Help us pick a whole-house standby generator


Old 12-13-09, 10:18 AM
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Help us pick a whole-house standby generator

We are 2200 sq.ft., a 200 amp panel in the garage and no sub-panels in the house. We are all electric.

We have some $$ set aside and because of two recent power outages with the temps in 6 to 10 degree range, we have decided to buy a whole-house generator with a ATS.

Big items are the split unit heat pump with strip heating, well pump, stove, washer/dryer and pool equipment.

Had a contractor come by and he favors an air cooled Guardian 5402, 20Kw, 125 amps, fueled by propane, since we have a tank on site. Includes 20Kw pre-packaged system with LTS load shedding switch, composite mounting pad, etc., etc.

I'm not sure if I need to go up to a larger, liquid cooled 22Kw to be covered 100%. What about start-up surge power draw?

I will probably have the contractor come back to put an amp meter on various equipment while running to see what's what.

Air cooled units seem to be in the $4000-5000 range and liquid cooled units are $8000 and up.

Any comments or suggestions, please?
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Old 12-13-09, 10:40 AM
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Some generators make "dirty" electricity and electronic things do not work or do not work well with these.

For example some people have tried powering their new furnace with an electronic control with a generator and the furnace does not work!

There are generators which say they are "electronics friendly". Be sure to get one of those... search for "electronics friendly" generator...
Old 12-13-09, 04:43 PM
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However there is one item it got my attetion senice you mention ATS { automatic transfer switch } with 2008 NEC code edition you will have to get the generator size matched to the main breaker rating so with single phase 200 amp service you will need at least 45 Kw generator I know it will drive up the cost unless you have MTS { manual transfer swtich } you can able sized it much smaller unless you have optional load shreading device on the ATS.

IMO I know it pretty crazy with this rules but hopefully with next code edition it may clear up some issue with this.

But somecase local area may override the NEC code to suit the local requirement so you may get by with smaller unit only if your local code stated allow for that one.

once I know what your intend is going and we will work it out from there.

Old 12-13-09, 06:33 PM
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Good point about the automatic transfer switch, Marc. I think that without a load shedding upon transfer that this requirement may stick.

As for the air-cooled vs. liquid-cooled question it depends upon how often this generator may be used and how long the use periods will be. Generally speaking a liquid-cooled generator will be significantly longer lasting and also quieter. If the generator is only used a few times a year and rarely runs for more than a few days at a time the air-cooled machine would probably be okay but if you are looking at frequent utility outages or outages that last for weeks then spend the extra money for the liquid-cooled unit.
Old 12-14-09, 03:02 AM
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Marc, I think you're misinterpreting the code a little.

The generator needs to be sized according to the load switched as determined by Article 220, not the size of the main breaker when automatically switched or the use of load management.

The OP will need to have a load calculation performed and size the generator accordingly or use the load shed transfer switch.

As for the "dirty power". Generac generators use electronic governors and "True Power" technology in all of their generator so voltage/frequency, etc. will not be an issue.

Be sure that the size of your propane tank is adequate for the generator selected to sustain you for at least 2 days. In the event of a major event, services may not be available to refill your tank. For example, the 20 KW uses almost 3 GPH at full load in addition to any other appliances that use propane. The 25KW, you're looking at almost 5 GPH at full load. This drops down at different % of rated load.

You can visitGenerac Power Systems - Residential generators for more information.
Old 12-14-09, 05:55 AM
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We recently went through what you're contemplating. You can save yourself a bunch of money (and make your propane last longer) by not backing up so much stuff. If it's for winter protection, why back up the pool equipment?? Same for the dryer. On the other hand, if it were me I'd back up the refrigerator and a couple of lighting circuits. Maybe the DirecTV too LOL.
Old 12-14-09, 06:09 AM
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An AHJ near me also has the same interpretation as Marc posted. Without the load shedding feature you are switching the same size as the service and they are making you install a genset able to feed the whole service load.

I don't agree with the way it is written, but I don't get to ignore it either. Gensets installed for life safety issues I can see, but for less critical loads I don't see it as a problem if the genset can't power the AC or the hot tub.
Old 12-14-09, 04:54 PM
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For the referince to this situation you will have to take a look at Art 702 that part it been rewritten a bit.

It did raise a bit of confusing conflects due the 702 is not clear but the 701 is fine.

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