Earth Grounding Questions (and many more) for a small off-grid system.

[Sunking]

I also notice that Jeff's article did not differentiate between GEL and ATM sealed batteries for this use. Any idea why?

No not really. If I had to guess just an oversight, or he did not want to get into that for fear from battery manufacture advertisers. When you are writing for a sponsored media, you have to be careful about what you say (censor) as to not upset your sponsors. Or a remote chance he is not aware of Gel battery limitations. In 2008 when that was written, there were not a lot of choices for batteries in RE applications. It has only been th elast couple of years manufactures responded to demand. Note he said golf cart batteries or RV/Marine batteries. Both of those are Hybrid and no real true deep cycle readily available then.


Who knows. Have not talked to Jeff in quite a while, but if I can remember I will ask next time I chat with him. Have not seen him since I left the NEC code making panel.

[FloridaSun]

Yeah I was pretty sure blade fuses only go up to 30 amps.

fuses aside.. I'm surprised you haven't said anything about using a 1750W inverter with 200Ah battery...... Seems a bit too much inverter to me.

[inetdog]

Well I feel vindicated now that you posted the link for all top see. If you read the article you should have picked up Jeff was reluctant to do this and only did so from pressure from the editors. So hopefully now you understand my reluctance.

I also notice that Jeff's article did not differentiate between GEL and ATM sealed batteries for this use. Any idea why? Low enough charge and discharge rate that GEL could handle it, or an insertion during editing?

[Sunking]

For sure that inverter would have to go directly to battery fuse. His fuse block is rated 100 amps max with 10-32 studs, each at 30a rating

Yeah I was pretty sure blade fuses only go up to 30 amps.

[FloridaSun]

OK you owe me big time. Ask anyone here, I do not do this type of thing.

For the MRBF fuse to CC = 30 amp using # 8 AWG
For the MRBF to Fuse Panel = 200 Amp using no less than 2 AWG

You also have a problem with your wire gauge from Fuse Panel to Inverter Input. A 1750 watt 12 volt inverter will take 145 amps at full power. That will require #4 AWG. Personally I would not connect the inverter to the fuse block. I would connect both positive and negative directly to the battery post using a second single battery MRBF Battery fuse (150 amp) which is not shown in the drawing. I do not think you can find a 150 amp blade fuse for the fuse panel.

For sure that inverter would have to go directly to battery fuse. His fuse block is rated 100 amps max with 10-32 studs, each at 30a rating

[Sunking]

OK you owe me big time. Ask anyone here, I do not do this type of thing.

For the MRBF fuse to CC = 30 amp using # 8 AWG
For the MRBF to Fuse Panel = 200 Amp using no less than 2 AWG

You also have a problem with your wire gauge from Fuse Panel to Inverter Input. A 1750 watt 12 volt inverter will take 145 amps at full power. That will require #4 AWG. Personally I would not connect the inverter to the fuse block. I would connect both positive and negative directly to the battery post using a second single battery MRBF Battery fuse (150 amp) which is not shown in the drawing. I do not think you can find a 150 amp blade fuse for the fuse panel.

[CanadianCabinSolar]

That is a good start, but does not protect the most important part of the system; the battery. This is why I do not like going into this detail. You do not even know the questions to ask, and I cannot read your mind or supervise. Please do not be offended, just pointing out the facts.

You are also going to need a Battery fuse block installed right on the battery terminal post. Blue Sea makes a really good dual unit you will need. One terminal will connect to the CC, and the other to your distribution panel you linked to. Give me a second and I will see what size MRBF fuses to use.

Cheers and thanks for the help.

[Sunking]

I am using a marine fuse block

http://www.amazon.com/Blue-Sea-Systems-Blade-Block/dp/B001P6FTHC/ref=sr_1_2?ie=UTF8&qid=1364518727&sr=8-2&keywords=blue+sea+fuse+block

as a DC panel. See my original post for a description of the circuits.

That is a good start, but does not protect the most important part of the system; the battery. This is why I do not like going into this detail. You do not even know the questions to ask, and I cannot read your mind or supervise. Please do not be offended, just pointing out the facts.

You are also going to need a Battery fuse block installed right on the battery terminal post. Blue Sea makes a really good dual unit you will need. One terminal will connect to the CC, and the other to your distribution panel you linked to. Give me a second and I will see what size MRBF fuses to use.

[Sunking]

Sorry. Here's the link www.backwoodshome.com/articles2/yago116.html

So... Sunking. With a system like mine (described in my first post), if I just ground the panel, the fuse system will work? A bare copper wire connected between the negative bus on my fuse block and a ground rod (which I have to drive anyway, over the Canadian Shield, no less) will not make the system safer?

Well I feel vindicated now that you posted the link for all top see. If you read the article you should have picked up Jeff was reluctant to do this and only did so from pressure from the editors. So hopefully now you understand my reluctance.

What Jeff is telling you is correct. You will use the same ground rod that bonds the panel frames to earth, to run a #6AWG or #8 AWG to the Breaker panel negative ground buss. From that buss in the breaker panel you use to bond to the inverter and CC ground terminal.

One added note here. YOu can use two or more ground rods. Say one directly below the panels, and another near the equipment. However if you do this you MUST BOND THE TWO RODS TOGETHER with a # 6 awg BARE CONDUCTOR BURIED IN THE GROUND. It is very important you clearly understand that point. Failure to do so puts you at great risk of burning your house down. So do not take it lightly OK. This is why Jeff and I hesitate to tell DIY's how to do physical installs. They simply do not understand how to , or why. Pros do understand and know how to. Well most of them do anyway.

[Naptown]

put fuses on the + and - of the battery
Those are the littlest words I could find

[CanadianCabinSolar]

The other way is to float the system and use protection devices on both polarities along with ground fault detection.

Please explain how to do it this way. With lots of small words please.

[CanadianCabinSolar]

Are you using a circuit breaker panel for multiple circuits?

I am using a marine fuse block

http://www.amazon.com/Blue-Sea-Systems-Blade-Block/dp/B001P6FTHC/ref=sr_1_2?ie=UTF8&qid=1364518727&sr=8-2&keywords=blue+sea+fuse+block

as a DC panel. See my original post for a description of the circuits.

[CanadianCabinSolar]

I know Jeff and he knows his stuff. Did not see a link to the story you are talking about, but I know what he is trying to say and not say. In order for a fuse to operate there has to be a planned return path. If you only want to use one protection device on one of th epolarities, th eother polarity has to be referenced to something. That something in your case is earth, but earth has noting to do with it. It is the path for the fault current to return on. The other way is to float the system and use protection devices on both polarities along with ground fault detection.

Sorry. Here's the link www.backwoodshome.com/articles2/yago116.html

So... Sunking. With a system like mine (described in my first post), if I just ground the panel, the fuse system will work? A bare copper wire connected between the negative bus on my fuse block and a ground rod (which I have to drive anyway, over the Canadian Shield, no less) will not make the system safer?
I appreciate your help.

[Sunking]

Thanks for the reply Sunking. If that's all you are going to say for now, are you going to say more later?
At www.backwoodshome.com, Jeffrey Yago, P.E., CEM discusses a small 12Volt system like mine and states " You also need to add a separate bare-copper wire from this same ground rod to the grounding bus bar inside the main circuit breaker panel."
I also read something somewhere about the fuses in a DC system not functioning correctly without an earth ground. Not correct?

I know Jeff and he knows his stuff. Did not see a link to the story you are talking about, but I know what he is trying to say and not say. In order for a fuse to operate there has to be a planned return path. If you only want to use one protection device on one of th epolarities, th eother polarity has to be referenced to something. That something in your case is earth, but earth has noting to do with it. It is the path for the fault current to return on. The other way is to float the system and use protection devices on both polarities along with ground fault detection.

[Naptown]

Are you using a circuit breaker panel for multiple circuits?