Shock from switch

wait4me

Peppa Cig wrote: »

..........the switch is next to bed and you can sometimes get a tingle from the bed as well as standing. The tingle is continuous at times. ....

If that wasn't so serious, it would be funny :eek:

2011

Plenty of food for thought.
Time to get an electrician.
This should not be difficult to solve and should not be ignored.

Irish Steve

Bruthal wrote: »

How did you discover this voltage?

When the plastic switch plate was changed to a brass plate, the induced voltage was enough to tickle!

From much painful experience in a couple of places in the UK, my first thought was static, but suitable discharge measures etc didn't solve the issue, so I went looking a bit more closely, and connected a "flying earth" cable to a known good earth that could then be used to check what was happening in the box, and an analog meter was capable of detecting the voltage being generated, as did a more accurate digital meter.

Fortunately, it wasn't enough to be dangerous as such, as there was nothing local to earth to, and it wasn't in a danger area.

At that point, I went looking more closely, and found a plastic juntion box in the roof that had a number of earth wires going in to it, but there was no connector on the wires, they'd been twisted together and then taped, and at some stage, they'd been pulled and one of the earth wires had separated from the rest of the bunch, so it was floating. Onve the wire was reconnected, and an appropriate junction termination made, the problem went away. It was a long 2 way light run, and the earth and live were parallel over about 20 Ft in conduit.

Bruthal

Irish Steve wrote: »

When the plastic switch plate was changed to a brass plate, the induced voltage was enough to tickle!

From much painful experience in a couple of places in the UK, my first thought was static, but suitable discharge measures etc didn't solve the issue, so I went looking a bit more closely, and connected a "flying earth" cable to a known good earth that could then be used to check what was happening in the box, and an analog meter was capable of detecting the voltage being generated, as did a more accurate digital meter.

Fortunately, it wasn't enough to be dangerous as such, as there was nothing local to earth to, and it wasn't in a danger area.

At that point, I went looking more closely, and found a plastic juntion box in the roof that had a number of earth wires going in to it, but there was no connector on the wires, they'd been twisted together and then taped, and at some stage, they'd been pulled and one of the earth wires had separated from the rest of the bunch, so it was floating. Onve the wire was reconnected, and an appropriate junction termination made, the problem went away. It was a long 2 way light run, and the earth and live were parallel over about 20 Ft in conduit.

It would be unlikely to be a danger anyway, from an induced voltage into an open ended earth wire, as the circuit would be high impedance because part of the circuit path is an open circuit. And even if the person were to contact both ends of it, its too short to have enough energy to do any damage.

It is often through capacitance that this voltage appears, such as on 2 way lights where it can be detected at the pendant fitting with bulb removed. There is no load on the strappers, so no induction, but capacitance.

I suspect that lightly touching a metal switch plate in such a scenario as you describe where you do perceive a tingle, that a tighter or heavier contact with it may reduce the sensation. This may happen in the op case also.

When testing a voltage in a high impedance circuit, the analogue meter may give a lower reading than the digital, because the analogue ones are much lower impedance meters. In series with the high impedance part of the circuit, they see less voltage than the digital one.

Both are correct for the circuit conditions they present though.

Cerco

Bruthal wrote: »

It would be unlikely to be a danger anyway, from an induced voltage into an open ended earth wire, as the circuit would be high impedance because part of the circuit path is an open circuit. And even if the person were to contact both ends of it, its too short to have enough energy to do any damage.

It is often through capacitance that this voltage appears, such as on 2 way lights where it can be detected at the pendant fitting with bulb removed. There is no load on the strappers, so no induction, but capacitance.

I suspect that lightly touching a metal switch plate in such a scenario as you describe where you do perceive a tingle, that a tighter or heavier contact with it may reduce the sensation. This may happen in the op case also.

When testing a voltage in a high impedance circuit, the analogue meter may give a lower reading than the digital, because the analogue ones are much lower impedance meters. In series with the high impedance part of the circuit, they see less voltage than the digital one.

Both are correct for the circuit conditions they present though.

Not doubting there is an element of capacitance but when you measure the strappers your meter's impedance is a load albeit high.

2011

Cerco wrote: »

Not doubting there is an element of capacitance but when you measure the strappers your meter's impedance is a load albeit high.

The "ideal" voltmeter has infinite impedance and the "ideal" ammeter has zero impedance. Obviously this is impossible but modern voltmeters have very high impedance resulting in only a tiny current flowing. This current would be larger when an analog meter is used (due to its inherently lower impedance) resulting in a lower voltage reading.

Bruthal

2011 wrote: »

The "ideal" voltmeter has infinite impedance and the "ideal" ammeter has zero impedance. Obviously this is impossible but modern voltmeters have very high impedance resulting in only a tiny current flowing. This current would be larger when an analog meter is used (due to its inherently lower impedance) resulting in a lower voltage reading.

in theory, yes. But depends on the scenario imo. I'd trust, or at least prefer a solenoid type tester on mini pillars and transformers etc than a high impedance Digital meter.

High impedance is good for electronic circuit testing or anywhere where an impedance presented to the circuit can change the circuit properties. Not need for testing power circuits.

If a voltmeter had infinite impedance, it would read 230 volts when testing from a live point to a piece of wire connected to nothing. And read 230v for everything near an ac circuit. Including it's own leads probably. Is that good? I wouldn't think so.

Already, Digital meters impedance is so high that the result for the above would be well over 100 volts, where as a solenoid one would read 0.

The high impedance meter showed 100v on a USB socket as seen on a thread recently. Everyone came to the conclusion that it was not there for all intents and purposes.

2011

Have a read of
www.phys.ufl.edu/courses/phy4802L/spring09/labs/Lab2_DC.pdf
where page 2 states

An ideal voltmeter has infinite resistance: It is an open circuit.

Also check out the link below where it states:

Obviously, the higher the voltmeter resistance, the less loading of the circuit under test, and that is why an ideal voltmeter has infinite internal resistance.

http://www.allaboutcircuits.com/vol_1/chpt_8/3.html

Bruthal

2011 wrote: »

Have a read of
www.phys.ufl.edu/courses/phy4802L/spring09/labs/Lab2_DC.pdf
where page 2 states


Also check out the link below where it states:




http://www.allaboutcircuits.com/vol_1/chpt_8/3.html

So you honestly believe an infinite impedance meter is the ideal meter? No analysis of your own?

Testing a power transformer needs the highest possible impedance in a meter? Rubbish I say.

2011

Bruthal wrote: »

So you honestly believe an infinite impedance meter is the ideal meter? No analysis of your own?

Yes.
Analysis later, busy right now.

What is the advantage of having a lower resistance voltmeter?

2011

Once a voltmeter is connected to a circuit it draws a current. This influences the circuit.
This can not be described as "ideal".

I guess that your point is that it is often such a small impact that it is irrelevant.

Bruthal

2011 wrote: »

Once a voltmeter is connected to a circuit it draws a current. This influences the circuit.
This can not be described as "ideal".

I guess that your point is that it is often such a small impact that it is irrelevant.

10 Mega ohm voltmeter connected to 230 volts is around 20 micro amps. It will affect nothing but micro controller type circuits. What it does do though, is give misleading results.

Is it ideal if one probe is connected to live, and second connected to ask 2 meter piece of floating wire, and 230 is displayed?

Bruthal

2011 wrote: »

Yes.
Analysis later, busy right now.

What is the advantage of having a lower resistance voltmeter?

When I used to test mini pillars, the solenoid type tester was far more intuitive than a high impedance Digital meter.

That same tester would have shown almost nothing on that USB scenario discussed recently.

2011

When I type "ideal voltmeter resistance" into Google the answer is consistent from all of the reputable sources.

Bruthal

2011 wrote: »

When I type "ideal voltmeter resistance" into Google the answer is consistent from all of the reputable sources.

Yea that may be. But just take an example.

Digital meter with infinite input impedance. It would seem ideal. The idea behind that is simple, and obvious. Its taught to apprentices, so why would anyone question it.

Now take a socket. Live wire intact. Earth also. Neutral open circuit at a junction box.

Digital meter with theoretical infinite impedance will show 230 from live - earth, and live - neutral. So the tester sees no problem.

Use a solenoid type tester and it becomes very clear the neutral has a problem. Same with analogue meter.

Use current Digital meter and anywhere up to the 230 is seen to the floating wire, usually a bit lower, making many think it's a bad connection.

And we seen the 100v USB thing, when you yourself posted that the 100v is not really there. Anyone with understanding of that will realise the very high impedance meter showed that, due to the nature of the circuit it was testing, and meter impedance.

Bruthal

Cerco wrote: »

Not doubting there is an element of capacitance but when you measure the strappers your meter's impedance is a load albeit high.

A bit about it here

http://www.fluke.com/fluke/uses/comunidad/Fluke-News-Plus/ArticleCategories/Electrical/DualImpedance.htm

Ghost voltages occur from having energized circuits and non-energized wiring located in close proximity to each other, such as in the same conduit or raceway. This condition forms a capacitor and allows capacitive coupling between the energized wiring and the adjacent unused wiring.
When you place your multimeter leads between the open circuit and the neutral conductor, you effectively complete the circuit through the input of the multimeter. The capacitance between the connected, hot conductor and the floating conductor forms a voltage divider in conjunction with the multimeter input impedance. The multimeter then measures and displays the resulting voltage value.

Interesting that fluke make dual input impedance meters.

2011

Bruthal wrote: »

Its taught to apprentices, so why would anyone question it.

Exactly, it was taught to you, me and all other apprentices.
As a generaly statement is is correct.

Bruthal

2011 wrote: »

Exactly, it was taught to you, me and all other apprentices.
As a generaly statement is is correct.

I guess you just accepted it. Nothing wrong with that. My point was that apprentices will just accept it, and never question it, in practically all cases. I just dont accept that the higher the impedance, the better, in all scenarios.

Infinite impedance? Endless misleading readings will ensue. Thats a fact really.

In closed, properly functioning circuits, the higher the impedance, the better, no problem there.

It is when there is an open circuit, and the meter is across that, that readings can be misleading.

I seen the exact scenario mentioned in the fluke meter thing above, in work last year. Circuit de-energised, but showing around 12 volts. Their top men down talking about ohms law 12v and if there was a short circuit, it could draw high currents. Absolute cluelessness. I mentiond to them that it was capacitance and or inductance from the circuit beside it, and the digital meter will pick that up in a misleading way. But it has no real energy in it. Might as well have been talking to the wall.

So when I see many sites saying that the higher the impedance the better, im not surprised. I seen them before.

Bruthal

Anyway another thing about the fluke thing.

Fluke

Cerco

2011 wrote: »

The "ideal" voltmeter has infinite impedance and the "ideal" ammeter has zero impedance. Obviously this is impossible but modern voltmeters have very high impedance resulting in only a tiny current flowing. This current would be larger when an analog meter is used (due to its inherently lower impedance) resulting in a lower voltage reading.

Agreed, which is why I said albeit high (impedance)

2011

Bruthal wrote: »

Anyway another thing about the fluke thing.

Fluke

Excelent link. This part illustrates your point perfectly:

Most digital multimeters for
testing industrial, electrical and
electronic systems have high
impedance input circuits greater
than 1 megohm. This means
that when the DMM is placed
across a circuit for a measurement,
it will have little impact
on circuit performance. This is
the desired effect for most voltage
measurement applications,
and is especially important for
sensitive electronics or control
circuits.
Older troubleshooting tools
such as analog multimeters
and solenoid testers generally
have low impedance input
circuitry around 10 kilohms or
less. While these tools aren’t
fooled by ghost voltages, they
should only be used for testing
power circuits or other circuits
where the low impedance
will not negatively impact or
alter circuit performance. They
rarely comply with the current
IEC 61010 safety standards
and North American regulatory

requirements.

To be honest I did not really get your point until now. Up to my eyes in work! I was trying to understand your posts by reading them on an iPhone while trying to guid a CAD technician with a project manager breathing down my neck. I just can't multi task

What you are saying is 100% correct.

The infinite impedance "ideal" volt meter applies to circuits that are functioning properly and the volt meter is for indication (not fault finding).

Bruthal

2011 wrote: »

Excelent link.

Funnily enough, I found that fluke meter by a "fluke", while looking for something else to do with clamp meters. First time I have seen these dual impedance ones.