In Western Massachusetts Knob and Tube wiring was a standard
system of open electrical conductors supported on ceramic knobs. It also used ceramic knobs where wires cross each other or pass through framing. This type of wiring was in common use from the 1880′s to 1930′s, in North America.
In Western Mass during this era when knob and tube was in common use, a typical home would have 30 or 60 amp electrical service, sufficient for general lighting and maybe a radio. In those days people were still using “iceboxes”, wood or gas stoves, coal heat, and no air conditioning. Professional wiring by electricians in homes was a new trade and there were very few rules.
American Electricians Handbook was the first home wiring guide to electrical rules which appeared around the turn of the century, when Terrell Croft wrote the Crofts books defining early wiring practices. One of Croft’s rules was that knob and tube wiring should always be run through, never over the house framing. The problem with running wiring over framing is that it can get bumped, snagged, and damaged.
The advantage of knob and tube wiring is that it dissipates heat into free air, and therefore has a higher ampacity than cable systems with equivalent wire size. When originally installed in the 1900′s knob and tube wiring was less expensive than other wiring methods. Due to the installation cost, owners and electricians would opt for knob and tube versus conduit wiring and metal junction boxes. The conduit methods were known to be of better quality, but their cost was significantly higher than knob and tube wiring.
Modern wiring methods assume two or more load carrying conductors will lie against each other, for instance the standard non-metallic – 2 cable. Since the load carrying wires are in close proximity, when they heat up, the heating is shared across the wires, limiting the overall current load they can support. Since the load carrying wires in knob and tube wiring are widely spaced, the wires are capable of carrying higher loads without risk of fire.
Knob and tube wiring was usually insulated with cotton cloth and soft rubberand porcelain insulators. Although the actual wire covering may have degraded over the decades, the porcelain insulators have a very long lifespan and will keep any bare wires safely insulated. These same porcelain insulators were used with bare wire electric fencing for livestock. These insulators can carry very high voltage surges without the risk of shorting to ground. Many electricians understand that by running the hot and neutral conductors farther apart from each other than today’s electrical cabling does make shorts between those conductors less likely, at the same time realizing there is not a grounding conductor.
Knob and tube is insufficient for current usage patterns. Contemporary households use a wide range and intensity of electrical equipment that was unforeseen at the time of knob and tube inception. Household power use increased following World War II, first generation wiring systems became susceptible to abuse by homeowners, who would avoid repeated blown fuses by over fusing the circuits, thus subjecting the wiring to heat damage due to higher levels of current.
In many instances deterioration and abuse have rendered the wiring unsafe. During building renovations and remodeling wiring can become damaged. The rubber insulation will become dried out, brittle when handled, damage by rodent, or simple carelessness…
If you live in Western Massachusetts and you’re concerned about the Knob and Tube wiring in your home, give us a call for an in home inspection and estimate.
Ron Desellier Electric (413) 478-6192
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