77VAC between Hot and Ground in my house!?

Discussion in 'General Electronics Chat' started by McPit, Jul 27, 2015.

  1. McPit

    Thread Starter New Member

    Aug 17, 2014
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    Hi there!

    I'm reading everywhere that wall plugs have a Neutral, Hot and Ground terminals, and that Hot is the one actually providing the alternating power.

    1) To me that would mean that one *cannot* get shocked by touching the neutral terminal? Yet I don't think that's what I experienced in the past...

    2) I've connected my voltmeter to a power plug in my house (Australia) and read:
    • 240VAC between Neutral and Hot. Ok.
    • 88VAC between Neutral and Ground :confused:!?
    • 77VAC between Hot and Ground :confused:!?
    To me this would rather tend to show that BOTH neutral and hot are involved in providing the alternating tension, which in turn would mean that one CAN get shocked by touching EITHER of neutral or hot..(!?)

    Can someone please confirm/explain this to me?

    Thanks a lot!
     
  2. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    Sounds as if you've a floating ground.... 'Tho I'd have expected
    H-G = 152V in said case... Is it really H--N and G or is it a center tapped arrangement H--N--H? if so the observed effects may owe to a 'tug-o-war' between 120V appliances about a faulty neutral feed -- In any event you're are advised to correct the condition STAT!
     
    Last edited: Jul 27, 2015
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  3. DickCappels

    Moderator

    Aug 21, 2008
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    Or perhaps a floating Neutral -put another way, there is a high resistance from Neutral to Earth and there is current going through Neutral to Earth where Neutral originates.

    You can be shocked by Neutral and even killed, though that is not supposed to be the case. Connections can become poor over time, especially when using aluminum wire and copper terminal or the other way around. In some localities, the electricians don't care of pay attention and get Neutral and Line swapped -if it can light a test lamp, it must be ok. I think it not wise to bet one's life that Neutral is what it is supposed to be.
     
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  4. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Read this article

    Can't happen in the USA and Can, because Neutral is jumpered to earth Ground with a short link right in the power distribution panel. Apparently, that is not the case in Australia.
     
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  5. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    ...Or the link connection is compromised or >yikes< absent...:eek:

    Indeed! -- I've seen this wayyy too many times in the form of 'inverse-polarized' outlets:rolleyes:

    Best regards
    HP
     
  6. McPit

    Thread Starter New Member

    Aug 17, 2014
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    Ok thank you all for your answers. Much appreciated.
    Fyi, it seems that neutral is supposed to be earthed too in Australia according to this link: http://www.build.com.au/how-are-electrics-installed
    so I might be having the neutral-earth high resistance effect mentionned by @DickCappels ?
    I'll raise the question to a local electrician next time I see one.
    Thank you all again.
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I think it would be advisable to get it checked ASAP.
    Not only a safety aspect but also electronic equipment can suffer.
    I am not sure if Australia is the same as UK (was) that the service provider does not provide a local earth ground, it is up to the end installation to come up with a suitable means, ELT and Ground rod or suitable metallic water supply.
    I believe you do have the same set up as UK as far as 240v from a 3ph and star point neutral GND Earthed at the transformer.
    I would check it out.
    Max.
     
  8. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
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    For your safety delay is inadvisable! -- You've described a dangerous situation requisite of immediate attention...

    Please take care!
    HP

    Edit: Sorry about the double-post @MaxHeadRoom :oops: --- Seems we're on the same page both literally and metaphorically!:D
     
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  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Not sure what the UK electric utility does these days, but it used to be the case that the mains inlet to a house was an armoured cable, the armour being galvanized steel wires. Neutral is bonded to Earth at the utility sub-station and the house 'Earth' is usually a wire bonded to the armouring. This means that there can be an induced voltage (generally just a few volts) between house Neutral and house 'Earth', due to the length and finite resistance of the armoured cable.
     
  10. MaxHeadRoom

    Expert

    Jul 18, 2013
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    It has been many years since I practiced in the UK electrical field, but I remember that then, unlike N.A. the neutral could not contact the earth ground at the installation and if the service provider used an armoured cable supply which was grounded, it could not be used at all for earth GND conductor.
    Things may have changed since?
    Max.
     
  11. dl324

    Distinguished Member

    Mar 30, 2015
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    You have an unsafe condition. Don't wait; do it now.

    Don't be tempted to ground at the problem site. It may be a code violation in addition to a safety issue. In our area, electrical code requires neutral to be connected to earth ground at the distribution panel, and only in one place.

    I wouldn't rely on water pipes for a good ground connection. Some (all?) building codes allow CPVC and PEX in place of galvanized steel/copper. I have two rods driven about 4 feet into the ground for my earth connection.
     
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  12. McPit

    Thread Starter New Member

    Aug 17, 2014
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    On the immediate intervention:
    I'm the tenant, not the owner, and I already know what the (chinese.. like most houses in sydney..) owners are going to say:
    1) Are you an electrician? No.
    2) Do your tv computers lights microwave etc work normally? I think so.
    Well then just stop fiddling with the wall plugs in my house!
    :cool:

    Also I won't feel too proud if an electrician gets sent over, checks, concludes it's actually normal because of the age or x and y, and charges 1 hour to the owners..

    But yeah I'll mention it to the agency...

    Thanks heaps anyway!
     
  13. dl324

    Distinguished Member

    Mar 30, 2015
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    Do you have a Health Department or Public Health Institute in your area that inspects rental housing for unsafe conditions? They may be able inspect your rental unit.

    I didn't know of their existence until I saw something on a reality TV show...

    Another option is to buy/borrow a tool to check outlets for wiring problems (reversed hot/neutral, missing ground). I have one that cost a few dollars. I used it to check the outlets in my house when I first bought it and found several outlets that were wired incorrectly; previous owners were clueless and hired an incompetent handyman/contractor to do work for them.
     
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  14. alfacliff

    Well-Known Member

    Dec 13, 2013
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    77 volts isnt half of 120 or 220 volts. have you been having a drought there? it could be that the safety ground rod for your house is in very dry soil, high resistance ground.
     
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  15. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    It should be checked. Whether or not it is an immediate fear for life and limb depends on what you are plugging into these outlets.

    How many of your appliances actually have a ground plug? In my home, my TV does not, my laptop computer does not, my toaster does not, my double-insulated drill does not, my vacuum cleaner does not, my cell phone charger does not. My clothes washing machine does, my dishwasher is hard wired and grounded...

    I don't know if you have dishwasher, clothes washing machine, or any other heavy items that do have (should have) grounding.
     
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  16. vk6zgo

    Active Member

    Jul 21, 2012
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    Call an Electrician,as you definitely have something wrong.
    The "Sparkie" will check your Neutral -to- Earth connection,& may be able to fix it then & there.
    This is too perilous a situation to wait around for your Landlord.
    It may cost you money if the Landlord denies responsibility,but a stay in Hospital,or a Funeral will cost a lot more!!
     
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  17. profbuxton

    Member

    Feb 21, 2014
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    I see that the OP is in Oz. Please be aware that you have a serious problem with your earth connection.
    ALL OZ systems run a MEN(multiple earthed neutral) whereby the earth and neutral are solidly connected via a link in the switchboard. This ensures that the neutral is a earth potential and since every household switchboard is so connected ensures that it remains so.
    If your earth connection is "bad" then the neutral will "rise" to some voltage depending on load and earth resistance. Also can be an indication that your neutral has a poor connection to the main. Get it fixed ASAP.
     
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  18. KeepItSimpleStupid

    Well-Known Member

    Mar 4, 2014
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    I've had similar issues in the US when outlet strips were used and I saw about 1/2 the supply voltage between what i thought was ground and hot and neutral.
    BTW, I found the root cause within minutes. One graduate student and a PHD spent all weekend trying to fix the problem.

    Leakage paths in RF filters that were present across some of the devices were symmetric. A ground was "lost" and being fed by this very low current voltage divider. It makes other stuff go poof like computers trying to communicate over ground.

    In friend's house there was something unusual and it was a bad connection in the service drop. "Other" appliances can feed voltages back the "other way"/
     
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