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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.
  • 0
    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.


    The phrase 'high inegrity earth ' is actually normally used to refer to systems where there is a redundant CPC path, so one credible fault cannot remove the earthing (like a ring final perhaps)  This is not that.
  • 0
    Can I really say it’s compliant though, as I’m essentially creating a TT island in the middle of houses equipotential zone? Like I’ve said if I could guarantee restricted access and guarantee no one will bring an extension into the room, in a theatre we would put set ups like this behind a locked door that only the engineers have access to.... this is a house with radiators in the room, within arms reach.


    You are correct, not exactly a high integrity circuit that I’m being asked to install but I believe when leaning over the whole salers counter I’ll be asking for what’s sold as a “high integrity, clean earth socket outlet”.
  • 0
    That's an ordinary socket out of the back of the van, isn't?


    Andy B.
  • 0
    Nope, the ones or the back of my van might have multiple earthing terminals but they’re all connected together. A clean earth socket has a terminal that’s used to keep your cpc separate from the clean earth terminal that earths the plugged in device, basically it’s just an insulated termination.


    IF
  • Former Community Member
    0 Former Community Member
    This range of MK Sockets and Switchsockets each have independent earth terminals so they can be used for ’clean earth’ as well as conventional earth installations. The Non Standard Switchsockets are for use on installations where restricted access is required and will only accept the MK LN647 13A Non Standard Plug with a ‘T’ shaped earth pin.


    Takes me back to when a well known make was still using their very old unshuttered 2 A socket-outlets in modern flat faceplates (when it was 1990's vogue to have the wall switch controlling table lamps/lamp standards) and their UK catalogue listed them as export only...............


    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
  • 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
  • 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.
  • 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 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?

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