Posting a message to the forum will remove the above advertisement
  1. angel While you're here, would you mind checking out our Electrician's Insurance section to see if we could save you a few quid? - Specifically our Van Insurance Deals and Public Liability Insurance Deals. Thanks for supporting the forum! angel

Discuss Unexpected voltages? in the Electrical Forum area at ElectrciansForums.co.uk.

Tags:
Please make sure you checkout our forum sponsors, many do discounts for members and, they keep the forum free to use.
  1. DaveL
    Offline

    DaveL EF Member

    Location:
    Monforte de lemos
    Hello from Spain!

    I am after some help and advice.

    Whilst checking my supply ( which is TT and the whole installation is protected by a 30ma RCD) I have found the following

    With the earth connected to the rod
    L to N 240v
    L to E 345v
    N to E 148v

    If I disconnect the earth rod, at the consumer unit I get

    L to N 235
    L to E 214v
    N to E 7v

    I rigged up a testing bulb and the voltage is real and not a phantom from my meter. The bulb lights up. Brighter on the higher volts. If I try this after the RCD it trips ( phew! ) which I'm guessing means the system is normally balanced.

    When I checked at the incoming supply point, with my Consumer unit isolated, I earthed to the metal leg that holds my supply box I get the same voltages of 345v and 148v.

    We live in a very remote rural location.

    Is it possible to have both the N and L energised?

    Thank you

    Dave
     
  2. marconi
    Offline

    marconi Regular EF Member

    • Like Like x 1
  3. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    Wonder what the OP is using to get the voltage readings ....?
     
  4. telectrix
    Offline

    telectrix Scouser and Proud of It Trusted Advisor

    Top Poster Of Month

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    slightly off topic, but i had an unusual voltage found yesterday. as part of a few other jobs, one was to replace a broken lamp holder on a pendant. ceramic rose, 60 years of paint crud over it, twisted cotton covered flex to holder. first quick check was with voltstick to see if it was switched on or not. either position of switch lit up the stick. so... carefully removing the terminal cover from the lamp holder, approved voltage tester (fluke) reads 230V with switch on. 24V with switch off. suspecting it's just a phantom, but wonder why the stick lit. i know you can't trust them, but it's strange.
     
  5. KEV 1 N
    Offline

    KEV 1 N Regular EF Member

    Location:
    Durham
    I’ve had that happen with volt sticks, I think they sense voltage as little 10v, as once mine was lighting up at a light switch yet there was no mains to it, only a signal cable from the LCM unit
     
  6. DaveL
    Offline

    DaveL EF Member

    Location:
    Monforte de lemos
    Guys, voltage is taken using a digital volt meter. I know these can give false readings hence wiring up an incandescent bulb to check that it is real. It is...

    The RCD trips when testing from the protected side but illuminates The bulb from the unprotected side.
     
  7. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    Before you start damaging all your electrical appliances I think you need a local spark to confirm the supplier voltages .......................

    Are you single phase or multi phase?
     
    • Like Like x 1
  8. DaveL
    Offline

    DaveL EF Member

    Location:
    Monforte de lemos
    In theory single phase.

    The voltage between L and N has always fluctuated. Any where from 230v to 245v. I've never checked the voltage to Earth before until a couple of days ago when I had an unexpected RCD trip. The weather has changed from dry and warm to wet and cold which I know can cause some issue with TT system. I've just checked the L to N voltages again with my back up inverter. It matches the same reading as my digital Meter. And is sitting at 238v. I've had no issue with the RCD since resetting other tripping it with the tester bulb when going from N or L to E.

    I'll get a local guy in to check the supply, but just want to know if there is a system where both L and N are energised to give a stable voltage between the 2?

    The infrastructure here is donkeys years old, wondering if this is a result of an upgrade from the old 120v system?
     
  9. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    If you have a fluctuating incoming voltage, this can trip your RCD
     
  10. static zap
    Offline

    static zap Regular EF Member

    Location:
    west midlands
    Does sound a bit 3 phase . (Local transformer- issue -lost earth )
    But a local spark will know whats normal for your DNO equivalent !
     
    • Like Like x 1
  11. dmxtothemax
    Offline

    dmxtothemax Regular EF Member

    Location:
    Australia
    Business Name:
    David Haddock Electronic Repairs
    Clearly your earth line is NOT at earth potential !
    You have currents in your earth lines,
    Someone somewhere has a bad/poor neutral,
    And your earth line is providing a partial return path for them.
    it doesn't always have to be you,
    sometimes it can be your neighbour.
    Try isolating circuits and see if that voltage on the earth
    goes down or away.
     
    • Like Like x 1
  12. Wilko
    Offline

    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    Hi - if I've understood correctly, it sounds like on the supply side their N is not connected to the General Mass of the Earth. If so, its likely a fault and needs looking at.
    IMG_0934.GIF IMG_0935.GIF
     
    • Like Like x 1
    • Agree Agree x 1
    Last edited: Dec 6, 2017
  13. Sparkingmad
    Offline

    Sparkingmad Regular EF Member

    Location:
    Dorset
    I would agree it needs checking ASAP. I don’t know what the energy supplier network is like in Spain but if you were to contact them first and give them the readings you have they should come out and test it at your property first then at various points back to their transformer. If the fault is on their side and not on yours which it definitely sounds is the case there shouldn’t be a charge to you. Also ask them what the fault was and get them to write down the Ze next to your meter. I have seen it too many times where they come out and you never know if they have
    A) found anything
    B) rectified it
    So when you phone up they can never answer you. This is especially useful when you carry out an EICR and find Ze reading is borderline or over and you have a circuit where the Zs is too close to maximum value allowed under working conditions. So you have to go back out to recheck for yourself. Customers usually don’t like this as they get charged again for it.
     
    • Like Like x 1
  14. marconi
    Offline

    marconi Regular EF Member

    My interpretation of the readings:

    With the earth connected to the rod
    L to N 240v
    L to E 345v
    N to E 148v

    and some on-line research which says TT is generally used in rural Spain, and areas which were once 3 phase 120V have been upgraded to 3 wire 220/240V distribution system

    is that your property has a 220/240 supply derived from a connection across 2 phases. Neither supply phase is earthed. Whether the secondary of the distribution transformer is star or delta I do not know but I would assume star so that the star point can be earthed. (There are ways of providing a star point for a delta winding using an earthing transformer see: Grounding transformer - Wikipedia - https://en.wikipedia.org/wiki/Grounding_transformer).

    The local potential of the earth rod with respect to the transformer ground/earth depends on all the earth leakage currents from each phase. See Millman's theorem: http://www.tandfonline.com/doi/pdf/10.1080/20464177.2003.11020168

    If all these leakage currents were absolutely equal then there would be no potential difference between local and transformer earths - which is impossible. If there is more leakage current from one phase than the others the local earth potential will be closer to that phase's potential.

    The readings to me indicate to me:

    1. the supply voltage is 240V.
    2. neither phase is earthed.
    3. the local star point is closer to the 'N' live conductor than the 'L' live conductor.
    4. the installation does not have a Neutral conductor it has two line conductors. Thus the use of N is wrong.
    5. If I am correct all switching will/must be double pole.

    This is my interpretation only - you need a Spanish sparks to check your installation is correct and that there are no external faults in the distribution circuit to your home.



     
    • Like Like x 1
  15. DaveL
    Offline

    DaveL EF Member

    Location:
    Monforte de lemos
    Thank you for your responses. I've had a chat with one of my neighbours, sometime in the past everything in the area was 3 phase and has been converted to 1. The actual date wandered around a bit as we discussed the issue so not too sure how reliable the info is. I've found a friendly electrician who when I explained the issue nodded sagely and will be coming out to have a look at the weekend.

    The network here in Galicia is good in the towns but patchy in the sticks where we are. Our little hub is right on the end of the line and there are abandoned and collapsed barns and houses around. It was common practice here to splice into the mains and give yourself electricity in the barns and sometimes the houses for free. Where these have fallen into ruin and there is no record of an installation I guess it is very possible that the problem could stem from there.

    I'm surprised that nothing was picked up when they installed the new smart later but then again I suppose the problem could have manifested after the install.

    Anyway, I'll have a clearer understanding after the weekend. Thank you for you replies.
     
    • Like Like x 1
Loading...
Similar Threads - Unexpected voltages Forum Date
Sensitivity to high voltages Electrical Forum Nov 21, 2017

Share This Page

Electricians Directory Post a Domestic Job Post a Commercial Job