Demand loads for schools, hospitals and other buildings

Houses and apartments have their own detailed rules because they are the most common buildings and because their loads are well understood. For everything else, from an elementary school to a hospital wing, a motel, an office, a store or a warehouse, the CE Code switches to a different style of calculation. Instead of listing appliances, it starts from the floor area and a load per square metre that depends on the type of occupancy, then adds specific loads such as heating, air conditioning and large equipment, and applies demand factors where the rule allows. This lesson explains that style and how to apply it on an exam.

The relevant rules are in the second half of Section 8: Rule 8-204 for schools, Rule 8-206 for hospitals, Rule 8-208 for hotels, motels, dormitories and similar occupancies, and Rule 8-210 for the other occupancies listed in Table 14, which gives a basic load per unit area for each type of building. The general rules at the start of Section 8, particularly Rule 8-106 on the use of demand factors, apply alongside them. Because the per-square-metre values and demand factors are the Code's own tabulated content, this lesson does not reproduce them. The worked examples use illustrative values that are clearly labelled, and you must look up the real values in your own copy before relying on any of them.

Why non-dwelling buildings use watts per square metre

When a school or an office is designed, the electrical designer rarely knows every piece of equipment that will be plugged in over the building's life. Floor area, on the other hand, is fixed early and predicts the general lighting and receptacle load well. Table 14 captures decades of experience about how much load each square metre of a given occupancy tends to need. Multiplying the area by the table value gives a basic load that covers general lighting and general-use receptacles, and the rules then tell you which other loads to add on top.

The occupancy categories in Table 14 cover the common building types: offices, stores, restaurants, warehouses, churches, garages, banks, clubs, barber shops and beauty parlours, and others. Each category has its own value, and some rules give separate values for different parts of a building, such as classroom area and other area in a school. The categories matter: a store and a warehouse of the same size have very different basic loads.

The general pattern

Whatever the occupancy, the calculation follows the same pattern. Work out the floor area that the rule asks for, which is usually measured from the outside of the walls, and multiply it by the basic load per unit area for the occupancy. Apply any demand factor the rule gives to that basic load. Then add the specific loads the rule lists: electric space heating, air conditioning, and other fixed loads such as kitchen equipment, process loads, elevators, pumps and exterior lighting, each with the demand factor the rule permits, or at full value where none is given. Finally, divide by the appropriate voltage to get the minimum service or feeder ampacity.

Schools

Rule 8-204 covers schools. It bases the load on the classroom area and on the rest of the building separately, because classrooms, labs and shops are more heavily loaded than corridors, gyms and storage rooms. It then adds electric space heating and air conditioning, and lets you apply demand factors to the heating in a school in a way that reflects how schools are used. Questions on schools typically give you a floor plan summary: classroom area, other area, the heating and cooling loads, and perhaps a kitchen or a shop. The trap is to apply one rate to the whole floor area.

Denise makes the study group redo that example with the values in their own code books, then compare answers. The method stays the same; the numbers change. That habit, separating the method from the values, is the most useful thing to take from this lesson, because it means you can handle any occupancy the exam throws at you as long as you can find its rule.

Hospitals

Rule 8-206 covers hospitals. Hospitals have heavy and continuous loads: lighting that is on around the clock, medical equipment, sterilisers, kitchens, laundries, ventilation and imaging equipment. The rule bases the load on floor area like the others, with its own values, and adds the specific large loads. Hospitals also have the essential electrical system required by Section 24 and CSA Z32, with emergency generators carrying life safety and critical branches. Those systems are sized separately and are covered in MELC-105; for the service calculation, the point is that the normal service must carry the full calculated load of the building.

Exam questions on hospitals tend to be shorter than those on schools, because the rule is applied less often in practice by contractors who sit master exams. When they appear, they test whether you found the right rule and whether you added the large specific loads, which in a hospital can exceed the area-based load.

Hotels, motels and dormitories

Rule 8-208 covers hotels, motels, dormitories and buildings of similar occupancy. The guest rooms are not dwelling units, because they lack the cooking facilities that define a dwelling unit, so the apartment rules do not apply. Instead, the rule gives an area-based load for the building and permits demand factors that recognise that not every room is occupied and drawing full load at once. Kitchens, laundries, pools, elevators and the heating and cooling equipment are added separately.

Other occupancies under Rule 8-210

Rule 8-210 covers the occupancies listed in Table 14 that do not have their own rule. This is the rule you will use most often for commercial work: offices, stores, restaurants, banks, warehouses, garages and so on. It applies the basic load from Table 14 to the floor area, and then has you add the specific loads. Where the table value already covers a category of load, such as general lighting, you do not add it again. Where a load is not general, such as a commercial kitchen, a large sign, show window lighting or process equipment, you add it.

Show window lighting is a good example of a specific load with its own allowance: the Code gives a load per metre of show window, measured along its base, rather than per square metre of floor. It is the kind of detail that appears as one line in a long exam question, and it is easy to miss.

Demand factors and Rule 8-106

Rule 8-106 sets out general situations where demand factors or reduced loads may be used regardless of occupancy. Where two or more loads are installed so that only one can operate at a time, only the largest needs to be counted. Where air conditioning and electric space heating are both installed, only the greater of the two counts, provided they will not be used together. Where cyclic loads cannot all be supplied at once, their combined demand can be reduced. The rule also allows other demand factors where they are supported by load data or calculations by a qualified person, as accepted by the authority having jurisdiction.

One provision of Rule 8-106 is especially useful for renovation work: when adding load to an existing service or feeder, the existing load may be based on the maximum demand actually recorded over the previous 12 months, rather than recalculated from scratch, with the new load added to it. Utilities and some meters can supply that data. For the clinic, if the strip mall's records showed a maximum demand of 150 kVA on a 400 A, 208 V service, which has a capacity of about 144 kVA at 400 A, the owner could not add the clinic without a service upgrade, whatever the calculation said.

Writing it up on the exam

For non-dwelling questions, examiners often care more about method than arithmetic, because the values come from tables. Priya's layout is the same as for dwellings: one line per item, the rule and the table value beside each line, the demand factor shown explicitly, and the voltage written at the top. If a question gives values in a table rather than asking you to look them up, use the given values even if they differ from your Code; examiners sometimes write questions with simplified numbers.

def occupancy_load(area_m2, w_per_m2, basic_factor=1.0, specific=(), heat_w=0,
                   cool_w=0, interlocked=True):
    basic = area_m2 * w_per_m2 * basic_factor
    hvac = max(heat_w, cool_w) if interlocked else heat_w + cool_w
    return basic + hvac + sum(specific)

# Illustrative values only: replace w_per_m2 and factors with your Code's.
clinic = occupancy_load(420, 50, specific=(6000, 7500, 3000), heat_w=24000, cool_w=9000)
motel = occupancy_load(2400, 20, 0.80, specific=(15000, 10000), heat_w=72000, cool_w=36000)
for name, w in [('Clinic', clinic), ('Motel', motel)]:
    print(f'{name:7s} {w:8.0f} W  {w / (3 ** 0.5 * 208):6.1f} A at 208 V 3-phase')

Clinic     61500 W   170.7 A at 208 V 3-phase
Motel     135400 W   375.8 A at 208 V 3-phase