Article 220 ● Branch-Circuit, Feeder, and Service Calculations
220.83 Existing Dwelling Unit
This section shall be permitted to be used to determine if the
existing service or feeder is of sufficient capacity to serve
additional loads. Where the dwelling unit is served by a
120/240-volt or 208Y/120-volt, 3-wire service, it shall be
permissible to calculate the total load in accordance with
220.83(A) or (B).
(A) Where Additional Air-Conditioning Equipment or
Electric Space-Heating Equipment Is Not to Be Installed.
The following percentages shall be used for existing and additional new loads.
220.83
(2) 1500 volt-amperes for each 2-wire, 20-ampere smallappliance branch circuit and each laundry branch circuit
covered in 210.11(C)(1) and (C)(2)
(3) The nameplate rating of the following:
a. All appliances that are fastened in place, permanently
connected, or located to be on a specific circuit
b. Ranges, wall-mounted ovens, counter-mounted
cooking units
c. Clothes dryers that are not connected to the laundry
branch circuit specified in (2)
d. Water heaters
Load (kVA)
Percent of Load
The optional methods described in 220.83(A) and (B) allow
an additional load to be supplied by an existing service.
First 8 kVA of load at
Remainder of load at
100
40
Calculation Example
Load calculations shall include the following:
(1) General lighting and general-use receptacles at 33 voltamperes/m 2 or 3 volt-amperes/ft 2 as determined by
220.12
(2) 1500 volt-amperes for each 2-wire, 20-ampere smallappliance branch circuit and each laundry branch circuit
covered in 210.11(C)(1) and (C)(2)
(3) The nameplate rating of the following:
a. All appliances that are fastened in place, permanently connected, or located to be on a specific circuit
b. Ranges, wall-mounted ovens, counter-mounted
cooking units
c. Clothes dryers that are not connected to the laundry
branch circuit specified in item (2)
d. Water heaters
(B) Where Additional Air-Conditioning Equipment or
Electric Space-Heating Equipment Is to Be Installed.
The following percentages shall be used for existing and additional new loads. The larger connected load of air-conditioning or space-heating, but not both, shall be used.
Load
Percent of Load
Air-conditioning equipment
Central electric space heating
Less than four separately controlled spaceheating units
First 8 kVA of all other loads
Remainder of all other loads
100
100
100
100
40
Other loads shall include the following:
(1) General lighting and general-use receptacles at 33 voltamperes/m 2 or 3 volt-amperes/ft 2 as determined by
220.12
National Electrical Code Handbook
2011
An existing dwelling unit is served by a 100-ampere service.
An additional load of a single 5-kVA, 240-volt air-conditioning unit is to be installed. Because the existing load does
not contain heating or air-conditioning equipment, the existing load is calculated according to 220.83(A). The load of
the existing dwelling unit consists of the following:
General lighting:
24 ft 40 ft = 960 ft2 VA per ft2
Small-appliance circuits: 3 1500 VA
Laundry circuit at 1500 VA
Electric range rated 10.5 kW
Electric water heater rated 3.0 kW
Total existing load
2,880 VA
4,500 VA
1,500 VA
10,500 VA
3,000 VA
22,380 VA
Solution
STEP 1. Following the requirements of 220.83(A), calculate
the existing dwelling unit load before adding any equipment:
First 8 kVA of load at 100%
8,000 VA
Remainder of load at 40%:
22,380 VA 8,000 VA = 14,380 VA 40% 5,752 VA
Total load
13,752 VA
(without air-conditioning equipment)
13,752 VA 240 V = 57.3 A
STEP 2. Prepare a list of the existing and new loads of the
dwelling unit.
General lighting:
24 ft 40 ft = 960 ft2 VA per ft2
Small-appliance circuits:
3 1500 VA
Laundry circuit at 1500 VA
Electric range rated 10.5 kW
Electric water heater rated 3.0 kW
Added air-conditioning equipment
Total new load
2,880 VA
4,500 VA
1,500 VA
10,500 VA
3,000 VA
5,000 VA
27,380 VA
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