Brian Posted October 6, 2013 Share Posted October 6, 2013 I removed the earth from the power plug... Such a bad idea. As it's a laptop it'll have a switch-mode power supply. As it's got an earth pin it means that the earth is being used to keep interference generated by the SMPSU down to acceptable levels. It's done with a circuit a bit like this... (exact configuration may vary but overall will be the same) The C2 capacitors connect each live conductor (ie L and N) to earth to shunt any HF down to ground. As long as ground is connected there is no problem. HOWEVER, remove the ground connection in the plug and now the junction of the two C2 capacitors will float to a level of around 1/2 mains voltage, ie around 120v. If this point, which was ground, is connected to other circuitry, or worse, any exposed metalwork or other connectors, you have now exposed 120 volts for anyone to touch. As I said, bad idea. Link to comment Share on other sites More sharing options...
david.elsbury Posted October 6, 2013 Share Posted October 6, 2013 I've never heard of a piece of gear where an "earth lift" switch is the mains earth. It's the signal earth in my experience. If an item of gear is designed to have a mains earth then that earth is needed for safety reasons. Removing it is risking lives.I guess it's all down to semantics and what things are called by different people, but this is why I try to refer to a signal ground, and a mains earth - to eliminate confusion. Fincaman, I hope you wouldn't do the same thing today... David Link to comment Share on other sites More sharing options...
Bobbsy Posted October 6, 2013 Share Posted October 6, 2013 I've never heard of a piece of gear where an "earth lift" switch is the mains earth. It's the signal earth in my experience. If an item of gear is designed to have a mains earth then that earth is needed for safety reasons. Removing it is risking lives.I guess it's all down to semantics and what things are called by different people, but this is why I try to refer to a signal ground, and a mains earth - to eliminate confusion. Fincaman, I hope you wouldn't do the same thing today... David I'm afraid that distinction doesn't really work when you go international David. In Canada (where I started out several decades ago) and the USA they're both "grounds" not earths--so you have "mains earth" and "signal earth" there. Hmmm...big feeling of deja vu...didn't we have this same conversation a few months back? Link to comment Share on other sites More sharing options...
fincaman Posted October 6, 2013 Share Posted October 6, 2013 I had noise problems doing this some years ago and cured it by disconnecting the earth on the computer. Try connecting the mixer directly to the computer, if you get noise unplug the computer power plug (providing the battery is good) if the noise goes it's an earthing problem.You removed the mains earth, or you removed the signal earth (ground)?? The word "ground" is used in America in England we use "Earth" I removed the earth from the power plug... Such a bad idea. As it's a laptop it'll have a switch-mode power supply. As it's got an earth pin it means that the earth is being used to keep interference generated by the SMPSU down to acceptable levels. It's done with a circuit a bit like this... (exact configuration may vary but overall will be the same) The C2 capacitors connect each live conductor (ie L and N) to earth to shunt any HF down to ground. As long as ground is connected there is no problem. HOWEVER, remove the ground connection in the plug and now the junction of the two C2 capacitors will float to a level of around 1/2 mains voltage, ie around 120v. If this point, which was ground, is connected to other circuitry, or worse, any exposed metalwork or other connectors, you have now exposed 120 volts for anyone to touch. As I said, bad idea.Your Circuit would allow full mains to the computer it is just a mains filter not a switchmode power supply Link to comment Share on other sites More sharing options...
OllieDuff Posted October 6, 2013 Share Posted October 6, 2013 I removed the earth from the power plug... Such a bad idea. As it's a laptop it'll have a switch-mode power supply. As it's got an earth pin it means that the earth is being used to keep interference generated by the SMPSU down to acceptable levels. It's done with a circuit a bit like this... (exact configuration may vary but overall will be the same) The C2 capacitors connect each live conductor (ie L and N) to earth to shunt any HF down to ground. As long as ground is connected there is no problem. HOWEVER, remove the ground connection in the plug and now the junction of the two C2 capacitors will float to a level of around 1/2 mains voltage, ie around 120v. If this point, which was ground, is connected to other circuitry, or worse, any exposed metalwork or other connectors, you have now exposed 120 volts for anyone to touch. As I said, bad idea.Your Circuit would allow full mains to the computer it is just a mains filter not a switchmode power supply My reading of Brian's post ("It's done using a circuit a bit like this") was that he was using the circuit as an example of a filter for a switch-mode power supply, not the whole power supply. Regardless, I'm not sure that what that circuit represents has any bearing on the validity of the arguments for and against (mostly against) removing the mains earth from equipment which is designed to be earthed. Link to comment Share on other sites More sharing options...
fincaman Posted October 6, 2013 Share Posted October 6, 2013 I removed the earth from the power plug... Such a bad idea. As it's a laptop it'll have a switch-mode power supply. As it's got an earth pin it means that the earth is being used to keep interference generated by the SMPSU down to acceptable levels. It's done with a circuit a bit like this... (exact configuration may vary but overall will be the same) The C2 capacitors connect each live conductor (ie L and N) to earth to shunt any HF down to ground. As long as ground is connected there is no problem. HOWEVER, remove the ground connection in the plug and now the junction of the two C2 capacitors will float to a level of around 1/2 mains voltage, ie around 120v. If this point, which was ground, is connected to other circuitry, or worse, any exposed metalwork or other connectors, you have now exposed 120 volts for anyone to touch. As I said, bad idea.Your Circuit would allow full mains to the computer it is just a mains filter not a switchmode power supply My reading of Brian's post ("It's done using a circuit a bit like this") was that he was using the circuit as an example of a filter for a switch-mode power supply, not the whole power supply. Regardless, I'm not sure that what that circuit represents has any bearing on the validity of the arguments for and against (mostly against) removing the mains earth from equipment which is designed to be earthed. I buy switchmode power supplies on a regular basis and they are all two pin mains input (I am in Spain) even when they come with English plugs the Earth pin is often plastic or not connected.The junction of the two C2 capacitors could just feasibly get to 120v but they are of such a value to filter RF and not pass 50HZ otherwise they would short out the output but yes they could read 120v on a very high impedance AC voltmeter but would be floating however that junction is ONLY connected to the earth wire which I forgot to mention would be cut back secured and insulated so non of the metal parts would be exposed to this. Out of interest I have just measured on my older Acer computer between the earth pin on the mains plug and the 19 v output both inner and outer and guess what ? no connection. To conclude LOTS of modern equipment i.e. FX boxes small graphics E.T.C. have external power supplies with no earth connection. Link to comment Share on other sites More sharing options...
Shez Posted October 6, 2013 Share Posted October 6, 2013 To conclude LOTS of modern equipment i.e. FX boxes small graphics E.T.C. have external power supplies with no earth connection.Indeed. And they're DESIGNED to not need an earth connection. They have the concentric squares symbol on them which means they're double insulated (class II). What people are taking issue with is disconnecting the mains earth on an appliance that is designed to require it. Take a computer with a standard metal chassis - the PSU has an IEC inlet and the chassis is bonded to the earth through the PSU body. If you lift the mains earth, the whole case can then float. And if a fault develops, the whole chassis can become live - a condition that the presence of the mains earth would prevent by blowing the fuse. Link to comment Share on other sites More sharing options...
Brian Posted October 6, 2013 Share Posted October 6, 2013 Your Circuit would allow full mains to the computer it is just a mains filter not a switchmode power supply Sorry, I'd hoped that when I wrote...As it's got an earth pin it means that the earth is being used to keep interference generated by the SMPSU down to acceptable levels. It's done with a circuit a bit like this......people would understand that I was illustrating the front-end filtering on a typical SMPSU with earth/ground connection. I should of course have written...As it's got an earth pin it means that the earth is being used to keep interference generated by the SMPSU down to acceptable levels; it's done with a circuit a bit like this... I buy switchmode power supplies on a regular basis and they are all two pin mains input (I am in Spain) even when they come with English plugs the Earth pin is often plastic or not connected.I'm now confused. If that was the sort you had then disconnecting the earth would make no difference. I agree that two-pin supplies are different in their filtering. They often have a, IMHO, more dangerous arrangement where a capacitor is connected from the LV side of the supply back to a low impedance (at HF) point somewhere in the HV circuitry. The idea being to take any noise on the output and dump it back to earth/ground via the mains supply. This capacitor can still induce mains hum in a system as your earth loop is now via this capacitor and, totally bizarrely, your earth-loop induced mains hum can sometime be cured by swapping around your two pin mains connector. However, this obvioulsy wasn't the situation in your case as you did state... I had noise problems doing this some years ago and cured it by disconnecting the earth on the computer. I removed the earth from the power plug,... ...but they are of such a value to filter RF and not pass 50HZ otherwise they would short out the output Their value needs to be low enough to filter out switching noise from the line but high enough not to pass too much current at 50Hz. A typical value on a well designed supply is 4n7 which will still pass enough current at 50Hz to give you a tingle. To conclude LOTS of modern equipment i.e. FX boxes small graphics E.T.C. have external power supplies with no earth connection.No argument there but worth noting my point that you can still get an earth loop even on unearthed equipment. Link to comment Share on other sites More sharing options...
fincaman Posted October 6, 2013 Share Posted October 6, 2013 To conclude LOTS of modern equipment i.e. FX boxes small graphics E.T.C. have external power supplies with no earth connection.Indeed. And they're DESIGNED to not need an earth connection. They have the concentric squares symbol on them which means they're double insulated (class II). What people are taking issue with is disconnecting the mains earth on an appliance that is designed to require it. Take a computer with a standard metal chassis - the PSU has an IEC inlet and the chassis is bonded to the earth through the PSU body. If you lift the mains earth, the whole case can then float. And if a fault develops, the whole chassis can become live - a condition that the presence of the mains earth would prevent by blowing the fuse. Don't you think I might know that after all it's only 53 years since I built my first transistor radio. We were talking about laptops I never said anywhere that a modern appliance of any type with a metal case should have it's earth removed Link to comment Share on other sites More sharing options...
OllieDuff Posted October 6, 2013 Share Posted October 6, 2013 To conclude LOTS of modern equipment i.e. FX boxes small graphics E.T.C. have external power supplies with no earth connection.Indeed. And they're DESIGNED to not need an earth connection. They have the concentric squares symbol on them which means they're double insulated (class II). What people are taking issue with is disconnecting the mains earth on an appliance that is designed to require it. Take a computer with a standard metal chassis - the PSU has an IEC inlet and the chassis is bonded to the earth through the PSU body. If you lift the mains earth, the whole case can then float. And if a fault develops, the whole chassis can become live - a condition that the presence of the mains earth would prevent by blowing the fuse. Don't you think I might know that after all it's only 53 years since I built my first transistor radio. We were talking about laptops I never said anywhere that a modern appliance of any type with a metal case should have it's earth removed Hang on - if you remove one of the two mains connections on a doubly insulated device with no protective earth, you have an open circuit, surely? Feel free to connect me, but if the protective earth is not needed on a device that is factory fitted with a BS 1363 plug, then it's usually either not connected or the earth pin on the plug is sleeved with an insulating material. On that basis, all questions of should-I-remove-the-earth reduce to two possible cases: Case 1: the device is double insulated, so the protective earth is not connected, so removing it is safe. However, if the earth is not connected then removing the relevant pin will make no difference to earthing issues, so there's no affirmative reason to remove the earth (and if you cut off the earth, the device manufacturer will tell you to sod off should you ever need to claim on the warranty). Case 2: the device is Class I and should have a mains earth for safety reasons, so you shouldn't remove the earth. Or is this too simplistic? Link to comment Share on other sites More sharing options...
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