Duplex Question - Many answer it seems

[mrford]

Hi guys,

I'm little confused here I've seen multiple answers to the duplex question using the standard method for the calculation. So I'll post the question and the answers in both formats I've seen and maybe someone could help me clarify.

Question as per post before (I'll use one used before)

5) A duplex served by a 120/240V 1 phase service has two
units each containing 1,900sq ft
1 9Kw Range 1 - 5A disposal
1 11A dishwasher 1 - 3Kw hot water
2 20Kw heater 3 - 3hp 240V A/C units
Using the standard method in amperes, what is the load on the building feeder.

Duplex Standard Method Unit 1 Mult Units Total

Square Footage General 1900 3 2 11400
Samll Appliance 3000 6000
Laundry 1500 3000
20400
Total Genreal Lighting / Small Appliance
1st 3000 @ 100% 3000 3000
Remainder @ 35% 0.35 17400 6090
Remainder @ 25% 0.25 0 0
9090VA **

Ranges
2 9000 Col C 11000VA

Appliance Load Qty Amp VA VA
Dishwasher 1 11 120 1320 2640
Disposer 1 5 120 600 1200
Water Heater 1 240 3000 6000
6 75% 9840 9840

AC/Heat Units
Heat 20000 2 80000
AC/Heat 17 240 3 12240 24480 Omit
80000
Total Load 114850VA 240V 478.54A

OR If we look in the NEC 2005
@ 220.82 b
First 100% of the 1st 10KVA
220.82 c 5
65% of the nameplate rating if less than 4 units or 40% for more than 4 units
(If you have a duplex and 3 units in each that would be 6 units as a total for the main feeder)


So what is the deciding factor to go with 220.82 as an option or the option of using the above shown method based on Table 220.42.

Frustrated and lost..

Mike





Or the alternate to this method

 

[S'mise]

I would take your appliance load of 9840 x .75(four or more..) and you'll have 7380va

If its a duplex I would say its 2 units. So you can use 220.82 if its a 120/240 or 208Y/120. If it's 3 units or more you'd use 220.84. Some people use one method to bid a job and another to show the AHJ.