The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 45 replies
  • Subscribers 31 subscribers
  • Views 11366 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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
    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.
  • 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).


  • 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
    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
    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
    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.


  • 0
    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?


  • 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.
  • 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
    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. :)

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines