# Non-Dwelling Buildings Load Calculations- Part Eight

I explained the Loads calculation for Non-Dwelling Buildings as per the NEC Standard Method in the following Articles:

I also indicated that the NEC Optional calculation method can be applied only for the following Non-Dwelling buildings as permitted by NEC, Part IV. Optional Feeder and Service Load Calculations:

1. Schools,
2. Existing Installations,
3. New Restaurants.

Today, I will explain the load calculations for these special Non-Dwelling Buildings (Schools, Existing Installations and New Restaurants) by using NEC optional method.

First: Schools

 Important!!! As with dwellings, there are two methods for calculating services or feeders for schools as follows: Standard NEC Method in Part III of Article 220, Feeder and Service Load Calculations, Optional NEC Method Part IV of Article 220, Optional Feeder and Service Load Calculations.

 Rule#1: Condition for Using NEC Optional Load Calculation Method for Schools In accordance with 220.86, using the optional calculation method is only permissible if the school is equipped with electric space heating, air conditioning or both.

 Rule#2: Load Calculation for Feeders within the School Building If the School building or structure has been calculated by the optional method, it will be necessary to calculate the loads of feeders within the School building or structure by the NEC Standard Method. Calculating feeders within the School building or structure by the optional method shall not be permitted.

 Important!!! If, by using the NEC Standard Method, the ampacity of an individual feeder is greater than the ampacity required for the entire building, it shall not be required that the ampere rating of the feeder be larger than the ampere rating of the service.

 Rule#3: Load Calculation for Portable Classroom Buildings Although many schools have portable classroom buildings, using the NEC Optional Method to calculate loads to those portable classroom buildings shall not be permitted. It must be calculated by NEC Standard Method.

 Rule#4: Neutral Load Calculation There is no optional method for calculating neutral loads; therefore, neutral loads must be determined in accordance with 220.61.

Procedure for School Load Calculation by NEC Optional Method

This optional method calculation procedure for schools can be divided into four easy steps as follows:

Step#1: Find the total connected load.

 Important!!! The connected load shall include all of the interior and exterior lighting, power, water heating, cooking, other loads and the larger of the air conditioning load or space heating load within the building or structure.

 Important!!! When calculating the total load of a school note the following: Use only 100 percent of the load, Do not multiply continuous loads by 125 percent, Do not derate receptacle loads, Do not derate cooking equipment, Do not increase the largest motor by 25 percent.

Step#2: find the average volt-ampere per square foot (VA/ft2).

Step#3: applying the Table 220.86 demand factors.

Step#4: multiplying the derated volt-ampere per square foot by the square-foot area of the school to get the new derated feeder or service load of the school.

Example#1:

What is the service load calculation for a school with a total connected load of 750 kilovolt-amperes (kVA) and a floor area of 30,000 square feet?

Solution:

Step#1: Find the total connected load

The total connected load is provided and is 750 kVA

Step#2: find the average volt-ampere per square foot (VA/ft2).

To find volt-amperes per square foot, divide the total connected load by the total square-foot area of the school.

The average volt-amperes per square foot = 750,000 VA ÷ 30,000 ft2 = 25 VA/ft2

Step#3: applying the Table 220.86 demand factors.

Multiply the first 3 (VA/ft2) by 100% = 3 VA/ft2

The Reminder = 25 – 3 = 22 VA/ft2

Multiply the next 17 by 75% = 17 x 75% = 12.75 VA/ft2

The Reminder = 22- 17 = 5 VA/ft2

Multiply the reminder by 25% = 5 x 25% = 1.25 VA/ft2

After applying the demand factors in table 220.86, the VA/ft2 = 3 + 12.75 + 1.25 = 17 VA/ft2

Step#4: multiplying the derated volt-ampere per square foot by the square-foot area of the school to get the new derated feeder or service load of the school.

derated service load of the school = 17 VA/ft2 x 30,000 ft2 = 510,000 VA = 510 KVA

Second: Determining Existing Loads for Existing Installations

 Important!!! there are two methods for calculating services or feeders for Existing Installations as follows: NEC Standard Method, Section 220.16 covers loads for additions to existing installations for both dwelling units and other than dwelling units. NEC Optional Method, Article 220.87 covers optional method load calculation specifications for Existing Installations regardless of the type of occupancy. Noting that Article 220.83 covers optional method load calculation specifications for an existing dwelling unit.

 Important!!! The purpose of doing service and feeder calculations for an existing dwelling unit is to determine if the existing service or feeder is of sufficient capacity to serve a required additional loads or not.

 Rule#5: Conditions Of adding new loads to An Existing Dwelling Unit In accordance with 220.87, when calculating a feeder or service load for existing installations, regardless of the type of occupancy, it shall be permissible to use actual maximum demand to determine the existing load where meeting three conditions: The maximum demand kVA data for a minimum 1-year period (or the 30-day alternative method from the exception) is available. The maximum demand at 125 percent plus the new load does not exceed the ampacity of the feeder or rating of the service. The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.

 Important!!! For condition#1 in Rule#5 above, If the maximum demand data for a 1-year period is not available, the calculated load shall be permitted to be based on the maximum demand (measure of average power demand over a 15-minute period) continuously recorded over a minimum 30-day period using a recording ammeter or power meter connected to the highest loaded phase of the feeder or service, based on the initial loading at the start of the recording. The recording shall reflect the maximum demand of the feeder or service by being taken when the building or space is occupied and shall include by measurement or calculation the larger of the heating or cooling equipment load, and other loads that may be periodic in nature due to seasonal or similar conditions.

 Important!!! For condition#2 in Rule#5 above, apply the NEC standard Calculation method to get the total load as follows: Total Load = Existing Load Value + New Load Where: Existing Load Value = Max demand Value for a 1-year period from 220.87(1) x 125% New Load = Continuous loads x 125 % +  Non-continuous loads x 100 %

 Important!!! If condition#2 in Rule#5 above is not verified, you need to increase ampacity of the feeder and/or rating of the service to be able to add new loads to an existing dwelling unit.

Example#2:

A business owner wants to add equipment to an existing building. The new equipment will not replace any of the existing equipment. The existing service has a rating of 1,200 amperes (A). A peak-demand meter has been connected to the service for more than a year. The maximum demand data from the peak-demand meter shows a demand of 743A.

The new equipment that has a calculated load (in accordance with standard load calculation procedures) of 251A. Does this existing service have an ampere rating high enough for the existing loads and the new loads?

Solution:

Existing Load Value = Max demand Value for a 1-year period from 220.87(1) x 125% = 743 x 125% = 929 A

New Service Load = Existing Load Value + New Load = 929 + 251 = 1,180 A

Since the existing service is rated 1,200A, this installation will be Code-compliant

Third: New Restaurants

 Important!!! As with dwellings and schools, there are two methods for calculating services or feeders for New Restaurants as follows: Standard NEC Method in Part III of Article 220, Feeder and Service Load Calculations, Optional NEC Method Part IV of Article 220, section 220.88, Optional Feeder and Service Load Calculations.

 Rule#6: NEC Optional Method Load Calculation of service or feeders for New Restaurants As 220.88 states, instead of using the NEC Standard Method in Part III of Article 220, the calculation of a service or feeder load for a new restaurant shall be permitted by the NEC Optional Method in accordance with Table 220.88.

 Important!!! In accordance with section 220.88, The feeder has overcurrent protection in accordance with 240.4, and the service has overload protection in accordance with 230.90.

 Important!!! In accordance with section 220.88, Feeder conductors shall not be required to be of greater ampacity than the service conductors.

 Rule#7: Neutral Load Calculation There is no optional method for calculating neutral loads; therefore, neutral loads must be determined in accordance with 220.61.

Procedure for New Restaurants Load Calculation by NEC Optional Method

This optional method calculation procedure for New Restaurants can be divided into four easy steps as follows:

Step#1: Find the new restaurant’s total connected load in kilovolt-amperes (kVA).

 Important!!! In accordance with the note under Table 220.88, the total connected load must include all electrical loads, including both heating and cooling loads.

 Important!!! When calculating the total load of a new restaurant note the following: Use only 100 percent of the load, Do not multiply continuous loads by 125 percent, Do not derate receptacle loads, Do not derate cooking equipment, Do not increase the largest motor by 25 percent.

Step#2: determine the type of the new restaurant: all electric and not all electric. If it is all electric, use the second Column of table 220.88. If it is not all electric, use the third column.

Step#3: Once the new restaurant’s total connected load has been calculated, select the row with the range of numbers that includes the total connected load.

Step#4: get the new derated feeder or service load of the new restaurant as follows:

A- for All Electric new restaurants:

• If the connected load is no more than 200 kVA, multiply the calculated load by 80 percent.
• If the total connected load is more than 200 kVA, an additional math step is required as per the appropriate row in table 220.88.

B- for Not All Electric new restaurants:
• If the connected load is no more than 200 kVA, the calculated load must be taken at 100 percent.
• If the connected load is more than 200 kVA, an additional math step is required as per the appropriate row in table 220.88.

Example#3:

What is the optional method service load calculation for a new restaurant with a total connected load of 180 kVA? This new restaurant will be all electric.

Solution:

Step#1: Find the new restaurant’s total connected load in kilovolt-amperes (kVA).

The total connected load is given = 180 KVA

Step#2: determine the type of the new restaurant: all electric and not all electric.

The type of new restaurant is all electric

Step#3: select the first row (0–200 KVA).

Step#4: get the new derated service load of the new restaurant as follows:

The connected load is less than 200 kVA, multiply the connected load by 80 percent

The new derated service load of the new restaurant = 180 x 80% = 144 kVA

Example#4:

What is the optional method service load calculation for a new restaurant with a total connected load of 394 kVA? This new restaurant will be all electric.

Solution:

Step#1: Find the new restaurant’s total connected load in kilovolt-amperes (kVA).

The total connected load is given = 394 KVA

Step#2: determine the type of the new restaurant: all electric and not all electric.

The type of new restaurant is all electric

Step#3: since the total connected load is given = 394 KVA, select the third row (326–800 KVA).

Step#4: get the new derated service load of the new restaurant as follows:

Calculate the amount over 325= 394 – 325 = 69 KVA

Now multiply the amount over 325 by 50 percent = 69 KVA x 50% = 34.5 KVA

Finally, The optional method service load calculation for this new restaurant = 34.5 KVA + 172.5 KVA = 207 KVA

Example#5:

What is the optional method service load calculation for a new restaurant with a total connected load of 455 kVA? This new restaurant will be supplied by natural gas and electricity.

Solution:

Step#1: Find the new restaurant’s total connected load in kilovolt-amperes (kVA).

The total connected load is given = 455 KVA

Step#2: determine the type of the new restaurant: all electric and not all electric.

The type of new restaurant is Not all electric

Step#3: since the total connected load is given = 455 KVA, select the third row (326–800 KVA).

Step#4: get the new derated service load of the new restaurant as follows:
Calculate the amount over 325= 455 – 325 = 130 KVA

Now multiply the amount over 325 by 45 percent = 130 KVA x 45% = 58.5 KVA

Finally, The optional method service load calculation for this new restaurant = 58.5 KVA + 262.5 KVA = 321 KVA

In the next article, I will explain Farm load calculations. Please, keep following.