Troubleshooting Ghost Voltages in Kitchen Lights

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Discussion Overview

The discussion revolves around troubleshooting ghost voltages encountered while rewiring kitchen lights, specifically focusing on the challenges of measuring these voltages with different types of multimeters. Participants explore the concept of low impedance (LoZ) measurement techniques and share various suggestions for alternatives to expensive equipment.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes experiencing ghost voltage while rewiring kitchen lights and questions how to create a LoZ feature without purchasing new equipment.
  • Another suggests using a small light bulb in parallel as a potential solution, but notes practical difficulties in handling multiple components simultaneously.
  • A participant recommends using a low-cost analog meter for household work, emphasizing its practicality over more expensive digital meters.
  • Discussion includes the input impedance of various meters, with one participant explaining how the impedance relates to the voltage scale selected on an analog meter.
  • Participants share preferences for different types of test equipment, with some expressing nostalgia for older analog devices and their reliability in certain measurements.
  • There is a mention of the usefulness of test lights in automotive work, particularly in avoiding confusion caused by ghost voltages.
  • Several participants express interest in slide rules, with discussions about their historical use and availability of simulations online.

Areas of Agreement / Disagreement

Participants express a range of opinions on the best tools for measuring voltages and the effectiveness of different methods. There is no clear consensus on the best approach to creating a LoZ feature or the superiority of specific types of meters.

Contextual Notes

Participants discuss limitations related to the functionality of their equipment, including the lack of LoZ features in certain multimeters and the implications of input impedance on measurements. The conversation reflects a variety of personal experiences and preferences without resolving the technical challenges presented.

Who May Find This Useful

Individuals interested in electrical troubleshooting, particularly in home or automotive contexts, as well as those curious about measurement techniques and historical tools like slide rules.

Guineafowl
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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?
 
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Guineafowl said:
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

upload_2017-9-24_20-48-53.png


Save the Fluke for when you need precision is my advice.
 
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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?
 
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
 
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Guineafowl said:
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
 
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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!
 
Guineafowl said:
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
 
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jim hardy said:
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.
 
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Guineafowl said:
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.
 
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  • #11
jim hardy said:
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.
 
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