I have never done a whole house generator from the beginning.Always been an engineerd situation.
Thinking of 1 for my own house.

200A main.
Would it have to be for the full 200A or can you size them down? Not sure where to start.
Thanx, Lee

Unless your house is total electric, you likely don't need a 48 kw generator. A generator that will handle the full 200 amps and the transfer switch is going to be realy pricey.

One of my customers has a 7000 sq ft house & the generator is 12kw if I remember correctly. We have it wired to a 200 amp panel & it is up to him which loads he wants to run during a power outage. Instead of using a 200 amp transfer switch, we used an interlock kit that allowed him to feed the panel with a smaller two pole breaker.

To size your generator, decide what loads you feel must absolutely be on and then if that number idoesn't breeak the bank add the loads that it would be nice to have & that would be the size generator you need.

Gotcha, Like I said the engineers have always done the work. I can size the portables comfortably(http://www.cumminsonan.com/residential/select/)
with this as a guide.
I'm at the infant stage right now so no particulars.
The idea is a transfer switch at the panel location.200 in to panel from the poco,then perhaps a 20KW (150A) Gen set.

Just not sure about the coralation between the 200A panel and the smaller Emerg side.
I would assume the T switch would need to be rated for the poco service size.
?

Generators are sized to the actual loads that they are expected to power. With an existing house, the easiest way is to measure the amps you're actually drawing with "everything on," and base your sizing on that.

You don't want to oversize. With generators, "bigger" is NOT better. Talk to your genny rep, but typically you want the generator tom operate at about 85% of its' rated capacity. For the 'normal' house, we're usually talking about a draw of about 70 amps.

Having a larger transfer switch is a good idea; but, again, there's no sense in overdoing things.

The most important thing about a generator instal is that the generator operate reliably. In practice, this means running the generator periodically, under load. There are two ways to do this.

One way is to have the generator turn on automatically, and have the transfer switch let it power the house for, say, an hour each month.

The other way is to add a "load bank" to the generator. A "load bank" is simply a very, very big toaster. The generator powers this load when it is 'exercising,' and does not use the transfer switch to power the house during this period.

The transfer switch needs to be large enough on the mains side to handle the potential maximum mains load, which in theory is as large as the main OCD level. I've never seen asymmetric transfer switches, though.

Instead of having the generator supply the entire residence and therefore would require a transfer switch equal in size to the mains OCD, you could supply all the loads that would be considered "essential" during an outage from a separate smaller panel and therefore a smaller transfer switch. This would also help eliminate the possibility of overloading the generator as non essential / high wattage loads can not ever be supplied by the generator.

A.D

IMHO sizing the genny for 200A is a total waste of money. In an emergency situation you should not need more than 50A at most for a 2200 sq ft house with gas heat. We live in a rural area (frequent power outages) and have a PTO 13.5kW generator that is cord connected to an whole-house inlet. That inlet back feeds a mechanical transfer CB (50A) and main switch inter-lock in position 2 on the main panel. In this manner we can operate any circuit we need without having to define it beforehand. We have enough power to operate the house plus one "big" appliance and I just dont try to run the dryer and the oven at the same time. General house load is 20A on each line. Remnants of hurricane Ike saw it getting 16h of use a day for 6 days without a hitch. Costs of generators above 12-13kW start getting up-there. The cost of the interlock (Square-D) and 50A CB was less than $50 3 years ago and beat the pants off related charges for any transfer switch system with pre-defined "critical" circuits, not to mention the simplicity of installation. I have yet to trip the breaker but a 50A at the panel and a 50A pop out breaker on the genny should prevent an undervoltage situation. I also had hubby wire up a frequency meter that plugs (two separate cords and caps) into two outlets (supplied by L1 and L2) that I identified and the display scrolls through voltage, frequency and rpm so we can keep an eye on the genny performance under different loads from in the house. The idiot gauge on the PTO generator is HOPELESS, and we use frequency to set the throttle on the tractor. I am very happy with the set-up and it was modestly priced for what we can do with it. Sure a auto-transfer and start would be nice but we would never get the utility out of it for what those units cost. Thats my 0.02.

I was always under the impression that an "Alternator" was for the most essential loads in a house, during times of PoCo system failure?
Things like lights, freezer and 1 recept.

Running a whole house on an Alternator,is just stupid,like you seriously need all them things under Emergency power conditions.

Just a few idle thoughts ....

I recall an ice storm when I was a kid, and the power was out for a week. It wasn't a particularly difficult time. A fireplace, a couple candles, the Coleman lantern and BBQ on the patio for cooking.

These days, folks seem to be asking for service drops that, in the past, would power an entire village. 800 amps? Even today, with the latest McMansions, I haven't seen an actual current draw of more than 70 amps.

What is with this dependence upon electricity? Is this fear a carryover of the Y2K silliness?

Looking back on that ice storm ....
If we had a tiny generator - one you could carry with one hand - we would have had normal heat in our home. Our primary heat was natural gas; electricity just powered the blower and controls.
A few lights would have been nice.
Some folks have wells, and, yes, you do need to keep the toilets flushing. Water storage is a moot issue; if you store it, you need to keep it from freezing.

Looking at this from a trade perspective .... perhaps we ought to consider this when we desigh homes, and feed these minimal (but essential) loads from a sub-panel, just to make the addition of a genny easier. After all, the latest NEC changes almost demand we have more than one panel in a home; how we split up the circuits is something to think about.

There is a contradiction in our goals. With LEED design, CFL bulbs, "Energy Star" appliances, etc .... our necessary service sizes ought to be declining, not growing. I'm sorry, I'm still shocked by all the 400+ amp household services I've encountered ... having grown up is a perfectly nice, full size house that had a 60 amp service! For that matter, we did it with 8-120v circuits and 1-240v circuit ..... as compared to the 40 circuits commonly found today.

Let me add a new word (well, 3 word combination) to the lexicon: service drop envy

Load calcs are always a compromise between what is usually on and what might be on. My house calculated out to around 180a using the optional method and over 200 with the standard method but since I have never had a $5000 electric bill it is clear all that stuff is not on very much.

Thanx all! Back to Earth I land.
You'r all correct. just a passing thought I guess. My 5.5KW worked fine this past storm,6 days, Microw,220 well,heat lights TV etc. (no cable but the old CDs got a bit of needed use). Looking back, Brought us back into perspective.
Warmth,warm showers and the like.
Conclusion: 8KW in the future,to take the load of the well better. (2k+ sqft). To fix my house as described, would essentialy equate to a service change (reorg.ckts and sub panels etc.)
However, It will be nice to know for future clients.
Thanx for the replies!

One detail I forgot to mention - shame on me! - is noise.

Short version: Get the optional 'sound package.' Then, still put the genny in a shed, and surround it with shrubs. Do everything you can to eliminate the roar of a generator. The 'standard' mufflers are simply a joke.

Ya, the Honda I use now is OK, My Coleman... Wow that is obnoxious!!!
I heard a LNG one the other day at a telco site, about 20KW, could barely hear it at 20 yards!

Sounds like you have pretty much the same setup as I do. That being, a 7200W, 10-circuit generator panel with 1-DP handle tie for the 240V well jet pump. I also tied in the microwave, oil burner, refrigerator, some kitchen counter receptacles, two bedrooms, bath lights, office and basement lights. No electric range though, but the Weber gas grill is always on the back deck. Of course, I can’t run everything at once, but this seems adequate for emergency use. I think I’ve only really needed it once in the 5-years since I put it in, but it’s a good feeling knowing that it there.
Right now I only have a 3700W Coleman with a little Suzuki engine. It sips gas and is pretty quite, but I was actually was thinking of going up to 4400W or so.
With most portable generators, I don’t know if you ever really get away from that initial brownout, voltage sag when the water pump or other motor load starts, like the refrigerator compressor.

I use the old Honda EM5000s. Nice little unit. Set up is the same,Only I need to tweek the chosen ckts. Looked ok, but after the 6 day outage,found a few flaws. no Kitchen rec. pleanty of light.

I can run every light, TV, computer, refrigerator, etc, in my house with my 3500W (15A 240V) gen. It can also run our microwave, coffee pot and garage doors, although I've always been careful not to do any of these simultanously. I can even run our range, though the lights blink every time the heating element kicks on. I think it *might* handle one of the 3 ton heat pumps, but I haven't been desperate enough to try it out yet. I'm just happy to have lights and all.

That said, you have to be careful of the small cheap generators; they're not regulated very well, and can put out excessive voltages if they're sized too large/loaded too lightly. The first time I used mine, I had to run around and turn on every light in the house to load mine down to 125V. Fully loaded (like when my stove is on), it's down to 110V. It's a common problem.

I am doing a little energy audit today and my house cruises at 9a on one phase and 3.1 on the other.
That is with the pool pump and spa (low speed circulation) pump running.
In the house there were a couple lights on, TV, a whole house fan on low, this PC, and all the stuff that never turns off.
The 36" S/S fridge wasn't running but it adds 2a when it is (I have 2)
The rub starts when I turn on the range, the water heater kicks on and the AC is running.

I often enjoy this subject since I went to a great amount of trouble to set my house up with a generator that now hardly ever gets used. When I first moved into my house, power outages were very lengthy and frequent, and with a house full of boys, the toilets became a huge problem since we are on well water. I was also surprised how low my total load was as well.

I installed a 100 amp sub panel with interlocked main breakers. In that panel, I managed to put the range, water pump, sewage ejector pump, sump pump, microwave, freezer, three refrigerators and almost all lighting and GPA circuits. I'm using a 5,500 watt generator and it does surprisingly well. True, it coughs pretty hard when we first throw the transfer switch, but I get around that by turning off all branch breakers first, transferring, then turning them on one at a time. I installed this sub panel in my garage since the main panel is at the opposite end of the house in the basement. Through some trickery in backfeeding or refeeding existing circuits, it worked out well. I also put an emergency light set in the garage so that we can see what we are doing in total darkness.

Although I am currently only using a 5,500, I still used a 60 amp generator main in the panel. That way, when I win the lottery, I can buy a larger generator and only have to change the inlet and cord set. If that happens, I might even belly up for an ATS.

Surprisingly, we run pretty comfortably with this setup. I'm a bit cocky, so when the power goes out and I'm on generator, I make sure to turn on all of the lights. We don't go as far as trying to cook Thanksgiving dinner during an outage, but with load management, I think we could in a pinch. I don't have my heat, water heater or washer/dryer on the transfer panel. There's no way I'm coughing up the money to run the heat pump too.

After all of that, we hardly ever lose power anymore. The POCO reworked our section of the grid about ten years ago and I think I may run the generator once a year now. It's still nice to know that we have the water issues covered, both coming in and out.

In the 25 years I have lived here I would have about 4-5 days on the generator (one day at a time). Any other outages are so short my UPS keeps the TV and PCs on.
If the FPL guy who lives across the street ever moves or retires that could change I guess.
His wife tells him he can't come home to a dark house, he still has something else to finish at work.

That's funny, Greg. I have a similar situation here, as my best friend is an area supervisor for Dominion-Virginia Power. Whenever there are widespread outages, he makes sure that his crews hit the critical areas first, then they are instructed to hit my area. Since I met him, I think our longest outage has been about four hours and that was due to a major substation issue.

I feel sorry for him since where he lives, they are served by a co-op where he is just a customer and has no control. While he goes out of his way to make sure we are warm and dry, his family sits on the "whenever we get to it" list.

I also have a large UPS that powers all of our TV's, electronics and smoke detectors that is connected behind the transfer panel. It does a good job of smoothing the irregular power output of the generator. Not to mention, it sure is nice to not have to have flashing "12:00" on all of the devices with a clock whenever there is so much as a flicker!

There's no reason any clock or VCR should have been flashing "12:00" since many years ago. Battery powered timing circuits are cheap. They can use the battery only to keep the timer oscillator and counter working, and power the display only with the wall cord supplied power. When there is AC power, recharge the battery. Now days they have those multi-farad capacitors that can do it. The only time when "12:00" should ever be flashing is when plugging in while also holding in the hidden "factory reset" button that erases all memories.

I'm still looking for a decent wall or large desk clock with big LED digits powered by the AC (and intermittent by battery while a "display" button is pressed when the AC is off), which keeps time under battery control when the AC is off. It needs to also have seconds on the display and sync to WWVB.

Hey... That’s a great idea putting in that emergency light unit.
I don't know why I didn't think of doing that in my basement, since that's where I have to go to get to the transfer panel.
Definitely going to put one of those in. I might also run a remote head to the basement stairway as well to keep me from falling on my arse. Thanks.

I have an emergency light in the hall that goes to the guest room. I figure they are the ones who need the most help in a problem. It also does a fair job lighting up the egress from the master end of the house.

I have a 200A service so I installed a 200A transfer switch but my gen is 6.5kw. Works fine. When I start the gen I throw the AC breaker - I figure that I can run the house or the AC. Otherwise life goes on as usual. I wanted the flexability of using anything in the house with a little discresion and it works fine. Using a two pole tran sw so I had to remove the ground - neutral bond at the gen.