Weekly Home Information Guide
KNOB and TUBE
Residential wiring up to the mid-1950’s had the use of a two-wire system for electricity known as knob and tube. The copper wires are easily identified as they were sheathed in a rubber compound and then wrapped in a cloth like insulation. These wires were singly strung throughout the home and where they passed through a stud, rafter, joist or sill they were inserted through a tube or anchored around a knob. This helped keep the wires from touching the wood members and each other. They were separated by about 8 to 10 inches. Knobs and tubes were made of hard ceramics. These wires were left exposed to the air in the wall, floor and ceiling cavities to help keep the wires cool. The joining of the wires were soldered and taped over. Most often they were #12 gauge and protected by a 20-amp fuse and may share a grounded neutral.
They did the job that they were intended for many years. Most homes usually had one receptacle (outlet) and one wall switch in most rooms, as there was very little demand for vast amounts of electrical conveniences. Lives were much simpler and the cost of electrical power was out of reach for most homeowners beyond the necessary appliances. There was no grounding wire associated with this system as can be seen by the two slots in the outlets.
The system as installed has proven relatively safe for the service years that it remains intact and unaltered. However the homeowner may have compromised the safety by adding a new switch/ outlet etc. to the bedroom, den, kitchen, living room and/or the attic/basement. Sub-standard connections may have created a dangerous condition. Hidden in the wall, under the floor or up in the attic these circuits remain a potential danger.
Any upgrades that are discovered should have no modern insulation covering it, be properly connected in a junction box, have a 15-amp fuse/breaker and in some cases be ground fault circuit interrupter protected. There are others.
We recommend that a certified residential electrician experienced with knob and tube systems further evaluate the system and do all tasks as they offer quality materials, proper installation requirements and a written guarantee.
Know that, for peace of mind, the care and attention you give your home will serve you well year after year and in comfort.