring to amperage. Probably AWG #6 in this case and AWG #4 from battery to inverter.

Good luck

Rick

[njp6x6]

Thank you for the information, I have a few more questions. The breakers that you provided the link to are not ground fault protection beakers. The ones you suggested are 12.50 apiece and the ground fault breakers are 89.00 apiece. So my understanding is that you don't think the ground fault breakers are necessary. Is that correct? One thing I should note is that I have built a small shed or "doghouse" that is well ventilated and 4'x4' to house all my components. My reasoning for this is that I expect these components will generate heat and my trailers will already be hot in the summer. Also, where I will be living is on a high plateau with absolutely no trees within a few miles so I think lighting strikes are a very real concern and I will often be traveling for a few days at a time and away from my trailer. I figure by keeping the system away from the trailer, if a lighting strike catches the whole thing on fire, at least it wont take my trailer with it. If I were to ground my components to the frame of my trailer would it then make the it more likely to have a catastrophe on my hands in the event of a direct lighting strike? Like I said in my original post, the reason I am asking about ground fault breakers and the grounding rod is because that what is shown in the CC manual but I assume they have to in order to be meet NEC standards. Also, you suggest using a 4AWG wire from the Battery to the inverter but the inverter calls for a 150 amp slow blow fuse which based upon the ampacity charts I have seen would require a 2/0 wire gauge? I should also point out that I wont be exceeding 200 watts of panels this summer but I would like to size all my breakers and wire so that I can grow to 400 or 500 watts in the future. Thank you for your help here

[Amy@altE]

Ground fault breakers are intended more for buildings than vehicles, you don't need one. You could look at using a Midnite Solar SPD for lightning protection. Although nothing will protect against a direct hit, it is good protection against a nearby hit. http://www.midnitesolar.com/productP...tOrder=1&act=p

[Raj]

The Charge controller you have is capable of handling a lot of power and can be used in a fairly large 24 or 48 volt system in a permanent structure so it will describe the use of ground fault breakers but for a small 12 volt system I wouldn't bother, but it is your choice. Again, for grounding, it is a small system, I would use the chassis. Lightning is looking for a way to ground. Your camper is on rubber tires is it not. I also agree with Amy, that a Midnite SPD would help better than anything else if you are concerned about lightning. Concerning the battery cable, I based the AWG 4 on the inverter. At 1000 watts it would draw about 83 amps. I think a #4 can handle about 105 amps. Use what ever the inverter manual calls for, thats probably best.

Rick

[Sunking]

You could look at using a Midnite Solar SPD for lightning protection. Although nothing will protect against a direct hit, it is good protection against a nearby hit

What? Lightning hit a RV, or nearby strike? Are you joking?.

[Sunking]

OK no ground of any kind is required or needed in your application anywhere. If you buy the right type of charge controller, MPPT, use grid tied panels wired in series, no fuses are needed or required between the panels and controller period.

All you need is 4 fuses installed directly on the battery term post. One pair facing the controller, and one pair facing the Inverter. The fuse sizes depend on Charge Controller Amp Output, and Inverter input current requirement. Size the fuses to 125% of device requirement. Just make sure the wire is rated for the fuse current. That is all you need for maximum protection. Anything else is just a waste of money. DO NOT CONNECT anything to the vehicle chassis.

[SunEagle]

The Charge controller you have is capable of handling a lot of power and can be used in a fairly large 24 or 48 volt system in a permanent structure so it will describe the use of ground fault breakers but for a small 12 volt system I wouldn't bother, but it is your choice. Again, for grounding, it is a small system, I would use the chassis. Lightning is looking for a way to ground. Your camper is on rubber tires is it not. I also agree with Amy, that a Midnite SPD would help better than anything else if you are concerned about lightning. Concerning the battery cable, I based the AWG 4 on the inverter. At 1000 watts it would draw about 83 amps. I think a #4 can handle about 105 amps. Use what ever the inverter manual calls for, thats probably best.

Rick

Just a little data concerning lightning and rubber tires. To get enough insulation between the vehicle and ground to stop the flow of electricity those tires need to much bigger (none currently made big enough) and consist of very high insulating properties.

The reason lightning does not "enter" a vehicle is because it acts like a "cage" and lets the the electrical charge go around the outside (across the tires) to the ground.

[njp6x6]

Thanks a lot everyone! I feel like the fog has almost lifted. In the little diagram above you show fuses on both the positive and the negative. I always thought you only needed fuses or breakers on the positive side? Also, I just want to make sure that even though all the equipment I have, has grounding wire posts, I can just ignore that?

[njp6x6]

One more question, my panel has MC4 (I think that's what they are called) connections wired to the panel and came with a pair of 12 inch pigtails that's plug into them. That wire is aluminum I assume (definitely not copper). Is there any reason not to solder my 6 or 8awg wire to those pigtail? I don't really see how else you would connect it

[Mike90250]

the pigtails are likely tin plated copper strands. Aluminum would be a poor choice of wire for that application. (but I got a set of cheap jumper cables made of copper plate aluminum wire)

[Amy@altE]

Thanks a lot everyone! I feel like the fog has almost lifted. In the little diagram above you show fuses on both the positive and the negative. I always thought you only needed fuses or breakers on the positive side? Also, I just want to make sure that even though all the equipment I have, has grounding wire posts, I can just ignore that?

Sunking is describing an ungrounded system. For ungrounded systems, you need to break both the plus and the minus. Negative grounded systems should not have the minus broken as it is the path to ground.

[njp6x6]

Ok, so I think understand this. A negative ground, such as in a car, actually has a connection from the negative battery terminal to the frame work of the vehicle. So that's why in a car audio system you only need to put a fuse on the positive cable. I hadn't even thought of that until now. I have only been asking about the ground post on the metal case for the CC and inverter which I understand is just to keep current from flowing though the housing. What are you opinions on using 4 of these from Amazon http://www.amazon.com/gp/aw/d/B01765...0XL&ref=plSrch they just seem appealling because they are inline and don't require the 45 dollar breaker housing that Raj suggested at the top of this tread. But is there is so e reason not to use them I won't

[SunEagle]

Ok, so I think understand this. A negative ground, such as in a car, actually has a connection from the negative battery terminal to the frame work of the vehicle. So that's why in a car audio system you only need to put a fuse on the positive cable. I hadn't even thought of that until now. I have only been asking about the ground post on the metal case for the CC and inverter which I understand is just to keep current from flowing though the housing. What are you opinions on using 4 of these from Amazon http://www.amazon.com/gp/aw/d/B01765...0XL&ref=plSrch they just seem appealling because they are inline and don't require the 45 dollar breaker housing that Raj suggested at the top of this tread. But is there is so e reason not to use them I won't

Those fuses are only rated for 12volts DC and used for DC loads so they might not work when the battery is being charged at a higher voltage.

[Sunking]

I have only been asking about the ground post on the metal case for the CC and inverter which I understand is just to keep current from flowing though the housing.

Wrong. If you use that terminal will force current to flow through the chassis. It puts the grounding conductor in parallel with the battery return (negative polarity) conductor. Most charge controllers and cheap automotive Inverters people buy, internally have the Negative Battery circuit bonded to the equipment chassis. . Huge flaw in design that wreaks havoc.

What are you opinions on using 4 of these from Amazon http://www.amazon.com/gp/aw/d/B01765...0XL&ref=plSrch they just seem appealling because they are inline and don't require the 45 dollar breaker housing that Raj suggested at the top of this tread. But is there is so e reason not to use them I won't

Stay far away form them. They are used by Auto Mobile Stereo Installers and very cheaply made. 12 volt only application and use mechanical pressure to connect wiring. Last thing in the world you want to use.

You want a OCPD (over current protection device) that mounts directly on the Battery Term Post. In this type of system the source of power is the battery, not the solar panels. Solar panels are current sources. You can short their output all day long and nothing happens. In fact that is exactly how you test a solar panel known as Isc test. Short a battery out and you have an explosion and vaporized copper wire.

This is why you install the OCPD on the battery post from the wires coming from the Controller instead of on the controller output. If you put the fuses on the controller output, you leave all that wire back to the battery unprotected.

One of the best OCPD I know of for battery systems is made by Blue Sea part numbers 2151 duals, and 5191 single. You would use a pair (2) of the 2151, one on each battery post. Then use 4 MRB fuses