ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Top Posters(30 Days)
twh 10
Admin 4
Recent Posts
Any UL 508 experts out there?
by sparkyinak. 05/21/17 08:57 PM
Heat pump conundrum
by sparkyinak. 05/21/17 08:49 PM
Interesting week
by HotLine1. 05/20/17 11:57 AM
Electrical Pricing Guide
by ElectricianBud. 05/18/17 12:17 PM
New in the Gallery:
SE cable question
Popular Topics(Views)
236,240 Are you busy
171,180 Re: Forum
164,256 Need opinion
Who's Online Now
0 registered members (), 74 guests, and 14 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate This Thread
#30652 - 10/24/03 12:53 PM Stray voltages  
aldav53  Offline
Member
Joined: Aug 2001
Posts: 545
Chandler, AZ USA
In testing some switches in a home I was found a bad 4 way switch. But was picking up some weird voltages from the 3-ways feeding the 4-way, about 50 volts, but not enough current to light anything, just my little neon tester and Fluke meter. Don't know where this was coming from, maybe the wires were coiled up between the runs causing a coil-like (inductance effect) inducing some voltages. Any ideas?


The Golden Rule - "The man with the gold makes the rule"

Work Gear for Electricians and the Trades

#30653 - 10/24/03 02:09 PM Re: Stray voltages  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
It's most likely due to capacitive coupling.

When the light is switched on, one of the travelers is effectively disconnected by the 3-way switches at each end. Its proximity to the other conductors results in a small amount of capacitance.

Because a digital meter has a very high input impedance (typically 10 megohms), it takes only a small amount of capacitance to produce a substantial reading.

If you shunted the meter with some load, or used a conventional analog meter with a lower input imedance, then you would see a zero or much lower reading.


#30654 - 10/24/03 02:54 PM Re: Stray voltages  
:andy:  Offline
Member
Joined: Oct 2003
Posts: 289
Germany
once at work i hat opened the breaker of a receptacle line for servicing. with the small neon screwdriver tester, i could see no difference between breaker on and breaker off. measuring with a tester with coil to montior the voltage then showed me the line was off.

Background: The cable was running in a troughing with several others. as both ends of the phase conductor were unconnected, the wire collected the field fromt he others...


#30655 - 10/24/03 03:20 PM Re: Stray voltages  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
As Paul has said, you are seeing the results of Capacitive Coupling (or some type of Reactive Coupling).

The Voltage reading on the DVM is from its high input Z (Impedance).
The Neon Lamp of the tester (probably a Proxy, non-contact type tester) is also seeing same thing.

Try reading with a Wiggy. The problem will go away.

p.s. With the Wiggy connected to the same circuit, try testing with the DVM; should have a very much lower Voltage reading now!

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#30656 - 10/24/03 04:31 PM Re: Stray voltages  
aldav53  Offline
Member
Joined: Aug 2001
Posts: 545
Chandler, AZ USA
That makes sense, thanks..


The Golden Rule - "The man with the gold makes the rule"


Member Spotlight
Scott35
Scott35
Anaheim, CA. USA
Posts: 2,707
Joined: October 2000
Show All Member Profiles 
Featured:

2017 NEC and Related
2017 NEC
Now Available!

Shout Box
Powered by UBB.threads™ PHP Forum Software 7.6.0
Page Time: 0.013s Queries: 14 (0.003s) Memory: 0.7682 MB (Peak: 0.9099 MB) Zlib enabled. Server Time: 2017-05-23 14:52:18 UTC