Unexpected Reading Between Earth And Neutral

[apprentice87]

Was just about to say that this bit; "Testing voltage at the main switch at the CCU: With the main switch on I recorded 245v across L and N supply and <25V across E and N and E and L" surely cannot be correct. If you have less than 25V between line and earth, then you have no earth..

john...

 

[ProDave]

A bit of dead R1+ R2 and Rn + R2 testing would sort this mystery out.

 

[apprentice87]

Definitely.....

john...

The only voltage readings i take any notice of are 230v, 400, [give or take a bit] and 0v. Anything in between and you have a fault that you should have found by dead testing!!

john..

 

[kerching]

http://isswww.co.uk/fluke-t150

http://isswww.co.uk/fluke-t51000-electrical-tester

Yep...I can vouch for both of those, i have one of each

Also have a dilog one...not impressed with it compared with the Flukes

Just saying

 

[not_shocked_yet]

Thanks John and everyone (including Paul, Lol),

Extensive testing to come, I'll report back next week.

 

[New Venture!]

OSG, check everything. Are there any more houses nearby? What is the earthing arrangement? Where? Connection?

Personally I carry a Fluke digital multimeter and an old analogue Avo for voltage checks. I don't rely on my Fluke MFT.

 

[apprentice87]

I got a Megger one.. Like it lots, voltage, resistance, lights up in the dark, torch on the front, and best of all, does not trip rcd's unless you ask it to, by pressing a button!! Oh, and phase rotation too!!

john...

 

[SPECIAL LOCATION]

If a voltage tester cannot show below 25v then how would you manage testing on any 12v downlights?

:shakehead

As has been said...

treat is as a new install go back and re test everything as per Chapter 10 of OSG (page 89 of the green one onward)

I got a Megger one.. Like it lots, voltage, resistance, lights up in the dark, torch on the front, and best of all, does not trip rcd's unless you ask it to, by pressing a button!! Oh, and phase rotation too!!

john...

Can it check the output of your welder too?????

:innocent

 

[apprentice87]

Happily not!!!! Thank god that was not the one i used on the welder!! My poor multimeter......

Was testing the windings of an ignition transformer for continuity today with my Megger 1730.. Bad plan.. I was holding the wires on the test probes with my fingers, when i removed the probes, the back emf from the thing was not nice!!!!! Hope that meter is ok.....

john....

 

[not_shocked_yet]

The reason the Kewtech 64DL shows a reading <25V is because 50 or less is not harmful to humans and less that 25 is not harmful to animals. If you need a specific voltage reading below 25 volts (which we don't need for domestic inspection and testing) then you just need a small household type multimeter. There you go Andy.

If a voltage tester cannot show below 25v then how would you manage testing on any 12v downlights?

:shakehead

As has been said...

treat is as a new install go back and re test everything as per Chapter 10 of OSG (page 89 of the green one onward)

 Why would I be testing the voltage across a 12 v light? I might want to check continuity of course. If there was something wrong with the transformer I would know as the light wouldn't work, I suppose I could double check the transformer voltage with a small multi meter to be sure before throwing it away.

Can it check the output of your welder too?????

:innocent

 

[Blue Duck]

How would you check if a bell transformer or intercom transformer was working? they could be outputting 3v or 24v?

as for transient voltages or cumulative earth leakage how are you going to measure for those?

All I am saying is that In your current situation is that you have <25v not exactly much to go on!

 

[kerching]

New Venture yes correct. I forgot to say that the reading was doc volts, I know that sounds absurd.Do voltsDc volts

Explain please

Just medicated

 

[steptoe]

Have you got reverse polarity?

I like to keep things simple to start with. 

 

[not_shocked_yet]

Kerching,

With the supply at the converted stable block still wired to the mcb at the house CCU (but with the supply to the CCU isolated) I read the following volts at the DB in the stable block:

L - N <25V  which I would expect

E - L  65V

E - N 65V

With the supply to the DB at the stable block disconnected from the MCB at the main house CCU (i.e. the L, N and E removed from the mcb and the board) there was no reading across L, N and E as one would expect.  This in my mind means that the 65V reading was not caused by voltage remaining in the cable between the house and the stable (which is about 250-300 feet away and appears to be 6mm Twin and Earth cable).

I repeated the test above at the main switch on the supply side at the CCU in the house and read the following results with the supply energised:

L - N    245V  which I would expect

E - L   <25V   which I would expect

E - N   <25V   which I would expect

However with the supply at the CCU isolated (the main RCD is between the meter and the CCU and this was tripped) the results were as follows:

L - N    <25V  which I would expect

E - L   165V   

E - N   165V   

It is entirely possible (though unlikely) that I made an error measuring the correct terminals and I will be re-checking on Monday morning - unfortunately it was getting late at this stage and the client needed me to leave.  I am confident that the readings at the stable were the correct terminals and I repeated the test several times as well as I was performing safe isolation.

The difference in the reading of 165V and 65V could well be due to voltage drop over the quite considerable distance.

I welcome your thoughts.

steptoe,

I wouldnt think so as the L and N proved correct, as did the L adn E and N and E when the system was energised, it seems to show faulty readings when the system is isolated from the main supply.  Also, the house underwent an inspection for insurance purposes 6 months ago.

Kerching,

I meant to say that the reading for the 65V and 165V showed up on my Kewtech 64DL multitester as dcv.  I contacted Kewtech (who are brilliant by the way) and their tech team told me that the 64DL couldnt read dcv.  They put me in touch with the man who wrote the manual and he concurred.  However a request for further information has been sent to Japan and I hope to hear more on this readout of dcv on Monday.

 

[not_shocked_yet]

Blue Duck,

Agree with you absolutely and I would use my small multitester to measure those voltages.  But the Kewtech 64DL obviously isn't designed to measure those levels.  Why not?  Ask Kewtech.  They sell quite a lot of them in a competitive market so they must have their reasons.

 

[Blue Duck]

It is a voltage indication device not really geared up for fault finding. great if your proving dead not so good for finding faults for that you need an MFT and a good understanding of testing.

not_shocked_yet

not_been_in_it_long_enough

 

[SPECIAL LOCATION]

Incorrect tool for the job...

ie.. using an MFT as a voltage indication..

The KT64 is does NOT list voltage identification as part of its spec..

http://www.kewtechcorp.com/sites/default/files/pdf/Datasheets/KT64DL_Data%20form.pdf

it is for Continuity, Ins Res, Loop Imp, PSC/PFC & RCD..

Hence NO AC/DC selection or voltage ranges on the switches.

For checking voltages you need a voltage detector such as:-

http://www.kewtechcorp.com/sites/default/files/pdf/Datasheets/KT1790%20Data%20form_rev1_0.pdf

(or one of many other makes)

Specification list includes Voltage detection & ranges!

Select the correct tool for the job ...

Know how to use interpret the test equipment correctly ...

Do the correct tests ...

and I think you will find the mystery is solved.

p.s.

I wouldn't rely too much on a basic multimeter either..

you have far greater change of reading phantom induced voltages with on of them!

 

[kerching]

^^^^^^^^^^

What he said

In my opinion....

Correct testing with correct equipment in a strutured and methodical manner, coupled with recording interpretation and understanding of the results

I would like to add that I would NOT

Quote. "Anyway, whilst performing safe isolation in the stable (with a Kewtech KT64DL". Use a KT64DL for safe isolation

Just saying

 

[kerching]

Best practice guide pg 13

Caution notices

In all instances where there is any risk that the supply could be reinstated, an appropriate warning/caution notice should be placed at the point of isolation. For distribution boards with ‘multiple isolations', a single suitably worded notice on each distribution board, such as the example shown below, would suffice:

Proving dead isolated equipment or circuits

It is important to ensure that the correct point of isolation is identified before proving dead.

Where possible and safe to do so, this may include testing with the isolating device first in the ON position and then in the OFF position to establish that the equipment or circuit is under the control of that device.

Following isolation of equipment or circuits and before starting work it should be proved that the parts to be worked on, and those nearby, are dead.

It should never be assumed that equipment is dead because a particular isolation device has been placed in the OFF position.

The procedure for proving dead should be by use of a proprietary test lamp or two-pole voltage detector as recommended in HSE Guidance Note GS38, Electrical test equipment for use by electricians.

The use of multimeters, makeshift devices and non-contact voltage indicators (voltage sticks) is not advised for voltage detection as such use has caused accidents.

page 13 ©The Electrical Safety Council

Example of a warning notice

CAUTION THIS DISTRIBUTION BOARD HAS A NUMBER OF CIRCUITS THAT ARE SEPARATEL Y ISOLATED. PRIOR TO REINSTATING THE SUPPL Y TO AN INDIVIDUAL CIRCUIT, CARE SHOULD BE TAKEN TO ENSURE THAT IT IS SAFE TO DO SO.

Typical devices for proving dead

Examples are given of suitable devices for safe isolation BUT the images will,not copy here

 

[apprentice87]

You can wonder and surmise all you like. The only way you will EVER sort this is by doing ALL the tests that you would for initial verification.....

Just ask you a few things...

How would you check for correct polarity on the incoming supply, and what is the simplest and BEST tool for doing this [steptoe's favorite tool i think!!!....]

Lets say there was a house next door and you suspected that they had a fault, or their supply had a fault, and that that their fault current was coming up your TT rod, how would you test for this...

john...