Comment Re:Natural gas backup generator (Score 1) 695
Woah buddy; important point -- don't forget to de-rate your generator!
If you actually use even close to 80% of your 100A service, that 17kw Kohler running on natural gas is going to fry.
Most gas generators can be fueled with either LP or NG, but when you burn NG, your efficiency is diminished. In addition, utility companies like to keep the BTU content of their gas close to the minimum they are legally allowed, so it's good even to overestimate. Rule of thumb on this is around 15% total below the advertised rating or 5-10% lower than the official NG rating of the generator. For that 17kW Kholer that puts you at around 14kW that you can realistically produce out of that genset at peak.
Also keep in mind that for a number of other reasons, you're not going to be able to get peak power out of that generator for a while after it starts up, and most "standby" generators are not rated for peak power during continuous duty. There is also power factor to consider, as well as some other minor unfavorable types of things that the marketing numbers don't really include, so you really need to de-rate about 10% more to figure the nominal size load you can protect.
SO just being conservative on that Kholer (which you need to be when you are considering an EMERGENCY generator), you could reasonably ask it for 55A or so. That might be sufficient for a whole home without major electric appliances, but it's not going to deal with electric heaters, ovens, clothes dryers, etc. all that well. You'd need either a larger genset or to do some selective circuit protection using a sub-panel.