Magic cable ?

[barneybodge]

Hi all,

If I told you I had an unconnected, undamaged 1.5 cable showing a weak current would you believe me ?

Well I have one that magically shows a small current when another cable next to it becomes live, I have just removed the 'non connected' cable and the insulation is not damaged at all, is it possible for current to leak from one undamaged cable to another ?

Cheers

 

[andy]

there is no such thing as magic

 

[barneybodge]

I was being sarcastic,

Is this a common experience, I have never noticed it before ?

 

[breezer]

its not leaking, its called induction, its how transformers work.

very basicaly, electricity generates a magnetic field (moving if its A.C.) put another "dead" cable next to a live cable and the magnetic field from the live cable will produce a magnetic field in the 2nd (dead) cable . now the exact opposite happens because there is now a magnetic field present (from live cabe) the electrons start to move and produce electricity

the amount produced in the dead cable depends on how much in the first , how close the cables are to each other, and in the case of a transformer how many coils and what is cable size

 

[shaggy]

Which can be detected by a neon screwdriver breezer?

 

[barneybodge]

Thank you for such an informative reply

Makes perfect sense to me, just hadn't noticed it before. Considering im not a pro 'sparky' you can imagine that I was pulling my hair out and questioning my own sanity :

"it cant be live, its dead"
"its dead, it cannot be live"
"my god, ive lost the plot" etc etc

The live cable is carrying power to 4 6 foot fluorescent bulbs and just that amount of current is lighting up another cable, no other circuits are live yet.

 

[barneybodge]

Which can be detected by a neon screwdriver breezer?

Thats what got me shaggy, I understand the magnetic induction bit but didnt think it would be enough to light the test screwdriver.

 

[breezer]

thats another reason i do not like those screwdrivers , they lie

 

[ban-all-sheds]

Hi all,

If I told you I had an unconnected, undamaged 1.5 cable showing a weak current would you believe me ?

No.

I'd believe an induced voltage, but I'd love to see you measure current flowing in an unconnected cable.

 

[securespark]

thats another reason i do not like those screwdrivers , they lie

That's why you should buy the new Acme Pinnochineodriver which has a patented handy built-in wooden nose that instantly alerts you to a false reading by growing substantially in length. Refills available for $4 each.

 

[pipme]

thats another reason i do not like those screwdrivers , they lie

Isn't it more akin to a warning triangle at the roadside ? Ignore it at your peril .. a nudge to be wary .. a warning of voltage present, not intended as a measuring device.

P

 

[Stoday]

I'd believe an induced voltage, but I'd love to see you measure current flowing in an unconnected cable.

How would you know there's an induced voltage? Got an electrostatic voltmeter?

 

[ban-all-sheds]

How would you know there's an induced voltage? Got an electrostatic voltmeter?

No. Why?

 

[barneybodge]

Hi,

Out of curiosity and wanting to learn more I have tried in vain to find more info on this type of induction, but came up with this :

http://www.iee.org/Forums/messageview.cfm?catid=205&threadid=4012

Im wondering what you guys think is an acceptable amount of induction and how much is too much ?

Also, im still confused as to how the 'cheap non pro test screwdriver that tells lies' managed to light up from induction created by an adjacent circuit supplying just 160 watts of lighting. And why have I not experienced this in the past with an exactly the same scenario ?

Cheers

 

[Stoday]

No. Why?

Your voltmeter draws current.