Generacinstaller
Hello,
I am trying to figure out when sizing a residential optional generator if part IV of nec 220 can be used or does it have to be part III? The power play app gives me the option on using either one. Reading 220.82(a), It says served by a "single set" of conductors with ampacity of 100 or greater. Not sure if this means "not parallel feeders". Or does this eliminate generators from this calculation because the generator feed is a "2nd set" of feeders?
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MEC
Part III must be used for essential circuits.
Either one can be used for whole house calc.
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MEC
Make sure you get the LRA off the unit and enter that instead of the default value if higher. Need to make sure the unit is sized large enough.
Also, don't know if your aware that the model numbers are usually in multiples of 12.
Which would be 1 ton. An 18 would be 1.5 tons as an example, a 24 is 2 tons etc etc...

Depending on where you are a good rule of thumb is for every 500sq ft figure 1 ton. I use this when the labels are illegible.

Another thing worth noting is for the 22kW AC unit calc. You have to watch and make sure the calc load isn't higher than 19.5kW on NG or it will default to the LC unit and won't tell you. If your on LP it wouldn't matter.
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BrentB
Part IV is used for whole house and it means the utility feeder.
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Generacinstaller
Awesome info. Thanks. I did not know that about the Ac model numbers, that's good to know, I was actually wondering how to figure how many tons an Ac is. So usually no matter what brand it will have a model number in 12s like that? Def woulda screwed myself at least once on the 22kw thing too, thanks so much
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MEC
No problem at all.
Always a learning curve on this type of stuff. They are making changes all the time to get it more user friendly. I actually use it now for the non powerplay leads. It is now more professional than my own proposal.
Customer checklist is a nice feature and you can add any attachments you want to it.

Re: AC units
Yes they all are setup that way. If there is a company that doesn't do it that way I would be very surprised.

The 22kW thing is on the list of things to get fixed. They didn't plan on there being a AC and a LC model with the same rating when it came out.
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ED01
I am curious as to how the LRA factors into calculating generator size?
My current 4 ton air conditioner has a RLA of 21.6 and LRA of 120. Since the LRA is much higher than the generators 15K rating I would have to assume either only a percentage of the LRA is used or there is a surge wattage for each generator.
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MEC
I don't have specific info on your app, but I do have the current numbers for the 16kW.
The surge rating for that one is 130 LRA.
It may be different on yours since there is a derate on the older ones.

Since it's so close I would put a soft start kit on the AC.
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hoghead
Great info MEC , I use the power play more and more. Do you have any tips when sizing heat pumps and heat strips.
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BrentB
MEC;35439 wrote:
I don't have specific info on your app, but I do have the current numbers for the 16kW.
The surge rating for that one is 130 LRA.
It may be different on yours since there is a derate on the older ones.

Since it's so close I would put a soft start kit on the AC.


Check with your gas provider! Our BTU content is so high here, we get 100% full load on NG! De rating is based on national averages! We get 100% operating amperage on NG! When I'm less than 1 kW on hitting my mark I use the hand written load calculation; I know the different fuel suppliers here, and some don't need to be de-rated!
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MEC
I just go by the book in case it's questioned by the inspectors.
Good point tho, I will find out and see. You've got me curious now, lol.
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MEC
I would also do the calc a couple of times. Sometimes it gets hung up on one option and doesn't update to reflect the other.
Still needs work, but it's a nice tool on the fly.

If it's questionable I always do it out on paper.
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