I was making a shake this morning and I had my new extech NCV tester laying on counter. When I got my hand close to it, it lit up. I started experimenting with it a bit. It kept lighting up but wouldn't light up on my santronics or other one. I'm guessing it's extra sensitive but am I putting off EMF's or something ? Anyone else notice this before? I made a video but having problems uploading now.
Hand triggers NCV Tester
- Thread starter Cletis
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K8MHZ
Senior Member
- Occupation
- Electrician
When it comes to NCV testers, get either a Greenlee or a Fluke. All the rest, and I have owned and worked with plenty, are problematic and not trustworthy.
I guess I would have to say the same about any kind of test equipment. The 'Harbor Freight' brands are OK for a home owner not working on live circuits. But for a trades person, quality test equipment is a must.
I guess I would have to say the same about any kind of test equipment. The 'Harbor Freight' brands are OK for a home owner not working on live circuits. But for a trades person, quality test equipment is a must.
- Location
- Massachusetts
You must have gotten the Extech BSD-X1 instead of the voltage tester.
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Curious nerd
Member
- Location
- Washington State, USA
You're a capacitor
You're a capacitor
More capacitive current can flow when you're touching the tester. If it's just barely out of range of something it should detect, then what you're reporting makes sense. I've been able to make a tester stop beeping by taking my hand off it.
You're a capacitor
More capacitive current can flow when you're touching the tester. If it's just barely out of range of something it should detect, then what you're reporting makes sense. I've been able to make a tester stop beeping by taking my hand off it.
I always thought "humans" were NOT a capacitor ? I thought that when we get close to the NCV tester that we are just increasing the capacitance of the plates in the NCV tester ? I've heard it only takes a few picofarads to set the tester off. Just curious really how it's working in a physics E&M sort of way.
kwired
Electron manager
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- NE Nebraska
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- EC
What is a capacitor? Two conductors separated by insulating material. The human body can be more conductive then some objects and less conductive then others so we can easily be either component of a capacitor - just depends on what your surroundings are. Many of these NCV testers require you to be touching a small metal part of the tester - this where you become connected to the circuitry of that tester and in effect your body is a probe component of the tester.
K8MHZ
Senior Member
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- Electrician
Not the Greenlee GT-11. I don't even have to be touching mine. Very useful for locating the breaker you need to turn off.
kwired
Electron manager
- Location
- NE Nebraska
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- EC
The solution to your problem here is figuring out what you are "capacitvely coupled" to and/or what is the tester coupled to that is operating the indicator on the tester.
By not touching the tester you kind of become the object being tested rather then being coupled to the tester. You do not need to be direct connected to a "power supply" you just need to exhibit characteristics the device is looking for.
NVC testers work great for detecting open/missing equipment grounding conductors. They light up or beep when in proximity to ungrounded objects as those objects are isolated from ground yet have capacitively coupled voltage on them that these sensors will detect.
Hold the leads of a digital meter (not a low impedance meter though) with one probe in your hand and just walk around with it comparing voltage readings with the other probe in just free air as well as touching other objects - both conductive and non conductive, you will see the meter reading change as the capacitively coupled voltage changes. Come close to electrical equipment and you may notice readings that are higher - though still low enough that there is no concern for your safety. You may even place the one lead directly on the insulated portion of an ungrounded conductor and get a fairly high reading compared to other objects tested so far. And of course if you directly touch the conductor how high the reading will go will depend on just how insulated you are from other conductors of the system - including the grounded conductor. Standing barefoot on concrete would yield a pretty high reading, standing in clean dry non conductive shoes will yield a low reading but higher then all the readings in those other mentioned tests, and on 120 volt circuit can get you a 5 or 10 volt reading where many other tests are probably only in millivolt ranges.
Curious nerd
Member
- Location
- Washington State, USA
Pet a cat and then touch a doorknob on a dry day. You can hold a charge. So can the doorknob. The physics of it, should be easy to find in a textbook, is that even a single conductive sphere in empty space has capacitance. That may not be relevant since it may be your connection to earth ground that matters. I've seen one person claim his NCVT doesn't work when he's on a ladder or on a high deck. I couldn't get that to happen in my own experiments but no reason to doubt the guy. Look at it another way. You're a conductor (bag of salt water) with insulation (skin and air) around you. Put you near a sort-of-conductive planet (which is connected to the AC circuit you're testing, hopefully) and you're one plate of a (very low capacity) capacitor. Alternating current can flow through you in trace amounts. Here's yet another way to look at it. You know how capacitive leakage is a design issue to take into account on distribution lines. 120 or 480 is a much lower voltage, but you're also much closer to it. You're absolutely right about picofarads. The current flow is very low because your impedance is so high. It's nonzero because your impedance is not infinite. Now, so I don't come off as a know-it-all, I'll ask an ignorant question. Does a lineman working up next to a 500KV line have a safety issue with capacitive current flowing through him? Are those conductive PPE suits worn to short out that field, or to provide a bypass for corona?
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rt66electric
Senior Member
- Location
- Oklahoma
Are you standing on a extension cord??
Are you standing on a extension cord??
I have had to explain to several electricians and homeowners, That if you are standing on a extension cord (and isolated, not touching anything grounded) and use a tic-tester, is will show a false positive on any grounded wire.
It also depends on the type of shoes a person is wearing.
Try the experiment again with bare-feet on tile , then wear new tennis shoes.
Are you standing on a extension cord??
I have had to explain to several electricians and homeowners, That if you are standing on a extension cord (and isolated, not touching anything grounded) and use a tic-tester, is will show a false positive on any grounded wire.
It also depends on the type of shoes a person is wearing.
Try the experiment again with bare-feet on tile , then wear new tennis shoes.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The isolated human body will exhibit measurable and calculable capacitance to any nearby conductor as well as to "ground" even when you are multiple feet away from any actual ground plane.
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