Author Topic: Bonded / Floating Ground Question (Read 8256 times)

Volvo farmer · « **Reply #33 on:** January 03, 2008, 10:38:21 PM »

Just to be clear.

There is no "negative" inside wiring in a traditional home. There is "neutral" inside wiring.

This comment brought to you by AC/DC fan... Volvo Farmer.

DamonHD · « **Reply #34 on:** January 04, 2008, 03:14:34 AM »

Hi,

My grandfather when young was on a crew that amongst other things helped install the grounding plates for one of their area's early electricity generators.

Apparently at the time the power was generated/shipped as DC, and he absolutely would not believe me as a kid when I told him that everything was now AC. Indeed, it took the intervention of both my university-grad parents to get him to back down and stop shouting at me!

So, many, many, many years ago I guess some houses did have DC mains feed! B^>

Rgds

Damon

wooferhound · « **Reply #35 on:** January 04, 2008, 08:21:19 AM »

The way that I understand it is something like this . . .

The 2 power leads coming out of the inverter are Floating (not connected to ground)

If you try to ground any of the 2 power leads you are Shorting that lead to ground

Of course this is an overload to the inverter and it blows up.

Therefore you can't have Neutral and Ground connected together anywhere in your system.

The Breaker Boxes in the US are wired with the Ground and Neutral "Bonded" together

wooferhound · « **Reply #36 on:** January 04, 2008, 08:44:14 AM »

Most houses have a single circuit going to the Breaker panel that runs most of the Lighting. If this is the case in your house. You could single out this lighting circuit and just connect your inverter to that.

Alternatively

You could just purchase some 12 vdc CFL bulbs and use them. Wire your 12 volts straight into the House wiring and forget the inverter and changing the panel all together.

DigitalMind · « **Reply #37 on:** January 04, 2008, 08:47:16 AM »

Hehehehehe. Thanks for clearing up the terminology for me Volcofarmer.

DigitalMind · « **Reply #38 on:** January 04, 2008, 08:49:31 AM »

Wooferhound,

I would actually love to connect that 1 existing wire for the lighting directly to the 12 volts and bypass the inverter alltogether. I was worried that there would be too much loss in the wiring

? (It's a Tiny 500sq Foot house, so there's not much!)

Can I really do this That would be great ..

jimjjnn · « **Reply #39 on:** January 04, 2008, 09:06:55 AM »

As a kid ,I lived in a community here in Denver that had their own steam engine generators. 120 volts DC !! Quite a shocker if you messed around with coat hangers in light sockets or wall outlets. Knocks you across the room if it lets go of you.

elvin1949 · « **Reply #40 on:** January 04, 2008, 09:27:58 AM »

The house wiring should be 12 ga.

CFL's are low amp YES it will work.

Just make sure you have DC rated light switches.

later

Elvin

DigitalMind · « **Reply #41 on:** January 04, 2008, 09:38:58 AM »

Elvin,

That's a bummer, didn't realize the switches would need to be changed if I converted the light fixtures to 12 volts. That's the killer in this situation. Doing all this on a crazy small budget. Can't really change all the light switches. (It's wierd, the whole house is just 1 room, with 5 light fixtures, and each light actually has it's own switch!)

I'll go to the hardware store ... obviously if it's just a couple bucks per switch it's no problem ...

Thanks !

Cloaked User · « **Reply #42 on:** January 04, 2008, 10:55:24 AM »

The loss in the wiring on that one circuit with DC cfl lamps might be less than the loss in the inverter.

If you just want to fire up one lighting circuit with the inverter, then you can leave the ground alone and make sure you have the black and white wires from the romex feeder going out of the panel. Connect them to the inverter, bypassing the breaker and the neutral bus, and ignore the ground on the inverter outlet. Just make sure the neutral is not grounded elsewhere. You never know. Any electrician will tell you that all sorts of weird things are possible, even on a brand new house. This way, the house stays grounded normally, the inverter doesn't blow its top, and you can use ordinary cheap lamps and switches. A four amp fuse, or so, between the inverter and the feeder for the lighting circuit would be a great idea.

ghurd · « **Reply #43 on:** January 04, 2008, 10:56:34 AM »

Might look for a switch that has a good solid "SNAP". Not the quiet soft touch kind.

Maybe rated to 277V too.

Cloaked User · « **Reply #44 on:** January 04, 2008, 11:02:34 AM »

Every time something like this comes up, and the thread gets long and confusing, I am reminded of my favorite Homer Simpson quote. Homer is trying to avert a meltdown, with sirens going off all over, as he studies a huge schematic of the plant.

"D'oh! Who'd have thought a nuclear reactor would be so complicated!"

ghurd · « **Reply #45 on:** January 04, 2008, 11:07:47 AM »

Or a $2 automotive toggle switch with screw connections, and a new switch plate/cover with a round hole, or no hole (drill your own).

DanG · « **Reply #46 on:** January 04, 2008, 11:20:16 AM »

If one waits long enough history will repeat itself.

Apologies to coldspot for flagging (flogging?) his posts!!

Inverter Chicago Electric Item #94009 1,000 watt

http://www.fieldlines.com/story/2006/6/22/02324/1164

I didn't listen !

http://www.fieldlines.com/story/2006/7/4/193146/8689

(Note the calm even voice of reason from the Tom. Keep up the good fight TW.)

SparWeb · « **Reply #47 on:** January 04, 2008, 12:52:11 PM »

Then my crappy inverter is even crappier than yours! LOL :-P

DigitalMind · « **Reply #48 on:** January 04, 2008, 03:00:23 PM »

Hey DanG that second link was great. I wish I came upon that one before I asked this question !! (I did look, and found a lot of similar ones)

Lots of great advice from TomW too !

Atleast I know to look out for the neutral - ground bonding now. When I go up this week to install everything I am going with a backup inverter "just in case".

I think it'll all be ok now. I just didn't really understand how the fuse panel worked (I opened mine from home up and just that helped alot) and I had never heard about the neutral to ground bonding that is usually done when a place in cabled for grid power.

Thank god for this forum where I accidentally learned about this !

Thanks everyone for the great advise and knowledge sharing. Everyone here is great for that.

DamonHD · « **Reply #49 on:** January 04, 2008, 04:14:43 PM »

Is this a reverse pissing contest? B^>

May I please stand a long distance up-wind?

Rgds

Damon

elvin1949 · « **Reply #50 on:** January 04, 2008, 09:43:56 PM »

A small cap across it will help tame the dc arc.

later

Elvin

scoraigwind · « **Reply #51 on:** January 04, 2008, 10:35:36 PM »

I know this has been a long thread and a bit old so nobody will read this but I thought it might be worth saying why it is that cheap inverters have this problem in the first place.

Cheap inverters use a high frequency inverter to produce a high DC voltage. They then 'chop' this into AC at 50 or 60 Hz. The high DC voltage is directly linked to the battery so that they share a negative. When the output is chopped, the hot wire goes negative, positive, negative etc.

Now if the neutral is grounded, the battery negative will go 'hot' every time the 'hot' goes negative. The battery negative should be grounded. If not then grounding the neutral makes the battery terminals hazardous. If it is grounded then there will be a short circuit on the output every half cycle. Hence the smoke.

Boss · « **Reply #52 on:** January 05, 2008, 07:47:44 AM »

Hugh wrote: The high DC voltage is directly linked to the battery so that they share a negative.

Not sure I follow this Hugh.

Are you saying cheap inverters (for the US market) need three separate terminals, because there is potential between the neutral and emergency ground because, of poor wave shaping? Or are you saying the case of the inverter is grounded to the negative terminal of the battery?

I traded to DanB an 100mhz quad trace oscilloscope. Very interesting results will be had by selecting which ground you use. In other words, the scope sees the potential between each device through the ground and displays the wave accordingly.

DigitalMind · « **Reply #53 on:** January 15, 2008, 07:33:39 AM »

Now that i've actually done it and it went well .. I will add this this thread that I originally started :

BASICALLY, I used mostly Ghurd's advice : MAKE SURE THE NEUTRAL WIRE IS NOT GROUNDED.

As simple as that.

I got my multimeter, and checked for continuity between the ground and neutral.

There WAS continuity.

So then I looked for how to disconnect them. In this case, unlike what Ghurd said but like what others said, the grounds were already on their own little bus bar, so I didn't disconnect them, I just had to find that big Screw that connected (apparently) the ground to the neutral. Once that was removed, no more continuity ! (Thanks to the person who mentioned the Green Screw, cause it would have taken alot longer to find what was connecting the neutral to ground)

Then I simply connected the inverter to the IN of the fuse panel and everything worked !! YAY !!!

TomW is right : Once it's there in front of you, it's pretty simple .. I was doing all this without seeing what I was going to be working with but I had to ask these things in advance cause once there, I have no internet, no phone, no nothing ..

Thanks for all the great advise from everyone !

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Author Topic: Bonded / Floating Ground Question (Read 8256 times)