Author Topic: Both AC prongs on inverter are hot (Read 6869 times)

valterra · « **on:** October 16, 2008, 10:08:50 PM »

I am thinking about removing a single circuit in my house from the grid.

Along the way I tested the individual wires and found a discrepency. In my house (USA), the smaller slit is hot, the larger is not.

With my multimeter:

Large to Small = live

Large to Ground recepticle = dead

Small to Ground Recepticle = dead

Large to ACTUAL ground = dead

Small to ACTUAL ground = voltage.

However, the same is NOT true of my inverter. On BOTH of my inverters, BOTH prongs are hot.

Am I measuring wrong? Always a possibility, though I fail to see my mistake at this point.

What gives?

SparWeb · « **Reply #1 on:** October 16, 2008, 04:24:25 PM »

I have an inverter like that. Yours is probably <1kw, 12V, and has receptacles built into the side, no matter what brand name.

I bet that inverter makes 120V RMS by putting about 60V RMS on one prong and 60V RMS (opposite phase) on the other prong.

Do not wire this inverter to your house AC!

You cannot safely ground this type of inverter.

BTW the house receptacle you tested doesn't seem to be grounded properly.

Get one of the plug-in receptacle testers (they have green/red lights on them) at the hardware store.

I did that a few years ago, after moving into a new house, and found 1/3 of the receptacles not wired properly.

ghurd · « **Reply #2 on:** October 16, 2008, 04:24:43 PM »

Dooh! (in my best Homer voice)

You measured it 100% correctly.

They don't work the same. That's why people blow up their inverters with crazy cords, and/or neutral (large slot) connected to ground, and/or more stuff like that.

Simple explanation, most US-type inverters have a simulated/false "ground".

G-

vawtman · « **Reply #3 on:** October 16, 2008, 04:33:11 PM »

Hi v

My guess is you live in an old farmhouse and somebody changed the outlets to adapt to newer appliances.However the ground is ungrounded.What are you using for the actual ground?

Mark

Airstream · « **Reply #4 on:** October 16, 2008, 04:34:38 PM »

I have read where on small portable inverters (including inverter generators) they do power both hot and neutral lines for safety - one side sees positive going 60V pulse, then other side sees negative going 60V pulse so the effect is transparent to the device as it still 'sees' 120VAC.

The safety aspect is since it is portable, slamming a car door or some such thing happening on a power cord cutting one conductors insulation only allows 60VDC pulses to 'leak' and possibly shock people.

If you do pull a branch circuit from utility power make very sure the ground never makes with the neutral - instant translation to the great hereafter for the floating ground inverter!

valterra · « **Reply #5 on:** October 16, 2008, 04:58:51 PM »

Thanks for all the quick comments! Okay, to cover the many topics raised:

This is a new house. New as in 1999 that is.

By removing from the grid, I mean COMPLETELY removing it from anything grid related. I have one of those power strips plugged into my inverter, and I want to basically turn SOME of the copper wires within my walls into a really big power strip... not any connecton to the grid AT ALL, just like my power strip isn't tied to the grid in any way.

Loose, independent copper wires are just that, right?

I see the point about the "dual DC" that an inverter puts out. Yes, small, outlets mounted in the side.

As far as neutral and ground busses being tied together, that should be easy to test once every ounce of real, live electricity is removed from the wire. Right? If I had a big ball of Romex, or if I was in a small shed where i'd run wiring but hadn't tied it in to the grid, I would simply measure for continuity between two of the wires, right?

I am NOT trying to do some quasi tied thing. If I do this, I will COMPLETELY sever the ties between the wires and the grid.

I did the same thing with one of my phone lines... Went outside to the "demark box" and completely severed the telco connection on line 2. Dead wires. Then I plugged my VOIP router into one of the (dead) line 2 phone jacks... voila! VOIP dialtone on Line 2!

What did I use for REAL ground? The REAL ground! As in, Multimeter prong stuck into the earth of my flower box.

valterra · « **Reply #6 on:** October 16, 2008, 05:06:18 PM »

As far as each line carrying a pulsed dc, I can certainly see how a neutral-to-ground connection in a house would translate to a hot-to-fake ground on an inverter!

POOF!

But once all ties to the grid are removed, they ARE just wires. After all, my solar and wind feed wires are cut extension cords... red positive and black negative. I could turn every outlet into 12vdc, or turn the into speaker jacks if I wanted.

By the way, I had this house built and did 80% of the wiring myself. Low voltage stuff EVERYWHERE inside these walls! I just didn't do the electrical and phone. But I KNOW this isn't an old house with a previous owner who did god-knows-what, etc.

ghurd · « **Reply #7 on:** October 16, 2008, 05:43:34 PM »

Link,

http://www.donrowe.com/user_guides/vector/vector_d_models.pdf

Page 13, #18.

Paragraph after #23.

Etc.

G-

Ungrounded Lightning Rod · « **Reply #8 on:** October 16, 2008, 07:51:58 PM »

Large to Small = live

Large to Ground recepticle = dead

Small to Ground Recepticle = dead

Large to ACTUAL ground = dead

Small to ACTUAL ground = voltage.

That outlet is DANGEROUSLY miswired. You have the hot and neutral swapped and the protective ground disconnected. (Not as bad as hooking protective ground to hot. But it's right up there.)

You need to wire protective ground back to the grounding system - NOT tied to neutral (except at the bond in the main breaker box) - with a separate wire at least the same wire gage as the ones feeding the hot and neutral.

zeusmorg · « **Reply #9 on:** October 16, 2008, 08:29:18 PM »

I don't believe you have your facts straight.

In the United States National Electric Code, the standard 120 outlet has 3 connections the small spade (brass coated screws) the HOT or 120 feed,(black or red wire, and in some cases other colors) the large spade(or silver screws)(white wire or gray) is neutral the third u shaped hole (green screw)(bare or green wire) is ground.

If you are describing a system other than that, my apologies, but if you are it would be better when giving specifics to specify which system you are describing.

So it seems to me, by his testing, only the ground is disconnected (which should be rectified!)

So it should be

small to large =120v

small to ground =120v

large to ground = 0v or low resistance

ground to actual ground = 0v, low resistance

large to actual ground = 0v, low resistance

It is possible on some systems to wire the ground plug to the case but this should only be attempted if the case itself is properly grounded.

dnix71 · « **Reply #10 on:** October 16, 2008, 08:41:50 PM »

Referring to the original question read this post

http://www.fieldlines.com/story/2008/7/13/15838/7798

His house wiring and inverter wiring sound correct, it's just that you can't connect a small inverter to house wiring in the US, and it's by design.

His inverter design is called "floating neutral"

Ungrounded Lightning Rod · « **Reply #11 on:** October 16, 2008, 10:03:20 PM »

You're right, I misread it. Hot and neutral are NOT swapped. (OOPS!)

But the protective ground pin is not tied back to building ground, so that still needs fixing.

valterra · « **Reply #12 on:** October 17, 2008, 06:41:37 AM »

The ground IS grounded. My Multimeter shows continuity between the ground plug and the muddy ground nearby. ;-)

SparWeb · « **Reply #13 on:** October 17, 2008, 12:46:46 PM »

The ground is grounded (maybe), but the neutral is not grounded.

That's what we're talking about.

Your tests do not confirm or refute it 100%, but somebody who knows the NEC should test the outlet, and maybe even check the CB panel.

Don't be surprised that this could happen in a house in the US built in 1999. Electricians are humans, too, you know!

TomW · « **Reply #14 on:** October 17, 2008, 03:29:44 PM »

Electricians are humans, too, you know!

Hmmm, not according to the Plumbers and Carpenters I know??

Tom

valterra · « **Reply #15 on:** October 17, 2008, 03:56:07 PM »

Good One, Tom!

Okay, I understand that the neutral and ground are tied together... or should be.

On the inverter, it is putting out what I will call dual pulsed dc on the hot and neutral lines. If that gets plugged into my house's wiring with the ground and neutral tied together, I am shorting one leg of that pulsed DC directly to ground. Poof.

But if I built a shed, or a cabin in the woods, and I ran Romex all around inside, I wouldn't tie my neutral and ground busses together, and I would power the place with an inverter... right?

How is this different, if a person can CONFIRM that there is indeed NO tie between neutral and ground ANYWHERE.

I could run new romex OUTSIDE the wall in that fancy channeling and install new outlets. Or I could run an extension cord to a power strip somewhere in the house... and nobody would have a problem with that, right?

Please don't read this as if I am a newbie stuck to my idea and telling the experts are wrong! I am perfectly willing to LEARN, even if that means I learn my idea won't work.

ghurd · « **Reply #16 on:** October 17, 2008, 04:29:30 PM »

In a cheap inverter powered cabin, everything (all 3 socket holes) runs to the inverter's outlet.

The inverter's case is grounded.

OR

The battery neg is grounded.

Usually pick one or the other.

Some inverters can have the inverter case and battery neg grounded. Not too many small cheap inverters will live through it.

"But if I built a shed, or a cabin in the woods, and I ran Romex all around inside, I wouldn't tie my neutral and ground busses together, and I would power the place with an inverter... right?"

Right.

The Live and Dead thing doesn't seem possible the way you have it written.

G-

valterra · « **Reply #17 on:** October 17, 2008, 05:10:03 PM »

Glen,

What live and deead thing do you mean? Sorry. Gettng confused.

If I went 3 feet out from my service panel box and snipped each conductor of the line leading to a room, I would have some dead copper wires in my walls, right?

I am not going to do that, but disconnecting all of the leads from the service panel is essentially the same thing?

Please guys, I know I am not dense. What am I missing (or perhaps not explaining correctly)?

Sorry if I mistyped and said I would tie neutral and ground . Of course I mean WOULDN'T.

valterra · « **Reply #18 on:** October 17, 2008, 05:20:50 PM »

Also I understand that there are MANY places where neutral and ground could be tied together besides inside the box. I would have to test for shorts.

SparWeb · « **Reply #19 on:** October 18, 2008, 09:33:03 PM »

Hello, valterra,

Hey, you've reached the point where you start to wonder about all the things everybody else seems to take for granted. Electrickery is totally mysterious, but "It just works".

If you hold up your small inverter, that device is designed to be a "mobile" and "floating ground" electrical device. What that means is that it is not intended to be a permanent part of a building. It is only meant to be installed in a vehicle, or temporarily where it will not interface with other electrical power supplies.

The wiring in your house, supplied by the grid, is designed to be permanent, grounded, and protected from a variety of fault conditions that the mobile inverter cannot do. It achieves this by grounding the enclosures of all receptacles and fixtures with a "non-current-carrying" ground conductor (the bare wire). The electrical circuit is carried entirely within the two insulated conductors. All black wires (or red if 240V) will have 120VAC supplied to them, and they must all be circuit protected at the box. All of the white wires must lead back to the box, and when no load is present, there must be no voltage applied to them. In the box, all of the white wires are "tied" to ground. Single point grounding of the white return wires ensures that they all have basically zero voltage. Those bare ground wires still have to be there, to protect against faults, lightning, water (or other contaminants) causing shorts, even though the do not play an active part in the normal electrical circuit.

Back to your inverter: it likely has a grounded case. From its point of view, "ground" is half-way between the black and white wires. This allows a certain amount of safety, but it does not permit grounding either the white or black wires. The white will have voltage, like the black, so you cannot short it without releasing the magic smoke.

Could you wire up a shed, in isolation, with that inverter? Perhaps, but it is not as safe. Twice as many wires have power, so are you going to put circuit breaker on both wires? Where is the circuit protection in the inverter? It is built into just one breaker. If you wire up the shed with Romex in several separate circuits (one set of lights here, some receptacles there) then what protects each circuit? It's the same nerve-center breaker that wipes out everything. If it's a fairly high capacity inverter, say 1800W, then it will take about 20 Amps to flip that thing. That 14 gauge romex isn't rated for 20 Amps.

It goes on and on... I'm only scratching the surface.

5 years ago, I didn't know any of the stuff I just wrote, either. This hobby has turned into an education for me, too.

Have a nice weekend.

valterra · « **Reply #20 on:** October 19, 2008, 04:44:25 AM »

Steven,

Thank you for the long reply. I appreciate al the detailed information.

It is way more complicated than I thought I guess.

I guess this is a rubber-meets-the-road situation for me. How do I put this energy I create to good use? Hardly seems worth it just to run my small portable radio. I was thinking of running my kitchen / dining room area with it (lights, etc.)

This all has to become pracitcal at some point, or else what is the point?

How to people do the off-grid thing is wiring a house with an invertert is too unsafe?

Ungrounded Lightning Rod · « **Reply #21 on:** October 19, 2008, 12:23:16 PM »

If it's a properly installed, up-to-code, grid-powered instalation there will be ONE connection ("bond") between neutral and ground (within your house). It will be in the main service panel, the first one after the meter.

However there will be another at the transformer (to the grounding system of the pole, which will also be tied by a pole-to-pole ground cable to other poles and their grounds), and yet another at each of the other houses fed by that transformer.

Opening the bond in your main box, if you're still tied to the pole, won't fully unbond the neutral from ground, nor will removing the meter (which is what the power company ususlly does, at first, if you ask them to unhook you). You have to actually unhook the neutral of the drop.

However if you want to move one circuit to the inverter you can unhook BOTH the hot (typically black) and neutral (white) wire in the breaker panel and move them both to the inverter. You'll then have a half-hot neutral, as with the inverter output. Be sure the protective ground is still tied to the building ground and that the inverter has whatever its manufacturer recommends for a ground.

(And DON'T tie the INVERTER's on-the-outlet protective ground pin to the building ground unless that's the only way to ground the inverter and its battery. Better to ground the battery negative if the inverter doesn't have a ground screw.)

valterra · « **Reply #22 on:** October 20, 2008, 07:32:26 AM »

This is exactly what I've been talking about.

From the box, remove the white and black wires from the grid. Now they are simply plain copper wires inside my walls. Like I said, I could use them as speaker wire for my surround sound system if I want.
To make sure there aren't any grounding surprises, double-check that the neutral and ground are now completely unbonded.

What is the problem with that concept? My "grid" power and inverter power will have NOTHING to do with each other. I'm not trying to do a half-a$$ job on that. If those wires are removed, they will be 100% RE.

SparWeb · « **Reply #23 on:** October 20, 2008, 01:06:49 PM »

"How do people do the off-grid thing...?"

Well you simply have the wrong inverter for what you propose. I replaced my little 12V portable inverter just this summer for a Xantrex 4024 Sine Wave inverter. The thing wires in to the house (if you want), can detect when the grid drops out, synchronizes to it when it is on, and can even start a diesel generator to recharge the batteries if it detects the voltage is too low. I'm not using mine with a grid-tie, myself, but I could.

I have it wired up to supply power to my barn, now, and it's grounded, the neutral wire is grounded, has proper circuit breaker panels, etc.

If you want to put your wind-generated electricity to use, either you have a project outside the grid in mind, or you are willing to buy the equipment that will interface with it. It's a "price of admission".

valterra · « **Reply #24 on:** October 20, 2008, 01:32:16 PM »

Steven,

Doesn't something like that require you to have a grid cut-off since if it grid tied?

If grid power goes out, I thought grid-tied stuff was supposed to shut off production.

DamonHD · « **Reply #25 on:** October 20, 2008, 01:48:24 PM »

Hi,

I hear what you say, but your insurers might have a fit if they thought you were repurposing existing wiring in a way that might result in an accident due to forgetfulness by you or someone else later.

There may well be rules/laws about what you can do with wires once they're laid out and installed as mains wiring to avoid confusion/accident.

Rgds

Damon

valterra · « **Reply #26 on:** October 20, 2008, 02:12:59 PM »

If I'd thought it out more, I may not have asked that question. Removing generation into the Grid and into your Home are two different things. Perhaps this type of inverter can separate your HOUSE from the GRID during an outage, yet still supply electricity to the inside of the home?

DamonHD · « **Reply #27 on:** October 20, 2008, 02:37:13 PM »

The SMA Sunny Island and Sunny Backup units can do just that (isolate the house from the grid and keep the lights on when the grid goes down), for example, and I'm considering getting one or the other, but the existing grid-tie that I have just stops pumping power into the grid if the grid goes down, which is safe but lets the lights go off when everybody else's go off...

Rgds

Damon

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Author Topic: Both AC prongs on inverter are hot (Read 6869 times)