Weird Earth Fault

[ThrownRazor25]

dunno what to do with this one.

 

[static zap]

... Strange thing is though i can touch the earth connection with the probes of my meeger and you can see and hear the zap,

If you can get 6mm of spark , that's aprox 10kV of static .

(was it pretty toasty there ? (mid winter also works when ground frozen))
Moving around -from shoes , sliding over a carpet / getting up from seating - will also re-charge you.
(If they are having computer problems - Ionisers /van der graaf !)

 

[Deleted account]

Sounds like it’s a build up of charge in the person rather than the switch screws.

When coming into contact with the well grounded/ earthed screws the charge is released.

 

[DPG]

Just to confirm, do you mean 10 Ohm live to earth, or 10MOhm when you test IR?

 

[ThrownRazor25]

10 ohm live to earth. Been reading a lot about loss of neutral on a tncs system. Could this be the cause?

 

[westward10]

Have you done a line to neutral loop test with the earthing conductor disconnected. Can you not see the effect of a 10 ohm resistance between line and earth.

 

[ThrownRazor25]

It is def 10 ohm between live and earth but then it disappears. Same as the zap once it zaps it disappears i can touch the backbox for as long as i want but walk away come back zap

 

[James]

Might seem daft, but if you get a zap then stand still for 5 min, do you get zapped again when re connected with it?

 

[ThrownRazor25]

Really dont know what to do with it. With main switch off, there is no continuity value just a constamt clicking on tester saying im getting continuity then not then getting then not etc
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Going back on thursday as homeowner is away till wednesday night. She says it has been like that since she moved in 6 years ago. I never tried that james.

 

[westward10]

Because with the main switch off you are isolating the neutral from the external neutral earth connection.

 

[ThrownRazor25]

Why is it clicking on off on off on off?
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I understamd what you mean about the 10 ohms between live and earth but thats what im getting and there is def not 20A therei can touch the casing.

 

[Midwest]

With main switch off, the 8-10 ohm disappears but the tester just clicks on off on off on off for continuity

Which 'meeger' are you using? When you say on off etc, are you measuring 10ohms then >999ohms, then back to 10ohms etc?

 

[marconi]

Before you next visit, buy yourself one of these voltage testers:

B&Q Pen-type Voltage tester | DIY at B&Q - https://www.diy.com/departments/b-q-pen-type-voltage-tester/177924_BQ.prd?ds_rl=1272379&gclid=CjwKCAjw_uDsBRAMEiwAaFiHa9ZxwsRXbRxw2NxxTNm5nvcGXgOFmmLoteDnUAVaLyMfwdiwjUu4JRoCGBMQAvD_BwE&gclsrc=aw.ds

Check it works first by touching something definitely connected to terra firma eg: a metal post in the ground. Then test it touching something electrically earthed eg: your home MET. Then test it on the Line side of a switch and then on the switched Line in the on and off position. Also touch the securing screw and neutral. Now you have a feel for the sort of voltage readings you will see. You use the 'direct contact' metal pad to put your finger on.

At the client's home with all turned on except for the light switches, walk up to a switch. Put your finger on the direct contact pad and then touch the securing screw with the tip of the voltage tester. What voltage reading do you observe? If it is a steady voltage then it is a potential due to leakage current flow or typical combined NE to local terra firma potential difference. If there is a brief rise in voltage and then fall to zero the likely cause is you being discharged to the screw; if this is what you see happen remove the tip for the screw, count to ten and then retouch the screw - what do you observe? I would expect you to see a steady 0V or very low voltage which indicates no potential difference between you and the screw.

Now, walk away from the switch and around the room/home for a minute and return to the switch. Touch the screw to discharge yourself. Then use the voltage tester and observe the reading. I would expect it to steady 0V or very low.

Now repeat all the above with the light switch on.

Hope this helps. Let us know what you find please.

 

[Midwest]

The Megger 1700 series does have a touch voltage contact. Thats why I asked which Megger it was. Just waiting for a Mod to approve my posts. In the meantime;

Checking touch voltage | Megger

Touch voltage is tested to ensure that people cannot get an electric shock from simply touching a metallic surface or two metallic surfaces simultaneously.

uk.megger.com

 

[ThrownRazor25]

It is an mft1721

 

[Midwest]

It is an mft1721

Try what Marconi suggested, using the touch contact on your 1721.
Any reply re my post 32, second question?

 

[ThrownRazor25]

No with the main switch off there is no ohms reading just the little symbol at the top of the screen clicks on then off on off on off

 

[Lucien Nunes]

99.99% this is indeed just static.

A shock caused by an electrical fault will be continuous - all the time you remain in contact and every time you touch the 'live' point, you will receive the shock. Static requires you to charge up your stray capacitance (to earth) by friction or some other means, during which the charging current is too small to notice although the ultimate voltage can be very high. Then, when you touch something earthed (or conductive and large in size which has a large stray capacitance to earth itself) your own stray capacitance discharges suddenly with a current that is large enough to feel. Then you feel nothing until you have charged yourself up again.

A good demonstration would be to get into a position where you would receive a shock from the switch but stand on an insulator such as a piece of dry wood or plastic before doing so. Your resistance to earth will then be guaranteed to be much too high to allow enough current to flow from a 230V electrical fault to be felt as a sudden shock. If you get the shock, then nothing, you have proven it was caused by your stray capacitance discharging.*

Your Zdb reading is good enough that there is no reason to suspect a disconnected CNE upstream, and there are none of the usual symptoms of the lights flickering and blowing and going very dim when anything else is turned on. It would not however manifest as a voltage between N & E within the system as they would still be connected together at the service terminals; rather between earth as defined by the equipotential zone in the house, and true earth outside. Your Zs at the switch also looks normal and indicative of a good enough earth that if there is a serious leakage or intermittent short from line, the OCPD will trip.

*Note incidentally that the stray capacitance of the body is high enough that you can sometimes detect a steady, faint tingle / buzz corresponding to a fraction of a milliamp of AC leakage if you brush lightly against a truly live metal surface, but that is not the effect described here.