Knob And Tube House Wiring
| Field | Construction, Electronics |
| Went Obsolete | 1950s to 1960s |
| Made Obsolete By | Romex-brand nonmetallic sheathed wire |
| Knowledge Assumed | Electrical Training |
| When useful | Not used |
House wiring used to be done with single-strand wires strung through the house with ceramic insulators (Knobs and tubes). They went obsolete when modern multi-strand wiring (Romex-brand) was invented.
While knob and tube often used wires that were of a heavier gauge than modern multi-strand house wiring, its use was forbidden by many building and electrical code for a number of reasons:
- Many houses wired with knob & tube had one single circuit that wound its way through the house. If the fuse blew for that circuit, every light in the house went out
- Knob and tube wiring provided no separate path to earth/ground, which posed a significant shock hazard, especially in areas where an outlet could be near water, such as in a kitchen or bathroom.
- As the number of electrical appliances in a house grew, and the amount of current those appliances drew from the house wiring increased, the wiring would heat up. In extreme cases, it could start an electrical fire. Part of this stemmed from the common practice of replacing screw-in fuses with units rated for a higher current (thereby defeating the safety provided by the fuse), regardless of what current the house wiring was rated to handle, if it was rated at all.
- Circuits were sometimes spliced together inside of walls, rather than using sub-panels or junction boxes.
The safety and reliability of modern house wiring has been greatly improved, both by the use of better materials (multi-strand wiring, resettable circuit breakers instead of screw-in fuses, mandatory grounding, resettable GFCI outlets for use near sources of moisture), and better installation practices (isolating high-draw appliances on their own circuits, partitioning a house into several smaller circuits, requiring electrical contractors to be trained and licensed, etc) enforced by more comprehensive electrical codes. Note that the National Electrical Code still recognizes knob and tube wiring in current residential use, but it is not used in new installation or remodeling. It can only be used to repair or extend an existing knob and tube installation.
