A connection from ground to earth should not only be looked upon as a source for hum loops. It has at least two other functions.
One is the safety function. The same wire that comes loose and can make contact to the case, can make contact to any other metal part, e. g. the outer ring of a connector. In a situation, where 230 V are present at the RCA connector, but no connection from ground to earth is provided, no fuse will blow. A person, who touches the RCA connector can be severely hurt or even killed. That is one reason, why all secondary voltages should be connected to earth with one end.
The second function of the ground-to-earth connection is that it stabilizes the ground reference, because virtual mass is added. Compare the mass of a ground trace or even plane on a PCB to the mass of the earth wiring in your house. Remember the analogy of electricity to water? Now imagine how easily the small trace or plane can be disturbed, and what it takes to disturb the earth wiring in your house. The nearer the ground voltage is to zero and the stabler it remains there, the better for the performance.
One is the safety function. The same wire that comes loose and can make contact to the case, can make contact to any other metal part, e. g. the outer ring of a connector. In a situation, where 230 V are present at the RCA connector, but no connection from ground to earth is provided, no fuse will blow. A person, who touches the RCA connector can be severely hurt or even killed. That is one reason, why all secondary voltages should be connected to earth with one end.
The second function of the ground-to-earth connection is that it stabilizes the ground reference, because virtual mass is added. Compare the mass of a ground trace or even plane on a PCB to the mass of the earth wiring in your house. Remember the analogy of electricity to water? Now imagine how easily the small trace or plane can be disturbed, and what it takes to disturb the earth wiring in your house. The nearer the ground voltage is to zero and the stabler it remains there, the better for the performance.
This is probably the millionth time someone says that in this thread but, please, do not tell people that ask for beginner's advice to design floating and non-grounded power supplies or systems. You are not aware of their skills and whether or not they'll make a system that is potentially very dangerous.
Despite all that's been said in this thread, I don't find proper grounding to be that much of a problem, that you'd need to leave the system floating.
Despite all that's been said in this thread, I don't find proper grounding to be that much of a problem, that you'd need to leave the system floating.
Hi guys
Remember though that if you do bring in what you are calling 'safety earth' into a double insulated, or non centre-tapped primary-side transformer, then any faults occurring on the mains can be taken into the secondary side of the transformer and that is not good. Be carefull !!!!
Cheers
Gareth
Remember though that if you do bring in what you are calling 'safety earth' into a double insulated, or non centre-tapped primary-side transformer, then any faults occurring on the mains can be taken into the secondary side of the transformer and that is not good. Be carefull !!!!
Cheers
Gareth
gareth said:
One must never modify a certified Double insulated device unless one have the skills, knowledge and equipment to prove that it still meets the double insulated standard.pacificblue said:
Adding a safety earth means that the equipment is not double-insulated anymore. Therefore it must not comply with the respective norms and regulation, but with the ones for safety-earthed equipment. The amplifier would have to be treated as if it was an entirely new design. If everything is then done correctly, the safety-earthed version is certainly an improvement.gareth[/i] [B]Remember though that if you do bring in what you are calling 'safety earth' into a double insulated said:
The use of a single-primary transformer does not exclude the use of a safety earth.
Which "faults occurring on the mains can be taken into the secondary side of the transformer" through a safety earth connection to the case? And what effect would they have?
Hi guys,
If your equipment is double insulated, classII, then any faults to earth on the suppliers side of your equipment, i.e. anywhere outside of your home, or outside of your equipment actually, can then be induced directly into the secondary side of your equipment bvecause you have added your own 'safety earth', as you call it.
I will try to draw something on Paint after I post this and I hope it will help you to understand better.
Basically Class II, by design, does not need an earth brought into it from outside, i.e your plug-top/socket.
The earth in Class II equipment is the centre-tap of the secondary in the transformer. So by adding a 'safety earth' you can 'open-up' your equipment to lightning strikes etc. You will see how when I post my drawing.....I hope!?!!?!!!
Cheers
Gareth
P.S. Drawing to follow......if I can get it to come out well!!!
P.P.S Sorry....The effects can be dramatic too! I will draw a basic diagram showing how peoples houses/commercial properties etc are connected together.
P.P.P.S. Have you ever wondered how sometimes when you have a power cut that not every house in your street has lost it's power?
If your equipment is double insulated, classII, then any faults to earth on the suppliers side of your equipment, i.e. anywhere outside of your home, or outside of your equipment actually, can then be induced directly into the secondary side of your equipment bvecause you have added your own 'safety earth', as you call it.
I will try to draw something on Paint after I post this and I hope it will help you to understand better.
Basically Class II, by design, does not need an earth brought into it from outside, i.e your plug-top/socket.
The earth in Class II equipment is the centre-tap of the secondary in the transformer. So by adding a 'safety earth' you can 'open-up' your equipment to lightning strikes etc. You will see how when I post my drawing.....I hope!?!!?!!!
Cheers
Gareth
P.S. Drawing to follow......if I can get it to come out well!!!
P.P.S Sorry....The effects can be dramatic too! I will draw a basic diagram showing how peoples houses/commercial properties etc are connected together.
P.P.P.S. Have you ever wondered how sometimes when you have a power cut that not every house in your street has lost it's power?
Quote,
"P.P.P.S. Have you ever wondered how sometimes when you have a power cut that not every house in your street has lost it's power?
Having worked for Norweb (not on the distribution side, but repairing the effects !! of these things) I have seen it all.
Had to argue the case for having our workshop as an "Earth free" zone. They just couldn't grasp the concepts 🙂
"P.P.P.S. Have you ever wondered how sometimes when you have a power cut that not every house in your street has lost it's power?
Having worked for Norweb (not on the distribution side, but repairing the effects !! of these things) I have seen it all.
Had to argue the case for having our workshop as an "Earth free" zone. They just couldn't grasp the concepts 🙂
In response to Mooly.......no earth, no fault.
Gareth.
P.S.
I was called out to a farmhouse once in the early hours of the morning. This was right out in the sticks, up in the Brecon Beacons. Anyway, we couldn't wotk out why all the metalwork around this farm was giving us a belt.
So, after a lot of head scratching in the rain we traced the fault back to a transformer up on a telegraph pole. What had happened was that the lightning had hit this tranny and reversed the polarity in it !!!!!!! We sent it off to Electrical forensics to confirm this and it was the case. That was pretty cool!
Sorry to go off track guys. I am going to draw up this diagram I mentioned now.
Gareth.
P.S.
I was called out to a farmhouse once in the early hours of the morning. This was right out in the sticks, up in the Brecon Beacons. Anyway, we couldn't wotk out why all the metalwork around this farm was giving us a belt.
So, after a lot of head scratching in the rain we traced the fault back to a transformer up on a telegraph pole. What had happened was that the lightning had hit this tranny and reversed the polarity in it !!!!!!! We sent it off to Electrical forensics to confirm this and it was the case. That was pretty cool!
Sorry to go off track guys. I am going to draw up this diagram I mentioned now.
Gareth,
What you are basically saying is that all Class-I (earthed)
equipment is unsafe ??????!
Please elaborate.
Klaas
What you are basically saying is that all Class-I (earthed)
equipment is unsafe ??????!
Please elaborate.
Klaas
In response to kvholio....no I am not saying that Class I is unsafe, I am saying that brimgimg an earth into ClassII equipment is basically...stupid.
The design of ClassII doesn't need a 'safety earth' as it is termed.
ClassI is designed to utilise 'safety earth' as part of it's design, Class II is not and by bringing in an earth you are 'linking' the centre-tap to any faults outside of the equipment straight onto the secondaries of the equipment concerned.
I need to get this drawing posted.
Cheers
Gareth.
P.S. If you have no earth, then you can't have a shock.
The design of ClassII doesn't need a 'safety earth' as it is termed.
ClassI is designed to utilise 'safety earth' as part of it's design, Class II is not and by bringing in an earth you are 'linking' the centre-tap to any faults outside of the equipment straight onto the secondaries of the equipment concerned.
I need to get this drawing posted.
Cheers
Gareth.
P.S. If you have no earth, then you can't have a shock.
Agreed.gareth said:
I don't see the difference between a Class-II converted to Class-I, and a Class-I component here.
A Class-I component can be designed with a direct connection between 0v/powersupply-gnd and safety-earth as well.
The only reason to use a disconnecting-network between powersupply-gnd and safety-earth in a Class-I device is to avoid a groundloop.
Klaas
gareth said:
Sorry? say what??
"reversed its polarity"??
Please explain how that is physically possible due to a lighting strike? I must be missing something in the translation here!
_-_-bear
Here is, where your confusion starts. The moment you connect a safety earth to any equipment it becomes Class I. If it was Class II before, it seizes to be that. Therefore the entire safety concept has to be revised.gareth said:
It is not recommendable to build Class II equipment at home without the adequate background knowledge.
The center-tap of the transformer secondary is usually ground not earth. Lightning strikes do not enter through the PE wire into equipment. Lightning does its damage through two effects. One is induction, the other is the so-called pace voltage. Pace voltage is not an issue within audio equipment, but the reason for the recommendation to maintain your feet close to each other, when you are out in the open, while there is lightning.gareth said:
So your house is floating a few meters above the ground in total isolation? Or do you have the entire floor and walls covered with thick rubber mats?gareth said:
Yes, please.bear said:
As I hinted at earlier I have seen (and repaired) many lightning damaged pieces of kit... mostly TV,VCR's etc and the "way" in which the equipment is damaged is surprising.
Often a TV with the copper print "lifted and vaporised" around the mains input and bridge would unbelievably work normally if this was repaired. Other items had no obvious damage, just countless "strange" semiconductor faults, leaky diodes, low gain transistors etc. Or a bridge rectifier thats missing, literally blown apart, replace and the sets fine.
If an aerial gets hit, that's a fairly direct route into the mains via "whatever" be it TV, VCR etc and that causes all the damage. Anything that happens to be plugged in. Surrounding houses too are quite possible affected as well. The phone system is another, I have seen a handset after it was literally blown apart, you would want to have had that up to your ear. If that's connected to an answering machine, that's another way in.
Often a TV with the copper print "lifted and vaporised" around the mains input and bridge would unbelievably work normally if this was repaired. Other items had no obvious damage, just countless "strange" semiconductor faults, leaky diodes, low gain transistors etc. Or a bridge rectifier thats missing, literally blown apart, replace and the sets fine.
If an aerial gets hit, that's a fairly direct route into the mains via "whatever" be it TV, VCR etc and that causes all the damage. Anything that happens to be plugged in. Surrounding houses too are quite possible affected as well. The phone system is another, I have seen a handset after it was literally blown apart, you would want to have had that up to your ear. If that's connected to an answering machine, that's another way in.
Here we go again....upsetting the ego's of DIYAudio. I seem to be getting pretty good at this. Maybe there are awards for the most annoying person on the site or something.
Anyway, where do i start?
The lightning strike.....yes, we (Western Power Distribution) found it hard to believe and as I said it took quite some time in the early hours of the morning to find the fault and that IS what it turned out to be. How it switched I do not know but it happened. As I previously said the metalwork of the entire farm (outbuildings and all) were giving off shocks and so we had to 'backtrack' down the supply network until we found the Tx on the telegraph pole. I suppose a couple of million/billion volts can do some weird things. Maybe thats where I get it from.
Class II casework is not connected to the incoming supply and utilises the centre-tap. Thus bringing in your 'safety earth', or plain simple earth, counteracts the design completely.
And obviously (DOH!) if you do not have earth then you cannot have a shock. Take for example the guys who work on the over-head supply lines, the ones on the platforms that hang off of 440,000v pylons whilst they are live. These guys are at the same potential voltage as the supply lines. Yes...at 440,000v !!!!!! They do not switch off these lines for maintenance and so it is made sure that THEY ARE NOT EARTHED otherwise they will feel the power of 440KV flowing through them, so thanks for the sarcasm but......if you don't have an earth then you cannot have a shock. Hence Class II design.
I used lightning strikes as the first example that came to mind, earth faults from your neighbour (for example) can, under certain circumstances, find it's way into your system.
Anyway, where do i start?
The lightning strike.....yes, we (Western Power Distribution) found it hard to believe and as I said it took quite some time in the early hours of the morning to find the fault and that IS what it turned out to be. How it switched I do not know but it happened. As I previously said the metalwork of the entire farm (outbuildings and all) were giving off shocks and so we had to 'backtrack' down the supply network until we found the Tx on the telegraph pole. I suppose a couple of million/billion volts can do some weird things. Maybe thats where I get it from.
Class II casework is not connected to the incoming supply and utilises the centre-tap. Thus bringing in your 'safety earth', or plain simple earth, counteracts the design completely.
And obviously (DOH!) if you do not have earth then you cannot have a shock. Take for example the guys who work on the over-head supply lines, the ones on the platforms that hang off of 440,000v pylons whilst they are live. These guys are at the same potential voltage as the supply lines. Yes...at 440,000v !!!!!! They do not switch off these lines for maintenance and so it is made sure that THEY ARE NOT EARTHED otherwise they will feel the power of 440KV flowing through them, so thanks for the sarcasm but......if you don't have an earth then you cannot have a shock. Hence Class II design.
I used lightning strikes as the first example that came to mind, earth faults from your neighbour (for example) can, under certain circumstances, find it's way into your system.
Now you're on the right track.gareth said:
You mean, if you are not connected to earth, e. g. by simply standing on the floor without isolation. Somebody, who opens up a Class II device and touches the transformers primary, will get a shock no different from the one he gets from Class I equipment.gareth said:
Class II equipment does not work by taking earth out of the equation. It only makes sure that mains are insulated from the touch.gareth said:
Those supply line guys do it the other way round. They try to make sure that they cannot touch earth, while working on the lines. Of course they have the problem to get there, that is why they are usually wrapped into protective clothing nevertheless.
Class I equipment ensures that you cannot touch line and earth potential at the same time, by blowing the fuses, when there is a short to the case.
You are aware that without earth our entire electricity distribution system would not work?
pacificblue said:
How come? No appreciable dist. current flows thru the earth. But without it there wouldn't really be a common reference.
The power companies and the distribution companies rely on balancing the load across the three phases of the supply.infinia said:
But inevitably there is always some unbalance. The unbalance could be hourly or by the minute or second or even cycle to cycle (~10ms).
The difference in phase loading will force the "earth" / "ground" / "soil" / "rock" / "water" to act as the return route for the power/current.