**Multi-Family Dwellings Services**

Calculating service requirements for multi-family dwellings is similar to calculating single-family dwellings. In fact, to calculate each unit, or apartment of a multi-family dwelling we would use the same method that we used in the previous chapter. That’s right, in the meter room of your apartment building (if you live in one) is your own personal main breaker whose size was calculated using the general or optional method we just learned. What we’re going to learn in this chapter is how to determine the size of the main breaker for the whole entire building.

General Method Calculation

**Article 220.84**covers multi-family dwellings in general. Here are some other important related articles...

After calculating the demanded loads in volt-amps (same as watts) they’re all added together to determine the main breaker (or fuse) and feeder conductor size. To simplify, we’ll deal with each area a step at a time.

General Lighting And Receptacles

**Article and Table 220-12**calls for 3 volt-amps (vA) per square foot for general lighting and receptacles in Dwelling Units...

*220.12 Lighting Load for Specified Occupancies.**A unit load of not less than that specified in*

*Table 220.12**for occupancies specified therein shall constitute the minimum lighting load. The floor area for each floor shall be calculated from the outside dimensions of the building, dwelling unit, or other area involved. For dwelling units, the calculated floor area shall not include open porches, garages, or unused or unfinished spaces notadaptable for future use.*

In the case of a multi-family dwelling we’re dealing with three, or more, dwellings in a single building. In determining the square foot area of a multi-family dwelling we would include the outside dimensions of the entire building including; living areas, hallways, storage rooms, laundry facilities, etc.

For example; An apartment building which includes 20 units at 800 square feet each would have a unit load per square feet of...

For example; An apartment building which includes 20 units at 800 square feet each would have a unit load per square feet of...

800 square feet x 3 vA x 20 units = 48,000 vA

Common areas including hallways, stairways, closets, storage rooms, laundry rooms, garages, pool facilities, and parking lots are referred to as House Loads. We’ll be dealing with those a little later.

Small Appliances

**Articles 210.11(C)(1) and 220.52(A)**specifies service requirements for small appliance circuits. These are 20 amp circuits for small cord-and-plug connected appliances in the kitchen, pantry, breakfast and dining room of each apartment.

**210.11(C)(1) Dwelling Units. Small-Appliance Branch Circuits.**In addition to the number of branch circuits required by other parts of this section, two or more 20-ampere small-appliance branch circuits shall be provided for all receptacle outlets specified by**210.52(B).**

**220.52(A) Small-Appliance Circuit Load.**In each dwelling unit, the load shall be calculated at 1500 volt-amperes for each 2-wire small-appliance branch circuit as covered by**210.11(C)(1).**Where the load is subdivided through two or more feeders, the calculated load for each shall include not less than 1500 volt-amperes for each 2-wire small appliance branch circuit. These loads shall be permitted to be included with the general lighting load and subjected to the demand factors provided in

*Table 220.42.*Remember, the Code requires a minimum of at least two 20 amp small appliance circuits in all dwelling units and the load that will be added to the service shall be computed at 1,500 vA each.

Refrigeration equipment can be supplied by these circuits or by a separate 15 amp circuit or larger.

If we put a minimum of two 20 amp small appliance branch circuits in each of the above 20 apartments we would add the following to our service calculation:

1,500 vA x 2 x 20 apartments = 60,000 vA

Remember, the Code requires a minimum of two 20 amp circuits, there may be more.

Laundry

**Article 210.11(C)(2) and 220.52(B)**requires at least one 20 amp circuit for laundry equipment.

*210.11(C)(2) Laundry Branch Circuits.**In addition to the number of branch circuits required by other parts of this section, at least one additional 20-ampere branch circuit shall be provided to supply the laundry receptacle outlet(s) required by*

*210.52(F)**. This circuit shall have no other outlets.*

*220.52(B) Laundry Circuit Load.**A load of not less than 1500 volt-amperes shall be included for each 2-wire laundry branch circuit installed as covered by*

*210.11(C)(2)**. This load shall be permitted to be included with the general lighting load and subjected to the demand factors provided in*

*Table 220.42**.*

This would add the following amount to our service load for the above 20 apartments...

1,500 vA x 20 apartments = 30,000 vA

That’s fine if there’s laundry facilities in each apartment. But, what if there are common laundry facilities on each floor of the apartment complex instead. Obviously, in this case we wouldn’t include a 1,500 vA laundry circuit in each apartment. Common laundry facilities would be considered a House Load. We’ll get to that later, I promise !

General Lighting Demand Factors

We can use the feeder demand factors for general lighting, general use receptacles, small appliance and laundry circuits from

**Table 220.42.****Table 220.42**gives the lighting load feeder demand factors.

**Articles 220.52(A) and (B)**allows us to include small appliance and laundry circuits in these demand factors.

Let’s add up the general lighting, small appliances, and laundry loads and calculate the demands we would have to add to the main service and feeder of our 20 unit apartment complex.

(1) General Ltg. & Rec. (800 x 3 x 20) = 138,000 vA
(2) Small Appliances (1,500 vA x 2 x 20) = 60,000 vA (3) Laundry (1,500 vA x 20) = 30,000 vA Total Connected Loadv = 228,000 vA |

Applying the demand factors of Table 220.42...

(4) First 3,000 vA at 100% = 3,000 vA
(5) Next 117,000 vA at 35% = 40,950 vA (6) Next 10,800 vA at 25% = 27,000 vATotal Demanded Load = 70,950 vA |

Notice that there are three levels of demand factors here. The first 3,000 vA is at the usual 100%, and the next 117,000 vA (3,001 to 120,000 vA) is at 35%. But, anything over 120,000 vA is at a mere 25%. Most single-family dwellings would not use this third demand factor. It seems to have been put there just for multi-family dwellings.

Fixed Appliances

**Article 220.53**permits a 75% demand factor for four or more fixed appliances such as water heaters, dishwashers, disposals, trash compactors, etc.

*220.53**Appliance Load - Dwelling Unit(s). It shall be permissible to apply a demand factor of 75 percent to the nameplate rating load of four or more appliances fastened in place, other than electric ranges, clothes dryers, space heating equipment, or air-conditioning equipment, that are served by the same feeder or service in a one-family, two family, or multifamily dwelling.*

Ranges, dryers, air-conditioning and heating appliances are dealt with in other Code articles.

This is a piece of cake in a multi-family dwelling because we get to count all of the fixed appliances in all of the apartments in the building. If every apartment in our 20 unit apartment building has the following...

1 Water Heater = 3,000 vA
1 Dishwasher = 1,250 vA 1 Disposal = 1,100 vATotal Connected Load = 5,350 vA |

We would actually have a total of 60 fixed appliances (3 x 20). Applying the demand factor from Article

**220.53.**Our demanded load would be...5,350 vA x 20 units x .75 = 80,250 vA

Multi-family dwellings have no problem in meeting the four appliance minimum needed to use the 75% demand factor.

Cooking Appliances

**Table 220.55**looks like it was made for multi-family dwellings. For instance; if each of our 20 apartments had a 10 kW range. We would just go to

**Table 220.55...**

20 Ranges (Column “A”) = 35 kW or 35,000 vA

Dryers

**Table 220.54**is very useful for multi-family dwellings. Derating factors go into effect with five or more dryers.

Don’t forget ! there is a 5,000 vA minimum for the dryer circuit, that is unless our nameplate rating exceeds 5,000 vA, then we have to use the nameplate rating.

*220.54 Electric Clothes Dryers - Dwelling Unit(s).**The load for household electric clothes dryers in a dwelling unit(s) shall*

*be either 5000 watts (volt-amperes) or the nameplate rating, whichever is larger, for each dryer served. The use of the demand factors in Table 220.54 shall be permitted. Kilo-volt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for loads calculated in this section.*

For example, if we have a 4,800 vA dryer in each of our 20 apartments.

5,000 vA x 20 units x .35 = 35,000 vA

It’s a bit confusing to have to raise the rating of each dryer from 4,800 vA to 5,000 vA before we reduce it by 35%. But, we’re really just allowing a minimum of 5 kVa per dryer, although, we’re betting that only 35% of the available dryers will be in use at any one time.

Air-Conditioning Versus Central-Heating

Demand factors are used because it is unlikely that all of the available loads will be used at the same time. Non-coincidental loads

Say each one of our apartments has one 6 kVa air-conditioner and one 5 kVa central-heater...

**(Article 220-60)**are so dissimilar that it is unlikely that both of them will be used simultaneously. Air- conditioners and central-heating units fit in this category. It would be impossible to turn them on at the same time when they’re on one thermostat. But, even if they weren’t, they would still be considered non-coincidental loads. In this case, the Code allows us to omit the smaller of the two when calculating feeders.

Say each one of our apartments has one 6 kVa air-conditioner and one 5 kVa central-heater...

1 Air-Conditioner at 6,000 vA x 20 units = 120,000 vA
1 Central-Heater at 5,000 vA x 20 units = 100,000 vA |

We will only apply the Air-Conditioner (120,000 vA) to our service and feeder calculation.

25% Of The Largest Motor

**Article 430-24**requires that we add 25% of the full load current (FLC) of the largest of all of the motors on a single feeder. In this case we would add 25% of one of the above air-conditioners to our service and feeder calculation.

6,000 vA x .25 = 1,500 vA

If, in this situation, the central-heat was larger than the air-conditioner we would have to find the next largest motor and add on 25% of that motor full load current.

House Loads

This is were we account for all of the loads not tied to individual apartments. Things like common laundry facilities, hallways, storage rooms, garages, signs, pool facilities and parking lot lighting are shared by all the inhabitants of an apartment building. Note that these items must be maintained by management on there own service and meter. But, because we are calculating the main service and feeder for the whole entire building, we must account for these loads.

Here’s a list of some common items...

1 Pool Pump = 1,500 vA
100 square feet of Storage Area (100’ x .25 vA) = 25 vA 200 square feet of Hallway Ltg. (200’ x .5 vA x 1.25) = 125 vA 1 Sign Circuit (1,200 vA x 1.25) = 1,500 vA Parking Lot Lights (17,000 vA x 1.25) = 21,250 vATotal Demand Load = 24,400 vA |

**Table 220.12**rates Halls, Corridors, Closets, and Stairways lighting at .5 vA per square foot. Storage spaces are rated at .25 vA per square foot.

**Article 430.24**requires us to multiply continuous loads by 125%. Hallway lighting. signs, and parking lot lights are considered continuous loads because they are usually on for three hours or more.

Service Requirements

Item General Lighting and Receptacles Demand Load(including small appliance & laundry) 48,450 vA Fixed Appliances 80,250 vACooking Appliances 35,000 vA Dryers 35,000 vA Air-Conditioning vs. Heating 120,000 vA (25% Of The Largest Motor House Loads) 1,500 vA House Loads 24,400 vATotal Demanded Load 344,600 vA |

To find amps we divide our total demanded load by 240 volts (standard voltages for services are 240/120, 1Ø):

**344,600 vA ÷ 240 v. = 1,436 amps.**Service Main Breaker Or Fuse Size

**Article 240.6(A)**lists the standard sizes of circuit breakers and fuses:

240.6(A) Standard Ampere Ratings.240.6(A) Standard Ampere Ratings.

*Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200,*

*1600**, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601.*

**Article 240.4(B)**allows us to round up to the next higher size for our main breaker or fuse. In this case a 1600 amp main would suffice.

Main Feeder Conductors

We are going to need feeder conductors based on our 1600 amp main breaker. Checking Table 310-15(B)(16) a parallel group of four #600 kcMil conductors (good for 420 amps each) would meet code requirements.

#600 kcMil (420 amps each) x 4 = 1680 amps

Multi-Family Dwelling Sample Problem...

A Multi-Family Dwelling: 20 units (1,200 square feet per unit), each contains an 8 kW Range, a 3 kW Water Heater and a 4.6 kW Dryer. Calculate service requirements at 208/120 volt, three-phase.

General Lighting (T220.12, 220.52(A & B), T220.42)
T220.12 1,200 Sq. Ft. x 3 vA x 20 = 72,000 vA220.52(A) 2 Appliance Ckts. x 1,500 vA x 20 = 60,000 vA220.52(B) 1 Laundry Ckt. x 1,500 vA x 20 = 30,000 vA162,000 vATable 220.42 162,000 vA - 3,000 vA (first 3,000 vA @ 100%) = 3,000 vA159,000 vA -117,000 vA (next 117 kVa @ 35% = 40,950 vA42,000 vA (remainder @ 25%) = 10,500 vA = 54,450 vAFixed Appliances (220.53) 20 Water Heaters (3 kW x 20) = 60,000 vA Fixed Appliance Demand (60,000 vA x .75) = 45,000 vA Cooking Appliances (T220.55) 20 Ranges @ 8 kW Cooking Appliance Demand (T220.55 Col. “C”) = 35,000 vADryers (T220.54) 20 @ 5 kW = 100 kW x 38% (Demand Factor 47% - 9%) = 38,000 vATotal Demanded Load =172,450 vA Feeder Amps = 172,450 vA 208 x 1.732 = 479 ampsUse 500 amp Main Breaker (240.6A) |