Spark Services Knob and Tube Replacement

Knob and Tube Replacement in California

Remove pre war wiring that has no ground and no room for it.

Knob and tube shows up in Los Angeles homes built before about 1950, and insurers now treat it as a reason to decline a policy.

The short version

It has two wires and no ground, by design.
Insulation packed over it traps heat the system was never built for.
Partly replaced homes are common and hide live legs in the attic.
A rewire is the only real fix, and it can be staged.

What it is

Knob and tube was the standard wiring method into the middle of the last century. A hot wire and a neutral wire run separately through the framing, held on ceramic knobs and passed through ceramic tubes where they cross wood. There is no ground wire anywhere in the system.

Installed well and left alone, it lasted a long time. What it cannot handle is a modern home. Every ground pin appliance, every added outlet and every splice made by a previous owner works against it.

Why insulation makes it worse

The system was designed to shed heat into open air, which is why the wires run apart from each other. When someone blows insulation into an attic and buries it, the heat stays in the conductor and the insulation on the wire dries and cracks.

That is why so many attics in older neighborhoods pass an eye test and fail a real inspection. The wire looks fine until it is moved.

Finding out what you have

Look in the attic and the basement or crawl space for white ceramic knobs on the joists. Two prong outlets through the house are a strong hint. So is a fuse box, though plenty of homes got a new panel and kept the old branch wiring behind it.

Partial replacement is the case that catches people. A previous owner rewired the kitchen and left the bedrooms, so an inspection turns up live knob and tube in a house that was sold as updated.

Questions people ask

Is knob and tube illegal

No. Existing wiring is allowed to stay. It cannot be extended, and most cities require it to go when walls open up.

Will my insurance company drop me

Some will not write a new policy on it at all. Others ask for an electrician letter. It is worth asking before you buy a home with it.

Can I just add grounds to it

No. There is no ground conductor to connect. A grounded outlet on knob and tube is a lie told to a tester.

Electricians who list knob and tube work

Google tells us very little about most businesses, so no listing names this work directly. Almost every electrician in the state does it. Start with the highest rated ones.