Renovations and older homes

Much residential electrical work is not in new houses but in existing ones: adding circuits for a renovation, upgrading a service, replacing a panel, finishing a basement, or making an older house safe. Older homes contain wiring methods and equipment that were legal when installed but would not be accepted today, and some have hazards that call for repair. Renovation work also has its own techniques, since walls are already closed. This lesson covers assessing an older electrical system, the main legacy wiring types and how to deal with them, the rules for extending and modifying existing wiring, service upgrades and panel replacements, and how to fish cable and add circuits in finished buildings.

Assessing an existing system

Before quoting or starting work, an electrician surveys the existing installation:

• Service: size of the service and main breaker or fuses, condition of the mast, meter base and service entrance cable, and grounding and bonding (water pipe bond, electrodes).
• Panel: make and model, condition, available spaces, signs of overheating (discoloured insulation, melted plastic), double-tapped breakers, and whether the panel is on lists of problem equipment.
• Branch wiring: cable types visible in the basement and attic, presence of a bonding conductor, aluminum branch wiring, knob-and-tube, signs of amateur work (open splices, cords used as permanent wiring, missing covers).
• Devices: two-slot receptacles, warm or discoloured devices, loose receptacles, missing GFCIs where now required.
• Load: the current calculated load and what the renovation will add (Lesson 1).

A written summary helps the homeowner decide what to fix now and what to plan, and protects the electrician by recording conditions found.

Legacy wiring methods

Knob-and-tube

Houses built before about 1950 may have knob-and-tube wiring: single conductors with rubber and cloth insulation, supported on porcelain knobs and passing through porcelain tubes, separated so that heat dissipates into open air. It was a sound method when installed, but after 70 to 100 years the insulation is often brittle, there is no bonding conductor, circuits are often overloaded or altered, and covering the conductors with thermal insulation (common in attic retrofits) traps their heat. Many insurers will not cover houses with active knob-and-tube, and replacement is the usual recommendation, especially before insulating.

Early cable without a bonding conductor

Cable installed before the 1960s often has only two insulated conductors, with no bonding (grounding) conductor, supplying two-slot receptacles. Replacing a two-slot receptacle with a three-slot one is not allowed unless a bonding path is provided, because the third slot would falsely suggest a ground. Accepted options are:

• Install a new bonding conductor to the box, run to an acceptable point in the bonding system.
• Replace the circuit with new cable.
• Protect the receptacle with a GFCI (a GFCI receptacle or breaker) and install three-slot receptacles labelled "No equipment ground" and "GFCI protected". The GFCI protects people from shock even without a ground, although it does not provide a fault path for surge protectors or equipment that needs one.

The CEC permits the replacement of non-bonded receptacles under specific conditions, including GFCI protection, and requires labelling; tamper-resistant receptacles are required for replacements in locations where new receptacles would need them.

Aluminum branch wiring

Between roughly 1965 and the mid-1970s, some houses were wired with aluminum branch-circuit conductors (15 A and 20 A circuits). Aluminum of that era expands and creeps more than copper and forms an oxide layer, so its connections at devices not designed for it loosen and overheat over time, causing fires. Remedies include:

• Replacing devices with ones marked CO/ALR, rated for aluminum.
• Pigtailing each aluminum conductor to a short copper conductor with a connector listed for joining aluminum to copper (for example special crimp connectors or listed set-screw connectors), so that copper connects to the devices.
• Rewiring with copper.

Ordinary twist-on connectors are not listed for aluminum-to-copper connections unless specifically marked. Larger aluminum conductors (for feeders, ranges and services) made with modern alloys and proper terminals are common and acceptable today.

Fuse panels and problem equipment

Fuse panels with screw-in plug fuses still serve many older houses. Their main hazard is over-fusing: replacing a 15 A fuse with a 20 A or 30 A one to stop "blowing", which removes protection from the wire. Type S fuses with size-rejecting adapters prevent this. Fuse panels are also usually small (60 A or 100 A) and lack spaces for new circuits.

Some breaker panels from past decades have documented problems with breakers that fail to trip or with poor bus connections; Federal Pacific Electric (Stab-Lok) and Zinsco panels are the best-known examples. Insurers and home inspectors commonly flag them, and replacement is often recommended.

Extending and modifying existing wiring

When a circuit is extended or a device is replaced, the new work must meet the current code, even though the rest of the house does not have to be brought up to date. In practice this means:

• Extensions and new outlets need the protection now required for that location: AFCI for most living-area circuits, GFCI in kitchens, bathrooms, basements, garages and outdoors, tamper-resistant receptacles.

In Canada, when a branch circuit supplying receptacles is extended or modified in a dwelling, AFCI protection is generally required for the extended part, and some provinces have specific provisions for renovations; check the local amendments.

• The existing circuit must have the capacity for the added load, and the panel must have a space (or a listed tandem breaker where the panel allows it).
• Splices to old wiring are made in accessible boxes, with care for brittle insulation; heat-shrink or sleeving can protect short lengths, but deteriorated wiring should be replaced back to sound cable.

Service upgrades and panel replacements

Upgrading a service, for example from 60 A or 100 A to 200 A, is one of the most common major residential jobs, driven by renovations, heat pumps and EVs (Lessons 8 and 10). The process:

• Load calculation and design: confirm the new size, plan the location of the meter base and panel, and the grounding electrode system (Lesson 3).
• Permit and utility coordination: the utility schedules disconnection and reconnection, may need to replace the service drop or lateral, and sets requirements for the meter base and mast.
• Installation: new meter base, service mast or conduit, service conductors, panel, grounding electrodes and bonding (water pipe, gas pipe as required), then transferring each branch circuit to the new panel, extending conductors in a junction box where they are too short.
• Inspection and reconnection: the inspector approves the service before the utility reconnects.

When circuits are moved to a new panel, each is checked: correct breaker size for its conductor (old circuits sometimes had oversized fuses), required AFCI or GFCI protection under the rules for replaced panels, labels for the directory, and any aluminum terminations rated correctly.

Fishing cable in finished walls

Adding outlets without opening walls is a craft of its own:

• Plan routes from accessible spaces: an unfinished basement below, an attic above, or a closet.
• Use old-work boxes, which clamp to the drywall or plaster, cut into the wall at the outlet location after checking for studs, pipes and existing cables with a stud finder and an inspection camera.
• Drill through top and bottom plates with long flexible bits, and pull cable with fish tape, glow rods or fish chains.
• Across ceilings, run parallel to joists where possible; crossing joists may require small access holes that are patched afterwards.
• Keep cables away from heating ducts and plumbing, protect them where they pass through framing near the face, and seal penetrations in fire separations and top plates.

Where fishing is impractical, surface raceway (metal or plastic) is an approved alternative that leaves walls intact.

Troubleshooting in older houses

Faults in older wiring often come from deteriorated connections. A systematic approach (building on Lesson 9):

• Gather symptoms: which outlets are dead or flickering, what was happening when it started, which breaker tripped.
• Map the circuit: find all outlets on it by switching off the breaker and testing.
• Divide and test: in a dead or intermittent circuit, check the first and last working outlets; the fault is usually at a connection between them, often at a backstabbed receptacle or a loose splice.
• Measure, not guess: use a multimeter under load (a plug-in heater or load tester) to find connections that pass voltage with no load but fail under current.
• Look for heat: an infrared camera or simply touching cover plates after a load test reveals hot connections.