Dwelling unit load calcs

[steve66]

Load calculations for electric clothes dryers and electric ranges/ovens in dwelling units are based on the appliance nameplate rating.

However, we never have a nameplate.

So, say we simply know there is a 240V, 30 amp dryer circuit and receptacle. What is the maximum load calc. for a dryer on that receptacle?

240V* 30A = 7200VA ?

Or would 240V* 30A *0.8 = 5760 VA be correct? (Because an appliance with a 30A continuous load would have to be on a larger circuit?)

Same question for an electric range? I'm not sure how Table 220.55 affects this calculation.

Is it possible that a range that needs a 30A circuit could actually pull more than 30 amps?

 

[tortuga]

Load calculations for electric clothes dryers and electric ranges/ovens in dwelling units are based on the appliance nameplate rating.

However, we never have a nameplate.

A optional calc requires nameplates but the general calc provides some default values, dryer, range I think EVSE now.
It depends if your doing a fancy custom home and they dont have any idea as to appliances you might need to get more info from the client.

 

[wwhitney]

Load calculations for electric clothes dryers and electric ranges/ovens in dwelling units are based on the appliance nameplate rating.
However, we never have a nameplate.

One answer is to require the nameplates first. Otherwise, you are left to guess at the expected nameplate value. Maybe try to pick an 80th percentile nameplate rating.

Or would 240V* 30A *0.8 = 5760 VA be correct? (Because an appliance with a 30A continuous load would have to be on a larger circuit?)

That logic doesn't apply, a dryer is not continuous but may intermittently be a load in excess of 5760 VA. Just looking at a few google image results for electric dryer nameplate, for 240V 6500 VA might be safe (I didn't see any higher), 7200VA is certainly safe.

Same question for an electric range? I'm not sure how Table 220.55 affects this calculation.

Table 220.55 has zero effect on an optional calculation. My electric range has a nameplate rating of 12.5 kW at 240V. So I would use 12.5 kW, which is more than 50A at 240V, even though the circuit is only 40A. As far as the final answer, the 40% factor still gives a lower figure than Table 220.55 would, just 5 kW = 21A.

Cheers, Wayne

 

[wwhitney]

P.S. It always has struct me as crazy that the information on an appliance nameplate is generally not available on the spec sheet.

Cheers, Wayne

 

[steve66]

P.S. It always has struct me as crazy that the information on an appliance nameplate is generally not available on the spec sheet.

Cheers, Wayne

Yes, cut sheets, and installation instructions both. They usually just say to refer to the appliance label. Most of the time they won't list the appliance rating, or even the required circuit size.

And it's rare we get an exact model number. Even when we do, I think the contractor is usually just picking a random appliance, and they are thinking they will just buy whatever is on sale when they do buy it at the last minute.

Then what if the appliance gets replaced with something different after 5 or 10 years? How can a load calc take that into account?

And what if there are 100 different apartments that have 100 different models?

 

[wwhitney]

Then what if the appliance gets replaced with something different after 5 or 10 years? How can a load calc take that into account?

It doesn't. If the new nameplate is higher, it's apparently incumbent upon that installer to do a new load calc.

And what if there are 100 different apartments that have 100 different models?

Either you get the data for all 100 apartments, or you decide that a representative sample of say 10 of them is good enough, and extrapolate.

Cheers, Wayne

 

[Elect117]

220.54 - 2023 NEC or 2025 CEC

"The load for household electric clothes dryers in a dwelling unit(s) shall be either 5000 watts (volt-amperes) or the nameplate rating, whichever is larger, for each dryer served."

You should be okay with 5000VA for each apartment for feeder and service calculations if you use the standard method. And then on your print, mark that the contractor can not install anything over 5kW without first getting approval from the EOR or something for revised calcs.

I don't know what to do about the range/oven though. That one can be quite a wide array of sizes. But I would think a typical 50A recept. + 40A "continuous" load calc should suffice.

But it is like the EV charger requirement, you are more than likely going to have a larger EV charger than 7200W (30A @ 240V). That is like the lower end of level 2 charging. But the code provides a minimum that should suffice for the purposes of service and feeder calcs.

 

[suemarkp]

Most 30" wide ovens can be put on a 40A branch circuit (Note 4 to table 220.55). Most 36" wide ranges need a 50A. That doesn't answer the calc question, but it depends on which calc you are using. If using the standard calc, a range up to 16KW will work out to 9.6KW which is 40A or 22KW for a 36" wide range. If using the optional calc you need the nameplate, but if you assume 16KW for a 30" wide or 20KW for a 36" wide, you should be covered with some margin in the calc.

Every 30" wide range I have had in houses was just over 12 KW.

 

[kwired]

"The load for household electric clothes dryers in a dwelling unit(s) shall be either 5000 watts (volt-amperes) or the nameplate rating, whichever is larger, for each dryer served."

You should be okay with 5000VA for each apartment for feeder and service calculations if you use the standard method. And then on your print, mark that the contractor can not install anything over 5kW without first getting approval from the EOR or something for revised calcs.

I don't think you will find many that are over 5500VA. Because of this using 5kVA is fairly safe to do and I would only go more than that if I definitely knew it would be more.

Similar thing with ranges - as others mentioned 30 inch ranges would seldom be more than a 12kW rating - which table 220.55 allows you to treat as an 8 kW load. should it be more than 12 kW the adder for each additional and the adjustment in note 1 only increases the demand load by 5% for each additional kW over 12, so if you don't know what they will have chances you won't be significantly in error if you use 8kW when you know it will only be a 30 inch range. Not really a big deal for single dwelling/single range. Large multi family dwelling - often you will know what they intend to install and often is same appliance in each unit so you can be more accurate if it is over 12 kW rating. Also rating is usually the 240 volt rating, large multifamily very well might be 208 volts, so that 12 kW rating is high to begin with on a 208 volt system and that aspect is also the same when it comes to dryers.