Understanding how to calculate range demand is useful for electrical professionals, especially when preparing for a licensing exam. These calculations are essential for properly sizing service entrance conductors and other components of electrical systems in residential and commercial kitchens. Mastering this topic is a helpful skill for passing NEC electrical exams and ensuring safe, code-compliant installations in the field.
A single-family dwelling has two ranges rated at 4.5 kW each and another range rated at 7 kW. Calculate the demand load for these kitchen appliances on the ungrounded service entrance conductors using the standard method of calculation for dwellings.
In a household kitchen, there is one range rated at 15 kW. What is the calculated demand load for this range?
A residential kitchen is equipped with two ranges: one rated at 14 kW and another at 18 kW. Determine the demand load for these appliances on the service entrance conductors.
Key phrases to look out for in range demand calculation questions:
When you spot these elements:
To correctly apply NEC Article 220.55, focus on these main elements:
To summarize, use Table 220.55 to determine the appropriate demand factor based on the ratings of individual appliances. Pay special attention to the notes, which provide guidance for specific scenarios and adjustments to the demand factors.
A single-family dwelling has two ranges rated at 4.5 kW each and another range rated at 7 kW. Calculate the maximum demand load for these kitchen appliances on the ungrounded service entrance conductors using the standard method of calculation for dwellings.
Step 1: Identify all ranges and their ratings
Step 2: Determine which column of Table 220.55 to use
Step 3: Calculate the total connected load
Total connected load = (4.5 kW + 4.5 kW + 7 kW) = 16 kW
Step 4: Find the demand factor in Column B for 3 appliances
Step 5: Calculate the demand load
Demand load = Total connected load × Demand factor
Demand load = 16 kW × 55% = 8.8 kW
Therefore, the calculated demand load for these kitchen appliances on the ungrounded service entrance conductors is 8.8 kW because it is in fact lower than the 14 kW demand that would be allowed by Column C.
Question: In a dwelling unit kitchen, there is one range rated at 15 kW. What is the calculated demand load for this range?
Step 1: Identify the range and its rating
Step 2: Determine which column of Table 220.55 to use
Step 3: Find the maximum demand in Column C
Step 4: Apply Note 1 under Table 220.55
Again, Note 1 states we have to increase the Column C demand (8 kW in this case), 5% for every kW the rating of the appliance is over 12 kW
Additional kW over 12 kW = 15 kW - 12 kW = 3 kW
Increase = 5% × 3 = 15%
Final demand load = 8 kW + (8 kW × 15%) = 8 kW + 1.2 kW = 9.2 kW
Therefore, the calculated demand load for the 15 kW range is 9.2 kW.
Question: A residential kitchen is equipped with two ranges: one rated at 14 kW and another at 18 kW. Determine the demand load for these appliances on the service entrance conductors.
Step 1: Identify the ranges and their ratings
Step 2: Determine which column of Table 220.55 to use
Step 3: Calculate the total connected load
14 kW + 18 kW = 32 kW
Step 4: Apply Note 2 under Table 220.55
Note 2 states: "Over 12 kW through 27 kW ranges of unequal ratings. For ranges individually rated more than 12 kW but not more than 27 kW, an average value of rating shall be calculated by adding together the ratings of all ranges to obtain the total connected load (32 kW) and dividing by the number of ranges (2). Then the maximum demand in Column C shall be increased 5% for each kW or major fraction thereof by which this average value exceeds 12 kW."
Average rating = 32 kW ÷ 2 = 16 kW
Step 5: Calculate the increase based on the average rating
Increase = (16 kW - 12 kW) × 5% = 4 × 5% = 20%
Step 6: Apply the increase to the base demand from Column C
Base demand for 2 appliances from Column C = 11 kW
Final demand load = 11 kW + (11 kW × 20%) = 11 kW + 2.2 kW = 13.2 kW
Therefore, the calculated demand load for the two ranges (14 kW and 18 kW) on the service entrance conductors is 13.2 kW.
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