Author Topic: Plug an Inverter Into the House Ring Main (Read 16217 times)

Marco · « **on:** February 06, 2006, 07:19:30 PM »

I was thinking of power from backup systems, batteries - iverter setup.

Would it be possible to run the house ring main by plugging

an iverter output straight into a plug socket - thereby supplying

the ring main of the house with the modified/true sine wave?

Of course I realise the mains supply would have to be isolated by switching

off at the fuse box.

I just wondered if is was possible and if it would run appliances correctly.

Marco Miglionico

apie · « **Reply #1 on:** February 06, 2006, 12:51:56 PM »

Marco, I think it is possible. But you must be SURE not to interfere with your main power supply. So I suggest the following:

shut down the fuse of the circuit you want to use
measure the voltage at the socket that you want to use. Make sure it is ZERO!
mark the fuse with a warning: "don't enable this fuse" or something like that
go ahead and plug in the output of the inverter

If it's a modified sine wave, some say you can have problems, but I didn't have any problems at all (up till now).

Do this at your own risk... (sorry, had to add this)

TomW · « **Reply #2 on:** February 06, 2006, 01:20:33 PM »

Marco;

I feel I must point out how dangerous this is.

First you will have live voltage on the main plugs exposed lugs you use on the inverter.

Second you eventually will plug in a hot inverter to a hot wall socket thus destroying your inverter and many other very bad things [tm] could happen as a result.

Electrically it will probably work but it is really not a smart thing to do for more reasons than i cited here.

Cheers.

TomW

kurt · « **Reply #3 on:** February 06, 2006, 01:27:58 PM »

it won't work even with the house mains turned off the neutral will still be connected to ground inverters don't like grounded neutral unless they are specifically designed to work that way. most inverters when hooked to a grounded neutral will fry immediately

veewee77 · « **Reply #4 on:** February 06, 2006, 01:31:59 PM »

I did this on a house I was working on for my son one time, but there was NO connection from the power company to it at all. And, it was only for testing purposes so we could make sure everything was ok before the power company came and turned on the juice. The house had been sitting empty for a number of years and fixtures were gone and things left undone, etc. If there is even a remote chance that there could be grid power applied to the house, DO NOT DO IT!

And remember, you MUST connect the wires in both plugs with the proper polarity, and it would be advisable to not connect the ground wire at all. Some inverters will die a quick death if this happens.

Also, make sure everything is plugged in completely before turning on the inverter!!! DO NOT turn on the inverter and then plug it in. If there is anything wrong in the house, you will likely fry the invertor(worst case scenario), blow it's breaker or fuse(replaceable) or burn the house down (worst case scenario)(Oh, I said that already. . .)

All in all, for any purpose other than an extreme situation, DO NOT DO THIS!.

Doug

Ungrounded Lightning Rod · « **Reply #5 on:** February 06, 2006, 01:54:30 PM »

An additional safety issue:

A normal breaker can be backfed. But a GFCI breaker (or outlet) will fry its GFCI funciton if it tries to trip while being backfed.

Voice of experience: Last power failure I carefully cut my main and all unnecessary circuits (to protect the linemen), hauled out the portable genny and its double-male "widowmaker" cable, and powered up my house by backfeeding the trailer outlet. (I had set up the wiring so all the emergency loads - refrigerator, bathroom light, emergency lighting, and TV system for news - were on the same phase, so I could do this sort of thing.)

Unfortunately, I brushed the test button on the $85 30A in-panel GFCI breaker feeding the trailer outlet. After about a half-second of buzzing (trying to trip) it had converted itself into an ordinary non-GFCI breaker. Had to buy another one to make the trailer outlet GFCI / safe again.

Marco · « **Reply #6 on:** February 06, 2006, 02:24:21 PM »

"And remember, you MUST connect the wires in both plugs with the proper polarity, and it would be advisable to not connect the ground wire at all"

So I should not connect the earth pin of the inverter to ther earth pin on the wall socket?? (In case my inverter doesn't like it)

As for the wires in proper polarity, as it is a/c I thought it would not matter which way round the live and neutral wires were (brown and blue in the u.k.)

Actually I was only thinking of this is times of power cuts!! Although I do like to experiment. Boom.

Marco

Opera House · « **Reply #7 on:** February 06, 2006, 03:11:48 PM »

There are panels they sell at the building supply stores that do this. Basically they use a THREE WAY SWITCH. This is the switch with three trminals that is used to turn on/off a light from two locations. This box is placed at the fuse box and switches a single circuit to either the normal circuit breaker or alternate power. Usually these boxes have about 4 circuits so you can power a hall light, refrigerator, furnace or other basic need. This allows you to do one at a time if your power is limited. You can not do it safely by just flipping breakers. Most inverters at best will shut down if they are grounded. It should also be noted that if the inverter and battery are allowed to float, they will be at about a 70-100 volt potential and be LETHAL. An isolation transformer should be used if a common inverter is used.

adelaide · « **Reply #8 on:** February 06, 2006, 03:21:59 PM »

Good advice so far,some inverters are electrically isolated ,so you wont have a neutral problem, It will be a problem if it isn't .

I did this to the light circuit and put note on fuse box , tape up the hole, hide the fuse and also I put a 5amp fuse on both sides of ac power from the inverter , then put into a light socket near inverter(bayonet fitting).You need to be careful I probably wouldn't recommend it, good if you can put it through an earth leakage detector to be on the safe side.workes well.

force9BOAT · « **Reply #9 on:** February 06, 2006, 03:33:11 PM »

Wow, after reading all the warnings by other members I suggest purchasing an extension cord to run from the inverter to what ever you need to power and not conenct at all to the house.

Rob

dinges · « **Reply #10 on:** February 06, 2006, 04:25:56 PM »

Hey,

You have a widowmaker too? I thought I was the only one foolish enough to build one.

(for those that don't know: a 220V plug, with cord. At the other end, 2 crocodile plugs are installed. Can sometimes be very handy, but is always VERY dangerous. I usually check 4 times that everything is ok before plugging it in)

As far as backfeeding is concerned: I do own circuitbreakers with a switch (I think made by GE?), that can be switched off and then locked by installing a padlock. Such a device (with you and only you having the key) could make such a system at least a little bit safer. No more 'accidental' turn-on.

Backfeeding with 220V on the prongs is something that I've done once, but not something I enjoy doing...

IF and only IF everything is done correctly and safely it will (continue) to work. But if anything should happen, I don't think insurance is going to cover it...

Peter.

dinges · « **Reply #11 on:** February 06, 2006, 04:30:38 PM »

Wait,

You've got a different kind of widowmaker than mine... Hmm, I should still have some male plugs lying around and a piece of wire. Good idea! (actually, it isn't a good idea, but will be built anyway )

Peter.

Experimental · « **Reply #12 on:** February 06, 2006, 06:16:49 PM »

I "second " Kurt on this -- as many inverters will smoke if the neutral is grounded in the breaker box ---AND most are in this day and age !!This is called "bonded", by electricians !!

Some inverters can tolerate this, but I would not take the chanch -- That "Magic smoke" is really expensive !!

Happy wireing, Bill H.........

Ungrounded Lightning Rod · « **Reply #13 on:** February 06, 2006, 06:58:20 PM »

I was playing fast and loose with the "widowmaker" definition.

Yes, the canonical version is male plug on one end of the cord, aligator clips on the other. (Typically found on the bench of a TV repairman's in the tube-set days, or some other electronic techie of the vacuum tube era, or electrical techie.)

However, I was stretching a point by using it to refer to a line cord with male plugs on both ends.

(Speaking of which, that cord is normally stored by plugging BOTH ends into the genny's outlets when the latter is put away, just to avoid accidentally plugging one end into something with the other end lying about on the bench or wherever. The genny is a 120-only so it's not going to short the phases if somebody cranks it up with the cable in storage mode. If I'm using the genny to do something other than backfeed the house, BOTH ends get unplugged and knotted together.)

dinges · « **Reply #14 on:** February 06, 2006, 07:13:43 PM »

I still remember the puzzled look on my brother's face as he saw my widow-maker for the first time.

Then, I gave him the end with the two crododile clips, saying, 'hold this for me', while pretending to want to plug it in. I've never seen someone letting go of something this quickly :-)

I won't repeat the language he used. LOL.

Peter.

drdongle · « **Reply #15 on:** February 06, 2006, 07:49:58 PM »

In the Navy we used to call this a "Kill Me Cord".

terry5732 · « **Reply #16 on:** February 06, 2006, 10:45:44 PM »

I had had a 220 volt water heater. I switched to gas and now have a connection box for generator. In a power failure, I simply turn off main breaker which cuts the two hot connections to the outside lines - everything remains connected to ground through the neutral. A three conductor cord from the old water heater disconnect goes to 220 volt on generator. Water heater disconnect turned on start generator. When line power comes back, turn off water heater disconnect, turn on main. I guess I could get something to do this for about $500 at Home Depot. If you don't know what you are doing - don't do it. Don't preclude yourself from learning, but you must learn what you are doing before you dig in. That sounds like an impossible catch 22, but really it just means that those with experience have been zapped repeatedly.

nothing to lose · « **Reply #17 on:** February 07, 2006, 03:57:27 AM »

Well you guys should know your not the only ones with me lurking around here that have a "window maker" so to say. My first one was probabably 10-11 years ago and about 5' long, the newest one was about 100' or so.

Now I only ever really use mine when there is no grid connected though. First trailer house here before getting a power pole, over at the rock house, etc... And I never backfed a GFI breaker or GFI outlet. Also so far I only do 120V since I only ever had 120V inverters.

I also used my "widow maker" to connect grid power to a trailer house that had no feed lines, mostly used just for storage. Then I had lights and could run the shop vac, drill, saws, etc.. while working in it. All lower power total than the cord was rated for of course. It backfed one breaker and only half the circuits were live. Power pole was about 75-80' away.

That tied ground can be a problem to watch for. Check to be sure or answer if you know for sure. If you ground the inverter but do not use the ground wire on the outlet, then tie into a bonded ground/neutral in a house will it fry the inverter, I don't "THINK" so? Also if the house ground and netraul are bonded but the inverter outlet ground not used, then the house is still grounded as it should be right. I think it works that way, but I don't remember for certain at the moment. As I am thinking (but confused at the moment) The house would be grounded, the inverter would be grounded, the cord would NOT be grounded, IS THAT CORRECT??

Be sure to note the uncertainty of the above before trying it yourself!

nothing to lose · « **Reply #18 on:** February 07, 2006, 04:32:17 AM »

If you only need to run 1 or 2 circuits another thing I have done is pull those out of the main box so they are not connected to ANYTHING. Then I put an outlet on those wires or a plug depending what I am doing and why.

So say you wanted to run backup for your kitchen for the fridge and such. Find that circuit you need, pull all the wires from the breaker box, put a twist lock plug on the wires correctly. Connect wires correctly to the breaker box where you removed that circuit from and install a twistlock outlet on those. Run wires correctly from your inverter to a twistlock outlet. Paint the breaker box outlet blue and the inverter outlet red (or what ever colors you want)and a label is good too.

Now no problem, plug the circuit into the grid power normally untill it goes down, plug into the inverter circuit when you need the back up power. Or you could swap back and forth anytime you want.

For anything important or high power I like twistlocks. You don't want the cat to knock the plug out and have the fridge unplugged for a day or two!

You could get as fancy with it as you want, and as safe as you want.

For instance, install a breaker box fed by the inverter and install the outlets for backup to those breakers. Then that one is not bonded but the grid one is. As long as there is no other bonds in the circuit then it should work great.

For awhile I had the breaker box for the grid, it was mounted high on the wall. I installed a breaker box for the inverter lower. Just under the grid box was the grid outlets and just over the inverter box was the inverter outlets. All painted and labled nice too.

Simple and easy to plug into either one as I wanted. I had a couple circuits wired to do that with. It was a nice way to add or subtract loads to the inverter to use more battery power when available and less grid power.

Sometimes you have lots of wind sometimes you don't. I figured why dump the excess or shut down the mill when I was around. Batteries get full plug more stuff into inverter, batteries get low plug more stuff into the grid

I took it back out because I used the inverter elsewhere for awhile, plugs and outlets too. And my wind gennies were more testing toys to play with then than real power, but they worked and charged batteries so I used what I could when I could and it worked very well.

Drives · « **Reply #19 on:** February 07, 2006, 06:18:03 PM »

On my ship we called it a "suicide cord"

We still use them to this day in my shop.

apie · « **Reply #20 on:** February 08, 2006, 01:49:05 AM »

Does anybody know why inverters don't like grounding? I fail to understand.

To me it's just a power source like any other.

ghurd · « **Reply #21 on:** February 08, 2006, 10:55:38 AM »

The grounding '3rd' prong on the inverter is kind of a fake ground on many inverters. It is kind of between the 2 hot voltages. So it doesn't like being connected to either.

In US house wiring, the neutral (white wire or longer plug slot) and the ground (3rd round hole, or the bare wire) are connected in the breaker box. The widow maker, or direct wired, will connect the inverters ground to neutral via the breaker box, shorting the inverter.

G-

apie · « **Reply #22 on:** February 09, 2006, 02:27:13 PM »

That makes sense. Thank you.

In the electrical installation of my house the neutral wire isn't connected to the ground. I know this pretty well as I did the installation myself ;-) Disadvantage is of course that the neutral wire is not really neutral. But I don't know of any regulation in my country (Belgium) that requires this connection.

So in short, IF you connect an inverter to an outlet (without any voltage on it), than you just need to be sure that the ground wire is not connected. Then it should be safe(r).

ghurd · « **Reply #23 on:** February 09, 2006, 02:42:15 PM »

I do not know.

Is there a connection between the neutral and ground somewhere outside the house?

Possibly measure the AC voltage difference between the neutral and ground and go from there?

Some things to keep in mind.

The TV, VCR, cordless phone, answering machine... All take some power when they are off.

Make very sure the mains breaker is off before the widow maker is plugged in.

I would recommend a simple extension cord or two instead of a widow maker.

apie · « **Reply #24 on:** February 10, 2006, 01:20:53 AM »

In my case, I'm sure there is no connection between the neutral wire and the ground as I can measure voltage between the neutral wire and the ground. But I know in some houses this is different. Nevertheless, if you disconnect the fuse, the circuit becomes seperated, so the connection is lost and it should be safe.

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Author Topic: Plug an Inverter Into the House Ring Main (Read 16217 times)