Dwelling Loads Calculation

Boltz

Member
Location
33877
Occupation
A little bit of everything
Hello everybody​
I'm new on the trade and also in the process of finishing my electrician studies, so sorry on my lack of knowledge on the topic. I got a few doubts on Standard Dwelling Load Calculation, basically with the terminology on the question: Demand Load, Demand Load Branch Circuit, Demand line and neutral on residence, etc. My understanding is when they asked for any "Demand calculation" it has to be determined by applying the proper demand factor to the loads by Table 220.42, 220.53, Table 222.54, Table 220.55, 220.60, 220.61, 220.82(C), etc. I'm not looking someone that give me the question's answer, only I would like to know if the process applied to get the answer was the correct or not. It wasn't I will appreciate any help of my mistake and any help to get right understanding. These are the 3 of the questions:​
QUESTION 1: What would be the demand load for this branch circuit for the loads 1, 2, and 3?
  • Load 1 : General lighting and Receptacle and Small-appliance
    • General Lighting & Receptacle
      • 3VA(3,800ft²) = 11,400VA/120V = 95A
    • Small-appliance
      • 1,500VA(3) = 4,500VA/120V = 37.5A = 38A
    • Total
      • 11,400VA + 4,500VA = 15.9kVA
        • Branch Circuit Demand Load 1 = 15.9kVA @ 133A
  • Load 2: Cooking Equipment
    • Per Table 220.55 Note #4
      • Cooktop: 8kW
      • Wall Oven1: 6kW
      • Wall Oven2: 6kW
        • 8kW + 6kW + 6kW = 20kW
    • Per Table 220.55 Note #1 & Column C
      • Equivalent Range = 20kW
        • 20kW - 12kW = 8kW
        • 8(5%) = 40%
        • 12kW = 8kW(1.4) = 11.2kW
        • 11,200VA/240V = 46.67A
          • Branch Circuit Demand Load 2 = 11.2kVA @ 47A
  • Load 3: Special Appliance
    • Per 220.53, 210.19(A)(1), 220.14(A)-(C), 220.18(A), 422.10 & 430
      • Water Heater: 28,000VA(0.75) = 21,000VA/240V = 87.5A
      • Dishwasher: 1,200VA(0.75) = 900VA/120V = 7.5A
      • Food Disposal: 1,200VA(0.75) = 900VA/120V = 7.5A
      • Attic Fan: 750VA(0.75) = 562.5VA/120V = 4.69A
      • Attic Fan: 750VA(0.75) = 562.5VA/120V = 4.69A
      • Total = 28kVA + 2(1.2kVA) + 2(0.750kVA) = 31.9kVA
        • Branch Circuit Demand Load 3 = 31.9kVA @ 149A

QUESTION 2: Determine the line and the neutral load for the dishwasher and range circuit in this residence.
  • The neutral load in a 120V circuit is equal to the line load.
  • Power Factor (inductive loads only): 1kVA = 0.85kW
  • Dishwasher: 1.2kVA(0.85kW) = 1.02kW
    • Per 210.19(A)(1) & 220.14(A)
      • I = P/E
I = 1,200VA/120V​
I = 10A​
  • Line & Neutral Circuit Load = 1.2kVA @ 10A
QUESTION 3: Determine the line and the neutral load for the water heater in this residence.
  • Water Heater: 28kVA
    • Per 210.19(A)(1), 220.14(A) & 422.10
      • I = P/E
I = 28,000VA/240V​
I = 116.67A = 117A​
  • Line Load = 28,000VA
  • The water heater (240V circuit) does not need a neutral wire, because the two hot lines complete the whole current path in the circuit.
    • Neutral load = 0
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Hello everybody​
I'm new on the trade and also in the process of finishing my electrician studies, so sorry on my lack of knowledge on the topic. I got a few doubts on Standard Dwelling Load Calculation, basically with the terminology on the question: Demand Load, Demand Load Branch Circuit, Demand line and neutral on residence, etc. My understanding is when they asked for any "Demand calculation" it has to be determined by applying the proper demand factor to the loads by Table 220.42, 220.53, Table 222.54, Table 220.55, 220.60, 220.61, 220.82(C), etc. I'm not looking someone that give me the question's answer, only I would like to know if the process applied to get the answer was the correct or not. It wasn't I will appreciate any help of my mistake and any help to get right understanding. These are the 3 of the questions:​

QUESTION 1: What would be the demand load for this branch circuit for the loads 1, 2, and 3?
  • Load 1 : General lighting and Receptacle and Small-appliance
    • General Lighting & Receptacle
      • 3VA(3,800ft²) = 11,400VA/120V = 95A
    • Small-appliance
      • 1,500VA(3) = 4,500VA/120V = 37.5A = 38A
    • Total
      • 11,400VA + 4,500VA = 15.9kVA
        • Branch Circuit Demand Load 1 = 15.9kVA @ 133A
You didn't apply the lighting load demand factor (220.42). I'd also be curious why three small appliance branch circuits.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Hello everybody​
I'm new on the trade and also in the process of finishing my electrician studies, so sorry on my lack of knowledge on the topic. I got a few doubts on Standard Dwelling Load Calculation, basically with the terminology on the question: Demand Load, Demand Load Branch Circuit, Demand line and neutral on residence, etc. My understanding is when they asked for any "Demand calculation" it has to be determined by applying the proper demand factor to the loads by Table 220.42, 220.53, Table 222.54, Table 220.55, 220.60, 220.61, 220.82(C), etc. I'm not looking someone that give me the question's answer, only I would like to know if the process applied to get the answer was the correct or not. It wasn't I will appreciate any help of my mistake and any help to get right understanding. These are the 3 of the questions:​

QUESTION 1: What would be the demand load for this branch circuit for the loads 1, 2, and 3?
  • Load 2: Cooking Equipment
    • Per Table 220.55 Note #4
      • Cooktop: 8kW
      • Wall Oven1: 6kW
      • Wall Oven2: 6kW
        • 8kW + 6kW + 6kW = 20kW
    • Per Table 220.55 Note #1 & Column C
      • Equivalent Range = 20kW
        • 20kW - 12kW = 8kW
        • 8(5%) = 40%
        • 12kW = 8kW(1.4) = 11.2kW
        • 11,200VA/240V = 46.67A
          • Branch Circuit Demand Load 2 = 11.2kVA @ 47A
This looks correct to me.
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Hello everybody​
I'm new on the trade and also in the process of finishing my electrician studies, so sorry on my lack of knowledge on the topic. I got a few doubts on Standard Dwelling Load Calculation, basically with the terminology on the question: Demand Load, Demand Load Branch Circuit, Demand line and neutral on residence, etc. My understanding is when they asked for any "Demand calculation" it has to be determined by applying the proper demand factor to the loads by Table 220.42, 220.53, Table 222.54, Table 220.55, 220.60, 220.61, 220.82(C), etc. I'm not looking someone that give me the question's answer, only I would like to know if the process applied to get the answer was the correct or not. It wasn't I will appreciate any help of my mistake and any help to get right understanding. These are the 3 of the questions:​

QUESTION 1: What would be the demand load for this branch circuit for the loads 1, 2, and 3?

  • Load 3: Special Appliance
    • Per 220.53, 210.19(A)(1), 220.14(A)-(C), 220.18(A), 422.10 & 430
      • Water Heater: 28,000VA(0.75) = 21,000VA/240V = 87.5A
      • Dishwasher: 1,200VA(0.75) = 900VA/120V = 7.5A
      • Food Disposal: 1,200VA(0.75) = 900VA/120V = 7.5A
      • Attic Fan: 750VA(0.75) = 562.5VA/120V = 4.69A
      • Attic Fan: 750VA(0.75) = 562.5VA/120V = 4.69A
      • Total = 28kVA + 2(1.2kVA) + 2(0.750kVA) = 31.9kVA
        • Branch Circuit Demand Load 3 = 31.9kVA @ 149A

You applied the demand factor to each load, but then added them up without the demand factors. 31.9kVA(0.75)=23.9kVA
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
General Lighting

sq. ft x 3 = 11,400
small appliance branch circuit 1500 x 3= 4500.... big house so I assumed that is why you have 3
laundry 1500x 1= 1500

add them up and take the first 3000 at 100% and the rest at 35%
Taken from Table 220.42
 

Boltz

Member
Location
33877
Occupation
A little bit of everything
You didn't apply the lighting load demand factor (220.42). I'd also be curious why three small appliance branch circuits.
You didn't apply the lighting load demand factor (220.42). I'd also be curious why three small appliance branch circuits.
I didn't apply the demand factors by how they stated the question. Branch-circuit and Demand load? But the branch-circuit should be able to manage the Load FLC? Mostly this is the main part that I get confused on.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
The question is faulty as you are not looking for the branch circuit load but the service load or feeding load for the dwelling
 

Boltz

Member
Location
33877
Occupation
A little bit of everything
The question is faulty as you are not looking for the branch circuit load but the service load or feeding load for the dwelling
From your understanding of the question: "What would be the demand load for this branch circuit for the loads 1, 2, and 3?" Should I calculate the Demand (using applicable demand factors) for the Load that is fed through the Branch Circuit as same for the feeders or service in a building, or should I calculate the VA supplied by the Branch Circuit to the Load? Which should be no less than the Load FLC that it supply? Thanks to all in advance for any explanation. Very great professionalism forum.
 
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