Connect with us

Reading 5V on a neutral wire? Hot wire going to ceiling fixture first.

Discussion in 'General Electronics Discussion' started by Mana Batalia, May 8, 2018.

Scroll to continue with content
  1. Mana Batalia

    Mana Batalia

    2
    0
    May 8, 2018
    Hi all! Thanks in advance for your feedback, really appreciate it! :)

    I'm a girl and studied Arts, so I don't know that much about circuits yet but learning online, bought a bunch of testers etc... I moved into an old studio in San Francisco that doesn't even have a circuit box in it :/ Checking wiring I found a lot of errors and could fix it, but one issue I really can't figure out:

    The light bulbs in the main ceiling fixture were always burning out in less than 2 weeks, so I removed the fixture to check things. There is only one switch that turns it on/off and it seems like an independent circuit because it's not connected to anything else in my place (but maybe neutral is being shared with other apartmentss on the floor?). There was only one wire in the ceiling connected to the fixture (no ground) and it's a hot one! So power is going straight to the fixture first, instead of going to the switch. I know that's wrong to start with, and wanted to fix it. Measuring the neutral on the ceiling (the one that becomes hot when the fixture is in place) relative to ground (a ground I'm sure is good) I get a reading of 5V. Measuring the same disconnected wire inside the switch box I also get 5V. Where is this coming from?! Is it a shared neutral with another circuit? Moreover, the metal box on the ceiling also shows 5V, that means power is touching it, when it shouldn't, right? Is that something to worry about? Is it ok to have power on the metal box and 5V on a neutral? Everything else looks good.


    The building electrician is an as***** and denies all errors, so I'm finding someone else to work with me soon, but was curious about this.

    Thanks so much you guys/ladies! :)
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    12,508
    3,000
    Nov 17, 2011
    5 V AC or DC? I guess AC. That shouldn't worry you. It is easily coupled from other wires nearby into your (probably sensitive) measuring instrument.

    As a word of caution: this may make you liable for any subsequent damages whether directly or indirectly caused by your manipulations. Even if the damage is completely unrelated to your manipulations. The NEC (national electric code) of the United States of America is not exactly my territory, but from what I hear about jurisdiction in the USA you wouldn't want toe be made responsible for an electric fault caused by inexpert tampering.
    When your building elctrician is the ****** you think, get another expert to fix the issues. Any subsequent fault is the his liability, not yours.
     
  3. Mana Batalia

    Mana Batalia

    2
    0
    May 8, 2018
    Thank you for your word of caution, Harald. I'm very aware of it. I just fixed some reversed neutral-hot outlets, a couple of disconnected grounds – nothing crazy. Definitely having an expert come in this week, but I needed to know what to tell him to check and fix. All my respect for experts.

    And yes, it's an AC circuit. I get 5.7 volts on a Fluke multimeter (just on this neutral and metal box). I read on another forum that more than 5V on a neutral might mean neutral overload, that's why I'm reaching out.

    Thanks so much! <3
     
  4. Minder

    Minder

    3,231
    701
    Apr 24, 2015
    There should be no conductor connected to the metal box except the Earth GND.
    If the neutral is being switched instead of the live conductor this smacks of a possible mis-wiring or original amateur type installation.
    If you are getting a reading from earth to neutral, I would see if it supports any current, IOW a load such as a test lamp placed between earth and N and see if the 5v between the two remains steady.
    M.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,505
    2,853
    Jan 21, 2010
    Voltage on the neutral conductor with respect to earth is typically caused by neutral currents through a non-zero resistance neutral wire. It is perfectly normal.

    If it is due to this, then you can often draw significant current (depending on the actual load current causing the voltage differential) but you can also cause the earth leakage breaker to immediately operate.

    If I had discovered reversed live and neutral, or disconnected earth connections, I would have had them fixed by a sparkie. That way you get documentation that they were incorrectly wired.
     
  6. GeekGuy

    GeekGuy

    25
    2
    Apr 7, 2016
    I'm not sure of the age of your building but in modern homes the neutral and ground are the same.

    The only circuits that would share a neutral are 3-phase circuits as far as I know, and I doubt you have 3-phase power.
     
  7. Minder

    Minder

    3,231
    701
    Apr 24, 2015
    Also N.A. centre tapped single phase 120-240v supply.;)
    M.
     
  8. GeekGuy

    GeekGuy

    25
    2
    Apr 7, 2016
    Lol, ok you got me ;-) What do you mean by N.A. though?
     
  9. Tha fios agaibh

    Tha fios agaibh

    2,239
    749
    Aug 11, 2014
    He is the expert. He doesn't need you to tell him what to check or fix.

    You likely have a slight voltage imbalance on your system which is generally not a problem. Nevertheless, not a bad idea to have it looked at.
     
  10. Minder

    Minder

    3,231
    701
    Apr 24, 2015
    N.A. = North America!
    M.
     
  11. Tha fios agaibh

    Tha fios agaibh

    2,239
    749
    Aug 11, 2014
    Actually, both of the statements are wrong.
    Neutral and Ground are often bonded together at the source, but they are Not the same. A neutral carries unbalanced current while a (equipment) ground only carries current when there is a fault.

    And as Minder mentioned, a Neutral can also be used for single phase circuits. Particularly multi-wire circuits that have two "hot" conductors.
    However, a two wire circuit (120v) doesn't use a Neutral. It uses a "grounded" conductor. The term Neutral is often misused. A Neutral is only a Neutral when it carries the unbalanced current of two ungrounded (hot) conductors.
     
    JWHassler and Bluejets like this.
  12. GeekGuy

    GeekGuy

    25
    2
    Apr 7, 2016
    I'm no master electrician, but I did spend a few years in the trade after high school in the late 90's and early 2000's (so it's been a while).

    Technically, you're right -- the neutral is the return while the equipment ground is there to shunt fault current to ground to save your life. However, I'm pretty certain that if I went and pulled the cover off my panel (house built in 1999) I'd see that the neutral and ground do tie together, either in the panel or at the ground rod outside.
     
  13. Minder

    Minder

    3,231
    701
    Apr 24, 2015
    Rather than ' .Shared neutral' I should have said directly referenced to each other.;)
    In N.A. it is done in the panel as well as the source.
    In other places, UK etc, N and Earth are only referenced at the source.
    M.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-