So in this case, if I keep the case plastic, signal ground's only connection to the PSU would be through the phantom power supply's negative supply?
A low voltage transformer with a split bobbin should be fairly safe provided mains wiring is kept well away from the secondaries. The idea is that under any conceivable fault conditions there is no way the mains can connect to the rest of the circuit e.g. any wire comes loose, any component goes short circuit, any insulator breaks down. That is why double-insulation is just that: two separate things must break before there is any danger, and each of them is of a quality that failure is very unlikely.
I might be prepared to take a few minor risks on DIY test equipment or amateur radio gear, but anything 'domestic' like an amp or preamp I feel should be above reproach where safety is concerned. For me that means proper safety grounding.
I might be prepared to take a few minor risks on DIY test equipment or amateur radio gear, but anything 'domestic' like an amp or preamp I feel should be above reproach where safety is concerned. For me that means proper safety grounding.
yes!!!!
all exposed conductive parts must be connected to Safety Earth
we are not competent to design, build, test and guarantee double insulated mains equipment. Therefore we must connect to PE, we have no choice.
if the mains input hot/Live breaks loose and touches some other low voltage part then potentially the whole device and all it's interconnects become live. If there is no PE to Safety Earth to exposed parts connection then the fuse will not blow. The equipment will appear to have turned itself off and the operator goes across to touch/fiddle/die.
To me and Davenport and DF and many others find this so obvious that we don't plod along ignorantly and put our families at risk.
Yet we see hundreds of Members who do exactly that.
What can the Forum do to protect those that just plod along?
Serious disscussion invited. New Thread?
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I respectfully disagree Andrew.
Please don't misinterpret my comment. The chassis should be grounded for safety. The input jacks need not be. They can be isolated from the chassis, with the result being that the entire secondary side of the mains transformer can be floating w.r.t. ground. You can't get a shock by touching this RCA jack. If your mains wiring is coming anywhere close to your input or output connections then you have a lot more serious safety considerations to deal with than what grounding will save you from.
If the secondary side is left floating, then if you touch it, it takes on your potential, so there is no potential difference to create shock. No possibility of shock. Of course if you stick two fingers/hands in there at different points, then all bets are off... no amount of grounding can save you from yourself. If you close the conduction loop by grounding any part of the secondary side, then you can get a shock by touching only one conductor (assuming your body is grounded elsewhere... an assumption you must always make for safety).
I really would like to hear why you think I am "seriously in error".
How can it break loose and touch some low voltage part? That is virtually impossible if you give your wiring a little thought. Your mains connections should be made far away from signal parts for many reasons, including reducing hum and noise from the line, but mostly for safety. The leads connecting the power transformer to the line should be short enough to not be able to reach any low voltage part even if they break loose. You should ensure good mechanical connection (wire through eyelet then twisted, etc.) before soldering. Don't just solder the wire to the side of the terminal.AndrewT said:
Grounding-everything-in-sight must not be used as a crutch that will save you every time. One day it won't. Never give yourself a false sense of security or you will end up missing or ignoring other important safety issues.
I am not sufficiently expert in hazard analysis to guarantee safety in the absence of a piece of grounded metal between me and mains. I therefore try to ensure that wires don't come loose, and ensure that a fuse blows if they do and then touch something they shouldn't. For me this is easier to do than full double-insulation standards.
Can you guarantee the insulation integrity of your mains transformer? If so, that only counts as one insulating barrier, so you need at least one more between the secondary and the user. OK if the circuit itself is sealed inside a plastic box with no external connections, or only via mains-rated capacitors, but no good if you have a signal ground coming out as that connects to the transformer secondary.
You need at least two barriers, or at least one barrier plus grounding. You seem to want to get away with just one barrier and no grounding.
Can you guarantee the insulation integrity of your mains transformer? If so, that only counts as one insulating barrier, so you need at least one more between the secondary and the user. OK if the circuit itself is sealed inside a plastic box with no external connections, or only via mains-rated capacitors, but no good if you have a signal ground coming out as that connects to the transformer secondary.
You need at least two barriers, or at least one barrier plus grounding. You seem to want to get away with just one barrier and no grounding.
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