My friends tell me I know just enough about electricity to be dangerous, but one thing I do know is that grounding is an essential element in electrical wiring. And that seems to be more than the very first electrical contractors knew.
Without getting too deep into the technicalities, a typical modern electrical cable contains three strands of wire – hot (or live), neutral, and ground. And for the purpose of this story all you need to know is that the hot and neutral wires aren’t ever supposed to touch each other – and I repeat, EVER!
But if they do, then that dangerous electrical current escapes safely through the ground wire without causing any harm.
Knob and Tube Wiring: What You Need To Know
In the early years of residential electrical wiring, the significance of the ground wire was either unknown or underestimated. Don’t let the hot wire EVER touch the neutral wire, was the mantra, and so the first electrical installations featured two-strand wiring, with the strands so heavily insulated from each other that in some ways it was safer than the modern three-strand system. If the two wires don’t EVER touch each other, after all, then the ground wire is redundant.
If you’ve ever had to deal with this early form of wiring, you’ll remember that its insulated sheathing is so thick and dense that it quickly dulls the sharpest utility knife blade, making the hacksaw the cutting instrument of choice.
As they pass through or along your houses’ joists and beams, these heavy duty cables are anchored by porcelain fittings known as knobs and tubes. The tubes are porcelain pipes that give the wiring an insulated passage through pre-drilled holes in joists and studs. And the knobs are porcelain clamps that insulate the wires whilst anchoring them to the sides of beams and joists.
Know and Tube Wiring Can Be Dangerous
Known as “knob and tube”, this early type of wiring is widely considered to be extremely dangerous these days. It often comes up as a required fix in the terms of homeowners’ insurance policies, and it should certainly be flagged by your building inspector, and it may even be cited as a reason to deny your mortgage application.
Although the original design had a lot of positive safety features, the problem today is that the materials themselves are no longer sound. The heavy sheathing is reaching the end of its shelf life, especially where it’s been stripped back in the vicinity of knobs and tubes and junction boxes. And it may have been exposed over the years to various conditions that could have caused it to corrode or rot or otherwise weaken. A damp basement, a squirrel in your attic, a mis-placed drywall screw. Any of these could compromise the sheathing, leaving bare wires inside your floors or walls, with no provision for grounding.
If you know more than I do about electricity, you might want to tackle the re-wiring yourself. It’s slow, tedious work, but at least modern wiring is color coded, so you can tell which wire is which.
And after you’ve torn out all the knob and tube, don’t just throw it out with the trash. The copper wiring has some scrap value, so call your local scrapyards and find out how much they’re paying.
Guest article was provided by Mitch Ribak a Melbourne real estate specialist servicing home buyers looking to buy Bay FL real estate and Port St. John real estate in South FL.