Article 220 of the National Electrical Law (NEC) provides ways to calculate electrical loads in residential, commercial and industrial buildings. For the ordinary user, these rules specifically enter when designing a sub -circuit or scaling a service panel.
This guide breaks the standard and optional methods, the main types of pregnancy, critical considerations such as persistent loads, demand factors, and neutral changes.
Branch circles for nutrients for services
The article determines download accounts for three levels of conductors in the electrical system: sub -circuits, nutrients, and service connectors.
Branch circles Serving Individual loads Like ports, lights, or one device.
Nutrients Energy carrying from Service equipment (Main Panel) L. Sub -BanilsService of groups of branch circles.
Service connectors Bring electricity from The service tool service point to Main service separation Or the main plate.
How accounts differ:
Branch circles It is calculated for each device or for each square foot (NEC 220.14 and 220.12).: Each device is used when connecting the load with a certain piece of equipment or exit, such as the range or dryer. Each square foot is used for public vessels such as lighting circuits.
Nutrients Combining multiple branch circles and application Variety/demand factors (NEC 220.42-220.61) Because multiple loads do not work at the same time.
Service loads Combining the entire burden of the building, including The largest pregnancy for heating or cooling Continuous pregnancy modifications (NEC 220.40, 220.60).
Each step applies up (Branch → Nutrition → Service) Group more and more modifications To reflect diversity in the real world and ensure a safe conductor scaling.
Methods of calculating pregnancy
1. Standard
(NEC 220.10-220.61)
Wanted to Unlike Or housing units that do not qualify for the optional method (less than 100a).
Accounting each load individually: lighting, vessels, devices, HVAC, engines.
Application of demand factors (NEC tables 220.42, 220.55, 220.54).
Add adjustments to continuous loads and the largest engine. Continuous loads (which are expected to operate for three hours or more) should be calculated by 125 % of their classification, and the largest system in the system should also be taken by 125 %.
Determine the neutral size based on unbalanced loads. The neutral conductor is based on the maximum imbalanced pregnancy.
Request factors via the standard method:
General lighting and vessels (NEC 220.42, Table 220.42)
Firstly 3,000 VA in 100 %.
It remains of the general load of lighting/bowl decreases based on the work type:
Housing units, hotels, motors and warehouses → 35 %
Hospitals → 50 %
Warehouses → 40 %
Stores, banks, restaurants, schools, etc. 100 %
Small devices and washing circles (NEC 220.52)
Each requires a branch circle for small accreditation and washing → 1500 va all.
Included in downloading public lighting before applying table 220.42.
Cooking equipment (NEC 220.55, Table 220.55)
It applies to home power ranges, wall furnaces, cooking meter.
The demand factor depends on the number of units and KW classification:
1 domain in 12 kWh = 12 kW.
2 domains in 12 kWh = 19 kW sum (no 24 kW).
12 domains in 12 kW = 65 kW sum (no 144 kW).
Special notes in Table 220.55 allow adjustments to the largest or smaller devices.
Clothes dryers (NEC 220.54)
Each dryer was calculated in 5000 VA minimal (Or a plate, which is larger).
The demand factor for multiple dryers:
2 dryers → 100 % for each of them.
3 or more dryers → 100 % of the largest + 85 % of all others.
Other devices installed in place (NEC 220.53)
If there is 4 or more square devices are in place (With the exception of HVAC), it can be a total pregnancy 75 %.
Motors (NEC 220.50)
The largest engine must be calculated in 125 % From the current full pregnancy.
The remaining engines in 100 %.
HVAC (NEC 220.60)
Unnoticed loads (such as heating against cooling) → only Load It includes.
Continuous loads (NEC 210.20 (A), 215.3)
Any pregnancy is expected to run 3 hours or more → calculated in 125 %.
Neutral download (NEC 220.61)
The neutral size of The maximum imbalanced pregnancy After all modifications.
2. Optional
(NEC 220.82-220.88)
Simplified approach only to Housing units 100a or larger. Instead of calculating each type of pregnancy individually with different demand factors (as in the standard method), the optional method combines general pregnancy together and applies the simplified demand factor.
Combining public loads:
Lighting/Vascular: 3 VA per square foot
– Small device: 2 x 1500 va
Washing: 1 x 1500 va
Add devices, HVAC, ranging in the tablet classification.
The application factor application by 80 % for the part is more than 10,000 VA.
Add 25 % of the largest engine.
Converting the total VA to Amprarage (VA ÷ 240 V).
important: Only use greater to the Heating load or coolingNot both, unless they run at the same time.
Download categories in Article 220
Public lighting and vessels (NEC 220.12)
Use unit loads for each square foot:
Housing units → 3 va/square foot
Offers buildings → 3.5 va/square foot
Retail stores → 3 va/square foot
Schools → 3 va/square foot
Warehouses → 0.25 va/square foot
Send And the hall → 1 va/square foot
Banks → 3 va/square foot
Gallery and beauty stores Halls → 3½ va/square foot
Churches → 1 va/square foot
Clubs → 3 va/square foot
Court halls → 2 va/square foot
Dormant → 2 va/square foot
Factories → 3 va/square foot
Hospitals → 2 va/square foot
Hotels and Motors (except for parts of the housing unit) → 2 va/square foot
Lodge rooms → 2 va/square foot
Museums → 2 va/square foot
Elderly care homes → 2 va/square foot
Restaurants → 2 va/square foot
Stables → 2 va/square foot
Storage buildings → 0.5 va/square foot
Theaters (Audience areas) → 2 va/square foot
Transport stations → 3 va/square foot
Hit the square shots with VA value. Apply demand factors from table 220.42 if possible.
Small devices and washing circles (NEC 220.52)
Small devices circles: 1500 VA per (minimum two required).
Washing circles: 1500 VA for dedicated laundry.
Both are included in public lighting for the purposes of the demand factor.
Devices installed in place (NEC 220.53)
Add all fixed devices (dishwasher, disposal, water heater, etc.).
The application factor application is 75 % if 4 Or more devices Related.
Do no It applies to domains, dryers, HVAC, or space heating (these have their own rules).
Rules for downloading devices within Article 220
Electrical dryers (NEC 220.54)
Home Cooking devices (NEC 220.55)
Devices used in educational programs (NEC 220.56)
Space and air conditioning (NEC 220.60)
These sub -sections go beyond the general rules and must be applied when necessary.
Electrical and Oven Plasts (NEC 220.55)
to 1-50+ electrical domains It has been ranked more than 1 kW, use Table 220.55. example:
1 domain = 100 %
2 ranges = 75 %
3 domains = 70 %
12-17 domains = 45 %
41-50 domains = 30 %
For domains exceeding 12 kW, set 5 % higher per kilowatt for 12 kW (see notes 1-3).
Heating loads for cooling (NEC 220.60)
Use Only greater to Heating or cooling loads if they are Naughty.
Add both of them If they can work simultaneously (for example, Heat Baseboard + Window AC).
Continuous loads (NEC 215.2 (A) (1) (a))
A Persistent pregnancy Is any load expected to be operated? 3 hours or more continuously.
Examples:
Office lighting or warehouses
Garage exhaust for cars
Emergency lighting or exit
a base: Hit the ongoing loads 125 % When changing the size of the conductors and OCPDS.
Power pregnancy accounts (NEC 220.14)
Each bowl = 180 VA minimum (One or multiple on one yoke).
For 4+ vessels on one yoke, you can use 90 va per bowl.
Neutral download (NEC 220.61)
the Neutral He carries Unbalanced Between linear conductors.
The full rule (artistic accuracy):
Neutral size for 100 % of the first 200a From a balanced pregnancy.
For any The excess is above 200aIt may refrain in 70 % of this excess.
example:
Unbalanced download = 400A.
The first 200a = 100 % → 200A.
The remaining 200a x 70 % = 140A.
The total neutral capacity required = 340a.
When 70 % does not apply:
If the important non -linear loads are present (consensus).
In commercial/industrial players where neutral imbalance cannot be predicted.
Where local AHJ requires complete neutral scaling.
Nutrition and service download accounts (NEC 220.40-220.61)
Download the Nutrition Unit: The sum of the sub -circuit loads in the direction of the river courseand Amended the demand factors and continuous download rules.
Download service: The sum of all feeding loads for the entire building in addition to adjustments to the largest heating or cooling load.
Optional service accounts (NEC 220.82-220.88)
This method is a simplified method of the size of nutrients or services for housing units 100a or larger. Instead of calculating each load separately with different demand factors, you can combine most loads in one total and then apply one reduction base.
Add general loads together
Public lighting and bowl carrying = 3 VA per square foot (220.12).
Small devices circles = 2 x 1500 va.
Washing circle = 1 x 1500 va.
Fixed devices, cooking equipment and other loads in Classification.
The application factor application
Take 100 % of the first 10,000 va.
Take 40 % of all VA above 10,000.
→ This is where most of the “savings” in the optional method – reduces calculated pregnancy compared to the standard way.
Add HVAC download
It includes Either carry heating or coolingWhich is greater.
Excuse: If both can run at one time, you must include both.
Add 25 % of the largest engine
Just as in the standard method, The largest engine It gets an additional 25 % to add the start/increase capacity.
VA’s total converting to amperage
Divide the total volt amps on the system voltage (usually VA ÷ 240 v) To obtain the feeding unit or service.
Common expert advice and risks
Unforgettable Expansion in the futureNEC does not require large nutrients, but it is wise to add a head room.
When using OptionalChecking the health that the conditions meet the NEC 220.82 before applying them.
Use Painting classifications On general estimates of fixed devices the more available.
Always check whether their local judicial authorities have Strong rules Or modifications to NEC.
to Multi -stone buildings,, NEC 220.40-220.84 Carefully apply various demand loads.
Covered devices in other articles (NEC Table 220.3)
Some devices and loads are subject to other NEC articles, which exceed or adjust Article 220:
Motors: Article 430
HVAC Equipment: Article 440
Elevators: Article 620
Venetic welding: Article 630
Irrigation: Article 675
EV chargers: Article 625
PVs: Article 690
Fire pumps: Article 695
Studios lighting: Article 530
