My 3-story office building has a full generator back-up. Back-up power kicks in shortly after the main power is lost. But, I was wondering: How come a commercial generator (apparently) does not need a MANUAL transfer switch, but a residential generator apparently does. Why can’t the transfer from main power to auxiliary be totally automatic and seamless to the resident?
Transfer switches are an optional piece of equipment on both commercial and residential generators. There are several reasons you don’t typically see them in residential neighborhoods:
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ATP switches are intended for use in applications where minutes matter. If a business can afford to send Joe outside to fire up the generator and throw the switch it’s fine.
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residential housing generally has no need for immediate transfer to generator power.
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commercial units normally have very large tanks that should hold enough fuel year round to run for 3-7 days depending on load. Residential units generally aren’t sitting there fully fueled and connected at all times.
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many commercial facilities have a UPS battery backup system that keep thing me completely transparent to the people inside. Power goes out. Batteries pick up. Generator runs and Ups backs down.
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All generators require a transfer switch. You don’t want to run one when your house or business is connected to the grid. That’s a good way to kill the guy who’s trying to fix the power.
There are automatic transfer switch systems for residential, but they’re expensive and typically only seen in high-end homes. Additionally, for the reasons Cubsfan mentioned, a residence generally doesn’t need a generator to kick in right away or run 24 hours a day.
It can be.
You just need to pay for an AUTOMATIC transfer switch to be installed. Most homes don’t, since being without power for a couple of minutes while someone runs outside, starts the generator, and throws the manual transfer switch is not critical. For many commercial buildings, it IS critical – they need an immediate, automatic switchover.
My Onan has such a system although I did not hook it up. Many Generac systems that come in the metal enclosures are sold with automatic transfer switches.
The Onan unit keeps the battery charged, starts and ties in the genny when needed, and restores the line when it comes back. Many units can be set to exercise the generator on a scheduled basis, just like the big boys.
The best commercial systems also include a battery UPS that takes the load without interruption while the generator starts and stabilizes.
Dennis
Yeah, here’s one right here.
Of course, these switches are so expensive it’s a better bargain to just buy a generator with a switch.
In most a commercial settings the building has a emergency power distribution system. It is normally powered by the utility. When there is a power outage the generator starts up. The ATS (Automatic Transfer Switch) disconnects from the utility and connects to the e-generator. The only the emergency circuits in the building have power. When the utility power is restored the following normally happens. After s to 5 minutes the ATS reswitches back to the utility and the generator runs through its cool down cycle 1 to 5 minutes. The the generator shuts off. This system is normally added to the building during construction.
To add a generator to your home with a ATS will take more work. either the generator has to be large enough to handle the whole load or major rewiring will need to take place. Determining which circuits are to be emergency circuits disconnecting them from the main panel and reconnecting to the emergency panel. Or it can be done manually. Connect the house panel input to a 3 way switch. One input connected to utility, one input to e generator and the load side to the home main. Power goes out. Start generator. Open all breakers on home panel. Switch from utility to generator. Then close the breakers to the circuits you want to power up, making sure you do not exceed generator out put.
I’ve had a 15kw whole house generator for 6 years and the ATS installation is a common practice.
Some of the ATS already do this. They have a row of breakers that you want to be powered. The breakers from the house run through those ATS breakers, and when the generator is used, only those breakers get powered up.
Dennis
My son has a gas fired generator with an automatic transfer. The gas is what comes from the gas pipes that the stove and dryer run on, so fuel storage is not an issue.
Wow. That generator is “only” $3,100. I imagined they cost more like $10,000. Of course site preparation and the electrical work probably adds another $3,000, but this is more affordable than I thought.
And that takes rewiring. The wires have to be removed from the home’s breaker panel and then wired to the panel with the ATS. Depending on the location of both not normally a quick job.
It shouldn’t be all that more complicated than wiring a manual transfer switch. If you can afford a generator and transfer switch big enough for every household circuit it’s just a redundant main breaker plus a big transfer switch. If you can only protect certain circuits a manual transfer switch still requires running a par of wires between every protected breaker and the “switch” (which is actually one switch per protected circuit).
I have a 5.5kW General wired to a 10 circuit manual transfer switch. Basically for each circuit you run a wire from the regular breaker to the transfer switch and back to the wire that you just disconnected from the breaker.
As others have mentioned, a transfer switch is the way to go.
Having said that, I have a portable generator I occasionally use as a whole-house generator, and decided not to install a transfer switch. Instead I installed a 50 A receptacle on the outside of the house. When the power goes out, I turn the main breaker off, and then hook the generator to the receptacle using a power cord with male prongs on each end.
I obviously do not recommend anyone else doing this. But I know what I’m doing, and it has worked well for me over the years.
When I was building my current home, 2003, I wanted a generator. I’m in a rural area and we all know they fix the problem that benefits the biggest group of customers first.
I have a 15K Generac unit running on propane with an automatic transfer switch with 12 circuits. Powers my heating/AC, refrigerators, microwave, septic system pump, and various lights. And my Ham Radio gear as well.
My wife was retired and I was still working an hour away. I knew she wasn’t going to hook up a generator and start it. It’s nice in summer if the power goes out and 30 seconds later it’s back on.
They don’t call that a “suicide cord” for nothing. 
Aside from the obvious danger of energized prongs, you can easily energize wires outside of your home ( not “you” you, but a dumber you) if you neglect to open the main breaker.
I’m the only one who messes with the hardware, and I am very careful. Furthermore, if we ever sell this place, the “suicide cable” is coming with me. So I have no worries.
If you don’t have a balanced load you might have some current going back to the pole on the grounded (neutral) conductor. That could be hazardous to a utility worker. It’s best to lift the neutral in the main panel to prevent this.
Open the main and lift the neutral.
Wouldn’t an interlock kit and a proper receptacle cost you a hundred bucks?
I don’t understand how that can possibly happen. Why would there be current on the neutral to the pole? Keep in mind current must flow in a loop.