Alarms, communications, smart homes and a house project

A modern house contains more than power wiring. Smoke and carbon monoxide alarms protect lives and are required by building codes; data, television and doorbell cabling connect the house to the outside world; and smart switches, thermostats and sensors make lighting and heating controllable from a phone. Electricians install much of this, and its requirements reach back into the power wiring: alarms need specific circuits, smart switches need neutrals in switch boxes, and network equipment needs power in the right places. This lesson covers these systems and finishes with a project that wires a complete house, drawing on every lesson of the course.

Smoke and carbon monoxide alarms

Smoke alarms are self-contained detectors with built-in sounders, unlike the system smoke detectors of commercial fire alarm systems (ELEC-120). Building codes require them in new dwellings and in renovated areas:

• Locations: on every storey including basements, in or near each sleeping area (the hallway outside bedrooms), and in each bedroom under most current codes.
• Power: permanently connected to the house wiring, with battery backup, so they work when the battery is dead or the power is out.
• Interconnection: all alarms in the dwelling interconnected, by wire or listed wireless means, so that when one sounds, all sound.
• Carbon monoxide alarms: required where there is a fuel-burning appliance or an attached garage, near sleeping areas; combination smoke/CO alarms are common.

In Canada, the National Building Code and provincial codes set where smoke and CO alarms go, and the CEC sets how they are supplied: generally from a lighting circuit or a circuit that also supplies lighting, not from a circuit protected by a GFCI, and without a disconnect switch between the alarm and the overcurrent device, so the alarm does not lose power unnoticed.

Communications and low-voltage cabling

Houses need data, television and sometimes telephone cabling, plus low-voltage control and signalling. Good practice is to run it during rough-in, when walls are open:

• A central location (a structured media enclosure in a utility room or basement) where the internet service enters, with the modem, router and a network switch, and a receptacle for their power.
• Category 6 or 6A cable from the central location to each room where wired connections are useful: televisions, desks, and ceiling locations for wireless access points, which can be powered over the cable by PoE (ELEC-120).
• Coaxial cable (RG-6) for television and some internet services, to the same rooms.
• Conduit from the central location to the attic and to the exterior where the service enters, for future cables.

Low-voltage cables must be separated from power cables, not share boxes without barriers, and enter through their own openings or low-voltage brackets (ELEC-120, Class 2). Their fire ratings must suit the location.

Doorbells, thermostats and sensors

Doorbells run from a small Class 2 transformer (typically 16 V AC) near the panel or in a box. Video doorbells often need more power than old transformers supply, so a larger transformer (often 16 V to 24 V, 30 VA or more) is installed. Thermostats need low-voltage cable with enough conductors, including a common (C) wire for smart thermostats, from the thermostat location to the furnace or air handler.

Smart home wiring

Smart switches, dimmers, receptacles and sensors are controlled by apps, voice assistants and automation. Electrically, they have a few special needs:

• A neutral at switch boxes: a mechanical switch only interrupts the hot conductor, but an electronic smart switch needs a small continuous current to power its radio, which requires a neutral. Older practice of running only a switch loop (hot and switched hot) leaves no neutral.

The CEC and provincial practices increasingly expect a neutral to be available in switch boxes; running cables so that the neutral reaches each switch box is good practice for new work.

• Box space: smart switches are larger than mechanical ones, so deeper boxes help.
• Compatibility: smart dimmers must match the lighting type (LED drivers vary), and three-way smart switching uses specific companion devices, not ordinary three-way switches.
• Wireless coverage: many devices use Wi-Fi, Zigbee, Z-Wave or Thread; good access point placement (with wired backhaul) avoids unreliable automation.
• Smart panels and energy monitors measure each circuit and integrate with EV chargers, batteries and solar (Lesson 10).

Surge protection and power quality

Electronics are more numerous and sensitive than ever. A whole-house surge protective device (SPD) at the panel diverts surges from lightning and utility switching (ELEC-120), and point-of-use surge strips protect individual equipment; the two work together. Since the 2020 edition, the NEC requires an SPD for dwelling services; in Canada, SPDs are permitted and often recommended. Good bonding of the electrical, telephone, cable and satellite systems to the same grounding electrode system is essential, so that surges do not create voltage differences between them.

House project: wiring a new home

The final project brings the course together. A new two-storey house of 180 m² (about 1,940 ft²) with a finished basement has: an induction range (11 kW), a dryer (5.5 kW), a heat-pump water heater, a cold-climate heat pump with 10 kW of backup strips, a 48 A EV charger, and a future rooftop solar system.

Step 1: Load calculation and service (Lesson 1)

The calculation, done by the method of the code in force, includes the floor area basic load, the range with its demand factor, the dryer, the water heater, the larger of heating and cooling (here the heat pump with backup strips), and the EV charger, unless it is controlled by a listed energy management system. The result for a house like this is typically in the range of 150 A to 200 A; a 200 A service is selected, with an EV energy management system so that charging cannot coincide with full backup heat.

Step 2: Layout and circuits (Lessons 2, 5 and 6)

A room-by-room layout places receptacles to meet the spacing rules, with kitchen counter circuits, bathroom, laundry and individual appliance circuits, lighting split from receptacles, and three-way switching at stairs and halls. The panel schedule has roughly 30 to 36 circuits, including two-pole circuits for the range (40 A or 50 A per instructions), dryer (30 A), heat pump (per MCA/MOCP), air handler strips (per nameplate), EV charger (60 A) and water heater (per nameplate), in a 42- or 48-space panel.

Step 3: Service and panel installation (Lesson 3)

The meter base and 200 A panel are installed with service conductors sized for 200 A, grounding electrodes and bonding to water and gas piping as required, a whole-house SPD, and working space in front of the panel.

Step 4: Rough-in (Lessons 4 and 8)

Boxes are mounted and sealed to the air barrier in exterior walls; cables are run, stapled and protected; neutrals are brought to switch boxes; heating and appliance circuits are run to their equipment locations; smoke and CO alarm cables are run with interconnect conductors; low-voltage data, coaxial and thermostat cables are run to the media enclosure and the air handler; conduit is run to the attic for solar. The rough-in inspection is called.

Step 5: Protection (Lesson 7)

AFCI, GFCI or dual-function protection is chosen for each circuit according to the code edition: AFCI for living-area circuits, GFCI for bathrooms, kitchen counters, laundry, basement, garage and outdoors, dual-function where both apply, and the protection for the EV receptacle or hard-wired charger as the charger and code require.

Step 6: Finish, testing and handover (Lesson 9)

Devices, luminaires and equipment are installed; every circuit is tested for continuity, polarity, insulation resistance and correct operation of AFCIs and GFCIs; the panel directory is completed; the final inspection is passed; and the homeowner receives the directory, test results, equipment manuals and an explanation of the energy management system and the solar-ready provisions.

Every decision in the project came from a lesson in this course, and every one is checked against the code edition the inspector enforces. That combination of planning, code knowledge, workmanship and testing is what residential electrical work is.