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Clean Earth sockets

IronFreely
I’m just wondering about how clean earth sockets (Some of you may call these high integrity sockets) fit into the requirements of BS7671 in terms of their use in domestic homes.


One of my clients has asked me to look into the use of some clean earth sockets to be used to power audio equipment in their home studio, the basic idea is that a completely separate Earth helps eliminate what’s known as an earth hum on audio equipment caused by functional earth leakage of other equipment connected to the same circuit and disturbances originating from the suppliers earthing arrangement. The basic concept seems to be to insulate the cpc from the earth terminal of the socket outlet which then has its own independent Earth electrode, high integrity sockets seem designed to accept and insulate a cpc and a separate earth. 


My concern is that this sort of thing is usually used in a restricted access environment where only IT or audio engineers are going to be around and might be considered trained and competent to understand the risk of introducing an earth potential to the equipotential zone that is not in itself connected to the equipotential bonding. It wouldn’t be a problem if I could guarantee restricted access or that the socket would only supply class 2 equipment, but as this is a home studio it seems a bad idea to have an earthed metal casing of some piece of audio equipment that may be completely separate from all other earthing and bonding in the property? 


id appreciate your thoughts and advice please, I’m confident a separate clean earth will resolve the earth hum problem which I’ve seen work well in theatres (essentially restricted access) before but never in a domestic property.


Edit: I should add that the property is a TT property but because the street is a hodgepodge of TNS and TNCS (I have other neighbouring clients really close by) you should assume the gas and water pipe are throwing in a bit of PME related disturbance.
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    I call it as I see it. I see a person obsessed with dropping ANY amount of hum, even if it's imperceptible, I also see a person being pragmatic.  Pragmatism always wins.  If you are a TT island in a sea of PME, there IS no solution that a customer who doesn't understand the basics can cope with.


    There are solutions, but a guy who doesn't understand the need for electrical social distancing (new term)... isn't going to like it

  • Former Community Member
    0 Former Community Member
    Meanwhile the beer fridge compressor just kicked in and is chugging along quite happily.


    You or the fridge chugging the beer Andy?


    Regards


    BAD
  • 0
    Meanwhile the beer fridge compressor just kicked in and is chugging along quite happily.
  • 0
    I'm sure it is measurable, audio amplifiers take signals at sub-millivolt levels and amplify them to many amps in the voice coil of the speakers. As such anything that introduces a voltage gradient at the millivolt level between the audio source and its the amplifier input. That could be hundreds of microteslas of stray magnetic field thouh wiring loops of a few square metres, or stray tens of milliamps through hundreds of milli-ohms of cable resistance or both effects in combination.

    In the days when a HiFi installation was all separates, this was common - the fact that the modern box is all in one small box reduces the problem for normal uses. There are ways of routing supplies to minimise both inductive effects and voltage gradients, but it is almost impossible to eliminate totally.

    There are also various nasty techniques like inserting impedances or nonlinear devices antiparallel diodes in the  CPC to reduce low level  circulating currents, but while OK inside a sealed box it is very easy to create a really dangerous system if this is done badly in a distributed system.
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    IronFreely:

    Let’s just assume both myself and my client have had a good old listen and carried out a few rudimentary tests to determine if the hum is due to local conditions or just faulty old gear. 


    MHR, thank you for your support.


    My point is that you may be wasting your time, and his money, chasing a dragon which doesn't exist. If there is hum in the output, it must be possible to measure it.


    Are you sure that he does not have tinnitus, possibly due to excessive exposure to sound?


  • 0
    I would not recommend SY... the cable's not compliant with any known british standards. It's ok when used within equipment (that doesn't come under 7671). It's also not actually very well screened (admittedly I tend to think of anything with less than 150% (100% on one layer and at least 50% on the other) as not well screened..., from an RF perspective.


    An alternative to SY or steel conduit would be FP200 or equivalent. That has a full 100% screen in intimate contact with the CPC (you'd need 3 core+E if you still wanted to run your clean earth, and the cable would be screened using the 'dirty' earth of the CPC, but you'd be way down into diminishing returns by that point.


    Finally... I'd like to say that Chris is very helpful;... it may be that in this case he is not seeing (or hearing) the issue, but he is most certainly trying to help. :)
  • Former Community Member
    0 Former Community Member
     earth leakage from the equipment will be significantly reduced, which will reduce any current that may follow along the cable screens of audio cables linking them, which will reduce the interference.


    I do wonder why, if the earth leakage from audio equipment is producing its own problem of "pleasurable noise" (sic), a better design of amplifiers is appropriate?


    Is it a case of the equipment design being the author of its own misfortune and reliant on an earth path to dump its byproducts?


    Regards


    BOD
  • 0
    Obviously enough to get the chap to consider paying me handsomely to sort out. You’re not exactly being helpful Chris.... I’ve come on here for guidance on the practical implications of installing a clean earth system where I’m not able to use the protective measures of placing out of reach, behind a locked barrier, signage and restricted access to professionals only as its in a domestic household. If you haven’t got any advice perhaps don’t irritate people by trying to second guess if we’re imagining a noise that you’ve not had the pleasure of listening to yourself. Let’s just assume both myself and my client have had a good old listen and carried out a few rudimentary tests to determine if the hum is due to local conditions or just faulty old gear. 


    To everyone else who’s kindly offered words of wisdom, thank you I’ve got some food for thought now. I think I’ll likely suggest a screened radial circuit (I reckon steel conduit or SY cable should screen quite nicely ) with an oversized 4mm Earth plus a plug and play power conditioner is probably a better option than creating a dangerous TT island in the middle of his home! Sometimes the client just doesn’t get what they want.
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    IronFreely:
    Chris Pearson:

    I have to say that I find it doubtful that the ordinary human ear can perceive this apparent "noise'. What is the evidence that it can?


    A 50Hz hum is within a lot of people’s hearing range as most of us can hear right down to 20Hz or so, the evidence...just ask any stage leckie or techie There’s only about a million of us in this country. We all know about low hums and earth loop noises (not the same as earth fault loop).




    I know fine well what mains hum is. So what is the amplitude of the one that you are seeking to abolish?


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    Sparkingchip:
    Dwallywombat:

    Note that "high integrity" sockets are unrelated to a clean earth; the former are for where high cpc currents are expected and two cpcs may be needed [543.7.1.204].


    Shoot me down if I have it wrong, if you have a second supplementary oversized CPC any voltage difference that may be present across the earth terminals of adjacent sockets supplying two items of audio equipment due to earth leakage from the equipment will be significantly reduced, which will reduce any current that may follow along the cable screens of audio cables linking them, which will reduce the interference.


     Andy Betteridge 




    You'd need to be talking some amount of "oversizing" to achieve this, perhaps above the csa that's allowed for in a BS 1363-2 socket-outlet - multiple functional bonds to a local earth bar are far more efective, as are so-called "cross-bonds". This is why rack mounted PDUs often have a separate external M4, M6 or M8 earth stud.


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