Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: 80v between earths

  1. #1
    Bronze Member ACEsterhuizen's Avatar
    Join Date
    Mar 2012
    Location
    South Africa
    Posts
    146
    Thanks
    103
    Thanked 18 Times in 14 Posts

    80v between earths

    I am stumped, +-8m piece of 2+E surfix, in trunking (or out, it does not make a difference), to extend a plug 8m on. The surfix meggers clean between all 3 cores. Both ends all three cores (L,N+E)of the loose new surfix are separated. No nicks where I stripped isolation.

    The existing plug tests clean. Live to N 230v, N to E 0v and Live to Earth 230v. Earth leakage trip normal with ramp tester.

    When I connect the Live (red) of the surfix to the Live wire of the plug, (with plug socket removed)and measure between the earth wire of the piece of isolated surfix and the earth wire of the existing plug I get 80v. Between L of the new Surfix and Earth of the existing plug 230v, N from new surfix to Earth at plug 0v.

    I don't get it. I don't even have a closed circuit for the fluke to register any measurement. There is no closed circuit in the 2+E surfix to draw a current and induce a voltage in that earth wire. Its open at both ends.

    It should be, if I am correct, insulation breakdown between L and E of the new surfx, but why does it measure clean with 2 different meggers?

    Moisture in surfix? High Impedance instruments? Induction? EMF? Incoming earth deterioration? Did i open up a wormhole in space?

    If I don't get my head around this I am giving back my trade test papers and my wiremans license.


    Click image for larger version. 

Name:	80V.jpg 
Views:	219 
Size:	24.0 KB 
ID:	6818

  2. #2
    Diamond Member Justloadit's Avatar
    Join Date
    Nov 2010
    Location
    Johannesburg
    Posts
    2,935
    Thanks
    108
    Thanked 595 Times in 505 Posts
    Blog Entries
    1
    The loose surfix acts as an antennae, and absorbs the voltage induced in the air by the cable connected to mains. Your instrument has a high impedance, so it does not load the cable, and hence registers a reading. If you grab the one lead of your multimeter probe, and place the other probe on the live of the plug, it will register a reading. This is the principle used in touch dimmers. Your body absorbs the residual energy in the air. Another example, when you are connecting the input or microphone to an amplifier, when you touch the loose end going to the amplifier, you hear the 50Hz hum in the loudspeaker.

    If you place a globe at the end of the surfix, and perform the same measurement, you will notice a difference in your readings, this is due to the lower impedance of the globe loading the line.

    Effectively, any material between two conductors, creates a dielectric path for voltage to flow, it is the basic principle for a capacitor, the difference here is the PVC of the wire is the dielectric between the live and the neutral, and the air around you is the dielectric between the live and you to earth. These are very high impedance paths, and hence the readings on the multimeter. Once you load the respective loose ends, then the dielectric value is so small that there is no longer a path for it to operate.

    If you use the old analogue instrument, it will show different results, simple because the internal impedance of the analogue instruments is far lower than the digital instruments.

    Check Dielectric for more detailed info on this.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar pumping, Solar Geyser & Solar Security lighting solutions - www.microsolve.co.za

  3. Thanks given for this post:

    ACEsterhuizen (25-Jul-17)

  4. #3
    Bronze Member ACEsterhuizen's Avatar
    Join Date
    Mar 2012
    Location
    South Africa
    Posts
    146
    Thanks
    103
    Thanked 18 Times in 14 Posts
    Ok then I have learned again today. Thank you very much.

    Is that why there is 0v reading between N and E because of the insulation on both conductors (increased impedance) which is obviously higher than the L and E impedance since the E is bare (no insulation)? Or should I be getting a reading on N to E as well because of the dielectrics? Pse note there is a ZERO reading, not 0. 0001 or something, but zero.

    ps. I am reverting back to analogue meters.

    Click image for larger version. 

Name:	80V.jpg 
Views:	92 
Size:	27.5 KB 
ID:	6820

  5. #4
    Diamond Member Justloadit's Avatar
    Join Date
    Nov 2010
    Location
    Johannesburg
    Posts
    2,935
    Thanks
    108
    Thanked 595 Times in 505 Posts
    Blog Entries
    1
    Effectively Neutral is connected to earth via a low value resistor at the supply transformer, so effectively earth and neutral are very close electrically and hence no residual voltage between neutral and any other floating conductor.

    Think of dielectric as a very high value resistor, and then it starts to make sense. A digital instrument has an impedance between 1 Mega ohm and 10 Mega ohm. So if we place a 1 mega ohm resistor resistor to Live and finish the circuit to earth with our multimeter, and lets say it is 1 Mega ohm, then effectively the point which the multimeter is measuring is half way of the measured voltage. So if you have 220V AC, then the meter will show 110V AC. You say that you measured 80V, so the dielectric impedance could be somewhere around 1.5 Mega ohm under the specific conditions of your measurement.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar pumping, Solar Geyser & Solar Security lighting solutions - www.microsolve.co.za

  6. Thanks given for this post:

    ACEsterhuizen (26-Jul-17)

  7. #5
    Diamond Member Justloadit's Avatar
    Join Date
    Nov 2010
    Location
    Johannesburg
    Posts
    2,935
    Thanks
    108
    Thanked 595 Times in 505 Posts
    Blog Entries
    1
    Digital multimeter have effectively been designed for electronic circuits which have low power requirements, and therefor the impedance's in these circuits are very high, so one does not want to influence the measured voltage with you instrument, and this is the reason that the digital multimeters have high input impedances, as we do not want the measuring device to affect the value that we are measuring. Using the previous example of the 1 Mega ohm resistor. Lets say that we have an ADC (Analogue digital convertor) which is measuring a voltage of some source, which has an internal impedance of 1 Mega ohm, but has a series resistor of 10 Mega ohm, it simply means that the ADC is now measuring one tenth of the voltage applied to the 10 Mega ohm input. Lets say it is measuring 500 milli Volts and the input of the ADC, now you want to check if this is actually 500 milli volts with your digital instrument, but when you measure it shows 250milli Volts, what the heck? Well the multimeter has influenced the reading. If the multimeter has an impedance of 1 Mega ohm, it will be like placing 2 resistors of 1 mega ohm in parallel, reducing the value of the measured point down to 500 Kilo ohm. This has now changed the value of the potential divider and hence the incorrect reading. Using ohms law you can prove this mathematically. Check out Voltage Divider for more explanation.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar pumping, Solar Geyser & Solar Security lighting solutions - www.microsolve.co.za

  8. #6
    Diamond Member AndyD's Avatar
    Join Date
    Jan 2010
    Location
    Cape Town
    Posts
    4,797
    Thanks
    559
    Thanked 910 Times in 735 Posts
    ^^ As justloadit says.

    They're generally referred to as 'ghost' or 'phantom' or 'stray' voltages in the electrical industry. Biggest problem is whenever you encounter a ghost voltage reading it's time consuming because you've got to prove it's not a back-fed voltage which is dangerous and can kill whereas a ghost voltage is safe because it doesn't have any short circuit fault current.

    You won't have the problem if like me you're old fashioned, set in your ways and you still use an analogue tester or even if your newfandangled, cloud enabled, facebook integrated digital tester has a 'Low-Z' range. Some testers you can buy an optional low impedance add-on kit. Here's some reading material;

    http://www.fluke.com/fluke/uses/comu.../dualimpedance
    http://www.testequipmentdepot.com/ap...rements_an.pdf
    http://www.ee.co.za/article/conciliu...ogies-039.html
    http://support.fluke.com/find-sales/...105317_A_w.pdf
    _______________________________________________

    _______________________________________________

  9. Thanks given for this post:

    ACEsterhuizen (26-Jul-17)

  10. #7
    Bronze Member ACEsterhuizen's Avatar
    Join Date
    Mar 2012
    Location
    South Africa
    Posts
    146
    Thanks
    103
    Thanked 18 Times in 14 Posts
    Thanks everyone, never to old to learn something new, or at my age to be reminded what i did on Monday, or did i pee or not, did i do that invoice? or did i...the list is long..i think.

    The (isolated) N showing @ 0v to E still haunts me. It is, after all, exactly the same as the E conductor, both disconnected, but NO "stray" V on it.

    Anyway would this be the ideal investment? anyone has something better or more value for money in mind?

    Thank for your input.
    Last edited by ACEsterhuizen; 26-Jul-17 at 04:23 PM. Reason: more and more INFO pse

  11. #8
    Diamond Member AndyD's Avatar
    Join Date
    Jan 2010
    Location
    Cape Town
    Posts
    4,797
    Thanks
    559
    Thanked 910 Times in 735 Posts
    I haven't had time to investigate how the VCHEK function works but it looks good at a glance.
    _______________________________________________

    _______________________________________________

  12. Thanks given for this post:

    ACEsterhuizen (26-Jul-17)

  13. #9
    Gold Member Sparks's Avatar
    Join Date
    Dec 2009
    Location
    Port Elizabeth
    Posts
    872
    Thanks
    18
    Thanked 123 Times in 94 Posts
    Can someone explain to me why a person would want to take a measurement as queried?
    If I want to measure voltage on a live cable and connect only the live with the second probe not connected to anything I get about 80V reading.

  14. #10
    Bronze Member ACEsterhuizen's Avatar
    Join Date
    Mar 2012
    Location
    South Africa
    Posts
    146
    Thanks
    103
    Thanked 18 Times in 14 Posts
    Sparks wrote: "Can someone explain to me why a person would want to take a measurement as queried?"

    (One of the several clues was when I noticed "sparking" between earths, and the little "bite" i got when touching the earth, hence my testing.)

    New edition 2017 Sans Regs: Test no. 10 on Additional Certificate: (Hazardous Areas)

    INSPECTION AND TEST REPORT FOR ELECTRICAL INSTALLATIONS IN HAZARDOUS LOCATIONS IN
    ACCORDANCE WITH SANS 10142-1, SANS 10108 AND SANS 60079 SERIES, SANS 10086-1

    SECTION 4 (continued) – INSPECTION FOR ELECTRICAL INSTALLATIONS IN HAZARDOUS LOCATIONS (Additional certificate)

    4.1 Classification of hazardous location(s)
    humidity, corrosion) which could adversely affect the explosion protection)


    10. Have sufficient earthing and bonding been done to all explosion-protected equipment, exposed and
    extraneous metal parts and structures in the hazardous area to prevent intensive sparking caused by
    static electricity, stray currents and lightning (See SANS 60079-14)


    11 Have all earth connections been secured against self-loosening and steps been taken to minimise the
    risk of corrosion which may reduce the effectiveness of connection in accordance with SANS 60079-14?
    12 Are all openings in walls for cables and conduits between different hazardous areas and between
    hazardous and non-hazardous areas adequately sealed in accordance with SANS 60079-14?
    13 Have all cable systems and accessories been so installed, as far as is practicable, in positions that will
    prevent them being exposed to mechanical damage, to corrosion or chemical influences (for example
    solvents), to the effects of heat and to the effects of UV radiation?


    Just to recap, there was also a major issue (after the fact) with the main earth going back to the supplier. Earth pens installed. Although my job was to only extend a plug, I have found a major earthing and bonding issues, which was rectified according to Test No. 10. "Have sufficient earthing and bonding been done"......to PREVENT sparking caused by "stray currents" etc."

    tO ANSWER your question: I just HAD to verify (by Testing) where this voltage comes from. And why. The spark it created would have been DISASTROUS in an area where they use Butane, Methane, Ethylene and a LOT of pure Oxygen.

    Just imagine in the distant (or near) future someone (anyone) must replace that plug socket, he decides to do it live because nobody wants to shut down the plant and its computers, and he did not do a flammable gas explosion hazard course, he removes the E first, and it "sparks". BOOM. Lives Lost. Because I did not do the tests to satisfy myself where, why and how. For every (in)action there is a reaction, causality, cause and effect.

    The Electrical Installation Regulations states: "....after having "satisfied" himself or herself by means of inspection and testing......

    And NO, not that "satisfying himself".
    Last edited by ACEsterhuizen; 28-Jul-17 at 08:37 PM. Reason: More Info

Page 1 of 2 12 LastLast

Did you like this article? Share it with your favourite social network.

Did you like this article? Share it with your favourite social network.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •