A master electrician is calculating the feeder demand load for a multi-family dwelling with 20 similar dwelling units. Each unit has an 8 kW electric range. According to NEC Article 220.55, what is the minimum demand load for the electric ranges?
- A25 kW
- B40 kW
- C35 kW
- D50 kW
Show answer & explanationAnswer & explanation
Correct answer: C. 35 kW
According to NEC Table 220.55, for 20 electric ranges, the demand factor is 25 kW plus 1 kW for each range exceeding 12 ranges. Therefore, 25 kW + (20-12) ranges * 1 kW/range = 25 kW + 8 kW = 33 kW. Wait, the table actually specifies 25 kW + 1 kW for each range over 12 for ranges rated over 1.75 kW. And for 20 ranges, Column C (for ranges 8.75 kW and over) is 25 kW + 1 kW for each range over 12. Let's recheck the table. For 20 ranges, Column C is 35 kW. My mistake in interpreting the table. The correct value from NEC Table 220.55 for 20 ranges, assuming they are 8 kW, is 35 kW (Column C for 12-27 ranges, not exceeding 12kW nameplate rating).
Why the other options are wrong
- A. Incorrect. This value is for fewer ranges or an incorrect application of the demand factor.
- B. Incorrect. This would be the demand for a different number of ranges or an incorrect calculation.
- D. Incorrect. This value is significantly higher than permitted by the NEC demand factors.
Electric Range Demand Load (Multi-family)
The minimum demand load for electric cooking appliances in multi-family dwellings is determined using NEC Table 220.55, which applies demand factors based on the number and rating of ranges.
- NEC Table 220.55 is used for dwelling unit electric range demand loads.
- Demand factors reduce the calculated load based on the number of ranges.
- Different columns in the table apply based on the range's nameplate rating.
Memory trick: Remember, many ranges mean less individual demand, so check the table for the right 'group' discount!