Troubleshooting Ghost Voltages in Kitchen Lights

[Guineafowl]

I was rewiring some bodged kitchen lights today, which are in two circuits switched by separate switches in the same box. Despite disconnecting the second switch from the power, my voltage stick still registered a beep (even with wires well away from the live ones). I guess this is a ghost voltage as the two switch wires run close together in the wall.

My Fluke 87V is sadly lacking a LoZ feature. I’d rather not buy another meter, or the very expensive Fluke stray voltage eliminator. Is there a handy trick anyone knows for ‘making’ a LoZ feature?

Light bulb in parallel? PTC thermistor? Enormous resistor?

 

[jim hardy]

Is there a handy trick anyone knows for ‘making’ a LoZ feature?

Light bulb in parallel? PTC thermistor? Enormous resistor?

A small 120 volt light bulb would work but you run out of hands to hold things.

I really recommend for most house and car work :
El Cheapo Analog Meter , about ten bucks at Walmart sometimes eight
i solder into it some nice ten or fifteen foot long leads , that makes it way more handy. I can set it on the floor under my stepladder and work in a ceiling fixture without fear of dropping the meter.
And when it gets blown up i haven't wrecked a $200 Fluke.
as you see it's only 2Kohms per volt

Save the Fluke for when you need precision is my advice.

 

[Guineafowl]

I do have one of those somewhere - it has a useful 1.5V and 9V battery test feature, no doubt a kind of LoZ in itself.

The Fluke has an input impedance of, I think, 10 Mohm for voltage measurements. I’m curious about the 2kohm/volt rating - what does it mean and what overall input impedance does it imply?

 

[jim hardy]

Really it means full scale deflection is about half a milliamp.
Multiply volts scale selected by 2K and that's its impedance, nearly all resistive..
On 10 volt scale it's 20Kohms
on 250 volt scale it's 500Kohms
on 500 volt scale it's 1 megohm

 

[jim hardy]

I do have one of those somewhere -

Find it, open it up and solder some good quality test prod wire into each socket, plenty long. I use alligator clips with boots on mine. I can always grab a nail in the alligator clip for a prod.

I'm partial to Meuller 60 clips and 62 insulators, that's their industrial line. Something you use so much is worth the few extra bucks.

http://muellerelectric.com/wp-content/uploads/DS-BU-62-@.pdf
http://muellerelectric.com/wp-content/uploads/DS-BU-60C.pdf

 

[Guineafowl]

Ah, so it’s related to the range switch position.

Odd that I have to dig out my old cheapo meter to step in for the fancy Fluke. The lack of LoZ is very annoying, as it’s useful for this problem as well as discharging capacitors. Also annoying is the default switch to AC current measurement, which causes brief consternation and puzzlement nearly every time I use it.

Thanks Jim!

 

[jim hardy]

Odd that I have to dig out my old cheapo meter to step in for the fancy Fluke.

The simpler is your test equipment the less apt it is to fool you.
The guys in the plant were always amused by my preference for a Simpson 260 and analog 'scope. The plant cartoonist/wag drew them into my caricature.

I brought my 20 inch slide rule to the control room one day when we were doing some high impedance measurements with an electrometer . I got answers quicker than the guys with calculators, to the great amusement of reactor operators. Next day several of the operators, former Navy Nukes, brought in their slide rules and we had a fun nostalgia session.

old jim

 

[Guineafowl]

The simpler is your test equipment the less apt it is to fool you.
The guys in the plant were always amused by my preference for a Simpson 260 and analog 'scope. The plant cartoonist/wag drew them into my caricature.

I brought my 20 inch slide rule to the control room one day when we were doing some high impedance measurements with an electrometer . I got answers quicker than the guys with calculators, to the great amusement of reactor operators. Next day several of the operators, former Navy Nukes, brought in their slide rules and we had a fun nostalgia session.

old jim

When working on automotive electrics, the first thing I grab is the test light. Quick, simple, long reach and isn’t fooled by ‘ghost voltages’ where a corroded connection becomes high resistance. Automatic current limit, and you can’t blow things up by leaving the leads in the ‘amp’ jacks...

I’ve never used a slide rule - I’d love to have a go one day.

 

[jim hardy]

I’ve never used a slide rule - I’d love to have a go one day.

search on virtual slide rule

http://www.antiquark.com/sliderule/sim/n909es/virtual-n909-es.html

 

[Baluncore]

I’ve never used a slide rule - I’d love to have a go one day.

There are several simulations available. Google ' slide rule simulator '
There are small circular and low cost linear slide rules available via eBay.

 

[anorlunda]

The simpler is your test equipment the less apt it is to fool you.

Love it. That's a real gem of wisdom. It is a correlary of the KISS principle.