Telescoping safety earth?

[abbey road d enfer]

Is the term "telescoping" correct here. Ime it applies to overlapping but not connecting cable screens.

I don't know if it's correct or not. I haven't seen a definitive answer to the question.

But here the question seems to be single cables going to a "Star Point" Vs daisy chaining PEC connections ?

Correct. It shows that, with a little goodwill, one can overcome the language barrier.

 

[sahib]

Correct. "Consisting in" is a malapropism based on french syntax.

Yes, they do.

It is still difficult to comment in the absence of how you intend to execute the design of the final instrument using these four individual devices.

However, I am assuming that you are housing all of them in a single case, and using the power amp IEC as the mains input to the entire system. I am also assuming that you have (no doubt) also solved all of the mains, low voltage and signal wiring issues within the design.

If so, then there would be no need to provide individual, hard wired safety earth to preamp, sound module and keyboard cases as long as good electrical bonding between the main case and the individual device cases is maintained through their mounting screws. However, as a precaution I would provide hard wired safety earth from the power amp IEC (or chassis stud point) to the main case. Now the other three are integral part of the system and take their safety earth from the main case chassis.

Edit: Reading your previous posts, above also assumes that 0V is connected to the chassis/earth only at the power amp end, and the preamp, sound module and keyboard cases are floating (or the circuitries inside the cases are floating).

 

[JohnRoberts]

Which voltage is a greater danger to humans, mains of 230VAC/16Afused or B+ of 350VDC/100mAfused?
Also, the safety earth wire must withstand all fault currents, including the short-circuit current of the heating voltage, if it is not floating.

In my country, any voltage higher than 50V is considered dangerous.

To answer the initial question, if it is a fixed setup, I would prefer star-earthing, if it is a setup that needs to be connected and disconnected frequently, I would prefer telescoping. Basically, safety earth should always be connected first and disconnected last, and this cannot always be ensured with separated cables.

The what is a dangerous voltage is kind of the wrong question... its the current that kills us and GFCI protection devices trip at roughly 6mA...

JR

PS: I joke that an AA battery could kill you if thrust deep into your heart.

 

[abbey road d enfer]

To make things clearer, the four elements are assembled in a common carpentry cabinet, with looms circulating between the different parts. It's a fixed set-up, however, for maintenance duties, they should be easily extractible and functional. Continuity between chassis is via wires.

 

[sahib]

In which case, and depending on the diagram in you post #2, cascaded connection from one equipment chassis to another makes more sense. I would imagine you will be using in-line connectors between the two equipment wiring, in which case, include the safety earth connection within the same connector.

 

[abbey road d enfer]

In which case, and depending on the diagram in you post #2, cascaded connection from one equipment chassis to another makes more sense. I would imagine you will be using in-line connectors between the two equipment wiring, in which case, include the safety earth connection within the same connector.

That's what I intended to do first, but I had doubts about how a safety agency would take it...

 

[Newmarket]

That's what I intended to do first, but I had doubts about how a safety agency would take it...

I think your doubts are justified. PEC on a shared connector ? Reliability issues ? and , depending on connector type, removable manually without a tool (while appreciating that the other power connections would likely also be disconnected at the same time).

 

[ccaudle]

depending on connector type, removable manually without a tool

Every IEC mains input connector has protective earth on a connector manually removable without a tool. Seems the most common way to do it.

 

[Newmarket]

Every IEC mains input connector has protective earth on a connector manually removable without a tool. Seems the most common way to do it.

You mean a crimp / blade "Faston" type connection ?

 

[zamproject]

Yes, most main connectors (with or without EMI/RFI filter ) have 6.35 faston connection, wile usualy at the other side of the wire (chassis mount) the rules seem you need a nut/bolt (M4 min) with approved washer and eyelet crimp connector.

You can buy double or quad faston receptacle in rivet form, obvioulsy for chassis/earth wiring, but can't say in which condition it's allowed.

unfortunately IEC documentations are so expensive...

 

[sahib]

I think your doubts are justified. PEC on a shared connector ? Reliability issues ? and , depending on connector type, removable manually without a tool (while appreciating that the other power connections would likely also be disconnected at the same time).

That is not correct.

In-line connector is internal to the equipment. IEC is the mains input.

One has to be dumb enough to service an equipment without disconnecting it from the mains. Even then there is a mechanism to eliminate that risk.

Every power supply whether in kit or built form we supply has a warning label on the top cover. "DISCONNECT FROM MAINS BEFORE OPENING THIS COVER".

 

[Newmarket]

Yes, most main connectors (with or without EMI/RFI filter ) have 6.35 faston connection, wile usualy at the other side of the wire (chassis mount) the rules seem you need a nut/bolt (M4 min) with approved washer and eyelet crimp connector.

You can buy double or quad faston receptacle in rivet form, obvioulsy for chassis/earth wiring, but can't say in which condition it's allowed.

unfortunately IEC documentations are so expensive...

True that's a typical connection method. Personally like to see those connections inside a "rubber" insulating boot. But I've had to design without previously where it wasn't practicable due to other components wired in there. Used the insulated type cable crimps - not that it should matter for the PEC connection but preferred for assembly.
I do recall the 'connector' aspect of it being questioned wrt LVD but it seemed to be accepted that that only happened to in line / "user friendly" type connections.

 

[Newmarket]

That is not correct.

In-line connector is internal to the equipment. IEC is the mains input.

One has to be dumb enough to service an equipment without disconnecting it from the mains. Even then there is a mechanism to eliminate that risk.

Every power supply whether in kit or built form we supply has a warning label on the top cover. "DISCONNECT FROM MAINS BEFORE OPENING THIS COVER".

Points taken. But I still think that an internal PEC connection via an in line connector might be challenged.

 

[zamproject]

One has to be dumb enough to service an equipment without disconnecting it from the mains. Even then there is a mechanism to eliminate that risk.

Now I wonder how all tech around do

 

[JohnRoberts]

Now I wonder how all tech around do

several years ago when I was designing an outlet tester to presumably prevent dangerous mis-wiring I did a deep dive into who was getting electrocuted. A significant number of deaths were professionals, engineers and technicians who were a little too confident when working around dangerous voltages.

JR

 

[ccaudle]

You mean a crimp / blade "Faston" type connection ?

No, I mean the power cord connecting mains power to the equipment. If the protective earth is on a connector, but disconnecting that connector disconnects all power entry to that module, then what is the problem with having earth on a connector? Every piece of gear with a removable power cable has protective earth on a connector.

My reply was a direct response to post #27 which stated "I think your doubts [about safety agency approval] are justified. PEC on a shared connector ?"
I was just pointing out that PEC is almost always on a shared connector, shared with mains power line and neutral, so just pointing out the fact that PEC is on a shared connector is not useful without additional detail. Useful information would be to point out the hazard to be avoided, the fault path in which that hazard becomes active, and why the questioned approach does or does not avoid that hazard.

 

[sahib]

Points taken. But I still think that an internal PEC connection via an in line connector might be challenged.

Possibly. But only if the execution has flaws. Otherwise there are numerous examples of this application out in the industry. There are even run of the mill in-line connectors that are vastly more reliable than the "compliant" spade connectors.

Now I wonder how all tech around do

Including me. I can not tell you how many times I zapped myself over the years.

But joke aside, repair and maintenance are two different things. Indeed there are times that a repair has to be done with equipment under power, but this is done in what you would call a controlled environment.

 

[Newmarket]

No, I mean the power cord connecting mains power to the equipment. If the protective earth is on a connector, but disconnecting that connector disconnects all power entry to that module, then what is the problem with having earth on a connector? Every piece of gear with a removable power cable has protective earth on a connector.

Yeah. Okay but that is an external connection. "Inline" connectors for mains connection , as opposed to pcb connection systems, are surprisingly difficult.
Many connectors that seem suitable are not recommended / qualified for mains application. Even though they would probably be fine and have often been used for such in the past. I'm coming from a UK / EU regulatory angle here. It maybe different in different territories.
And I'm not saying that's its not possible - I've spec'd in some excellent Neutrik connectors in the past although in the assembled product the Earth connections were bonded independently of the Earth connection made by that connection - or that it's a danger technically.
But from experience it might be challenged depending on who is evaluating it.

My reply was a direct response to post #27 which stated "I think your doubts [about safety agency approval] are justified. PEC on a shared connector ?"
I was just pointing out that PEC is almost always on a shared connector, shared with mains power line and neutral, so just pointing out the fact that PEC is on a shared connector is not useful without additional detail. Useful information would be to point out the hazard to be avoided, the fault path in which that hazard becomes active, and why the questioned approach does or does not avoid that hazard.

As previously - it might be challenged. If it has been properly thought through and implemented then - yes - you could make a case in favour.
But would you really want to put your time and effort into that rather than 'play safe' and avoid the possibility of your case being rejected ?
Of course, as always, the benefits might be worth it but the risk is usually best avoided ime.

 

[Newmarket]

Possibly. But only if the execution has flaws. Otherwise there are numerous examples of this application out in the industry. There are even run of the mill in-line connectors that are vastly more reliable than the "compliant" spade connectors.

Well it might be challenged even if there's not a problem. But you are then faced with making your case.
If it makes sense to go that route with a particular product / system then fine but I'd avoid it if practicable.
Agree that there are better / more reliable connectors than the spade etc type.
ime audio kit design is often ahead of other product areas in connectorisation. It's something that I've often tried to bring into my non-audio work (sometimes accepted / sometimes resisted) where crimps / spades / blades etc seem to be predominant.

 

[sahib]

Newmarket, buddy, you are hanging onto this for no reason. Yes, if one wants to be awkward one can challenge anything. There is nothing stops one from doing it. But the data talks awkward one walks.

Of course, if you use 0.1" molex header for mains connection and ask me to test it for safety, I'll fail it. But what would be the objection to, say, gold plated fully sealed in-line connector with a couple of thousand insertion life?

There are gazillions of applications out there with 3 way in-line mains connections. I have serviced broadcast equipment where the connection between IEC and the (switching) power supply is made through locking header, or industrial equipment with in-line mains connection. From lighting, to automation the industry uses 3 prong in line connections for mains left-right-centre. There are water proof (if not chemical) 3 prong in-line mains connectors that are designed for outdoor use. Who can object using it inside an equipment. There is in-line male/female IEC. Who can object using it inside an equipment?

On being awkward, part of my business used to be in modelmaking/prototyping. For indemnity insurance the risk assessor had insisted that the safety guard on the circular saw had to remain fitted at all times. I had demonstrated an operation to him that the safety guard was the very thing that would guarantee that you would end up with your fingers chopped off. And I have seen somebody chopping his fingers off that way.