Earthing light fixtures?

[Sangoma]

I don't know if the sound of snoring would have the same effect on the mind as a mechanical noise.

Are the plugs 15A? And no fuses in them?

The subway can cause ground currents, it is often found that metal water pipes corrode more quickly near an electric train line, especially if it travels around an area (sort of U shape)

You can of course make the bulb light up by putting the switch in either line, but if you put it in the neutral line, it means the live to the light socket is always live, which is dangerous, and will also make worse the problem you want to cure.

On trains, we lived in an area where the main road dropped 1000ft in 5 miles, obviously the trains could not follow that route, but they still had a fairly steep descent, and we used to get a very distorted sine wave when they were going downhill, they use regeneration as one method or braking. They were also on a mainly separate system, but it had to be tied into the grid at points to get power.

 

[regulaz]

I don't know if the sound of snoring would have the same effect on the mind as a mechanical noise.

Are the plugs 15A? And no fuses in them?

The subway can cause ground currents, it is often found that metal water pipes corrode more quickly near an electric train line, especially if it travels around an area (sort of U shape)

You can of course make the bulb light up by putting the switch in either line, but if you put it in the neutral line, it means the live to the light socket is always live, which is dangerous, and will also make worse the problem you want to cure.

On trains, we lived in an area where the main road dropped 1000ft in 5 miles, obviously the trains could not follow that route, but they still had a fairly steep descent, and we used to get a very distorted sine wave when they were going downhill, they use regeneration as one method or braking. They were also on a mainly separate system, but it had to be tied into the grid at points to get power.

maybe the mechanical noise has something to do with it but it is too low to be of much concern.

that is an interesting scenario, i guess every situation is unique.. the train here is on flat level.

the MCBs have no fuses they just trip in case of overdraw. they are 10/20/25/32 amps depending on the circuit.

edit:ill have this live/neutral thing checked for lights because the sockets seem to be wired correctly.

 

[Sangoma]

Sorry, what I meant was do the plugs have fuses in them?

I think you use the same round 3 pin 15A plug as South Africa does, that used to be used in the UK (supposedly they set the original standards for both SA and India)
If it is, you almost certainly do not have a ring system.

What you need is a "neon" screwdriver (most are LCD now) which will glow when you touch the live, but not the neutral (unless it is faulty) that way you can see if the live or neutral is switched

 

[JimB]

I think that I can explain this phenomenon quite adequately.

If I understand the situation correctly:
There is a light fitting with a metal body/framework which is not connected to earth
The light works normally.
Measuring from the frame to a known good earth, there is some random voltage.

The voltage on the frame is due to the small (parasitic) capacitance between the mains wiring and the frame of the light.
The capacitance is only a few pico farads and so is a very high impedance at 50hz.

Measuring this stray voltage is possible with a high impedance voltmeter, the higher the impedance the higher will be the measured voltage.
If a low impedance meter* were to be used, then there would hardly be any voltage indicated on the meter.

* Something like an old AVO model 7, 500 Ohms per Volt sensitivity.

Is the stray voltage a problem?
Probably not, but will be very dangerous in the case of a low impedance fault between the live wire and the body of the lamp.

Is it bad practice to have an un-earthed metal case?
Yes.

JimB

 

[regulaz]

Sorry, what I meant was do the plugs have fuses in them?

I think you use the same round 3 pin 15A plug as South Africa does, that used to be used in the UK (supposedly they set the original standards for both SA and India)
If it is, you almost certainly do not have a ring system.

What you need is a "neon" screwdriver (most are LCD now) which will glow when you touch the live, but not the neutral (unless it is faulty) that way you can see if the live or neutral is switched

thats right it 15 amp plugs 3 pin for power sockets and lower rating for light sockets.

i checked with the tester all wiring at the mcbs is where live and neutral should be on the mcb.

 

[regulaz]

I think that I can explain this phenomenon quite adequately.

If I understand the situation correctly:
There is a light fitting with a metal body/framework which is not connected to earth
The light works normally.
Measuring from the frame to a known good earth, there is some random voltage.

The voltage on the frame is due to the small (parasitic) capacitance between the mains wiring and the frame of the light.
The capacitance is only a few pico farads and so is a very high impedance at 50hz.

Measuring this stray voltage is possible with a high impedance voltmeter, the higher the impedance the higher will be the measured voltage.
If a low impedance meter* were to be used, then there would hardly be any voltage indicated on the meter.

* Something like an old AVO model 7, 500 Ohms per Volt sensitivity.

Is the stray voltage a problem?
Probably not, but will be very dangerous in the case of a low impedance fault between the live wire and the body of the lamp.

Is it bad practice to have an un-earthed metal case?
Yes.

JimB

so earthing the light fixtures is in order. but why do some light fixtures show 0VAC no stray voltage despite as all fixtures and wiring and switches are of the same age?

 

[regulaz]

(repeat post from a similar thread on electrical wiring issues)

the electrician who came visiting did a preliminary check. he said all earth wires from the different rooms at the fusebox panel were joined to a single green earth wire going to the busbar panel but he couldnt locate that wire at the busbar panel. he said rest of the residents also dont have an earth going to their premises from the busbar panel.

there were 3 live and 1 neutral coming from the busbar panel to the fusebox and an earth wire he couldnt locate at the busbar panel but is going from the fusebox alright. he took one 10mm live wire and disconnected it and connected it to the busbarpanel frame at one end and the earth wires in the fusebox on the other end.

that did not change the voltage i measured at the light fixtures.

do i have another rookie electrician at my disposal? i think so.. :/

after he left i disconnected the new earth wire (converted from live) at the fusebox from all the earths of the rooms congregating at the fusebox and measured the voltage at light fixtures no change.
i also disconnected the original green earth lead at the fusebox which goes to the distribution panel (which he could not locate at the busbar panel) and put a multimeter from live to that green wire and it showed 235VAC.
seems to be a working earth?
do i need to locate a separate earth point like the waterpipe? isnt the busbar panel frame good enough for an earth?

 

[Sangoma]

you asked...........................do i need to locate a separate earth point like the waterpipe? isnt the busbar panel frame good enough for an earth?


Not easy to answer that, as we can't see it. If the busbar panel is properly earthed, probably not.

However, any metal water pipes and other metal in the house should be bonded to the supply earth for safety reasons. If the supply earth goes above ground because of a fault or bad wiring, and metalwork is not bonded, there could be a fatal difference between the two.

We also don't know the quality of your electricians and normal wiring practices. In South Africa and the UK standards for both are very high, with people doing it commercially having to be qualified and registered, and set down wiring standards. In the Philippines for example, quite often anyone with a hammer is a carpenter, and anyone with a screwdriver is an electrician, and standards, if they exist, are not followed (ie electric showers with a wall socket next to the shower unit, or the earth wire hanging down loose from the shower unit, in hotels!!).

I also really believe that the voltages you describe are insignificant, bit like chasing ghosts. The radiation round your house consists of a broad spectrum of frequencies, and RF has a far higher "transfer efficiency" to the human body than low frequencies, as shown by the danger of a leaking microwave and the relative safety of an induction hob.

I just took a Fluke meter, held onto one probe, and dangled the other lead in front of the laptop screen, and it shows 5V5, touch it on the metal of the RS232 port and it shows 36V8. It is fed from a power pack where the input is isolated from the output, though it probably has low value capacitors across both to ground to prevent RFI.

If what we hear on the TV is correct (and it is often not) water supply is a problem there, with some people not getting any because others are sucking it out of the system with pumps, and often the pumps compete with each other and the supply dries up. Maybe the stresses of water supply are what causes people to wake up at the sound of pumps. I can't help feeling the cause of sleep problems is more tangible than a little stray voltage on light fittings. Maybe that combined with your worry about the house wiring.

At the same time, it is important to make the house safe, if the light fittings can be touched, they should be earthed.

 

[regulaz]

you asked...........................do i need to locate a separate earth point like the waterpipe? isnt the busbar panel frame good enough for an earth?


Not easy to answer that, as we can't see it. If the busbar panel is properly earthed, probably not.

However, any metal water pipes and other metal in the house should be bonded to the supply earth for safety reasons. If the supply earth goes above ground because of a fault or bad wiring, and metalwork is not bonded, there could be a fatal difference between the two.

We also don't know the quality of your electricians and normal wiring practices. In South Africa and the UK standards for both are very high, with people doing it commercially having to be qualified and registered, and set down wiring standards. In the Philippines for example, quite often anyone with a hammer is a carpenter, and anyone with a screwdriver is an electrician, and standards, if they exist, are not followed (ie electric showers with a wall socket next to the shower unit, or the earth wire hanging down loose from the shower unit, in hotels!!).

I also really believe that the voltages you describe are insignificant, bit like chasing ghosts. The radiation round your house consists of a broad spectrum of frequencies, and RF has a far higher "transfer efficiency" to the human body than low frequencies, as shown by the danger of a leaking microwave and the relative safety of an induction hob.

I just took a Fluke meter, held onto one probe, and dangled the other lead in front of the laptop screen, and it shows 5V5, touch it on the metal of the RS232 port and it shows 36V8. It is fed from a power pack where the input is isolated from the output, though it probably has low value capacitors across both to ground to prevent RFI.

If what we hear on the TV is correct (and it is often not) water supply is a problem there, with some people not getting any because others are sucking it out of the system with pumps, and often the pumps compete with each other and the supply dries up. Maybe the stresses of water supply are what causes people to wake up at the sound of pumps. I can't help feeling the cause of sleep problems is more tangible than a little stray voltage on light fittings. Maybe that combined with your worry about the house wiring.

At the same time, it is important to make the house safe, if the light fittings can be touched, they should be earthed.

the busbar panel frame also is the common frame for housing electricity meters for 10 other houses. it is at ground level and the frame is buried in the rooms brick and cement walls and floor.

LOL yeah the issue is somewhat similar around here but still a little better, because you can get proper services only thing is they cost an arm and a leg for small things. its a good idea to get everything done right while the construction is underway but that doesn't always happen.

water shortage isn't an issue because you can call the community water storage/water pump handler over intercom anytime and ask him to switch on the supply. 4am-8am and 4pm-8pm is just the scheduled time. so its not an issue to stress over.

i did manage to locate the problem. part of the house has old metal conduits. newer extension of the house has plastic conduits. whole house wiring was newly installed the old metal conduits were used as is because they were buried in cement/concrete. the light fixtures attached to the metal conduits show 0VAC while the fixtures attached to the plastic conduits are showing 9-12VAC. it took sometime to catch this issue but i guess the only solution is to run an earth wire in the fixtures using plastic conduits.

maybe the community water pump isnt grounded or something or it is the subway and water pumps turning on around the same time in the early morning but whatever it is this problem is resolved.

 

[regulaz]

while i've figured out why the 9-12VAC is showing up where it is showing up (unearthed fixtures on plastic conduits), i'm still wondering where and why is it being generated at all. Any ideas where i should start looking for it? is it simply the nature of all electrical fittings when turned on to do this?

edit: is that just the voltage being generated across the arc of the 100watt incandescent bulb as mentioned previously in this thread?

 

[MrAl]

Hi,


I think JimB came up with a similar idea to this one...

It dawned on me that we should probably be using an analog meter not a digital, i assume you are using one too. The problem with a digital here is that the input impedance is so high that even the slightest inductive or capacitive coupling would cause a reading to show up as a voltage. and the voltage would depend on many very unusual factors like how much switch leakage, how close the wires are to each other, stuff like that, and the switch leakage may be only 0.1 microamp to show a significant reading on the digital meter. The analog meter would not show so much.

For example, even a 10pf capacitive coupling could cause a (very roughly computed) 5 volt ac reading on the meter, and that's not much capacitance which can be had with just two wires close to each other.

I too measure this in the bath and when i touch my finger to the meter probe and one to the light fixture metal case, i still see a voltage reading of around 40 vac on the meter but dont get a shock. So the current has got to be very light, just enough for a voltage reading but not enough to make any serious power. For example, this would never run an LED bulb (with rectifier diode) it would just "short out" the 10pf or whatever capacitance.
I could have done one more test:
Use my body as a conductor and measure the voltage developed across the body. I would bet it is very small because the human body would act as a 'load' which would overload the 'power supply' which is the 120vac coupled signal. So it's like shorting out a power supply...the voltage goes to zero or close.

So to model this, say we have a voltage source of 120vac and that is connected in series with 100pf capacitor, and we want to know what kind of power output we can get from this circuit with a human body load. I think it would be negligible. Same with inductive coupling, where the two mutual inductance coils would be so far apart there would be hardly any power transfer. Dangerous? I dont think so, but i would not be sure about a person with a pacemaker.

 

[regulaz]

Hi,


I think JimB came up with a similar idea to this one...

It dawned on me that we should probably be using an analog meter not a digital, i assume you are using one too. The problem with a digital here is that the input impedance is so high that even the slightest inductive or capacitive coupling would cause a reading to show up as a voltage. and the voltage would depend on many very unusual factors like how much switch leakage, how close the wires are to each other, stuff like that, and the switch leakage may be only 0.1 microamp to show a significant reading on the digital meter. The analog meter would not show so much.

For example, even a 10pf capacitive coupling could cause a (very roughly computed) 5 volt ac reading on the meter, and that's not much capacitance which can be had with just two wires close to each other.

I too measure this in the bath and when i touch my finger to the meter probe and one to the light fixture metal case, i still see a voltage reading of around 40 vac on the meter but dont get a shock. So the current has got to be very light, just enough for a voltage reading but not enough to make any serious power. For example, this would never run an LED bulb (with rectifier diode) it would just "short out" the 10pf or whatever capacitance.
I could have done one more test:
Use my body as a conductor and measure the voltage developed across the body. I would bet it is very small because the human body would act as a 'load' which would overload the 'power supply' which is the 120vac coupled signal. So it's like shorting out a power supply...the voltage goes to zero or close.

So to model this, say we have a voltage source of 120vac and that is connected in series with 100pf capacitor, and we want to know what kind of power output we can get from this circuit with a human body load. I think it would be negligible. Same with inductive coupling, where the two mutual inductance coils would be so far apart there would be hardly any power transfer. Dangerous? I dont think so, but i would not be sure about a person with a pacemaker.

that 40VAC could be an issue if its in your sleeping area night after night. specially if you've got over voltage issues at night. grounding is a good idea.

 

[Nigel Goodwin]

that 40VAC could be an issue if its in your sleeping area night after night. specially if you've got over voltage issues at night. grounding is a good idea.

As it's pretty well an imaginary value, and it's not connected via wires to your body, why would it be of any concern?.

 

[tvtech]

I am mystified

Regards,
tvtech

 

[regulaz]

As it's pretty well an imaginary value, and it's not connected via wires to your body, why would it be of any concern?.

that imaginary value goes to 0VAC when you earth it. its of concern in a sleeping area because your body is repairing itself where all signals are going through the body electrically (via the nervous system), an artificial electric field even of that low value could disrupt the bodies repair.

 

[tvtech]

that imaginary value goes to 0VAC when you earth it. its of concern in a sleeping area because your body is repairing itself where all signals are going through the body electrically (via the nervous system), an artificial electric field even of that low value could disrupt the bodies repair.

Whatsha smoking dude ??

Can I have some too??

As Always

tvtech

 

[regulaz]

Whatsha smoking dude ??

Can I have some too??

As Always

tvtech

yeah man the best hash around manala - have it and get zapped

 

[tvtech]

Zap zap zap and I am outa here.

Be good all

tvtech

 

[Nigel Goodwin]

that imaginary value goes to 0VAC when you earth it. its of concern in a sleeping area because your body is repairing itself where all signals are going through the body electrically (via the nervous system), an artificial electric field even of that low value could disrupt the bodies repair.

If you believe such utter rubbish what are you doing on an electronics site?.

 

[unclejed613]

it is a relatively new installation around 5 years old but done by amateurs who were pretending to be professional unfortunately. but you're right this is with the lamp on.. incandescent bulb on E27 type.

i'd check places where wires are joined, and see if the voltage drop exists across the connection. if this is with current flowing, then it is generating heat somewhere. you may find a bad connection if you find any of the wire junctions on the neutral wire that are warm.