strange one

[revjames]

Guy at work (a fitter) told us his lights were going dim at home and TVs dropping out etc. We lent him a MFT and told him to plug it in and observe the voltage. He took photos of the display, which at one point was indicating 135v! 

Heres the strange thing. When the voltage is low, if he switches a kettle or cooker on, the voltage instantly goes up to 245v. He even videoed the display and you could see the voltage going up when he put the kettle on. The only thing I could think of was some kind of voltage regulator on the DNO side which ups the voltage when a load is detected. But really, 135v?

 

[poni]

no neutral? 

 

[Sharpend]

I'm with Poni here this is symbolic of a poor neutral connnection. 

 

[revjames]

really? can you explain how that would make the voltage go back up when a heavy load is applied?

 

[Sharpend]

Without giving too much thought V=IR ? Resistance will be near constant however Amps increase therefore V must increase? 

 

[binky]

loose connection, under heavier loads it will arc across  - that's my theory anyway 

 

[SPECIAL LOCATION]

I am thinking if you imagine a circuit.......

Suppliers Live to one side of an open circuit load [call this "A"].

Other side of open circuit load to one side of a high resistance neutral joint [call it "B"]

Other side of a high resistance joint direct back to suppliers neutral [Call this "C"]

When reading the low voltage between A & B you have a high resistance back to the Neutral via B & C.....

If you read A to C you would have full voltage.

With no load connected, If you read between B and C you would have negligible voltage as the load is open circuit.

But if we stick a low resistance (high power) load across A & B,... 

the potential between B & C will rise because the load is now a low resistance bring B nearer to the suppliers live potential..

As the potential rises it will eventually breach the high resistance gap and break down the poor N connection.....

While the resistance between B & C is lowered the voltage at A & B will increase back to the suppliers potential.

Or at least that's what my Friday night head tells me.....  Guinness Guinness Guinness Guinness Guinness

 

[poni]

what he says

 

[revjames]

errr thanks for the concise reply. My friday night/saturday morning head is now hurting. My advice to him was to contact DNO in any case so hopefully they will sort it. 

 

[roys]

Might not be DNO fault, could be slack in consumer unit.

 

[ProDave]

I would want to see that volt meter on the input terminals of the CU before making any diagnosis.

It clearly needs fixing, so he needs an electrician.

 

[Sharpend]

He hasn't had a new meter fitted recently? 

 

[Andy™]

what are you trying to say? the ex office worker who's had 1 day basic trainign in electrics might not have tightened the screw properly or wired it wrong?

 

[Sharpend]

Oh please Andy, do you really believe the myth of meter monkeys!! 

They're real people :C  

 

[Tony S]

On a there phase area supply with a failed neutral somewhere near the transformer weird things happen to the Ph → N voltage but totally opposite to what’s happening here. Testing Ph → E and N → E voltage would help as it will point to which side of the supply is acting strangely.

Are his neighbours having problems?

Whatever it is the DNO will have to be involved.

 

[apprentice87]

What voltage is he measuring?? Phase/neutral or phase/earth??

Earthing type???

john..

 

[revjames]

havent visited the property as he lives in the sticks but am assured all connections are tight

What voltage is he measuring?? Phase/neutral or phase/earth??

Earthing type???

john..

not sure of earthing type but its an overhead supply so could be TNCS he is measuring voltage by plugging MFT into a nearby socket

 

[apprentice87]

havent visited the property as he lives in the sticks but am assured all connections are tight

not sure of earthing type but its an overhead supply so could be TNCS he is measuring voltage by plugging MFT into a nearby socket

If it is overhead, then it would be TT surely??

john..

 

[Andy™]

If it is overhead, then it would be TT surely??

john..

some are TNCS

 

[apprentice87]

Thanks Andy!! You live and learn!! Well, at least i try to!!

john..