Mike Dolt Enterprises
Mike Dolt Enterprises
User: PerryLackowski, Location: Cleveland, Ohio, USA
Asked on: Friday, March 7, 2025 at 12:46 pm EST
Answered on: Tuesday, March 11, 2025 at 9:32 pm EDT
Question: I'm working on a hotel space, and effectively one floor of rooms will be fed from a single panel, so I'm trying to size the feeders for that panel. I'm a bit confused though, because 215 and 220 seem to have conflicting instructions for sizing the feeders. I'm working from the 2023 NEC.Starting with 220. It's important to qualify here that the hotel rooms will not contain kitchenettes, so they do not qualify as dwelling units. Additionally, the mechanical loads are fed from separate panels. So in 220, we head to Part III for Feeder and service load calculations. 220.40 says the calculated load should be not less than the sum of the loads on the branch circuits supplied, per Part II. Part II (220.10) says the branch loads can be calculated based on 220.44 for hotels, which sends us back to Part III. 220.44 says that effectively all the lighting and receptacles in the room can be can be rolled into one VA/Sq Ft calculation using table 220.42(A), so 1.7VA*292 sq ft = 496.4VA.Let's look at 215 next. 215.2 says the feeders must be sized as not less than the larger of the non-continuous + 125% continuous loads, and the load after any correction factors have been applied in 310.14. So basically a straight load calculation. I can't know the exact loads for the devices, but we estimated:Mini Fridge & Coffee - 10 AmpsBathroom - 10 Amps (running a hair dryer)General Rec and LTG - 6 AmpsIf we anticipate these loads per room, it will be 26 A per room, or 26*120=3120VA.The 215 results are over six times larger than the minimum from 220. They also haven't factored in the diversity - there's no way every room on the floor is using both their coffee machine and hair dryer at the same time. However, I see no exceptions in 215 allowing you to consider diversity in your calculation. And my understanding is that both 215 and 220 apply, so we're stuck with much larger loads. At the panel, if we have 29 rooms, it's the difference between 80A and 252A, which is the difference between a 100A panel and a 400A panel.Does anyone have any thoughts on this interpretation? Do we need to go with the oversized panels or is there something I'm missing?
You've hit upon a common point of confusion when applying the NEC, especially to commercial buildings like hotels. You're right in thinking that both 215 and 220 apply, but you're missing the critical element of demand factors. NEC 215 tells you how to size the feeders, while NEC 220 tells you how to calculate the load before applying 215.Here's the breakdown and where the misunderstanding lies
1. You're correct about 220.44 and the 1.7 VA/sq ft calculation.
This is the minimum general-purpose load you must account for. However, this is just the first step.2. The Misunderstanding: Applying 215 DIRECTLY to the Room Loads You calculated 3120VA per room based on hypothetical usage. This is a connected load, and it's not the same as the demand load. You can't directly multiply this by the number of rooms and call it your feeder size requirement per 215.
Here's the correct approach
Calculate the Minimum General Lighting and Receptacle Load (220.44)
You did this correctly: 1.7 VA/sq ft area = 496.4 VA/room.
2.
Calculate the Load from Known Appliances (Coffee, Fridge, Hair Dryer)
Coffee & Fridge = 10A 120V = 1200 VA Bathroom = 10A 120V = 1200 VA General Rec and LTG = 6A 120V = 720 VA Total Known Appliances = 3120 VA3.
Apply Demand Factors (220.42(B) or Engineering Judgement)
This is the KEY step you're missing. This is where you account for the fact that not every room will be drawing its maximum potential power at the same time. This is where you consult the demand factor tables or rely on your own experience.
Consider Table 220.42(B)
This table offers demand factors for receptacles in other than dwelling units. Because a typical hotel room has more receptacles than a typical office or bank, for example, the demand factor of the table may not be appropriate, and some engineering judgement may be required to accurately model the load.4.
Calculate the Total Demand Load per Room
This is the load you will use to calculate the feeder size. Add the demand of the general lighting and receptacles load to the demand from the other appliances.5.
Aggregate the Room Loads
Sum the demand loads of all 29 rooms.6.
Apply Feeder Demand Factors (220.42(B) or Engineering Judgement)
You can further reduce the load by applying a demand factor to the aggregated room demand load. For example, Table 220.42(B) offers a demand factor for feeder demand in hotel occupancies.
7.
Consider Other Loads (If Any)
Don't forget any other loads on the panel, such as hallway lighting, laundry facilities, or vending machines. These should also be calculated with appropriate demand factors.8.
Calculate Feeder Size (215.2)
Now you use 215.2 to determine the minimum feeder size based on the total demand load calculated in the previous steps.
Example (Illustrative, Requires Engineering Judgement)
Let's say after considering typical hotel occupancy, you decide on a demand factor of 60% for the "known appliances" load and a demand factor of 80% for general receptacles: General LTG Demand Load/Room: 496.4VA 80% = 397.12VA Appliance Demand Load/Room: 3120VA 60% = 1872VA Total Demand Load/Room: 2269.12VA Total Demand Load for 29 Rooms: 29 Rooms 2269.12VA = 65804.48VA Total Demand Load w/ Demand Factors: 65804.48VA 70% (Example Demand Factor) = 46063.14VA 46063.14VA / 208V / 1.732 = 128ABased on the calculation, a 200A panel would be suitable for the loads, although this might need to be upsized due to voltage drop on longer runs.
Important Considerations
Voltage Drop
Always check for voltage drop, especially with longer feeder runs. This can necessitate upsizing the conductors. 310.15(A)(1).
Continuous Loads
If any loads are considered "continuous" (operated for 3 hours or more at a time), they need to be multiplied by 125% (215.2(A)(1)(a)).
Future Expansion
Consider the possibility of future expansion or changes in occupancy when sizing the feeder.
Consult an Engineer
This is a complex calculation. If you're not experienced with load calculations and demand factors, consult a qualified electrical engineer. They can help you accurately assess the loads and ensure the installation complies with the NEC.
Use Software
There are electrical design software programs that can help you with load calculations and feeder sizing. These tools often have built-in NEC tables and demand factors.
In summary, the key takeaway is that you CANNOT simply add up the theoretical maximum loads of all the rooms and use that to size the feeder. You MUST apply appropriate demand factors based on anticipated usage patterns. NEC 220 provides the rules for calculating these loads and demand factors. Flag for review