# 220.85 Duplex calculation proof.

#### Tyler Cavanaugh

##### Member
Here is an example I have come up with myself. Will someone please go though it and see if I solved this correctly! Thank you
1452sqft duplex 230V/115V
9.6KW electric heat
5HP A/C 230V
1200VA dishwasher 115V
1/2HP disposal 115V
4.5KW water heater 230V
4.0 dryer
15KW range

General method
1452 x 3va x 2units. 8712
1500x 3va x 2units. 9000
Demand. 8149
1200DW x 2 x 75% 1800
1127 disp. X 2 x 75% 1691
4500wh x 2 x 75% 6750
5000 dryer x 2. 10,000
11kw x 1.15 range. 12650
9600 heat x 2. 19200
Largest M. 1127x25% 282
73172/230V = 318A
Optional.
1452sqft x 3va x 3units. 13068
1500 x 3 x 3units. 13500
9600 heat x 3. 28800
1200 DW x 3. 3600
1127 disp. X 3. 3381
4500 W.H x 3. 13500
4000 dryer x 3. 12,000
15000 range x 3. 45000
132849 X 45% = 59782VA ÷ 230V = 260A

So you would use the optional method on the master electrical exam because the optional method is smaller amps? Correct? Is this how you use 220.85 correctly?

#### Dennis Alwon

##### Moderator
Staff member
You are missing the washer, no? but it looks good

#### Tyler Cavanaugh

##### Member
No. The washer is included in the 1500VA x 3. Two branch circuits and one laundry load. Just combined them for simplicity.

#### frofro19

##### Member
Here is an example I have come up with myself. Will someone please go though it and see if I solved this correctly! Thank you
1452sqft duplex 230V/115V
9.6KW electric heat
5HP A/C 230V
1200VA dishwasher 115V
1/2HP disposal 115V
4.5KW water heater 230V
4.0 dryer
15KW range

General method
1452 x 3va x 2units. 8712
1500x 3va x 2units. 9000
Demand. 8149
1200DW x 2 x 75% 1800
1127 disp. X 2 x 75% 1691
4500wh x 2 x 75% 6750
5000 dryer x 2. 10,000
11kw x 1.15 range. 12650
9600 heat x 2. 19200
Largest M. 1127x25% 282
73172/230V = 318A
Optional.
1452sqft x 3va x 3units. 13068
1500 x 3 x 3units. 13500
9600 heat x 3. 28800
1200 DW x 3. 3600
1127 disp. X 3. 3381
4500 W.H x 3. 13500
4000 dryer x 3. 12,000
15000 range x 3. 45000
132849 X 45% = 59782VA ÷ 230V = 260A

So you would use the optional method on the master electrical exam because the optional method is smaller amps? Correct? Is this how you use 220.85 correctly?
Why is everything multiplied by 2 units on the general method and multiplied by 3 units on the optional method? And where did the 45% come from?

#### Tyler Cavanaugh

##### Member
Why is everything multiplied by 2 units on the general method and multiplied by 3 units on the optional method? And where did the 45% come from?
Why is everything multiplied by 2 units on the general method and multiplied by 3 units on the optional method? And where did the 45% come from?
This caculation is for a service feeder for a "duplex" therefore there is 2 of everything for the general method. Then if you read 220.85 it states to do the caculation of three identical units and use the optional method. The 45% is from table 220.84

#### frofro19

##### Member
This caculation is for a service feeder for a "duplex" therefore there is 2 of everything for the general method. Then if you read 220.85 it states to do the caculation of three identical units and use the optional method. The 45% is from

#### frofro19

##### Member
I see that now. I posted too quick. Thanks.