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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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    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 


  • 0
    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].
  • 0
    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.


     

    In general in buildings where Automatic Disconnection of Supply is used, only one earthing system is permitted at once unless there's no possibility of exposed-conductive-parts being touched at the same time(411.3.1.1). It's very unusual for separate cpc to be run, and where OPDs are used for fault protection, the cpc must be run in the same wiring system, or its immediate vicinity. It is permitted to run an additional cpc. If you want to make a separate TT system, all earthed parts on one earthing system must be at least 2.5 m from earthed parts of the other system.

     

    Protective earthing requirements take precedence of functional earthing (e.g. noise reduction) requirements. A separate earthing system with separate earth electrode, that is not bonded to the MET, might cause surge protection issues.


    I would also question, for a house, what a separate earth electrode system just for an audio system might actually achieve - especially in an area where there is PME connected to underground metallic services, because currents pass through the ground itself, and also voltages are transferred between buried metalwork.


    The current approach for functional earthing would be BS EN 50310 - and this can be achieved with a star-earth (i.e. separate circuit) in this case to avoid "earth loops" and noise from other circuits. But regardless, this standard. The best approach for this particular installation may well be dedicated circuits fro the studio - perhaps its own CU - with a separate conductor from the MET  (depending on length) to a dedicated earth bar in the studio, which is in turn bonded to the earth terminal in the studio CU. Routing of cabling and consideration of metallic containment for it would help.
  • 0
    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).


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    As I understand it, the main feature of such a clean earth system has nothing to do with the fixed wiring but is a means of ensuring that all the audio kit has only one path back to earth, i.e. that every bit of kit and the screens of the cables between them is earthed once and once only.

    This can only be achieved by careful attention to detail while connecting up the audio kit. Nothing you do in the house wiring will help.
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    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?
  • 0
    perspicacious:
    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. 


    This would appear to assume that the client's earth electrode is in a different "lump of soil" to that of any that the supplier's or other clients are using.......................


    Regards


    BOD


    I’m not sure about that, PME is the small music venues and amateur radio enthusiasts nemesis especially in TT hating London! There’s not a venue in London without a low hum unless they’ve used every trick in the book right from where cable runs to legendary sound engineering on the mixing console. I’ve spent thousands cleaning up the buzz from the laundrette next door, quite literally. Oh for a nice clean patch of tera firma.


  • 0
    I’m just wondering about how clean earth sockets (Some of you may call these high integrity sockets) fit into the requirements of BS7671

    :

    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

    From a BS 7671 perspective the answer for that kind of arrangemet is easy - it's prohibited. Even when good functional reasons might want something different BS 7671 is clear that the safety requirements take precedence.


    "Clean earth" is rather an out-dated concept these days - and I think often misunderstood. When I dealt with it (from a computing perspective many years ago) the "clean" earths weren't a completely separate system - they merely had their own separate paths back to the MET - to reduce pick-up from other devices on the same circuit and often with enlarged c.s.a. in an attempt to reduce impedance - but shared the same earthing system back to the supply.


    These days standards (see BS 7430 & BS EN 50310 etc) tend to go almost the opposite approach - i.e. bonding everything together as much as possible to reduce impedances between things, rather than try to insulate things apart.


    There are things you can do to reduce noise (which is as likely to be on the live conductors as well as c.p.c.s) - use radial circuits rather than rings, have a separate dedicated final circuit for the audio equipment and feed it all the audio equipment that's connected together from the same point. You can even use a screened wiring system (e.g. steel conduit or BS 8436 cables) to reduce coupling from other nearby circuits.


      - Andy.
  • Former Community Member
    0 Former Community Member
    Unless your two earths are bonded somewhere, there is a possibility, during fault, that they could be a few hundred V apart for a short duration.  Ideally then class 1 kit on one system should be not simultaneously in reach of class 1 kit plugged into the other.

    A 2m or maybe 3m separation between the special and normal sockets would be good.


    A well known electronic repair high street company had installed a suitable all insulated bench, shelving, chairs, flooring which worked well till the one TV repair guy brought in his favourite bench lamp that you could angle anywhere (cough) and plugged it in. He had no concept of what Class I kit adjacent to his often "very live" chassis could result in.............. He soon did though...................


    Regards


    BOD
  • Former Community Member
    0 Former Community Member
    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. 


    This would appear to assume that the client's earth electrode is in a different "lump of soil" to that of any that the supplier's or other clients are using.......................


    Regards


    BOD

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