Dryer calculation changes

[Hotwork480]

I’m hoping to get some clarity, I’m studying for a test and using the Mike Holt prep book. In Unit 9 there are service calculations that I get wrong due to the dryer calculation. One of the questions has this listed in the Answer Key, “Dryer (nameplate, not 5,000W) 4,000VA” another has “Dryer rated 4,500W 5,000 Minimum value“. Both these questions are under “9.7 Standard Method Load Calculations Example” page 423 questions 24 & 25 of the “Electrical Exam Preparation“ based on the 2017 NEC.

Can anyone help me understand what is going on? It has been beat in my head that it is 5kw or nameplate, whichever is higher.

 

[Julius Right]

In Art. 220.54 it is written:
the load shall be either 5000 W [or Volt-Amper] or the nameplate rating whichever is larger.
That means if the nameplate rating is less than 5000 W [ or 5000 VA] the load will be 5000 W any way[4500 W, 4000 W and other shall be 5000 W]

 

[Dennis Alwon]

The standard calculation using 5,000 va for an dryer less than 5,000 and the nameplate for anything over 5000

The optional calculation used the nameplate period, no matter what size the dryer may be.

 

[kwired]

Real life applications - you generally don't know the exact model that will be installed. Not many are over 5500 VA AFAIK anyway. Those that are likely still work out ok using 5k as a load calc as the max demand time is likely shortened with higher watts.

Keep in mind 30 amp @ 240 volts is 7200 VA that potentially can be supplied by the branch circuit without tripping anything though typical units used are not that high of draw. Many of them would run on a 20 amp breaker and possibly never trip it, they are just barely over that much current draw.