Knob-and-tube wiring and Federal Pacific or Zinsco panels: what buyers should know

Many Vancouver houses built before the 1950s have been renovated three or four times, and the wiring tells the story. A panel from one decade, a kitchen circuit from another, and behind a bedroom wall, wires that were installed when the house was new. Two things come up more than any others at the electrical panel: old wiring methods, and certain brands of panel.

Knob-and-tube wiring

Knob-and-tube was the standard wiring method in North America from the late 1800s until it was replaced by cable in the mid-twentieth century. Individual wires, wrapped in a cloth or rubber-based coating, run separately through the framing. They are held off the wood by ceramic knobs and pass through framing members inside ceramic tubes. There is no ground wire.

On its own, the method was not unsafe when installed. The wires were designed to lose heat to the air around them. The problems come from age and from what has happened since.

• Insulation. The original coating dries and cracks over decades. Bare copper can then touch framing.
• Burying. Blown-in insulation placed over the wires holds in the heat they would normally lose to the air. Loose-fill and spray foam insulation should not cover knob-and-tube wiring, but it often does in attics.
• Overloading. Modern houses draw much more current than these circuits were designed for. Fuses were replaced with larger ones.
• Amateur splices. Over the years, owners connected new cable to old wire. These splices are frequently poorly made, and some are hidden inside walls.
• No ground. Three-prong grounded equipment cannot be used safely. We commonly see adapters that defeat the ground.

What we do and do not see

An inspector sees knob-and-tube where it is exposed: in the attic, in an unfinished basement, in the crawl space. We cannot see it inside walls, and a house that looks clean at the panel may have more behind the plaster. When we find it, we note where, whether it is covered by insulation, and whether any of it looks live. A licensed electrician can test which circuits are still energized and quote on replacement.

Insurance

This is often the practical issue. Insurers treat knob-and-tube differently. Some will not insure a house with active knob-and-tube. Some will insure it if the wiring has been replaced or if it is replaced within a set time. Some charge more. Requirements change, so ask your own insurer before you remove subjects, and ask in writing. Do not rely on the seller's agent or an old policy.

Panels with known concerns

Two brands of panel have a history of concern, and both have been found in BC houses built from the 1950s into the 1980s.

• Federal Pacific Electric (FPE) Stab-Lok panels. Testing and field reports have raised concerns that some Stab-Lok breakers may not trip when they should.
• Zinsco and Sylvania (GTE Sylvania) panels. In some of these panels the breakers can overheat and fuse to the metal bus bar, so that they cannot be turned off.

Not every panel of those brands has failed. The concern is that the breaker's job is to cut off power under fault, and if it cannot be relied on to do that, the risk is fire. Inspectors identify the brand from the label and recommend that an electrician evaluate the panel, and in most cases that a replacement be considered.

Other things we see at the panel

• Double taps. Two wires under one breaker terminal, when the breaker is not rated for it.
• Small services. Older houses may have a 60-amp service with fuses. A modern household with a heat pump, an induction range or an electric vehicle charger may need more.
• Missing or open knockouts. Gaps in the panel cover, or in the box, let in dust, and let fingers in.
• Mixed brands. Breakers from one manufacturer in another's panel, unless listed for that panel, are a concern.
• Scorch marks and corrosion. Signs of heat or moisture at the panel are written up as Safety.
• Aluminum branch wiring. In houses from roughly the mid-1960s to the mid-1970s, the lighter aluminum wire sometimes loosens at connections. An electrician can advise on approved ways to correct it.

What to do before you remove subjects

1. Read what the report says it saw. Note the words "visible", "not visible" and "not inspected".
2. Call your insurer. Describe the wiring and panel brand. Ask what they require and how long you have.
3. Get an electrician's opinion. If the house is a serious candidate, have an electrician look at the panel and the attic wiring, and ask for a written quote for replacement.
4. Price it in. Rewiring a whole older house means opening walls and repairing them, and it is a real cost. A quote lets you negotiate or walk away with numbers.
5. Ask what has been done. A permit record or an electrician's invoice for a previous upgrade is useful. Ask the seller.

Selling a house with old wiring

If you are selling, an inspection first lets you know what the buyer's inspector will find. Replacing a panel is a smaller job than rewiring, and some sellers do the panel and disclose the rest. See how to prepare your home and pre-listing inspections.

In short

Knob-and-tube and old panels are common, they are manageable, and they are a reason to ask questions, not to panic. The answers are in your insurer's requirements, an electrician's opinion and a quote. An inspection tells you what is visible. It does not tell you what is in every wall.