The most common method is to move the desired circuits to a separate panel and then provide enough generator capacity for that panel's load.

There is nothing more complicated to it than that.

Unless you have enough generator capacity to back up an entire panel you cannot use an automatic crossover to that panel.

We have as brickeyee suggested...two panels....one for the generator and one not.

We have a kohler...don't know why, but our electrician was not impressed with generac stuff and recommended we go this way instead. It is hooked up for automatic start and stop as the power goes on and off.

Only thing we didn't do, and should've, is put a remote starter on it. When we're out of power, someone has to go to the machine to turn it off at night and again to turn it on in the a.m. or throughout the day as we typically don't run it 24/7 when we're out of power....rather enough to keep the fridge going. That's more of a pain if it's raining, but then again, I have spent several nice nights appreciating the milky way which I would've missed if we had the remote starter.

I have talked to a couple electricians as well and they steer clear from Generac. I have had small Generac equipment and it has let me down.

That being said, I would go with a Cummins Onan series generator that runs off natural gas. They use automatic transfer switches and will turn on and off automatically when there is a loss or regain in power.

"This way I dont have to dedicate circuits in a transfer switch.."
The circuits are dedicated i the panel the trafer switch feeds.

The NEC issue is not just backfeeding, but having enough power to allow for automatic cut over to the generator.

The generator must be capable f supporting al th loads it could be connected to.

If you tried to automatically back up a 200 A panel with a 50 or 10 A generator, all sorts of bad things can happen when the system tries to cross over.

Electronic portions of systems have a very nasty habit of failing before things like breakers can operate.

Panel has 150 A load, power goes out, tries to operate from 50 A generator.
If you are lucky the generator simply disconnects itself under the overload without damage.
If you are unlucky the output stage of the generator fails before the 50 A output breaker has a chance to move.

A 100 microsecond overload to a breaker is just the time it takes to operate.

A 100 microsecond overload to the voltage regulator circuits i a modern generator simply destroys components.

And of course the other thing we have to do to "Jenny" is shovel her out, as we did in the last snow storm to make sure the air vents are clear.....

Jenny is in the foreground. I wanted to put her under the deck but there were all kinds of rules and regs about proximity to combustible materials, etc....so she ended up down below.

" 15kw PTO generator feeding a 50A double pole breaker in the main panel"

What are the loads in the main panel?

NOT the sum of the breaker ratings, the actual loads matter.

The 50 amp breaker is thereto protect the wiring, not the generator from overload.

If you have decent size central air system you may not have enough generator capacity to get it started.

The compressor pulls a lot more current at start-up than once it gets running.
A LOT MORE.

30 amps running may be well over 100 amps at start-up.

Brickeyee-

Obviously i am not powering my house with the AC on, every light fixture, microwave, etc during an outage. By backfeeding I allow myself to power a light in a bedroom while not having to dedicate a breaker in a transfer switch just to power that one light bulb.

Also, during a power outage, i will refrain from using my compressor and welder.

What in the world do you do during a power outage? Sheesh

"Obviously i am not powering my house with the AC on"

I would never assume you would not need AC since do to medical problems I DO.

And I have the very large gen-set needed to allow automatic crossover (though I turn that off for the most part when home).

As long as the crossover is manual you are free to have a mismatch between loading and generator capacity.

YOU just have to remember to shed some load (turn off breakers) before switching to the generator.
Make a mistake and risk damaging your generator.

What you CANNOT due is have an AUTOMATIC crossover if the generator cannot power the entire panel it is hooked to (based on the actual loads preset, not the what the 'sum of the breakers' is).

What you CANNOT due is have an AUTOMATIC crossover if the generator cannot power the entire panel it is hooked to (based on the actual loads preset, not the what the 'sum of the breakers' is).

Correct, that's why, like I stated, I have a mechanical interlock cover which, as you know, requires me to manually set the breakers.

As for the OP-
I recall when we built our electrician quoted us $5k for a 12kw nat gas unit with automatic transfer switch and $2k for a 7kw unit with automatic transfer switch. Both units were Generac which they seemed to like and i see most often around here...though I have no opinion either way on them. If i were to do it all over again, i would probably be more willing to work with the electrician at the building stage rather than afterwards. Best of luck!

I appreciate the feedback:

I am specifically interested in using the new transfer switches that manage load so that all the circuits are available to use the generator but obviously cannot be all turned on at once. The "smart switch" automatically turns on and off the AC units switching between the two of them.

These apparently have only been available for about 3 years now and the generator companies all advertise them over the traditional automatic switch, where you can only have a few dedicated circuits that can be used during a power outage.

I have several Kohler, GE, and Generac Dealers and service companies near me but only one Cummins Onan which is over 50miles away.

Refer to these links for what I am talking about.

http://www.generac.com/Residential/Transfer_Switches/Managed_Whole_House/Nexus_LTS/
and
http://www.generac.com/Residential/Transfer_Switches/Managed_Whole_House/Nexus_Smart_Switch/

http://www.generac.com/Residential/Brochures/ (see GenReady brochure)

Thanks again!

I've heard good things about Cummins Onan. Can they be coverted to propane? We don't have natural gas available where we live.

typically nat gas units can easily convert to LP- that shouldnt be an issue

If it says generac stay away.

I doubt their other equipment is any better quality than their actual generators.

I would also inspect the code listing to make sure the NEC (through the testing agency that provided the code listing) is even going to recognize their 'smart' equipment as suitable for use.

This post was edited by brickeyee on Sun, Feb 17, 13 at 12:37

It's probably too late to ask, but why a need for a "whole house" back up electrical system? Seems very excessive and unnecessary unless there is some special need or situation, unless living in an area where the power goes off weekly for extended periods.

Good luck with your project.

same question I mull VC. we live in an older neighborhood w lots of trees, we are not on the same grid as any hospitals, so we tend to be lower priority to restore power. last ice storm was 10 years ago, no power for 7 days. at the same time, in a new build w price tags in the $700k range, spending $3-$5K on back up power doesn't seem out of line. if it does hit the fan, the neighbors would love us!

We live on 8 acres in a very rural area with many Amish neighbors. Since they don't connect to the electric grid, our area is one of the last to have power restored in an outage. Last summer, after a nasty storm took down old trees and knocked out a large part of the northern Central Ohio area, we were without power for 6 days in 95 degree heat. The biggest concern to rural folks with wells is that when the power goes out, there is no way to pump water from the well into the house. No water = no toliet flushing, no bathing, no dish washing, no cooking water. We had drinking water and water for our pets, but little else. Our wonderful Amish neighbors put our horses into their barn so we wouldn't have to carry water and invited us to their house for showers and dinners. They thought it was pretty funny because the power outage didn't affect their way of life at all!

Where we live in SE Pennsylvania (about 30 miles west of Philadelphia), we live on acreage with all eletric homes. For us, the power seems to seldom go out in the summer (during the cooling season), it's always in the winter during the heating season.

So for us the essential circuits for a generator are:
--Refrigerator and microwave in the kitchen;
--Our two geothermal heat pumps;
--Our well pump and pressure tank;
--Our basement sump pump;
--Our garage door openers;
--A few lighting circuits on each floor

I may be forgetting something, but this has managed to be sufficient for over 15 years. IMO, there's little need for a whole-house generator supported system unless there is some outstanding need.

Im a big fan because I live in Texas. We get some bad storms with large power outages. 2 years ago we went without power for 4-5 days. Losing all your food in the fridge and food in the freezer was a couple hundred dollars. Being uncomfortable for a couple days, not having anything to do at home, etc. For $5000, I would easily pay it to not lose power once or twice a year. Even if it is only for a few hours.

Just received quotes for a Generac and a Kohler generator system from an electrical company with "36 yrs expereince," specializing in generators.
They say the configurations are comparable and they do not recommend one system over the other. They install both, service both and are certified to sell and service both.

The quote for a Kohler 20kw with 200Amp ATS and energy management is approximately $1000 more than the quote for a Generac 20kw with 200amp SE rated ATS with Nexus Energy Management. The Generac comes with a 3 year warranty and the Kohler comes with a 5 year warranty.

Any advice as to which would be better / is the Kohler worth the extra money?
Thanks

Kohler by far..there have been multiple people in this thead including me that have mention Generac being junk.

While I would not suggest that anyone choose a brand based on one anecdotal data point, in a slight defense of Generac our 15kW Generac whole-house generator has been outstanding in both performance and reliability for the 8-10 years we have owned it. Our small New England town tends to get power restored later than most because we only have about 1300 people. We lose power at least several times a year. The Generac was particularly nice to have during the 11 days we were without grid power during the ice storm of 2008 (until the Quebecois crew arrived to get us connected again).

Maybe we have the only good Generac in the world. Or maybe their build quality is terrible now compared to when we bought ours. But ours is great and has been worth every penny. One of the best purchase decisions we've ever made.

Having it wired to power the whole house seems like overkill to some people. Well, to be fair, it is overkill for some people. By "power the whole house" I do not mean turning on every electrical device and running them all full tilt simultaneously. It means that the generator can power any circuit we have rather than a select few.

To be honest, I just didn't want to think about what circuits to connect. I did want to be able to use anything I have anywhere on the property. Maybe I need to keep the heater going in the cow trough and a light on in the chicken house because it's 10 degrees outside. Or it is August and I need to run the two freezers in the barn because they are full of moose. Maybe I want to watch TV in this room and use the laptop in that room. I want to do whatever I want or need without rewiring all the buildings or moving things around just so I could pick a few circuits to be powered. And I can.

bws

We have had a Generac generator on a auto transfer switch in our new home for 6.5 years and our last house from 1993-2006. My parents have had two on their main home since the mid-80s, and they have one on their lake house and my sister has one as well. The only one that as had problems is the lake house generator.

That said, our generator guy is now recommending and installing Kohler. We recommended him to 4 of our neighbors and each went with the Kohler. He said there are less issues vs Generac.

I think Generacs are not made as well as they used to be, having their down cycle like appliance companies seem to drift through over decades.