To power a house from a generator safely, you have to make sure it’s disconnected from the power company. Should be easy, just a transfer switch that connects the two hot buses either to the generator or the power company, but not both.
But there don’t seem to be products to do this, despite what the Wikipedia article says. Instead, you buy a whole separate circuit breaker panel, and decide ahead of time what circuits you want to be able to use, and rewire them through this new panel, and power this new panel through a switch that goes either to the main panel or the generator.
Am I missing something, or is this why people avoid using transfer switches?
I have a 200 amp main panel and figure it’d be 30 to 50 amp generator. I think what I really need would contain a two pole 200 amp breaker, a two pole 50 amp breaker, and a mechanical link that prevents them both being on. What’s that called and where do I find one?
People avoid using transfer switches because they think a $50 generator cord and their smarts are enough. They’re often wrong.
You really don’t want to plug your whole house into a generator and try to manage the power distribution manually. A transfer switch handles the changeover safely and lets you select a subset of your house circuits to power independently.
If you just manually switch over from mains to generator, something like a oven, dryer or AC unit kicking on would blow main breakers or even damage the generator.
ETA: It’s really, really easy to be stupid with generators. After three big storms here, I’ve watched even sensible, educated people do the dumbest-ass things. Be smart; put in a good transfer switch with an exterior power jack wherever it’s safest and most convenient to put the generator. (That is, consider the issues of monitoring and fueling it in crappy weather, and having it run while people are trying to sleep, and just not being driving crazy by the noise.)
the generator subpanel has the advantage that only the crucial circuits are on it. this makes overloading the generator or wasting power harder and you don’t have to throw 30 breakers off. also the generator subpanel has a smaller easily operated switch, a 200A switch is harder to operate.
I have an installed generator with an automatic switch. It’s really nice to lie in bed and hear the generator start and automatically switch the load. Just sayin’
They just talked about this on the final episode of the current This Old House project. The oversized the generator (30KW IIRV) and used it to run the whole house instead of a separate panel. There was still a transfer switch, but the lines fed back into the main box.
Here it is. Skip to 9:30. I’ve never looked at transfer switches very closely (since I don’t have/need one). But in this case, it seems that the power comes from the grid, to the switch and from the generator to the switch and then from the switch to the main panel.
Contrast that with ‘normal’ ones where power comes from the grid to the main panel and from the generator and to the emergency panel and the switch picks one side or the other.
I don’t know if any switch can do that depending on how it’s wired of if you have to get a specific kind.
I have a plug and a switch with a mechanical lockout on the breakers on the outside of my house. I turn off the public electrical feed, plug in my generator, flip a second breaker, and my house is powered. I do need to turn off the big load items before hand, such as A/C, water heater, and oven, as mentioned above.
The upside is that while I can’t run the whole house at once, I can turn a TV or light on in whatever room I happen to be in.
I had a licensed electrician install the switch and plug.
A ‘whole-house’ generator is going to cost a lot of money, in the thousands, not including installation. Most small back up generators are between 1-4KW (1000-4000 watts). If you’re going to need 220V (for say a well pump) you’ll need at least a 3500W one, as that will provide 15 amps at 220 volts (the minimum). That’s still well below ‘whole-house’ capacity.
To use my house as an example: We have a 3500 watt generator. We have one four-plug outlet in the center of the house (near the refrigerator) that is only connected to the generator via a cord in the basement. There are two other cords, one is for the furnace, the other the well pump (220V). These all plug into the generator and the furnace & well ones go to two simple switch boxes (same size as a light switch) with three positions: AC / Off / Generator. When we lose power I start the generator, plug the three plugs into it (no load), then flip the furnace & well switches over to ‘Gen’ then go upstairs and simply plug the fridge into the devoted outlet.
Only the furnace, the well, and the refrigerator are than directly connected. We just use extension cords inside the house from that one outlet box that the fridge is plugged into to run a few other things (TV, lights etc.) At 3.5KW this is about the maximum it can handle. Even so the light in the fridge is noticeably yellow when on the genny.
Point is unless you’re going to go with a powerful, ‘whole-house’ turn-key generator it may be easier to just add a couple of ‘generator-only’ circuits rather than bother with switching your main.
Correct, but they’ve become surprisingly cheap. When I looked into them around maybe 1995, residential standby generators were pretty much a buck a watt - a 4-5kw unit cost $4-5k, and a whole house unit cost in the range of $20k.
I am considering replacing our aging 7.5kw Generac with a 20k whole-house unit; it will probably cost less than the original unit, about $4k plus installation. The nice thing about that much power is the transfer does indeed take place right at the incoming mains; one switch, passed to your whole service panel, no mucking around with partial power.
But yes, the gas-fueled standby units are 6-10 times as expensive as mobile construction and backup generators. You pay for the convenience.
1st thing before wiring in any generator into your house contact your utility. Nothing scares a line man like hearing a generator running in a neighborhood during a power outage, and not have a record of an inspected insulation.
The generator should be connected with a three pole double throw switch. Wired in with 2 inputs, one from the utility and one from the gen set, and one output to the house. both hots and the neutral need to be broken.
If you want to go before main panel and not have an emergency subpanel then the generator needs to be able to handle the load. If you have a 200 amp main then the generator needs to be 200 amps. Anything less and you are looking for trouble and will get it.
People advoid properly installed and inspected transfer switches because $$$$$$
the cutoff switch kits are expensive which is probably why nobody buys them so they attempt a last minute connection to the panel.
IF you had every outlet mapped out and IF you were willing to unplug everything in your house and IF you calculated what amperage you wanted to plug back into the correct outlet then it’s a simple matter of turning off your mains and adding in a 220 breaker to cover both sides of the buss. You’d have to physically lock out the main breaker and all the unused breakers with a plate.
I think it would be cheaper to buy a small panel and wire a couple of emergency outlets directly and just bypass all the guesswork. One outlet for the furnace, one for the refrigerator and a couple for lights which of course would be LED.
I see you found something, but for completeness - no, I don’t remember how much it cost. It was done as part of a bigger job, including adding some circuits to clean up something the previous home owner did, and to wire in a hot tub.
