[Bubbleboy76]

Hypex recommends earthing the chassis from the xlr-earth. So the chassis should not be un-earthed.

[James Romeyn]

Hypex recommends earthing the chassis from the xlr-earth. So the chassis should not be un-earthed.

Please correct as necessary.  The "earth" you describe is not technically "earth."  Nothing necessarily guarantees the audio source at the XLR connects to earth.  "Earth" describes 12AWG solid core copper in the 3rd receptacle of the wall outlet directly shorted to a copper pipe 3' or 4' into the earth. 

In the case you describe, the chassis shorts to the 0V present at the audio output of the source, which nothing guarantees connects to "earth."  The best and most conclusive example is battery operated preamp or other source with variable output.  Such source has no "earth."  It may be common error to confuse a 0V audio signal reference with "earth."  The two may or may not necessarily be the same. 

Another example: Ncore input is open.  Ncore is not earthed. 

That is the whole point with shorting the actual real "earth" in the mains 3rd conductor to the chassis.  Whenever mains voltage is present, Ncore chassis is earthed.  Obviously if the mains source is not up to current code, all bets off.   

[Julf]

Indeed, one would think risk increases of electrical shock if the case is not earthed.

Are you familiar with IEC Class II principles?

I was surprised to read Bruno's instructions that unearthed chassis meets electrical wiring code.

"A Class II or double insulated electrical appliance is one which has been designed in such a way that it does not require a safety connection to electrical earth (ground)."

I ignored his advice to not earth the chassis.  I earthed chassis of all eight NC400 I built.

And that is the safe thing to do if you aren't comfortable with Class II.

I presume Ncore would not contaminate other components in reasonable proximity, but I also suspect external sources could contaminate Ncore, and that earthed chassis minimizes contamination in both directions.

What "contamination" would be affected by safety earth?

From a signal point of view, not connecting mains earth to the chassis is theoretically better.

Possibly, Bruno clearly knows every potential current flow fault, and NC400 and all Hypex power supplies would instantly sense such fault (including +V to chassis) and immediately default to error mode, opening (stopping) the mains current flow.  BTW, the protection I describe above may be lacking with non-Hypex power supply.

No. Bruno assumes following Class II rules.

But this still does not address the potential of outside sources degrading and/or contaminating Ncore, and potential for earthed chassis to minimize such. 

And how would connecting the chassis to mains earth minimize the "degradation" or "contamination"?

If unearthed chassis only improves audio performance with absolutely no increased risk of danger and no increased risk of contamination either direction, then there is every reason to follow Bruno's advice.  To the same degree I suspect the first item is true I suspect the last two are not.

They are if you follow Class II guidelines. If you don't, please connect mains earth to the chassis for safety reasons - as Bruno has stated. To quote the nc400 data sheet: "No safety earth connection was depicted. This is entirely acceptable if class II construction is used throughout. Otherwise, connect the safety earth."

[Julf]

Hypex recommends earthing the chassis from the xlr-earth. So the chassis should not be un-earthed.

Xlr "earth" (as in the sheath of the coax cable) is not the same thing as mains earth (centre pin of IEC connector).

[Julf]

"Earth" describes 12AWG solid core copper in the 3rd receptacle of the wall outlet directly shorted to a copper pipe 3' or 4' into the earth.

"Mains earth" describes whatever mains safety earth your local wiring code prescribes. Specifics vary from country to country.

[srb]

"Earth" describes 12AWG solid core copper in the 3rd receptacle of the wall outlet directly shorted to a copper pipe 3' or 4' into the earth.

As Julf points out, requirements vary by country, county, city, etc., but in the U.S., if not superceded by local codes, the NEC requirements are two 1/2"D X 8 ft. solid copper ground rods (or 5/8"D X 8 ft. if copper plated) spaced 6 feet apart.

The term "rod" denotes solid construction and hollow pipe or tubing is not permitted.

Steve

[James Romeyn]

Yes, I typed "pipe" while thinking "rod."

Would someone please describe Class II specifically related only to NC400? 

Reading between the lines it appears that shorting the chassis and input neutral conductor shields Ncore equal to earthing the chassis? 

[AluminatiSound]

Man i am getting excited to start this project. Did a rough size mock up but will start drawing models up at the shop next week. The case will be a two piece design, a hollow out (machined out slab) box and a 1/2" cover.

Probably anodize the box clear and the cover will be black

Matt

[Julf]

Would someone please describe Class II specifically related only to NC400?

There is noting in the class II rules that relate specifically to the nc400, and the nc400 has no special requirements in that regard. Class II is class II.

Here is what Bruno commented on the matter on diyaudio:

IMNSHO the word "ground" should be forcefully removed from the school curriculum. The conflation of "chassis potential", "earth potential", "power supply return" and "reference potential" into that one little sneaky cowardly word "ground" is the source of an absolutely incredible array of engineering problems the world over. Conversely, the simple act of not using the same galvanically connected network for both reference potential and any combination of the other three solves all problems. Chassis, earth and PSU null may be interconnected in any way you like provided that actual signals are accompanied by another wire carrying the reference potential of the source. The receiver, of course, should be capable of subtracting the voltages between the two wires, not attempt to take a shortcut by forcing one of the two to its own "ground" (or to try and force its own "ground" to follow the potential of the reference wire).

Class I equipment needs direct earthing of the chassis for safety, class II equipment does not. However, in the latter case you may not use earthed mains inlets. You may have noticed that mass market consumer audio gear has class II wiring and a 2-prong mains cord. This is because unbalanced connections simply do not mix easily with earthing.

If you cannot construct per class II, floating the secondary ground is a commonly used and very bad practice. Very bad because it requires star connections which are a source of HF problems. It is much better to use a differential input to float the reference terminal ie the RCA shell and sense between the shell and center pin without making a direct connection to chassis or any other of the irrelevant "grounds". One would place a cap and perhaps a resistor to chassis to limit the voltage between the two and stop the connection from becoming an antenna.

That way the differential input acts like an input transformer: only the voltage between two input pins matters, not the voltage with respect to whatever one may think is "ground". There is always an easy solution that does not require fancy floating schemes if you have a differential input at your disposal. There is neither a simpler nor a better solution than the one already in place in the UcD modules. The only thing we can do is write a very long and detailed document explaining the operation of differential inputs. Trust me, once the penny drops you'll bang your head and say "if only I knew it was that obvious". One thing you're guaranteed to do, for instance, is immediately adopt the scheme on the right hand side of the wiring application note. This is much better than any floating secondary or differential RCA connection you can dream of.

[James Romeyn]

What about NC400 design makes it appropriate to Class II?

There are only 2-conductors on the mains cord of my Pioneer receiver and Sony CDP.  Does that necessarily mean the chassis is not earthed?  (I will test with a meter latter.)  They are both as mass market as exists.  If yes, that would apparently answer the question of relative safety. 

But does it also not mean that some internal error could possibly result in positive voltage on the chassis?  Voltage that would, if the chassis was earthed, cause internal fuse to open and/or external circuit breaker to open?

I've been shocked touching more than one old tube amp, hi-fi and music instrument.  Last time was a couple years ago with a 60s Gibson my luthier owns.  I've only been to hundreds of fires caused by faulty mains-connected appliances.   

[Julf]

What about NC400 design makes it appropriate to Class II?

I am not sure I understand your question. Bruno prefers not to have mains safety earth connected (and I agree with him). Not having mains safety earth connected means the design has to comply with Class II rules.

To recap: Class I appliances have the chassis connected to mains safety earth - and thus, as you say, protect against voltage somehow being shorted to the chassis by causing the fuse or circuit breaker to operate. Class II is appliances that don't have mains safety earth connected to the chassis, and that therefore must ensure safety by double insulation.

There are only 2-conductors on the mains cord of my Pioneer receiver and Sony CDP.  Does that necessarily mean the chassis is not earthed?  (I will test with a meter latter.)

If there is no 3rd conductor (and thus no mains safety earth connection) in the mains cord, how could the chassis be earthed to mains safety earth?

Appliances with a 2-pin mains connector are Class II devices and have to comply with double insulation rules. In Europe there is a special symbol for that:

.

Does your receiver or CD player have that symbol?

They are both as mass market as exists.  If yes, that would apparently answer the question of relative safety.

It really doesn't have much to do with mass market or not. Either the chassis is connected to mains safety earth (Class I) or the construction has to be doubly insulated (Class II).

But does it also not mean that some internal error could possibly result in positive voltage on the chassis?  Voltage that would, if the chassis was earthed, cause internal fuse to open and/or external circuit breaker to open?

Yes. That is why you need double insulation.

I've been shocked touching more than one old tube amp, hi-fi and music instrument.  Last time was a couple years ago with a 60s Gibson my luthier owns.

If you think that is bad, wait until your mouth touches a microphone that has the metal shell at mains voltage...

[James Romeyn]

I seem to remember Roy Buchanan's amp had some lively stray voltages too. 

I guess I'm a believer now.  Never thought I'd be convinced to not earth the chassis but here I am.  Wish I had one of my NC400 here to audition with the earth lifted.

Years ago I'd often employ 3-pin to 2-pin mains adapter to lift component earth.  This would often improve sound quality, sometimes very dramatically.  In some cases similar benefit resulted by inverting the mains.  In later years adapters were polarized.  In such case I trimmed the neutral blade to the same size as the Line blade to allow it to invert.   

One thing apparently worth taking from this: if the component is not double insulated and is designed Class I, in such case risk increases of accidental shock by lifting the earth with an adapter or any other means. 

[Julf]

Years ago I'd often employ 3-pin to 2-pin mains adapter to lift component earth.

Just don't tell your insurance company

One thing apparently worth taking from this: if the component is not double insulated and is designed Class I, in such case risk increases of accidental shock by lifting the earth with an adapter or any other means.

Absolutely. So unless you really know what you are doing and are familiar with Class II designs, I suggest connecting the mains safety earth.

[James Romeyn]

Well, we're back to: What is necessary to know to safely wire NC400 Class II? 

Yeah, I considered legal risk relative to the adapters as I typed.  I felt my risk was somewhat less than a self-described "civil servant" posting YT video of himself riding about 160mph on FL freeways on "test ride" of 2012 Ducati Superbike (actual top end potential well over 160...the video included him riding up to the dealer to get his bike for his "test ride").  Frankly I've not employed such adapter for years.

[Julf]

Well, we're back to: What is necessary to know to safely wire NC400 Class II?

There is no simple answer.

I guess the only formally proper, safe and correct answer is "IEC standard 61140", where it is specified that you need "two layers of insulation or reinforced insulation on the equipment chassis". The IEC definitions for those are:

3.10.3
double insulation
insulation comprising both basic insulation and supplementary insulation
[IEV 195-06-08]

3.10.4
reinforced insulation
insulation of hazardous-live-parts which provides a degree of protection against electric shock
equivalent to double insulation
[IEV 195-06-09]

Basically you have to make sure all the circuits are sufficiently isolated from the case (and that means not connecting the nc400 base plate to the case).

My personal answer would be "if you have to ask, don't even think about it"

I felt my risk was somewhat less than a self-described "civil servant" posting YT video of himself riding about 160mph on FL freeways on "test ride" of 2012 Ducati Superbike (actual top end potential well over 160...the video included him riding up to the dealer to get his bike for his "test ride").

Did he at least work for the Department of Transportation?

[James Romeyn]

The man in the video described himself as a "fire fighter" or something similar.

Around 2000 I attended a medical training session at San Francisco's Presidio, where the SFFD medical division had offices.  I read the strangest article of my entire career on a bulletin board at that time.  This article was written by a professional medical training specialist.  The gist of the article (I wish so badly I had a copy) was that no ambulance ever saved any life that could not have been saved by a station wagon.  All I know is that in about 28 years of doing that kind of work, the primary goal of first responders is to transport the patient away from their current location to nearby available hospital.  I have no idea if the article was accurate or not but I can't say I have any personal evidence to the contrary. 

 

[Julf]

All I know is that in about 28 years of doing that kind of work, the primary goal of first responders is to transport the patient away from their current location to nearby available hospital.

Interesting question - and I have absolutely no clue, my only experience on the topic is from the military, and there the circumstances are somewhat different. But I would imagine the expertise/knowledge/experience of first responders is an important factor - you still need to know how to stabilize the patient and not cause additional damage.

[medium jim]

The man in the video described himself as a "fire fighter" or something similar.

Around 2000 I attended a medical training session at San Francisco's Presidio, where the SFFD medical division had offices.  I read the strangest article of my entire career on a bulletin board at that time.  This article was written by a professional medical training specialist.  The gist of the article (I wish so badly I had a copy) was that no ambulance ever saved any life that could not have been saved by a station wagon.  All I know is that in about 28 years of doing that kind of work, the primary goal of first responders is to transport the patient away from their current location to nearby available hospital.  I have no idea if the article was accurate or not but I can't say I have any personal evidence to the contrary. 

 

I can guarantee it is not true....as Julf said, the initial thing to do is to stabilize, then transport....the technology available to the Paramedics today is amazing, just ask my older brother who was a Paramedic before working his way up to Engineer (he had a career ending injury before he made Captain).

Jim

[jtwrace]

This is a thread for Hypex questions and answers. 

[Julf]

This is a thread for Hypex questions and answers.

Noted. So the message is "if you are comfortable with Class II design rules, leave mains safety earth unconnected. If not , connect mains safety earth to chassis - or you might just end up testing the ability of your local First Responders and Ambulance Crews."