Any tutorials on off-grid wiring?

PorkChopsMmm · February 2011

Our off-grid cabin is nearing completion and I have a few questions on how to finish the electrical wiring and load center configuration. Like my progress so far, I learn best from reading or looking at pictures of what others have done. I have found the site below, but it doesn't answer all of my questions and it was for a pre-existing on-grid house.
http://2manytoyz.com/gridless.html

***As a caveat to the questions below, there is no grid power in the area and I doubt there ever will be.***

My main questions are centered around the wiring of the off-grid cabin itself and actually hooking up the inverter(s) to the load center. I have a Xantrex Prosine 2.5 2500 watt inverter/charger. Technical specifics are lean on the inverter so I called Xantrex and found out that it is not split phase. From what I have been reading on these forums, I could hook up the 120 output of the inverter to one 'leg' of the load center so that one side of the box is powered. This inverter uses a lot of power, so I was wondering if I could wire in a low power inverter on the other 'leg' of the load center just for the LED lights that we will run in the cabin. I have read that sharing the ground of the load center could be a problem -- do you see if being a problem for such a setup with 2 entirely different inverters going to the same load center? Also, I have generic questions about wiring up the cabin for such a scenario. We worked with a retired electrician to wire the cabin and he did an excellent job, but I am pretty sure some of the electrical outlets are tied in with some of the overhead lights -- so some of those sockets would be feeding off of the lower power inverter while other sockets and lights may be feeding off of the other side of the load center and tied to the Xantrex inverter.

What makes this all a little more difficult is we just finished insulating the cabin so much of the wiring is no longer visible. Did I drop the ball by not trying to take care of this beforehand?

Thanks in advance for your comments. These forums are a great resouce.

ggunn · February 2011

Re: Any tutorials on off-grid wiring?

PorkChopsMmm wrote: »

I have a Xantrex Prosine 2.5 2500 watt inverter/charger. Technical specifics are lean on the inverter so I called Xantrex and found out that it is not split phase. From what I have been reading on these forums, I could hook up the 120 output of the inverter to one 'leg' of the load center so that one side of the box is powered. This inverter uses a lot of power, so I was wondering if I could wire in a low power inverter on the other 'leg' of the load center just for the LED lights that we will run in the cabin. I have read that sharing the ground of the load center could be a problem -- do you see if being a problem for such a setup with 2 entirely different inverters going to the same load center?

I think a better solution would be to incorporate an autotransformer to generate the other leg of the split phase.

arkieoscar · February 2011

Re: Any tutorials on off-grid wiring?

It sounds like you don't need split phase but are trying to avoid the loss in the large inverter. Two things- your load center had two lugs on the top but they alternate going down the rows of breakers. This will make your panel pretty confusing as to which source is feeding a breaker. It would be better to have two smaller load centers and tie the two lugs together in each one. Earth ground should not be a problem to share between the two. Feed each panel with an appropriate size, single pole breaker. Neutrals would not be shared or connected between the two sources.

icarus · February 2011

Re: Any tutorials on off-grid wiring?

There is no reason that I know of that you cannot jumper between both sides of a spilt phase panel, and feed each leg off of on single phase inverter. (There may be legal issues, but I really can't see what they might be).

As long as the main disconnects both legs the inverter isn't going to care, nor will the individual breakers as far as I know.

As for adding a second inverter, I have considered adding a second Shursine 300 on one side of my load center. I haven't considered the grounding issues, and since I don't need it I haven't bothered. Someone smarter than I will surely know that answer.

Tony

Cariboocoot · February 2011

Re: Any tutorials on off-grid wiring?

Right you are, Tony!

That's exactly what I did with my system: the inverter's hot simply feeds both legs. Mind you, I have a small distribution box: six positions and no main (there really doesn't need to be one as shutting off the inverter kills all power, and the inverter will 'trip' (fault) before any breaker does.

Note: if you're going to link the neutrals and grounds on two different inverters make sure you know what inverters they are: mixing in an MSW type is going to be instant bad news.

PorkChopsMmm · February 2011

Re: Any tutorials on off-grid wiring?

This is all great advice, thanks guys! So I could just use a 4 gauge wire or some such to jumper the 2 legs of the breaker box? That sounds straight forward enough. I need to look at my existing wiring to see if I can segment off some of the lighting so I can run it to a separate, smaller, breaker box for a low watt inverter.

I get a lot of draw down on my batteries because the inverter is pretty inefficient and my gel 8 55 amp hour gel batteries have seen better days (purchased used). You all are a wealth of knowledge.

icarus · February 2011

Re: Any tutorials on off-grid wiring?

Yank the lighting circuits off their breakers, mount another load centre next to the other one and use the original load centre as a J Box. The other thing you could do is us a manual transfer switch system like this, so that you can feed the lighting circuits from either source.

http://www.amazon.com/Reliance-Controls-Transfer-Switch-Kit/dp/B000BQN4T2/ref=sr_1_3?s=garden&ie=UTF8&qid=1297983981&sr=1-3

Tony

tr0y · February 2011

Re: Any tutorials on off-grid wiring?

Here is what I did, I am 19 miles from the nearest powerline, through a federal wilderness area so grid power is never coming to my home.

Wired house as if grid tied 120v would be the main power source, used standard high voltage gear, wired the house with 12g romex and larger where needed for bigger amperage, and wired for 240v future expansion where needed and capped it in the boxes and panel.

I just jumped the busses to provide power to both sides of the panel, I have quite a bit more power available ( 5 to 8 X ) than you do. I jumped mine with 8g. 120A X 2" of wire not worried about it at all.

120V / 200A you can run 8g wire 3.74' with a 1% voltage drop.

That might be some food for thought here is a fun wire size toy.

http://www.electrician2.com/calculators/vd_calculator_all_distance.html

Good Luck

techntrek · February 2011

Re: Any tutorials on off-grid wiring?

Go ahead and use your existing panel, just make sure you didn't wire up any multi-branch circuits and you'll be fine. MBC = two circuits sharing one neutral. Keep in mind that the lugs in the panel probably aren't rated to hold more than one wire at a time so split the output of the inverter into 2 wires to bridge the busses, don't run it to one buss and then use a short wire to bridge to the other one (which leaves you with two wires in one lug).

icarus · February 2011

Re: Any tutorials on off-grid wiring?

techntrek wrote: »

Go ahead and use your existing panel, just make sure you didn't wire up any multi-branch circuits and you'll be fine. MBC = two circuits sharing one neutral. Keep in mind that the lugs in the panel probably aren't rated to hold more than one wire at a time so split the output of the inverter into 2 wires to bridge the busses, don't run it to one buss and then use a short wire to bridge to the other one (which leaves you with two wires in one lug).

Multibranch circuits are typically (but not always) wired with 3 wire cable, 1 red, one black and one white (plus bare copper) The red goes to one breaker on one buss, the black to a breaker on the other buss, and the white to the neutral buss bar. The neutral carries current from each circuit, but because it each buss is out of phase, you can't overload the neutral with out overloading the fuses hot.

Tony

PorkChopsMmm · February 2011

Re: Any tutorials on off-grid wiring?

Thanks for the comments. This is now sounding a lot easier to wire up.

Icarus, thank you for the simple explanation on MBC's... that is the easiest to understand definition I have heard so far. We have no such circuits, nor do I ever plan to.

Any tutorials on off-grid wiring?

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