Multifamily Dwelling Calculations/Advanced NEC Calculations
*Step 2: Appliances [220.53]*
A demand factor of 75% is permitted for four or more appliances fastened in place, such as dishwasher, kitchen waste disposal, trash compactor, water heater, and so on. this doesn't apply to air conditioning equipment *[220.50]*, space heating equipments *[220.51]*, clothes dryers *[220.54]*, or cooking appliances *[220.55]. * Note*: When calculating for more that one unit add all the appliances together and apply the 75% demand factor. For example; a building that has 20 units for sure have more than four appliance fastened in place like let say 105 appliances. This is confusing at first, but as long the total building appliances pass four we can apply the rule. * We can also calculate the Neutral Load at this stage. we can find this example at the multifamily dwelling calculation exercise in the Mike Holt book. First remove the 240 v load from the total and then multiply it by the number of units. The result should also be multiply by 75% percent to get the Total Neutral Load for the appliances*
*Step 4: Cooking Equipment[220.55]*
Household cooking appliances rated over 1 3/4 kva can have their feeder and service loads calculated according to the demand factor of *Table 220.55 and Notes*.
*Multifamily Dwelling Calculations-General* The following steps can be used to determine the feeder or service size for a multifamily dwelling using the standard method contained in Part III of Article 220: *Step 1: General Lighting and Receptacles, Small Appliances, and Laundry Circuits [Table 220.42]*
The NEC recognize that lighting, general use receptacles, and small appliance and laundry circuits won't be on, or loaded, at the same time. It permits the following demand factor to be applied to these loads*(220.42)* *Step a* -Total connected load. Determine the total connected general lighting and receptacle load (3va per sq ft) *[220.12]*, the two small appliance circuits (1500a each) *[220.52 (A)]*, and the laundry circuit load (1500 va) *[220.52 (B)]* of all dwelling units. The laundry load can be omitted if laundry facility are provide on the premises and are available to all building occupants *[210.52 (F) Ex 1]* *Step b* -Demand factor- Apply the *Table 220.42* demand factors to the total connected load(step a). The fist 3000 va is calculated at 100% demand, the next 117,000 va (120000-3000) is calculated at 35% demand, and the remainder at 25 percent according to *Table 220.42*
*Step 3: Clothes Dryers [220.54]*
The feeder or service calculated load for household electric clothes dryers located in dwelling units must be less than 5000W (or 5000 va), or the nameplate rating (whichever is greater) and may be adjusted according to the demand factor listed in *Table 220.54* *Note*: A dryer load isn't required if the dwelling unit doesn't contain an electric dryer. Dryers in common laundry rooms must no have their loads calculated according to this method. *The contribution to the neutral of the feeder/service for the clothes dryers load is calculated by first multiplying the dryers calculated load by times 70%. 220.61 (B)(1)*
*Step 6: Feeder and Service Conductor Size*
The feeder/service conductors are sized according to *Table 310.15(B)(16). Conductors are presumed to be cooper unless otherwise stated and systems are presumed to be single phase unless otherwise stated. *Notes*: -Table 310.15(B)(7) can be used to size the 120/240V feeder conductors to the individual dwelling units of a multifamily dwelling, but Table 310.15(B)(16) must be used to size service conductors that supply two or more dwelling units. -Section 110.14 (C)(1)(a) states that terminals are rated 60°C for equipment rated 100 A or less marked 75°C. In real life, most terminals are now rated 75°C, so in this unit, we assume all terminals are rated 75°C unless 60°C is specified. Insulated conductors will be presumed to be 90°C rated. For exam purposes, read the problem carefully to be certain you know what terminal rating the exam question specifies. If unspecified, use the rules of 110.14(C)
*Step 5: Air Conditioning versus Heat [220.51 and 220.60]*
When the air conditioning and heating loads aren't on at the same time (simultaneously), only the larger of the two loads must be used *[220.60]*. - Air conditioning. The air conditioning load must be calculated at 100% *[220.50]*. - Heat. Electric space heater loads must be calculated at 100%*[220.51]*.
