Author Topic: How to wire inverter into main panel  (Read 5082 times)

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somemathguy

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How to wire inverter into main panel
« on: March 14, 2007, 12:19:16 PM »
I have cobbled together a small 12V solar setup with two 55W Solarex panels, Morningstar charge controller, 320Ah of 12V deep-cycle batts, and 1500W cheapo square-wave inverter. I'm embarrassed to admit it, but I have in the past used the 'shut down the main panel breaker, then use a male-male cord from my inverter into an outlet' trick to electrify part of my household during power outages. I didn't know this at that time, but even though I only have a 1500W inverter it is possible that a linesman could still get a shock from my system if working on the lines outside of my house when the grid power is off.


I want to wire a 'transfer panel' into the main breaker panel and hook up about 6 of the house circuits so that in case of a power outage, I can hook my inverter up to the transfer panel (like you would a generator) and run those circuits off my solar setup.


My question is, all of the transfer panels I have seen have a 240V plug for input (as from a generator). My inverter does have two 120V outlets which I suppose I could wire into a 240V plug, but might the two 120V currents be out of phase with each other or something?


If anyone has any advice as to how to proceed, or how they hook their own solar systems partly up to electrical circuits in their house, I would appreciate it!


Cheers,

Kevin from Nova Scotia, Canada

« Last Edit: March 14, 2007, 12:19:16 PM by (unknown) »

Titantornado

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Re: How to wire inverter into main panel
« Reply #1 on: March 14, 2007, 06:37:34 AM »
You could just wire it into the 240 plug, and you'll have a 120v only panel. There won't be a phase issue. (if you opened the inverter, you'd see a hot jumpered between the two outlets)  Just be sure the neutral isn't bonded to ground.
« Last Edit: March 14, 2007, 06:37:34 AM by (unknown) »

coldspot

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Re: How to wire inverter into main panel
« Reply #2 on: March 14, 2007, 06:52:53 AM »
" Just be sure the neutral isn't bonded to ground."

That can't be said enough times!

A quick cooking of inverter if it is.

« Last Edit: March 14, 2007, 06:52:53 AM by (unknown) »
$0.02

Nando

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Re: How to wire inverter into main panel
« Reply #3 on: March 14, 2007, 07:18:08 AM »
Kevin:


For one you need to take an AC voltmeter and determine if you have 240 volts or not.


If you have 240 and two 120 volts then your cheapo inverter may be one of the better that may have the Neutral without any pulses and good for house wiring ground connection, THOUGH make sure that such is the case and the best way is to use an Oscilloscope to see the wave forms and to determine that the Neutral is really neutral.


The way to automatically furnish power when the GRID goes (Hydro in Canada) is to have an isolated power string for the emergency lighting.


this string should have a relay DPDT ( double Pole Double throw) that normally connects the GRID power to the isolated string, when a power failure occurs, the GRID power detector turns ON the relay switching the string to the cheapo inverter that is as well turned ON.


When the GRID returns the detector drops the relay to reconnect the isolated string to the GRID power.


This way no power is sent down the power grids that by the way, most of the time, will present a short to the cheapo inverter.


Nando

« Last Edit: March 14, 2007, 07:18:08 AM by (unknown) »

nothing to lose

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Re: How to wire inverter into main panel
« Reply #4 on: March 14, 2007, 05:35:43 PM »
Also you can just wire a second breaker panel next to the main panel. On the second panel put a heavy wire and plug, more than actaully needed to power your circuits. Now take the wires out of the main panel for those circuits you'll want to run from the inverter and wire those into the second panel.


Place inverter outlets near second panel and wire a heavy outlet from the main panel.


Now it is as simple as deciding what you want to use as power source, grid or inverter, and plug the second panel to that source as you want it.


Or you could just wire several 120V outlets under your panel and put heavy duty plugs on the crcuit wires, plug them in like an extension cord to either the grid power outlets or the inverter.


I have done and do both ways.


Also I have done that extension cord trick, plug into inverter and wall outlet. While not a good thing to do for other reasons, really if main power breaker is off then nothing should be backfed into the grid. Should be no danger to line workers. CHECK to be certain. Things could be wired other ways than normal.


 Wiring may vary! All I have done like that, the main breaker either flows power or breaks the flow, in or out does not matter, it's either on or off. Since both hots of a 240v grid (2 120V lines) goes through the main 240V breaker then if breaker is tripped OFF no power can flow either way through it.


I have seen some boxes wired direct and there was no main breaker though!

Or once I found a 120V breaker for one leg and other wired direct to the box. The guy used the breaker side for heavy 120V shop stuff and other 120v leg wired direct went to low power house stuff.


I have 4 breaker panels here, 1 at meter, 1 at well, 1 in house, 1 in kitchen. Grid starts at meter and runs in that order to where power is used, through each box in series in that order. I you can shut off the grid at some point before it enters the box like I can, then you can shut of the grid, test for no grid power at the box. Wire the extension cord trick or other stuff and check again to be sure the grid side of box is still dead when main breaker is off in that box.


That's another trick we used to use on a portable office. Grid power when on location, a generator when moving. We used a simple 2 breaker setup. One 240V breaker was the genny, another the grid. The breaker simple act as a main breaker and power only flowed to the box through the on that was on. The breakers switch was connected together so only one could be on at a time. Turning one on forced the other one off.

 The point here is basically that is what back feeding through an outlet does, the breaker for that 120V outlet is simply a main breaker then for the power going into the panel on that line. Once in the panel all the breakers for that leg of the box will be live. The other leg of the box will be dead still. Mostly I have done this when grid power was not available and I needed a few outlets or light working in various rooms.

 If you turn off that breaker your feeding into, then all the rest of the circuits on that leg should go dead. All outlets on that same circuit you are plugged into will still be live direct from the inverter still though.


 This has been a good way for me to find what all is on a 120V breaker when I don't know the wiring of a house or such.

 I make sure there is no grid power!!!! Normally there is not or I could just turn off the breakers one at a  time and see what don't work.

 So I wire to back feed an outlet with an inverter, maker sure ALL breakers are off.

 Check every outlet and switch to see what is live and mark them. Then plug into a dead outlet and see what is live now. Continue untill all 120V breakers are known.

 To find out what breaker is for the outlet you plugged into if you don't know, turn on several other 120V breakers, then simply flip on a breaker till you find one that turns on other lights that don't work when it was off, that's the breaker for the circuit you plugged into. 2 Breakers will operate one circuit this way, the one acting as your main, and the one for the other circuit with the light, so have 4 or so breakers on and the one that shuts off your other 3 is your feed circuit from the inverter.

 Of course easiest to just shut them all off and test with a meter to find the live one, but if a meter is not handy that works.

« Last Edit: March 14, 2007, 05:35:43 PM by (unknown) »

nothing to lose

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Re: How to wire inverter into main panel
« Reply #5 on: March 14, 2007, 05:44:30 PM »
Also please note that I am talking USA grid power I do this with, I don't know about power in other  countries, it may not work the same for any of that!
« Last Edit: March 14, 2007, 05:44:30 PM by (unknown) »

somemathguy

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Re: How to wire inverter into main panel
« Reply #6 on: March 15, 2007, 06:19:45 AM »
Don't think that would work titanTornado...when I look at the picture of this transfer panel

http://www.nbmc.com/emergen/6-5001.html


it looks to me like you can have six 120V circuits routed through the transfer switch (ie. six house circuits you can commandeer with your inverter if the grid goes down). You can see in the pic that you can make two 120V circuits into a 240V by tying them together on the transfer panel, which leads me to believe that the 3 circuits on the left are getting 120V power from the red wire on the 240V generator input plug, and the 3 circuits on the right are getting 120V from the black wire on the 240V generator input plug. When the two middle circuits C and D are connected in series, you can get 240V from the red+black. So if I only powered 120V, only half of my circuits on the transfer panel would work...unless I guess I wired the 120V hot into both the black and red of the 240V to electrify both sides. Would this work?


Ok, tell me if this sounds right: assume that in a 240V generator output cable (the one that plugs into the transfer panel), there are two 120V hot wires, one neutral, and one ground. I wonder if I could just make a custom cable with a 240V male 4-prong plug on one end and two male 3-prong 120V on the inverter end. The hot from one 120V prong would go to the black in the 240V, and the hot from the other 120V prong would go to the red. The neutrals would both go to the white on the 240V and of course the ground would go to the 240V ground.


Or the other way I guess would be to have only one 120V prong coming out of the inverter connected to both the black and the red in the 240V male prong, as I mentioned above.


I know people who have hooked power up to their house circuit by cutting a circuit, putting an outlet junction box on each end, then re-connecting them together with a male-male extension cord. Then if the power goes out, you just shut off the main power breaker and then put one end of the extension cord into your inverter...this will electrify either the left or right half of the circuits in your home's breaker panel. I do want to do it the 'code' way if possible using a transfer switch, plus make it easy for the 'missus to transfer power in an outage if i'm not home (don't want her to have to mess with the main breakers and pulling plugs etc).


Any advice appreciated, thanks for your comments.

Kevin

« Last Edit: March 15, 2007, 06:19:45 AM by (unknown) »

Titantornado

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Re: How to wire inverter into main panel
« Reply #7 on: March 15, 2007, 12:27:04 PM »
It will work. Just remove the jumper on the double pole so you'll have six single 120v breakers.


Yes, just as you say, tie the red and black together, or feed each leg from each outlet. (the result is the same)  The wattmeters should work normally too.


Oh yea, and make sure the neutral isn't in any way bonded to ground. ;o)

« Last Edit: March 15, 2007, 12:27:04 PM by (unknown) »

hydrosun

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Re: How to wire inverter into main panel
« Reply #8 on: March 16, 2007, 08:41:56 PM »
You can get a simple metal strip that fits over two square D brand breakers that turns them into a nice transfer switch. I found them in one old style  hardware store but had to go to a wholesale electrical shop for the last one I bought. So I used a 6 position square D breaker box to install these breaker that choose between grid power or inverter power to power the other breakers in this box.  The other way to do it legally is to get a bracket that installs over the main breaker in a Square D QO 250 amp box and covers either the main or the breaker in the top right position. This guarantees that you can't backfeed the inverter into the grid. I just passed inspection at my nephews house with that setup.

Chris
« Last Edit: March 16, 2007, 08:41:56 PM by (unknown) »