high induced voltage 8

[stevemechanical]

what could cause high induced voltage on a 110v line?

 

[wbd]

How high a voltage are you seeing? Does the line run alongside any high voltage lines? Are there capacitors attached to this line?

 

[stevemechanical]

the high induced voltage is on a 110 volt circuit that
serves elevator controls. Thank you wbd.

 

[Skogsgurra]

I think that the voltage you may be seeing is capacitively coupled from other live conductors nearby.

It usually is something like half or less of the voltage in the close live wires and it goes away completely when you try to load it. If you use a modern DMM, you will read tens of volts. But if you use an old iron core meter, you will probably not read any voltage at all.

Simple test: Connect an incandescent lamp between wire and ground. Then measure. If you still have a voltage, it is NOT "induced" but real. Be careful.

Gunnar Englund

http://www.gke.org

 

[wbd]

"If you use a modern DMM, you will read tens of volts."

That's why I still keep an old Simpson 260 meter around!!

 

[Skogsgurra]

The "simpa"! Still wanting one...

Gunnar Englund

http://www.gke.org

 

[Warpspeed]

If you have ever connected a Dranetz mains disturbance analyzer to your supply, what goes on can be a real revelation.

http://www.used-line.com/c4909676s13-DRANETZ_626.htm

Voltage surges and sags, and voltage spikes to several Kv are not that unusual. Some of these are only in the microsecond range, but they can still be surprisingly frequent.

The nature of the overvoltage can vary quite a lot. Lightning striking transmission lines can be one cause, another can be high induced inductive voltages caused by sudden abrupt current changes in long transmission lines. These can be caused by very high fault currents that quickly clear. A violent event can travel for miles and disturb a wide area.

The entire power grid is a very big place, and there are little, and not so little dramas going on all the time.

 

[waross]

I like the light bulb test skogs. Simple cheap and effective.
Respectfully

 

[itsmoked]

I use the lamp test all the time. You hook up your DMM and stare at the 60V. Then you take your drop light, and stick alligator jumpers on the prongs. Hook one jumper to the object and the other to a known 'good' ground. If the DMM doesn't drop to zero flip the drop light switch. Either the DMM reading will hit zero or the lamp will glow. Lamp glows = bad problem. Lamp doesn't glow and DMM hits zero = grounding/leakage problem. Nothing changes at all and DMM reading doesn't change = lamp blown(last person dropped it while it was on).

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[bigbillnky]

This is the main reason I still keep a wiggy handy, even when everyone says they are outdated and useless compared to modern DMM. Ignorance is bliss, I suppose.

Bigbillnky,C.E.F.....(Chief Electrical Flunky)

 

[drivechanger]

Good discussion....sorry for the delayed post. Amen to the chorus of faithful "hangers-on" to the ancient practice of measuring electrical quantities with a moving coil! As much as I like DMMs, I still prefer a moving-coil meter for checking for potentially-lethal voltage. It is also essential when checking circuits that are switched by solid state devices such as SCR's, triacs, etc. Forward resistance of these devices in the OFF state is enough to cause a high-impedance DMM to read full voltage even though the circuit is in a safe condition.