Incorrect testing....
Electricity in water?
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xyousefb
Community Member
Can you please inform me of how my testing was incorrect? I connected the COM wire of the multimeter to the ground of my wall outlet and then plugged the red wire to the voltage port of my multimeter. I got about 59-60V. I was informed that the light fixture is probably grounded so I put the COM wire in close contact with the fixture and obtained similar values ~57V.
How can I improve my measurement techniques?
Trying to save the guys life not throw stupid insults. Where do you come up with your >12 ma? stick a bare black wire in water will the GFI trip? I think not. Anyway I am done with this.
No the animals never noticed. I did when I worked in the tank and kept getting shocked.
The animals in the tank are in a similar situation to people working on power lines from a helicopter. They have no ground to touch so a current never flows through them. In the case of the helicopter linemen they are working on live 110,000v lines.
I have never seen that question answered in an expert way. I personally do not think so. In my case the ground probe and all the equipment in the water is in another room away from the tanks with the only connection being several feet of plastic pipe filled with saltwater.
You measure the voltage of a source with an circuit open and the current with a circuit complete.
This is what the ground probe does. It completes the circuit and the voltage "disappears".
You are left with the tiny current flow.
You will need someone more educated than I am to answer if there are any negative effects from that. If there were most humans in cities would be dead now though I would think
This is what the ground probe does. It completes the circuit and the voltage "disappears".
You are left with the tiny current flow.
You will need someone more educated than I am to answer if there are any negative effects from that. If there were most humans in cities would be dead now though I would think
Simon_M
Active Member
I have a new Fluval SEA EVO 52 litre aquarium that I'm using as a QT tank. I'm also an electronics engineer and I'm interested in having electricity "isolated" from my saltwater tank. The ideal situation would be that there is no electric shock potential in an aquarium setting. That is different from saying that "electricity" is not present in the aquarium.
My digital multimeter has a very high input impedance and several "safety features". There is a non contact voltage (NCV) feature which is designed to make identifying live circuits before they are touched. The optimal arrangement is to turn off mains circuits at a circuit breaker (isolates the live and neutral), remove the supply fuse and display a sign to say that maintenance is in progress e.g. don't interfere. The NCV feature can be used to increase safety when investigating an electrical problem. For my meter the NCV feature has a probe that can be placed near the neutral conductor on a socket and also near a live conductor on the same socket. When a live potential is "observed" the display changes to orange and the "H" symbol is displayed and there is an audible alert. On aquarium products e.g. my LED lights over my tank, I did an initial check that the DC PSU wasn't directly connected to either of the mains live/neutral - it isn't, before using it.
I did return the aquarium because one of the corners was chipped and it shouldn't have been supplied like this. I also commented that there was "electricity" felt on the top of the LED light unit. I could measure 120V and there is a leakage current through me to ground - my stone floor of 60 uA. The NCV also alerted me to 120V along the cable. Is that normal? Is that a problem? Some of us are more sensitive - I can often detect the electricity "tingle" on the keyboard on some of the older laptops in my local Apple Store when they are plugged into the mains - it is the same effect.
My mains voltage in the UK is 230V 50 Hz. If I measure the mains voltage it is often about 247V AC and always 50Hz. If I look at the voltage on the top of the lights, I can see that the DC power unit is indeed providing 12V DC to the lights and the negative lead is at 120V. If I hold the negative lead, I don't get an "electric shock" but if I stroke the top of the lights, I can "feel" a buzz. Further investigation shows that the AC potential is pretty constant as I cycle the lights through OFF, BLUE or ON but that the frequency varies and is between 2 kHz and 10 kHz as the amount of power varies.
Is that normal? It probably is. Is that a problem - I don't think so. If I had measured 120V and 50 Hz then I would immediately think there is a leakage issue. The lights come in three parts, there is the plastic hood, an aluminium light unit that is powder coated and contains the LED lights, electronics in a "potted" configuration and also the mains power unit. I'm told that it would be safe to drop the LED lights in the tank with no ill effect - I have not tried it.
What we have is a strange situation. The power unit is double insulated and has a plastic case and the mains input is indeed without a direct earth. The two conductors are insulated and there is an outer plastic sheath. As a unit it can be said to be doubly insulated. The "problem" is that it is connected to the aluminium light which is connected to the user - when you touch it. The "problem" is caused by plugging the lights together. It is convenient to be able to disconnect the lights e.g. for maintanance. If the lights were "tethered" to the PSU, I doubt that the total unit could be labelled (correctly) as "double isolated". Like an electrical appliance, it would need to be earthed because there is a metal case - the LED light unit. The paint on the lights is not sufficient to say that it is "isolated" from the user. Part of the issue is that I have the aquarium in a Utility Room and there is a stone floor. If I had the tank in a different setting there might be carpet or a wooden floor and I wouldn't notice the "problem".
The issue is due to electrical regulations which require compliance to certain standards. We have a user in the UK, buying a product sourced in China and sold into a European (or US) Market. It is not unknown for Chinese Vendors to create products and have them certified and then later on omit some of the components (to reduce cost). Surprisingly these products don't have the "feel" of the buzz that I experienced.
Inside a wall wart PSU (aka a "cheap PSU) there is a switched mode PSU. It works by converting the mains potential into DC and switching it a high frequencies through a step down transformer and then to a smoothed DC voltage. This is what the output supplies to the LED lights. There are two sides to the circuit, the "hot" input side and the "isolated" output. This would be OK if the transformer DC "isolated" the two sides (it does) and there was a reference to earth (it doesn't) and there is no connection between the "hot" and the "isolated" side (there is a connection). To comply with Radio (RFI) standards there are additional components added that bridge between the two sides. These can often be seen as "blue" capacitors in switched mode PSU. I measured my PSU and there is no DC electrical connection between the earth pin and the neutral and live pins of the plug (that's good) but there are capacitors between the L + N + E pins (I can measure these as being about 75 pF). Without the capacitors the PSU would fail the RFI tests and the company wouldn't source the products from China, especially if they noticed that components were being routinely omitted. The slight "tingle" effect is not itself harmful. It could have been designed in a way to minimise the effect e.g. using a screened transformer and a different circuit for different markets e.g. US, UK, Europe, Asia - but at increased cost. For most consumers the problem is "swept under the carpet" - quite literally as standing on carpet will isolate the user. The situation is because we demand inexpensive products that are "safe" but not completely "perfect". Ironically, the laws which govern compliance often introduce the problems, but if your Radio or TV was affected then you might be glad that the compliance was in place.
With the multimeter it is perhaps a bit disconcerting that I can put one probe in the tank and one to an earthed connection e.g. a tap and measure an AC potential - about 60V and a small current - about 15 uA. Everything in my aquarium is double isolated. The PSU for the lights does have an earth pin but it isn't connected to the DC output. It is an interesting fact that I can hold my multimeter probes in the air and measure an AC potential. Between the earth (a tap) and the mains socket (a supply) there is 230V AC and the multimeter has a very high impedance - so it is also very sensitive to the electricity "in the air". Of course as soon as I touch the probe, I change the "circuit" and my body provides a "load" and the potential seen collapses. With the LED light PSU the frequency seen isn't the mains 50 Hz. It is the switching frequency of the PSU which varies with the load. If it was the mains 50 Hz and there was any indication of a DC resistance to the plug pins that would indicate an issue.
A friend in my Radio Club suggested that I should "earth" the LED lights. This does indeed remove the slight "tingle" as there is now only a 12V difference to the house earth. It's perhaps not a good solution in the aquarium because if the insulation on the LED lights were to be affected and the lights to be in contact with the water e.g. I dropped the unit in the tank this would provide a ground. Further, if a second device like my heater were to break, it would introduce a "live" potential. At this point, my hands in the tank would be exposed to a potential and I would receive an electric shock. It's for that reason that I don't modify the circuit and why I have a double pole switched socket to isolate the power to the aquarium. When I switch the power off it isolates the live and neutral (some sockets my only isolate the live connection). There really should be no need to maintain power and have your hands in the tank e.g. break a "live" heater with a rock (none in my QT tank, but you get the idea) and you will regret it!
Simon
My digital multimeter has a very high input impedance and several "safety features". There is a non contact voltage (NCV) feature which is designed to make identifying live circuits before they are touched. The optimal arrangement is to turn off mains circuits at a circuit breaker (isolates the live and neutral), remove the supply fuse and display a sign to say that maintenance is in progress e.g. don't interfere. The NCV feature can be used to increase safety when investigating an electrical problem. For my meter the NCV feature has a probe that can be placed near the neutral conductor on a socket and also near a live conductor on the same socket. When a live potential is "observed" the display changes to orange and the "H" symbol is displayed and there is an audible alert. On aquarium products e.g. my LED lights over my tank, I did an initial check that the DC PSU wasn't directly connected to either of the mains live/neutral - it isn't, before using it.
I did return the aquarium because one of the corners was chipped and it shouldn't have been supplied like this. I also commented that there was "electricity" felt on the top of the LED light unit. I could measure 120V and there is a leakage current through me to ground - my stone floor of 60 uA. The NCV also alerted me to 120V along the cable. Is that normal? Is that a problem? Some of us are more sensitive - I can often detect the electricity "tingle" on the keyboard on some of the older laptops in my local Apple Store when they are plugged into the mains - it is the same effect.
My mains voltage in the UK is 230V 50 Hz. If I measure the mains voltage it is often about 247V AC and always 50Hz. If I look at the voltage on the top of the lights, I can see that the DC power unit is indeed providing 12V DC to the lights and the negative lead is at 120V. If I hold the negative lead, I don't get an "electric shock" but if I stroke the top of the lights, I can "feel" a buzz. Further investigation shows that the AC potential is pretty constant as I cycle the lights through OFF, BLUE or ON but that the frequency varies and is between 2 kHz and 10 kHz as the amount of power varies.
Is that normal? It probably is. Is that a problem - I don't think so. If I had measured 120V and 50 Hz then I would immediately think there is a leakage issue. The lights come in three parts, there is the plastic hood, an aluminium light unit that is powder coated and contains the LED lights, electronics in a "potted" configuration and also the mains power unit. I'm told that it would be safe to drop the LED lights in the tank with no ill effect - I have not tried it.
What we have is a strange situation. The power unit is double insulated and has a plastic case and the mains input is indeed without a direct earth. The two conductors are insulated and there is an outer plastic sheath. As a unit it can be said to be doubly insulated. The "problem" is that it is connected to the aluminium light which is connected to the user - when you touch it. The "problem" is caused by plugging the lights together. It is convenient to be able to disconnect the lights e.g. for maintanance. If the lights were "tethered" to the PSU, I doubt that the total unit could be labelled (correctly) as "double isolated". Like an electrical appliance, it would need to be earthed because there is a metal case - the LED light unit. The paint on the lights is not sufficient to say that it is "isolated" from the user. Part of the issue is that I have the aquarium in a Utility Room and there is a stone floor. If I had the tank in a different setting there might be carpet or a wooden floor and I wouldn't notice the "problem".
The issue is due to electrical regulations which require compliance to certain standards. We have a user in the UK, buying a product sourced in China and sold into a European (or US) Market. It is not unknown for Chinese Vendors to create products and have them certified and then later on omit some of the components (to reduce cost). Surprisingly these products don't have the "feel" of the buzz that I experienced.
Inside a wall wart PSU (aka a "cheap PSU) there is a switched mode PSU. It works by converting the mains potential into DC and switching it a high frequencies through a step down transformer and then to a smoothed DC voltage. This is what the output supplies to the LED lights. There are two sides to the circuit, the "hot" input side and the "isolated" output. This would be OK if the transformer DC "isolated" the two sides (it does) and there was a reference to earth (it doesn't) and there is no connection between the "hot" and the "isolated" side (there is a connection). To comply with Radio (RFI) standards there are additional components added that bridge between the two sides. These can often be seen as "blue" capacitors in switched mode PSU. I measured my PSU and there is no DC electrical connection between the earth pin and the neutral and live pins of the plug (that's good) but there are capacitors between the L + N + E pins (I can measure these as being about 75 pF). Without the capacitors the PSU would fail the RFI tests and the company wouldn't source the products from China, especially if they noticed that components were being routinely omitted. The slight "tingle" effect is not itself harmful. It could have been designed in a way to minimise the effect e.g. using a screened transformer and a different circuit for different markets e.g. US, UK, Europe, Asia - but at increased cost. For most consumers the problem is "swept under the carpet" - quite literally as standing on carpet will isolate the user. The situation is because we demand inexpensive products that are "safe" but not completely "perfect". Ironically, the laws which govern compliance often introduce the problems, but if your Radio or TV was affected then you might be glad that the compliance was in place.
With the multimeter it is perhaps a bit disconcerting that I can put one probe in the tank and one to an earthed connection e.g. a tap and measure an AC potential - about 60V and a small current - about 15 uA. Everything in my aquarium is double isolated. The PSU for the lights does have an earth pin but it isn't connected to the DC output. It is an interesting fact that I can hold my multimeter probes in the air and measure an AC potential. Between the earth (a tap) and the mains socket (a supply) there is 230V AC and the multimeter has a very high impedance - so it is also very sensitive to the electricity "in the air". Of course as soon as I touch the probe, I change the "circuit" and my body provides a "load" and the potential seen collapses. With the LED light PSU the frequency seen isn't the mains 50 Hz. It is the switching frequency of the PSU which varies with the load. If it was the mains 50 Hz and there was any indication of a DC resistance to the plug pins that would indicate an issue.
A friend in my Radio Club suggested that I should "earth" the LED lights. This does indeed remove the slight "tingle" as there is now only a 12V difference to the house earth. It's perhaps not a good solution in the aquarium because if the insulation on the LED lights were to be affected and the lights to be in contact with the water e.g. I dropped the unit in the tank this would provide a ground. Further, if a second device like my heater were to break, it would introduce a "live" potential. At this point, my hands in the tank would be exposed to a potential and I would receive an electric shock. It's for that reason that I don't modify the circuit and why I have a double pole switched socket to isolate the power to the aquarium. When I switch the power off it isolates the live and neutral (some sockets my only isolate the live connection). There really should be no need to maintain power and have your hands in the tank e.g. break a "live" heater with a rock (none in my QT tank, but you get the idea) and you will regret it!
Simon
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