Author Topic: Bonded / Floating Ground Question (Read 8257 times)

DigitalMind · « **on:** January 02, 2008, 07:52:47 PM »

Before people start telling me to run away and NOT do this, I will mention that the existing AC breaker Box that I am wanting to connect to has NO POWER going into it AT ALL. This home is completely Off-Grid, but during construction city code forced them to install wiring for electrical outlets, light fixtures, and an AC breaker box.

I'm using a cheap-o 300 Watt Inverter. I was originally just planning on putting a good extension cord from the AC plug on the inverter, and putting it in the "INPUT" of the existing electrical panel. (I'm just figuring out now how electrical panels work) I thought this would be easy so I didn't think about it much, but now, days before I do this install I've discovered that most places cabled for Grid Power has the Neutral Bonded to the ground which is (apparently) very bad for cheap-o inverters like the one I have. SO, how do I un-ground the neutral at the panel ?

Any links on how to connect the inverter to an AC panel that doesn't have grid power would be great. (Or how to modify the existing panel kinda thing)

Thanks as always for the information.

Flux · « **Reply #1 on:** January 02, 2008, 01:06:00 PM »

Take this with a pinch of salt, I am not in N America and I don't know much about your distribution system but I think you are in trouble.

Most of your low power usage is at 110v and that is likely all a small inverter can drive. The higher power loads are supplied at 220v. The supply is effectively a 220v centre tapped transformer with tap earthed. You take big power from the ends at 220v and smaller power from either end to centre tap at 110v. Your inverter will supply 220v loads within its rating but it doesn't have any hope of supplying loads at 110v as it has no centre tap.

If you can manage with 220v loads within the inverter capability you will be ok but otherwise you would be better off with a 110v inverter supplying the smaller loads.

You can't even use 2 110v inverters in series as they will not be frequency or phase synchronised ( there are specials but not your cheap ones)

Our distribution system is different and this problem doesn't arise.

Flux

ghurd · « **Reply #2 on:** January 02, 2008, 01:07:57 PM »

Guessing there is a aluminum looking bar with about 1000 holes.

The holes have white wires and bare wires.

The bare wires are the grounds. The white wires are neutrals.

You need to get the bare wires out of the holes.

Then the inverter has 2 slots and a round hole.

The Longer slot is neutral, and goes into the bar.

The Shorter slot is "Hot".

Not sure it makes any difference with a cheap inverter.

G-

Flux · « **Reply #3 on:** January 02, 2008, 01:17:47 PM »

Perhaps you meant a 110v inverter. In which case you can use it for 110v loads if you remove the ground. You would have to reconnect the 2 110v sections in parallel to use the whole outlets. Then you have no 220v option and it will not be compatible with generators designed for split rail 220v.

Flux

DigitalMind · « **Reply #4 on:** January 02, 2008, 01:36:03 PM »

Thanks for replying Flux. Everything I use here is 110 volts. The inverter i'm using is 110 volt output. (Sorry I always forget to mention that, just like you're used to talking about 220 always I only talk 110)

DigitalMind · « **Reply #5 on:** January 02, 2008, 01:38:56 PM »

Thanks ghurd that seems simple enough. So just remove all the bare wires from the neutral bar ? Then connect the - from the inverter there, and then connect the + at the bottom for the 2 110 volt inputs. ?

Thanks alot !

ghurd · « **Reply #6 on:** January 02, 2008, 02:01:12 PM »

Yes.

Some inverters (Vector and some others) have a psyudo-ground. Not sure if yours does. It might be good to connect the ground wires to the fake ground, but be sure it isn't actually grounded somewhere, like the big bare one from the meter box, or something going to a water pipe...

wooferhound · « **Reply #7 on:** January 02, 2008, 02:11:06 PM »

There is usually a big Green Screw that connects the Neutral Buss Bar to the metal of the Breaker Box. You would probably want to remove that screw too.

quest0111 · « **Reply #8 on:** January 02, 2008, 03:42:04 PM »

Then take all your bare wires, get a grounding bar for your panel, all the bare wires will connect to that seperate from your neutrals. There will be holes in your panel for the ground bar. Connect also to a earth ground.

DigitalMind · « **Reply #9 on:** January 02, 2008, 03:48:52 PM »

By doing this my system will be properly grounded and more or less "according to code" in the regards

I'll be able to tell an inspector with confidence that the panel and all wiring is properly grounded ? (Atleast on the panel's end)

Thanks guys as always !

ghurd · « **Reply #10 on:** January 02, 2008, 04:19:51 PM »

That can lead to <pop>, followed by Magic Smoke.

DigitalMind · « **Reply #11 on:** January 02, 2008, 04:41:26 PM »

Ghurd,

actually grounding the 3rd ground wire in the inside cabling would damage my cheap-o inverter ?

TomW · « **Reply #12 on:** January 02, 2008, 04:48:53 PM »

G- ;

Exactly why these grounding questions seem to be such a waste of effort. Everyone has an opinion and they are all different.

Why manufacturers have installation instructions, I guess.

I do know cheap inverters often have a dislike for nuetral / earth bonding.

I wired mine according to what Outback said on the grid side [for charger and pass thru]. The other side is the supplied circuits and they are connected to the Outback and not to anything else. I use heavy plugs to switch those circuits to grid or inverter but my inverter will pass through Grid voltage if I tell it to.

Every time this comes up we get this parade of marginal and sometimes downright bad advice mixed with good. And nobody will be responsible for screw ups from bad advice.

I think if a person cannot figure this one out with their electrician and the instructions they need a different electrician.

Some things just may be beyond some users' ability to do and a professional should be hired and consulted.

Sorry, but thats a fact.

Cheers.

TomW

vawtman · « **Reply #13 on:** January 02, 2008, 05:41:47 PM »

Hi Tom

I got laughed at today by old ladies playing cards at a senior center that my wife manages.Attempting to adjust a new projector for their movies.(no nudies)

They said"Kim(my wife) look he's reading the directions"

I showed them the 50+ page manual and the only english part was one sentence on the front page that said"for english see foldout"

Funny watching them pick through it.

Are we getting that stupid that we need big foldout section i thought.

DigitalMind · « **Reply #14 on:** January 03, 2008, 09:08:48 AM »

"I think if a person cannot figure this one out with their electrician and the instructions they need a different electrician.

Some things just may be beyond some users' ability to do and a professional should be hired and consulted.

Sorry, but thats a fact.

Cheers.

TomW"

... Gee Tom, Thanks ... Do you also think it's wrong to double-check with other people that have done this? Personally I want to understand how it's done and how it works. Not hire someone to connect 2 wires (and disconnect a couple) for me when it's well within the range of things I can figure out on my own. If this electrical panel would have been live I wouldn't even try. I never take any 1 person's advise as being "right", I always check, double check, and triple check. Also, i'm not shy in saying that something is over my head and need to hire someone, but first I need to find out that it's over my head ! I'm not the kind of person that gives up before I even know what I need to do !

I would have appreciated your advice on this subject. Not just "you should figure it out on your own or with your electrician" I have a lot of respect for you TomW because of all i've read from and about you, but this was just plain'ol not helpful other than confirming that you know that SOME cheap inverters don't like the neutral being grounded. I wouldn't have minded that you share some knowledge, and REMIND me that "maybe" a professionel should do it or just let me know of the dangers. (Which I already know, I am a cable guy) Maybe I took your post the wrong way, but it sure didn't seem very helpful and nice like most people's posts around here are.

I have no manual for this inverter. It's old. I might buy a new one, but I wanna understand the neutral/ground bond thing first. (Which I know believe I understand thanks to Ghurd)

Take care ..

TomW · « **Reply #15 on:** January 03, 2008, 09:58:41 AM »

Digital;

Well, gee, sorry for being honest.

As I said before, this whole grounding subject is just a confusing mass of opinion. Some good some bad some stupid.

There will always be people who should stay away from certain subjects.

If you actually read this forum regularly you would have seen all the same basic comments WRT a grounding scheme posted multiple times recently.

I can't tell from text on a screen if you are a moron about technology like inverters, wiring, etc. Some subjects truly do defy safe online advice. This is one of them. I saw one comment here that, if followed, would pop any cheap inverter dead bang now. Am I supposed to shut up so that persons feelings are not hurt while you follow bad advice and destroy equipment? I see you have been around for a couple months now so you kind of got a pass and I let this stay despite the recent stories on exactly this subject.

No thanks necessary, its part of the job.

Cheers.

TomW

Cloaked User · « **Reply #16 on:** January 03, 2008, 10:35:27 AM »

There are a lot of variables involved. To take just two, what you will find in your panel depends on which electrician did the work, and what model of panel was used. There might just be a neutral bus, with all the white wires attached to it, and a ground bus, with all the bare wires hooked up there. If that is the case, then they are either connected electrically, or not. Sometimes the connection is a "bonding screw" which is usually green in color, but maybe not. Sometimes there is a connector that came with the panel, made specifically for the purpose. There might be a big fat wire connecting the two bus bars (neutral and ground). If the electrician had experience with off grid systems, and knew an inverter was going to be hooked up, there might not be a bonded neutral there at all. We have no idea. It's much more likely that there is a single bus bar with all the white wires and all the bare wires connected there, often in random order. In that case, you are probably in for a bit of work.

If it were my house (and that is the limit of my authority!) I would make sure the neutral was not grounded anywhere, and hook the inverter up with the case grounded and the ground terminal in the outlet hooked to the ground in the panel. Then the neutral slot hooked up to the white wires, and the "hot" connected to both of the buses the breakers attach to. If it were me. I did work for an electrical contractor in a previous life, in the 80s, and I have wired a few houses and done a lot of work on temporary power setups, but I am not a licensed electrician. I hire currently licensed people to do the hard stuff on my own house, too.

Since you are a cable guy, you probably have a good multimeter, and know how to use it. So it's pretty easy to tell if the neutral is grounded in your system.

We are all do it ourselfers here, but you have to be careful about giving advice. Even a 300 watt inverter can be lethal, so, you know, you really should hire an electrician. Please let us know how this turns out.

ghurd · « **Reply #17 on:** January 03, 2008, 10:51:36 AM »

"... and hook the inverter up with the case grounded and the ground terminal in the outlet hooked to the ground in the panel"

That 100% will smoke 94% of cheap 300W class inverters.

And 5% don't have the outlet ground terminal connected to anything anyway, so it's a waste of effort and wire nuts.

The last 1% is the one someone will post "It didn't smoke mine", which may fall into the above 5%.

The ground terminal in the outlet of the inverter must not be connected to the case.

Unless the manual says to do it.

G-

terry5732 · « **Reply #18 on:** January 03, 2008, 11:30:02 AM »

There is about zero chance of any inspector passing your set-up. The system in the US is geared for grid-tied electric connections. The main breaker box is specifically designed for this. At a minimum you would need a different main box to pass. One purposely made for 110V. They are still going to want you to have GFICs where required - no can do without ground wires.

DigitalMind · « **Reply #19 on:** January 03, 2008, 11:33:34 AM »

TomW;

I've read all the previous posts before asking my question. It's because of those posts that I asked it at all. I did alot of research before asking the question I needed to know. I wouldn't have minded you saying either NOTHING or that "it's not a safe question to answer". I totally get that. I do that also in my line of work.

Anyways i'm going to stop B*tching since you're a smart guy and I appreciate your part in this forum and otherpower, I just didn't appreciate the way it was said.

fungus · « **Reply #20 on:** January 03, 2008, 11:38:31 AM »

Please correct me if I'm wrong on this but..

The problem seems to be because the neutral and earth are connected together already inside the inverter, this is also connected to the negative on some inverters, which is usually grounded too. If you have more than one grounding point then it can create a ground loop, causing damage to the inverter, I would suspect that it would be able to pass code if the inverter case was the point of grounding? As I said,, correct me if I'm wrong..

DigitalMind · « **Reply #21 on:** January 03, 2008, 11:38:39 AM »

Thanks guys all these things help.

I don't have the panel in front of me so I will find out when i'm onsite but I think I have it figured out now.

THANKS!

SparWeb · « **Reply #22 on:** January 03, 2008, 12:44:04 PM »

Get a multi-meter.

Stick the probes into the hot and neutral slots in the inverter's receptacle. 120V

Now stick the probes into the hot and ground slots in the inverter's receptacle. 60V!

Now stick the probes into the neutral and ground slots in the inverter's receptacle. 60V again.

And finally... stick one probe into the neutral slot and touch the other to the case. 60V again (probably).

That's why this won't work. I have one of these cheap-o inverters, you see...

Conducted the same experiment myself.

TomW's only mistake was not telling you to quit sooner.

Cloaked User · « **Reply #23 on:** January 03, 2008, 01:05:05 PM »

I'm in that 1% then. Manual said to do it. I have released more than my share of magic smoke into the atmosphere over the years, but no inverters yet. I am surprised to learn that the ground inside the outlet is not connected to anything. Anyhow, thanks for the warning. I have a 400 watt vector that I haven't used for much of anything yet, and that is certainly in the cheap category!

Cloaked User · « **Reply #24 on:** January 03, 2008, 01:08:13 PM »

I beg to differ on the gfci with no ground. This is commonly recommended as a solution to the usual two-wire outlet found in old houses, especially in bathrooms and kitchens. The gfci will function normally, but there will of course still be no ground. That's why the recepticals come with those stickers that say "No Equipment Ground," that one is supposed to attach to the gfci and all downstream devices in such an installation.

fungus · « **Reply #25 on:** January 03, 2008, 01:16:24 PM »

SparWeb:

Just did the same test on my [230v 50hz] inverter, I get 230v between the live and neutral but none to ground, however putting a voltage tester on the earth and live or neutral then both light up .. also when on the negative terminal of the battery and inverter case .. not sure on that one.

DigitalMind · « **Reply #26 on:** January 03, 2008, 01:51:08 PM »

Steven,

doesn't disconnecting the ground on the panel from the neutral cabling fix all of this ?

.... I don't believe in quiting, there's always a solution ...

DigitalMind · « **Reply #27 on:** January 03, 2008, 01:59:01 PM »

Maybe it would be easier to just change electrical panels

I have no problem with disconnecting the existing wiring and putting it into a new panel.. Do they make panels that would make this easier ?

I don't see the big problem here, inverter has a plug and I need to extend those 2 live wires onto the existing wiring. If I was just a little stupider, I'd just pull out all the existing house wiring from the electrical panel, and make a huge splice of all the +'s and -'s onto the output of the inverter ! (I would never REALLY do that, but basically that's all I wanna do here PLUS have a fuse for each wire which is where the panel comes in)

This system is only being used to power 5 CFL Bulbs ...

ghurd · « **Reply #28 on:** January 03, 2008, 02:35:31 PM »

DM,

Pull out the bare wires,

make sure the box isn't grounded,

connect the inverter.

That's it.

From a Vector manual. I honestly LIKE them for the price and feel they are a lot better than the average Chi-kneess flea-market inverter, but this about covers it for the whole lot.

Inside front cover...

Page 17 can be left to one's imagination if a windmill or tall PVs would be subject to lightning...

Page 14...

G-

(So sorry Tom. I'm done now)

ghurd · « **Reply #29 on:** January 03, 2008, 02:39:10 PM »

damn.

Make sure the Al looking bar isn't grounded.

DigitalMind · « **Reply #30 on:** January 03, 2008, 02:46:41 PM »

Thanks so much Ghurd. This is very simple stuff as long as you know. If I was installing 2 days ago I would have made a big mistake since I didn't know cheap-o inverters reacted badly to the 2nd ground on the neutral. (Which makes sense)

I do have a good multimeter and know how to use it, I will make sure the negative inside wiring is NOT grounded before connecting anything and I will do it all in steps and be VERY VERY careful.

Thanks again everyone, including Tom , who's worried for my life ?

Cloaked User · « **Reply #31 on:** January 03, 2008, 03:08:16 PM »

I don't think anyone here suggested hooking the inverter's output ground conductor to the negative battery terminal. I certainly did not. I just looked at an Aims 2500 watt inverter I hauled in from the garage, and there is a good solid connection (according to a good digital meter) between the ground terminal and the ground in the 120v receptacle. There does not seem to be any connection between the ground terminal (clearly marked as such and fastened to the inverter's finned housing) and either of the DC input posts. So with that inverter, why would the connection I described above cause any sort of problem? Does something change when the inverter is switched on? Am I missing something? At $220 it was cheap enough, but I don't want to smoke it!

Ungrounded Lightning Rod · « **Reply #32 on:** January 03, 2008, 08:58:22 PM »

First: Do NOT unhook all the bare wires. They go to ONE of the strips (the ground one, which is also hooked to the box case), while the white wires go to the other one (the neutral one, which is insulated from the case). You need the ground to keep the housings of your three-wire appliances from being hot if there is an internal fault.

If your wiring was done to code there will be a "bond" between the neutral and ground in the MAIN panel only. (If you have any subpanels they will NOT be bonded, but will run the neutral and ground back to the main panel for the single house bond.)

Remove the bond in the main panel. Make sure the ground remains connected to the GROUND connections (green/bare/case/conduit) and that the NEUTRAL (white) is floating. Use an ohmmeter to be sure there isn't a second ground somewhere.

Then hook:

- Red and black to "hot" on your inverter.

- White to "netural" on your inverter. (Note that white will now also be "hot" on the house outlets, lamp shells, etc.)

- MAYBE hook inverter ground to green/bare ground:

Check your inverter with an ohm meter when it is powered down and unhooked from anything. You should find that the ground pin on the plug is connected to the case of the inverter and to the ground screw you should find there, and both sides of the battery are isolated from that.

- If this is the case, you can connect the building ground EITHER to the ground pin OR to the green ground screw on the inverter. Separately ground whichever side of the battery is convenient for your DC system.

- If one side of the inverter's battery input is connected to the case/ground screw/ground pin, DON'T connect the house ground to the inverter but be sure that side of the battery is the ground side.

If there is continuity to the battery side, recheck what you think the inverter's internal connection is using the voltage range of your multimeter with the inverter connected to the batteries, powered up, and still disconnected from the panel. The inverter's ground output should be at the same voltage (AC and DC scale both) as the one you your ohm meter previously said it was bonded to. (Don't do this test if there was no continuity: Stray capacitance will make the box and ground connections rise to some AC voltage when the inverter is running and the ground connection is floating.)

Remember the golden rule of grounding: The ground must be connected as a tree. NO LOOPS. No double paths. Everything that is supposed to be grounded must have exactly ONE path to ground.

In a cheap inverter you have a high voltage power supply - run from the battery - with one side grounded. The inverter switches BOTH the "hot" and "neutral" outputs, alternately, between the ground and the hot side of this internal DC power supply to provide an AC output. (With "MSM" it also spends two parts of the cycle with both grounded, in between giving each a hot pulse.) This is why bonding the neutral to ground lets the magic smoke out: For part of the cycle the "hot" wire is at ground and the "neutral" wire is connected, through a transistor, to the high voltage output of the inverter's internal voltage converter. Bonding neutral to ground causes the poor transistor to try to short out the power supply and discharge the capacitors through itself.

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Author Topic: Bonded / Floating Ground Question (Read 8257 times)