Electric Dryer Load Calculations

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Doc_Larry

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I have a project where the homeowner wants to install a clothes dryer in an apartment that has a 60A service. The specific dryer manufacturer specifies the 120/240V 3-pole dryer load at 2,700VA and has provided an engineering technical memorandum that states that the dryer circuit may be protected by dual 15A breakers.

The 2011 code specifies that the dryer either be included as a 5,000 VA load in the Standard 220.42/220.52/220.54 calculation or (for this dryer) a 2,700VA load in the Optional 220.82 calculation. However, either way the calculated load exceeds the 60A service.

A third possible alternative is to consider the dryer service to be two additional 15A laundry circuits wired to provide a 3-pole, 4-wire 120/240V 15A supply. Doing it this way the dryer load is then included as 3,000VA, but it and all other loads above 3,000 VA will be subject to the 35% demand factor provided for in the standard calculation.

If the dryer circuit is accounted for as two additional laundry circuits, the calculated load is within the capability of the 60A service, but is this approach code compliant?
 
Are you performing a complete load calculation, using the standard and optional methods? If so, then I don't believe you can count the dryer as part of the general lighting load. It is a specific load called out in 220.14(B). I note, however, that that article includes the phrase, "shall be permitted." I wonder if that means that you don't have to use 220.54, and can instead revert to 220.14(A), which would allow you to count the dryer at 2700 VA. I don't know if that would help you, even if it was allowed.

Have you tried 220.87?
 
Electric Dryer Load Calculations

Charlie,

Thank you for your quick and thoughtful response. Here are my comments:
1. Yes, I am performing a calculation with both methods.
2. I don't think that the phrase "shall be permitted" allows for any wiggle room. It appears to me that 220.14(B) is saying that one is permitted to include a dryer if you do it according to 220.54.
3. Including the dryer at 2.7 kVA in the optional calculation does not help because I then cannot use the 35% demand multiplier for the general loads between 3 kVA and 10 kVA.
4. 220.87 is not helpful because this is vacant residence with no historical data.

However, there is a statement in one article that appears to be an "orphan", but it raises a question about treatment of dryer loads. This is in 220.82(B)(3)c, which requires separate accounting for dryer loads for, "Clothes dryers that are not connected to the laundry branch circuit...". This appears to allow that there are cases when dryers ARE connected to a laundry circuit. However, this is the only reference to a dryer on a laundry circuit that I can find anywhere in the Code. Does this give us any justification for such a connection, which would then include the dryer load in Laundry Circuit contribution to the General load category?

My client also questions whether we cannot simply install additional laundry circuits on each of the two lines (for a total of three) and then use a plug-in Y adapter to a 240V 3-pole, 4-wire receptacle for the dryer. The client has pointed out that folks with electric cars are doing this where a 240V line is not available or too expensive to install. And, there is even a commercial product offered at http://www.quick220.com. Of course, I cannot comment on the code implications of using this device!

Any further thoughts will be greatly appreciated.

Thanks!

Doc_Larry
 
If you install two 20 amp (can't be 15 amp, per your original posting) circuits, and called them "extra laundry circuits," then you could certainly count them with the other loads that get the 35% demand factor applied. That said, I don't think this will solve your problem. Here is the real problem:
Doc_Larry said:
The specific dryer manufacturer specifies the 120/240V 3-pole dryer load at 2,700VA and has provided an engineering technical memorandum that states that the dryer circuit may be protected by dual 15A breakers.
Click to expand...
The 2011 NEC article 240.15(B)(3) will allow use of a pair of 15 amp (or 20 amp) breakers to protect the circuit you describe. But it requires the two breakers to have a listed handle tie. The result is no longer a pair of 120 volt circuits, but rather a single circuit rated at 120/240 volts. That is not the description of a "laundry circuit." You can't use the two circuits and call them laundry circuits, because the laundry circuit is defined by 210.11(C)(2) and 210.52 as being a 120 volt circuit.

By the way, are you sure you live in New York and are an engineer, and are not my youngest brother in disguise? :lol: He lives in Texas, has the given name of "Larry," and has everyone calling him "Doc." :happyyes:
 
Doc_Larry said:
The 2011 code specifies that the dryer either be included as a 5,000 VA load in the Standard 220.42/220.52/220.54 calculation or (for this dryer) a 2,700VA load in the Optional 220.82 calculation. However, either way the calculated load exceeds the 60A service.
Click to expand...

Even if the Optional 220.82 calculation worked for you, you wouldn't be able to use it because it only applies to feeders/services with an ampacity of 100 or greater.

You don't indicate that you tried 220.83(A). You get to use the nameplate data for the appliances, and there is a 40% demand factor for everything over the first 8kVA. Give that a try.
 
Charlie and David,

Thank you both for the excellent advice that you posted. Charlie, of course you are correct about the necessity for the listed handle tie and its effect. I am a bit red in the face for having overlooked that. Thanks for keeping me out of trouble!

And, David you hit the ball out of the park with your suggestion of Article 220.83(A)!. It addresses exactly the situation I am concerned with, and the numbers work out beautifully with that methodology.

Thanks again to both of you!

Best,
Doc Larry

P.S. Charlie I do live in NY, I do not believe that we are related, and the choice of my handle is purely coincidental. However, if you are wealthy and generous I might consider claiming you as a brother.;) Please clarify so that I know how to proceed!
 
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Question

As a follow up to the earlier posts: 220.83(A) covers, "Where Additional Air-Conditioning Equipment or Electric Space-Heating Equipment Is Not to Be Installed."

In the case where only a dryer is being added to a dwelling that has pre-existing HVAC loads, it appears that the pre-existing HVAC is lumped in with all other loads subject to the 40% demand factor above 8 kVA. Is this correct or is 100% HVAC loads added in at the end of the calculation? If the HVAC is a 100% load in 220.83(A) where is this specified?

Thanks!
Doc_Larry
 
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