Hello all and Happy New Year.
To earth or not to earth power amp chassis?
That is the question.
The most common way to implement safety ground for power amps is to use a ground lifter consisting of antiparallel diodes and a resistor.
On bonsai's brilliant writeup ground loops he says;
In a few countries in europe there are no grounded sockets in living areas.
There are only grounded sockets in wet rooms like bathrooms, kitchens, basements and outside.
So my question to all your knowledgeable people here.
What is the best practise with regards to grounding ( not grounding ? ) the chassis of a power amplifier that is connected to the net without a grounded socket ( no live, neutral and ground, only 2 live connections )
thank you
rebone
To earth or not to earth power amp chassis?
That is the question.
The most common way to implement safety ground for power amps is to use a ground lifter consisting of antiparallel diodes and a resistor.
On bonsai's brilliant writeup ground loops he says;
In a few countries in europe there are no grounded sockets in living areas.
There are only grounded sockets in wet rooms like bathrooms, kitchens, basements and outside.
So my question to all your knowledgeable people here.
What is the best practise with regards to grounding ( not grounding ? ) the chassis of a power amplifier that is connected to the net without a grounded socket ( no live, neutral and ground, only 2 live connections )
thank you
rebone
Hello rebone, are you sure about the sockets not having a ground connection? What does the electrical wiring code say about safety grounding in your country?
That’s probably the best place to start here.
I would say if equipment is double insulated then you don’t need an earth connection BUT double insulation comes with heavy certification standards and is IMV beyond the scope of DIY builders - me included.
That’s probably the best place to start here.
I would say if equipment is double insulated then you don’t need an earth connection BUT double insulation comes with heavy certification standards and is IMV beyond the scope of DIY builders - me included.
all depends if the transformer of your amp
is well insulated between primary and secondary meeting the double insulation standard. then no ground connection needed. this is mostly the case for consumer Japanese amps (kenwood yamaha, pioneer, jvc, sono etc) they have a metal case, the transformer is bolted to the case and the mains cable has no ground connector. in General they have EI or R core transformer that have good isolation from primary to secondary. never seen one with toroidal.
insulation of toroidal is more difficult and capacity between primary and seco dare can lead to high voltage at secondary.
had a new toroidal 150va and touching the secondary wire I could feel a bit of current.... maybe it was 1mA and some 50V to ground
the rcd can safe you life if transformer isolation fails but if at the same time the rcd fails you are dead.
if you have sockets without ground wire at your home first easier step is to put rcd everywhere
in Germany before the 80s it was possible to bridge the earth pin of the socket with the neutral.... but if the neutral gets some voltage (becomes live) then it is worser than leaving ungrounded
so best is rcd + ground in plug + grounded case
I decline any responsibility if someone is applying what I wrote.
this text is only for technical information
is well insulated between primary and secondary meeting the double insulation standard. then no ground connection needed. this is mostly the case for consumer Japanese amps (kenwood yamaha, pioneer, jvc, sono etc) they have a metal case, the transformer is bolted to the case and the mains cable has no ground connector. in General they have EI or R core transformer that have good isolation from primary to secondary. never seen one with toroidal.
insulation of toroidal is more difficult and capacity between primary and seco dare can lead to high voltage at secondary.
had a new toroidal 150va and touching the secondary wire I could feel a bit of current.... maybe it was 1mA and some 50V to ground
the rcd can safe you life if transformer isolation fails but if at the same time the rcd fails you are dead.
if you have sockets without ground wire at your home first easier step is to put rcd everywhere
in Germany before the 80s it was possible to bridge the earth pin of the socket with the neutral.... but if the neutral gets some voltage (becomes live) then it is worser than leaving ungrounded
so best is rcd + ground in plug + grounded case
I decline any responsibility if someone is applying what I wrote.
this text is only for technical information
Unfortunately there is always the possibility that the chassis gets mains on it if there is a wiring problem inside the amp or the transformer fails so I always earth(ground) the chassis.
thanks for your reply Bonsai
If you look at he socket there are only 2 plug holes with live wires, the third one is a screw.
I don't know about rules and regulations but the praxis is to have earthed plugs in rooms where you can touch water pipes ... etc.
Double insulation is beyond me too.
If you look at he socket there are only 2 plug holes with live wires, the third one is a screw.
I don't know about rules and regulations but the praxis is to have earthed plugs in rooms where you can touch water pipes ... etc.
Double insulation is beyond me too.
Thanks for your reply marconi.
There is a metal shield between primary and secondary on my donut, don't know if that is sufficient?
I would have to do some rewiring of house to get earth to the amplifier point.
There is a metal shield between primary and secondary on my donut, don't know if that is sufficient?
I would have to do some rewiring of house to get earth to the amplifier point.
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In many EU countries unearthed sockets are not allowed in new installations. However older installations with unearthed sockets do not need to be upgraded and it is possible to buy e.g. unearthed extension cords. But new unearthed sockets have deeper recess than the one in your picture. Deeper recess makes it more difficult to get electric shock from partially fitted plugs.
Using amplifiers with earthed metal chassis in unearthed sockets is less safe but in practice only option as safe (or certified) double insulation is not for diy.
Using amplifiers with earthed metal chassis in unearthed sockets is less safe but in practice only option as safe (or certified) double insulation is not for diy.
My toroidal trafo is resting on 2 rubber sheets and the bolt goes through epoxy in the middle, son no part of the trafo is touching the chassis.
... apart from the wire from the shielding between primary and secondary.
... apart from the wire from the shielding between primary and secondary.
From a safety point of view, IMHO the best thing is a Residual Current Circuit Breaker.
This can be in the distribution board by your electricity meter, or it can be between your wall socket and your amp/system.
Beyond that, the chassis can be 'grounded' in various ways. From a safety point of view, you'd like the fuse to blow (or the RCCB to trip) if the chassis became close enough to 'live' to be dangerous. That may not be the same as grounding it for small signals or DC or high frequencies.
Your input signal returns may be different from mains ground. Your speaker 'black terminals' could be different again.
I have worked in high power labs where instruments often have their chassis 'floating'. It is a complex subject and I'd suggest the simplest way for safety is to have the amp chassis grounded and have an RCCB. From a signal and ground loop POV having everything else double insulated may keep it simple.
I have an optical out from my PC audio which avoids grounding that signal. All our CD players are double insulated.
The only other mains ground point is my Tektronix scope.
The Cambridge A3i in bits on my desk is double insulated. It's not that onerous for a manufactured product of this era to have 'double insulated' status.
If you're going to spend time with the lid off, a plastic cover over the mains area of the PCB is an idea. I sometimes use a thickish piece of mylar film.
If there's one thing more complex and hard to understand than the physics/electronics of grounding, it's the legislation.
This can be in the distribution board by your electricity meter, or it can be between your wall socket and your amp/system.
Beyond that, the chassis can be 'grounded' in various ways. From a safety point of view, you'd like the fuse to blow (or the RCCB to trip) if the chassis became close enough to 'live' to be dangerous. That may not be the same as grounding it for small signals or DC or high frequencies.
Your input signal returns may be different from mains ground. Your speaker 'black terminals' could be different again.
I have worked in high power labs where instruments often have their chassis 'floating'. It is a complex subject and I'd suggest the simplest way for safety is to have the amp chassis grounded and have an RCCB. From a signal and ground loop POV having everything else double insulated may keep it simple.
I have an optical out from my PC audio which avoids grounding that signal. All our CD players are double insulated.
The only other mains ground point is my Tektronix scope.
The Cambridge A3i in bits on my desk is double insulated. It's not that onerous for a manufactured product of this era to have 'double insulated' status.
If you're going to spend time with the lid off, a plastic cover over the mains area of the PCB is an idea. I sometimes use a thickish piece of mylar film.
If there's one thing more complex and hard to understand than the physics/electronics of grounding, it's the legislation.
Thanks again, this is definitely not my area of expertise.
We do have a RCCB with 30mA sensitivity / 40A in the distribution board.
Kitchen, bathroom, outside and some other sockets are grounded.
I have found a nice RCCB from Schneider A9Z20216 with a sensitivity of 10mA / 16A.
This one could be between my wall socket and my amp/system (soft start case).
But, the RCCD unit I think is something we used to call "earth fault breaker".
Will a RCCD work without an earthed socket?
We seem to have a system here where one of the two wires (I assume neutral) are at the same potential as earth.
The other wire (I assume live) has 220V to the other wire and to earth.
The plugs here are not directional.
Sorry about all this. I have had floating chassis on power amps for years and no one got hurt yet, but this time I would like to do it right.
Picture of an earthed socket below.
RCCD's work by sensing the difference in current between live and neutral, ie detecting leakage from the circuit to anywhere (in practice to earth), so you don't need 3-prong sockets for it to work.
In Australia, the Earth and Neutral circuits are collectively connected at the meter box (main switchboard). I know other countries do this, but have no idea which.
I would say a lot of consumer style multi-channel amplifiers, although they are supposed to be 'double insulated' are in reality only single insulated. I really don't understand how they pass type approval. The fundamental flaw is that they often clamp mains wiring directly onto the left hand side of the metal chassis using cable ties. In that case there is only 1 layer of insulation between the live conductor and the user. In the event of a single fault in that insulation, the user is exposed to mains voltages.
Your power transformer has single insulated wires internally and the power wires to it. These are "basic insulation", so exposed metalwork that they might contact has to be earthed or protected by a RCCD. 30mA is OK, 10mA is only required in places with water around.
I agree that most amplifiers are NOT double or reinforced insulation. Clamping a two or three core power cable, that has two correctly rated insulation layers is fine.
I agree that most amplifiers are NOT double or reinforced insulation. Clamping a two or three core power cable, that has two correctly rated insulation layers is fine.
Thanks for your reply Mark
So if I were to install a RCCB with a sensitivity of 10mA on the 2-prong socket for the stereo unit, that would be safer than relying on the 30mA unit in the distribution board?
Is a RCCB sufficient or would you still recommend to get an earthed socket.
If I were to only use RCCD, would you recommend to install safety ground to chassis like this
or would you recommend to leave the chassis unearthed.
I know that there are a lot of legalities regarding this but I would appreciate your opinion.
I see no purpose to the above if the chassis does not have an earth connection
On those R core transformers, I have yet to see one with any regulatory approvals, prove me wrong.
On those R core transformers, I have yet to see one with any regulatory approvals, prove me wrong.
I know that an earthed socket and safety earth in the amp is the standard way for safety.
At the moment I am searching for an alternative as at the moment I only have a 2-prong no earth socket where the stero is.
At the moment I am searching for an alternative as at the moment I only have a 2-prong no earth socket where the stero is.