Back feeding from inverters

Firstly, there should be a changeover switch, either manual or automatic that stops this happening on any legal installation.

If the installation is not following correct codes, usually, due to the load of other consumers still on the mains supply, the inverter will fail/breakdown trying to feed the local neighborhood on that phase!!!

In some cases, you would not only be trying to feed the neighbors lights etc., but you might be trying to back feed through any substation transformer, that had not automatically isolated itself from the local loads.....usually though, breakers will have dropped off preventing this happening in any western country at least....

Which is good as it would be dangerous for any line workers if power was coming from "the wrong direction!". They usually put a dead short on any "dead" line that they need to work on, to make sure that nothing untoward can happen....

The inverter will not back-feed unless you plug the outlet in to a wall outlet using two male plugs in order to power lights, radio , etc.

We had a hurricane and I used my inverter to power some low wattage lights - it lasted hours - but I simply plugged the lights directly into the inverter.

If you back feed a circuit in your house (with an inverter or a small generator, you must trip the main disconnect to prevent the possibility of killing someone. I had a friend killed in Houston working for Houston Power and Light by a back-fid generator.

Used as it is meant, the inverter will not back-feed into the house wiring.

I think the query was that it was NOT being used as meant (in a safe manner!)....which was the reason for the query in the first place.

I personally would never use an inverter to feed a house in the first place, but there are plenty of people with powerful home generators that think nothing of doing just that and without the changeover switch!!!

......And some of them post on CR4 too believe it or not as they "Know that they will never make a mistake!!!!" - thats how dumb and self centered some people can get!!!!

There are some inverters that are meant to backfeed the grid during normal operation. This is the net metering scheme (spinning the meter backwards) that is used in many renewable power systems. These intallations use a special flavor of inverer known as a grid tied unit. These special inverters either require exitation from the grid to operate or at least have detection circuitry, to verify that the grid is still up. Whese units detect a loss of grid power they immediatly drop out, ie shut off. In order to use one of these set ups you must arrange for authorization from your local power company. So, they can make sure that your system will not backfeed the grid when it is down. Odds are they will take extra steps when working around your house to make sure that you are not backfeeding the lines.

Several years ago I was asked to help an apartment building owner who had set up a battery-powered inverter system. The purpose of his system was to power sump pumps and garage doors for the underground garage. A previous general power failure during a heavy rainstorm had trapped all the cars in rising waters. The owner was having continuous trouble with destroying his batteries due to overcharging. When I got to the site, I found he had simply put two switches to start the inverters and connect them to the door motors and pumps. I was horrified. He could have easily fed power back to the grid endangering powerline workers. The only right thing he had done was choose a good inverter. I installed a large relay which switched the door motors and pumps to the inverter and turned on the inverter automatically in the event the grid power was lost. With this setup there was no way human error could send power back to the grid. And I chose an automatic two-stage battery charger which would quickly recharge the batteries and then drop the voltage to keep them float-charged. It was just a lucky thing he had bought the wrong battery charger and was forced to ask for help.

WOW, well done!!!!

The way people use the "cheap" chargers for continuous charging is beyond me. There ought to be a law banning them completely!!!

When there are frequent power failure due to breakdown or regular planned load shedding (Pre planned Load shedding by the power supplier due to shortage of power production)It is common practice to install power generating sets by consumers( inverter or engine powered generator) used as a stand by power source.They are of two types.

1. Un interrupted power supply units or UPS. These units are designed to be kept 'on' all the time and the battery is kept floating and energy is normally drawn from the power source. These units are designed not to give any feed back to the power grid.There is in built safety circuit to prevent any back feed.

2. Inverters or engine driven generating sets are installed, which are automatically or manually switched on when regular power source fails. They are to be operated as alternative power source.Since these source are connected to the regular load, they must be interlocked to prevent any back feed. Some manufacturers provide automatic change over system with built in inter lock . If that is not available positive interlock must be ensured to avoid back feed.Interlock can be either automatic change over or manual change over switch.

It is very dangerous if power from the local alternator / generator is fed back to the supplier' grid. It can cause major accidents as the feed back voltage will be stepped up by the transformers if there are no undervoltage tripping relays. Suppliers do not provide under voltage trip to avoid recharging after resumption of supply. The people working on lines may be electrocuted.

It is mandatory safety requirement to provide interlock for captive generators.

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"It is mandatory safety requirement to provide interlock for captive generators."

Most definately true. Another point, if you are backfeeding with your generator or inverter and the power comes back on out of phase, there will be massive amounts of smoke and fire works. I have been made aware of cases when rather large generators, approx. 3/4 MW and weighing several tons, have literally thrown themselves off of their mount pads due to being suddenly connected to an out of phase grid.

A very good point that I neglected to mention......well put!

Standing near to one could easily be the last thing you ever do on this earth, even if it was only a couple of Kilowatts!!!!