Slim:
The transfer switch provides a positive mechanical interlock to avoid closing in the generator breaker with the "main" breaker also closed in. The bigger danger in this is that a standby generator, backfeeding thru into the local distribution lines will also backfeed the transformers. Result is the "high side" of the transformers will be energizing the dirstribution lines with whatever distribution voltage is (could be 33,000 volts, 13,800 volts, or a few other common ones). For this reason, the National Electrical Code and any local electrical codes will call for a transfer switch with a positive mechanical linakge to insure there being no way that BOTH breakers can be closed at the same time.
In answer to your question: YES, a person can use a standby genset by FIRST opening the main breaker to cut any tie to the local distribution lines and then closing in the breaker connecting the genset to their service panel. Understand I am in no way recommending this method or offering it as an alternative to the use of transfer switches with positive mechanical linkages between the generator and main (line) breakers.
I have a setup I use in my own house for standby power. I do not endorse or recommend this method as it is not in accordance with NEC or any other electrical codes. It consists of a 60 amp fused safety switch with a 60 amp receptacle out in the garage. This switch is wired to a 220 volt breaker on my panel in the basement. Normally, I run the air compressor and a 3 HP Cincinnati Bickford drill off that 60 amp receptacle in the garage. I have a Lincoln gasoline driven welding machine with 6.5 Kw of 220 volt 1 phase power available. When we do have an outage that goes more than a couple of hours, I use it for standby power. Here is my method:
1. Get a flashlight and go in the basement and OPEN the main breaker.
2. Go into the garage & make sure the 60 amp safety switch is OPEN.
3. Roll out the Lincoln Welder. I have a heavy lead cord made up with appropriate 220 volt male plugs at each end. This lead cord is "mobile Home Cord" and good for at least 60 amps. The cord is kept ready to go, hung on a rack by the garage door. After the welding machine is rolled outside, I plug in the lead cord to the receptacle on the welding machine and to the receptacle in the garage. I then hook up a grounding jumper from the welding machine frame to a ground stake.
4. I start up the welding machine and get it running on "high idle". After it smoothens out, I plug in a 110 volt floodlight to get some base load on and get the generator governor to take over.
5. I then close in the 60 amp switch in the garage. This hits the welding machine with whatever loads in the house happen to be there- refrigerator, freezer, well pump, and oil burner all come on as a block load. The welder pulls it.
When we are hanging ont he welder, we do not run it continually. We run perhaps 30-40 minutes to an hour every few hours. This is enough to charge the well pressure tank for toilet flushing, and keep the food cold and the house warm. We cook on a propane range, so do not need electricity to cook with. We have an assortment of Coleman liquid-fueled lanterns (bought for 1-5 bucks apiece at yard sales) for lighting and these are kept fueled with good mantles, pumped up and ready to go on a rack in the garage. We use the Coleman lanterns for steady light. If the outage goes overnight, we keep a couple of the old Dietz wick type kerosene lanterns going with the wicks turned low for night lights. We also keep about a full cord of dry wood in the basement, so keep a fire in the wood stove thru the winter as well. There is no way that a Lincoln Wleder with an air cooled engine is a base-load generator.
The tricky part is knowing when the power has been restored. We lived away from any other houses, though a couple have been built in sight of us, so I suppose we will look for their lights. If you live in a remote spot as we did, the thing to do is to wire up a couple of indicator lamps on the incoming side of your main breaker. If those lamps come on, it means power has been restored.
One time, years ago, we had a windstorm outage and were out for about 12 hours. It was night time, and we had had our supper and the Lincoln Welder was powering the house. I had fueled it not too long before. Suddenly, the lights started flickering and going bright and dim. I could hear the engine on the welder starting to "hunt", which was uncharacteristic as it simply conks out when the fuel runs out. I ran out to the garage and opened the 60 amp switch taking the welder off line. I then went into the basement and close din the main breaker and found the power had come back on. In thinking things over, I realized the neutral leg of the wiring between my house panel and the distribution grid is hard wired- the main breakers do not disconnect it. I thought I might have had a backfeed from the grid via the neutral leg when the power was restored. I asked an electrical engineer about it and he told me that when the power was restored, the slug of load on the system caused a phase-to-phase imbalance on the primary (high side, 3 phase power) side of the distribution transformers in my localized area. This had the effect of putting a momentary current into the neutral leg and backfeeding the welding machine. Weirdly, single pahse transfer switches do not usually break the neutral leg, as this is a rather uncommon phenomena.
To give an example of a transfer switch gone wrong: I was on a job in Venezuela years ago. A telex (predated faxes and no cell phones back then) arrived at the jobsite, asking me to travel to Trinidad to handle an emergency job involvinv a melted-down generator. It was a bit of a job to get from the rural jobsite int he back reaches of Venezuela to Trinidad, but I did. I arrived at the Nelson Street Telephone Exchange a day or so later and was shown about a 350 Kw diesel genset. The engine looked fine, but the generator was burnt up and had molten copper coming out some of the vent openings on the stator. A new generator had been shipped from England and my job was to change out the damaged generator and make sure that genset was OK. The story of what had happened was pretty simple: a transfer switch the people at the Nelson Street Telphone Exchange had malfunctioned following a power outage. The gist of it was this: The electrical engineers there had designed their own transfer switch. What they used was two independent circuit breakers with automatic clopsing/opening by means of heavy springs. The springs were kept "charged" by small electric gear motors following each breaker operation. The breakers were worked remotely by control circuits. The phone exchange engineers had designed and built circuitry which sensed a 10% or greater voltage drop on the incoming grid power (or a loss of it) and opened the main tie breaker to the grid. At the same time, the diesel set was auto started. When it had built voltage, the circuitry then closed in the generator breaker. No mechanical interlocks between grid tie breaker and generator breaker. When grid power was restored, the circuitry sensed it and a time delay relay kept the place ont he generator for perhaps 20 minutes more to make sure the power was really back. After 20 minutes, the generator breaker would be opened and the grid tie breaker closed in. The generator was then run unloaded for another 20-30 minutes to cool it down as it was a turbocharged diesel set. This system had worked fine for years until a malfunction occurred. AN outage had occurred and the gneerator had come up and on line, carrying the telephone exchange. When grid power was restored, the time delay realy ran out and called for closing in the grid tie breaker. Unfortunately, some component in the control circuitry failed to provide the input that the generator was still on line with the generator breaker still closed in. The result was that the grid backfed the generator. The odds of the generator being synchronized (phased in) to the grid were so remote as to be impossible. The grid, having megawatts of power behind it simply overpowered the generator. The diesel engine was turnign the generator and the grid was trying to twist it into phase. The diesel had enough beef not to let this happen, so the windings melted down. I installed the new generator, checking the diesel for mechanical damage in the process. The diesel was fine. I advised the electrical engineers at that phone exchange to go get a transfer switch with a positive mechanical linkage between the grid tie breaker and the generator breaker to prevent a recurrence. I took a flight out of there the next morning so never heard any more about it.
There is a reason for using a transfer switch with a mechanical interlock, and it is to make things as relaible and absolutely foolproof as possible. I am not one to talk, using the system I do. I didn't hav eone installed when we were building our house- too costly and things happening too quickly. Now to install one would mean having the meter pulled to de-energize the incoming feed. The system I use works fine as long as it is done "by the numbers", without deviation.
Joe Michaels