Safty and grounding

[TEK]

Hi

Jon and I had a discussion about grounding and safty a while back. This is a thread for discussions and questions regarding safty and grounding.
Hopfully we will be able to nail down a few basic conclutions here that can be used as a reference point when building NC500 based amps.

Conclutions:
- Recommended solution:
Use balanced input only (not RCA).
Connect signal ground (=the shield of the balanced cabel) to chassi as close to the balanced input as possible (ref 1, page 9)
Amplifier must be build according to double insulation safety standards or be connect to safty earth.
- If using RCA inputs, alternativ 1: floating chassis and bounded RCA inputs (ref 2, section 12.3.2)
- If using RCA inputs, alternativ 2: grounded chassis and semi-floating RCA inputs(ref 2, section 12.3.3)


Safty standards:
Double insulation safety standard (referenced to from several hypex documents)
[Need to fill inn information about what the standard actually says]

Safty eartch (grounding) in Norwegian houses:
- In new houses all wall sockets are connected to ground
- In old houses only wall sockets in wet areas (bathroom, kitchen and so on) are grounded. Non-grounded wall sockets will not allow usage of grounded plugs. In dry areas, where there should be no danger of getting in contact with ground, wall sockets are not grounded. These wall sockets will allow the usage of grounded plugs.

Safty eartch (grounding) in Candadian houses:
[I have no clue - please fill inn if there is anything to say about this]

Safty eartch (grounding) in American houses:
[I have no clue - please fill inn if there is anything to say about this]

Reference litterature:
Hypex - wiring diagram for balanced and unbalanced
Hypex - pin 1 appnote
Bruno Putzeys, The G Word, or How to Get Your Audio off the Ground
NC400 datasheet, read page 12, 13, 14
Jon's NC400 assembly reference
Jensen transformers, Ground Loops: The rest of the Story

[TEK]

As you can see, from what I have read the chassie can be connected to safty eartch when using XLR input and that should not cause hum issues.
As I think that is easier and safer than not using safty earth - especially since I'm very unsure what it means that someting is build according to "class II standard" - I'm planning on using safty earth connected to the chassie.
From what I have read up, the important part is that the balanced signal is connected to the chassie as close/direct as possible.

If I have misunderstood something I would really like some comment about that.

[benthe8track]

That's how I did mine as well. I all balanced and used techflex as the 2nd shielding, worked well.

[TEK]

That's how I did mine as well. I all balanced and used techflex as the 2nd shielding, worked well.

So you did go for a class II construction without safty earth.
BTW, found this as a short intro to the classed: https://en.m.wikipedia.org/wiki/Appliance_classes

I looked at that and I was wondering if techflex actually is thick/unconductive enough for 16A 250V?

Many of those (that I think of) is not air tight and I would not dear holding a bear wire with just that as isolation. Do anyone know if there are requirements to the thickness of the second layer of insulation?

I see that techflex is a brand. What type did you use?

[TEK]

I think that I would like my builds to have saftey earth, and then I will try my best to build it accordingly to class II. Better safe than sorry...
What I'm not sure about is if it is nessesarly to use a resistor between safty earth and the casing when using only balanced connections - or if that technic only is nessesarly when you have rca connections as well.

[benthe8track]

So you did go for a class II construction without safty earth.
BTW, found this as a short intro to the classed: https://en.m.wikipedia.org/wiki/Appliance_classes

I looked at that and I was wondering if techflex actually is thick/unconductive enough for 16A 250V?

Many of those (that I think of) is not air tight and I would not dear holding a bear wire with just that as isolation. Do anyone know if there are requirements to the thickness of the second layer of insulation?

I see that techflex is a brand. What type did you use?

Well the techflex closes up pretty tight when applied. I used some "carbon fiber" colored techflex I got off ebay back in my car audio days. The Risk Assessment (carry over from the day job) I did went something like this:
Could something abrade the techflex and wire shielding? No, nothing inside moves.
What is the likelihood of me touching the case if the house got hit by lightning? Low.
Does this method eliminate any potential ground loop issues down the road. Yes.

Also, I made the case essentially explosion proof.

[TEK]

I'm quite sure your construction is safe enough for your usage ;-)
I'm a bit curious not just regarding the practial safty in my own home, but also according to what is needed to furfill any safty regulations. Stuff that I do have some issues finding out is for example what requriments there is to that second protection layer.

If you read page 2 in the SMPS1200A700 manual you can see some hint of the "Class 2 Safety Directive" (I suspect that to be something else than the "double insulation safety standards").
It says that there is something about 6mm clearance from the bottom side of the PCB to the chassie. Or insulation with a minium thickness of 0.4mm (instead of 6mm clearance).

[TEK]

I have started to mount together my SMPS1200, NC500 and converter board to test a bit.
Anyone know what fuse that would be right to use for the power intake box?

[TEK]

Anyone know if the +21V output from the SMPS have to be protected as if it was a high voltage output? (double isolation, mouting away from the chassie and so on)?