ECN Forum Forums General Topics of the Trade General Discussion Area knob and tube wiring

John,

I have seen them and Guys I know used them. Does that me old too!

I have tried a non-contact voltage tester... they often light for the neutral and maybe a sneeze...I don't like them.

They light when you rub one on your shirt.

evad73:

Keep in mind that there can be return current flowing in the neutral!

PAteen:
Static electricity??

What about static on the line? Wouldn't that set it off?

PAteen:
One of our deep theory members can get into 'static' issues, perhaps Greg or Scott.

Important for all to keep in mind that these devices are indicators of possible live conductors, and NOT a true tester that anyone should 100% 'trust'. Remember Trumpy's cardinal rule....verify, test, verify!

I doubt you can get static electricity in a conductor. What you see there using a high impedance meter is the antenna effect. I doubt that will be enough to light a neon but it may trick a solid state ticker.

For your amusement:

High impedance meters/ digital auto-ranging meters us solid state chips to dope out the values.

In particular they us RC circuits: Resistance + Capacitance. The resistance is considered the known as is the capacitance. An extremely high frequency switching circuit clocks/times the circuit.

Upon test lead contact, current fills up an entire array of femto-capacitors. Then using the wizardry of digital logic resistance or voltage is back calculated in the blink of an eye.

Because the chip's capacitors are s-o-o-o tiny even the tiniest amount of current can fill them up. This is where false positives come from -- especially from either static electricity or by induction or capacitive effects.

In comparison, a Simpson analog meter is driven by a sequence of entirely separate 'ranged' circuits selected by dialing a stepping switch/knob. Thus it can't be 'autoranging.'

However, in an analog meter the current or voltage is shunted through resistors, coils and whatnot so as to provide a nearly linear response to the current or voltage which can then be read out on a swinging beam across a field of values. Such 'analog circuits' can't be faked out because they are driven by the laws of electricity -- directly. ( No brain assumptions )

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It is highly desirable to have both types + an influence / non-contact tester if you want to make rapid steady progress at all times.

For super speed, the voltage-tick/ non-contact tester can work wonders, especially on circuits you, yourself installed.

When facing the unknown -- face it -- you just can't trust anything. This is especially true with Churches and any 'owner-installed' projects. With them wire color means nothing. Black could be on any phase and at any voltage and even be neutral or ground. As time goes by you'll be astounded as to how crazy some buildings are wired. That's why:

Always start with voltage-tick,

Then DDM, with auto ranging,

If you're suspicious of false positives fall back to an analog meter.

Analog meters out of China go for a whopping $13 at Harbor Freight. That makes them cheaper than a voltage tick! ( And just about the same weight.)

For DMM I prefer Fluke or Greenlee. If they ever go dead check both batteries AND fuses -- inside.

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Slightly off topic: DeWalt battery chargers have a hard-wired fuse in them. The VAST bulk of dead chargers have simply blown this fuse! Open yours up, you can't miss it. It's easy to test for 'open.'

Whatch out for 3ways with those non contact testers as well. They light up like there is power on everything sometimes. lol

Ob

PS
I have most of the above mentioned technics. Mostly the Noncontact thing in my ideal tester/wiggy.

I suppose it should be mentioned that K&T has attracted the wrath of big insurance in recent times

at least here in K&T central, New England

I've been lucky to gain a lotta biz from it all, yet i do get asked the Q "Why is it so bad"? from a few sorts keen to what they feel is Big Insurance simply on another one of their infamous jihads


To be truthful, and only due to K&T being original, no other wiring method has lastest 80-90 years.

If (and it's a slim if) it's left alone, unaltered, in a consistent enviroment, consideration to it's legality (sans life saftey issues) by right of grandfathering every other method's install could be granted

One such situation arose for me in town, an entire 2nd floor of a local inn , all K&T, had been handed a cancelation by their insurance co.

I argued that, if they had no $$$ to insulate, they certainly had no $$$ to buy an electrician, so if all the life safety issues (smokes, gfi's) had been met, what was the problem?

I ended up asking them to ask their insurance co about installing an afci on the circuit in question, they were turned down by the original co, but the next one bit

So i simply replaced the type S fuse with an afci in a two ciruit can. The state inspector went along with it all too, although he (and truthfully i as well) considered it buying time, the burden of the devices efficacy being thrown in the lap of big insurance (as it should be)


and so the old new england electrical ambiance was maintained for posterity , the turnkey switching, the single bulb pendants, for tourism's sake via the mighty afci, faster than a speeding arc, more pwerful than a local ahj, able to leap tall shorts in a single click

~S~


~S~