Forums Music Audio Visual Don’t try this at home (unless you really know what you are doing)

This topic contains 3 replies, has 2 voices, and was last updated by Avatar sinner69 August 26, 2014 at 1:22 pm.

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  • #1057520
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    General Lighting
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    Apologies for shaky video; but you might understand why my hands are shaking. (I was checking that earth connections are good for some wiring possibly 2 years older than myself, if I could get a “board earth” from a direct point) and wanted to check the power usage with a clamp meter but decided this isn’t the safest place to do this).

    its not a good idea to crack the UK Power Networks seal in the meter cupboard area (which would enable me to put the earth wiring through the same route the tails go) as meter readers report things like that; there is already “above average usage” for my electric meter records and I would get cops knocking the door to check if I’m growing “tomatoes” upstairs.

    Ironically if it wasn’t for all those new rules (which mean I am competent to work on a 400V dis board far bigger than this supplying power for safety critical circuits but not to do certain jobs in my own house) I could haul out this old stuff and rewire the lot in a far safer way….

    #1278142
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    General Lighting
    Moderator

    there is a reason why I wanted an extra earth connection (as all the equipment with metal frames should have protective earth from the mains sockets) which I will explain in another thread [it can solve a lot of audio and radio interference issues]; but for safety this earth must always come from the same point as the protective earth (earth ground) used by the electricity distributor at your site.

    Otherwise you create a variety of hazards to yourself, any other creatures in the building and whatever equipment is connected (stray electricity can appear between the different “earths”).

    the protective earth in your site should not have any appreciable current going down it anyway (definitely not to the point where you get even mild shocks on touching anything metal) or there is a bad defect in the wiring; and you or your landlord should immediately get a registered electrician to fix it. In most EU countries there is a requirement to inspect wiring in communal accomodation and industrial premises every so often; to guard against situations like this.

    general-lighting-albums-random-pics-picture86219-dangerous-electricity-26.jpg

    So I tested the earth in my house;

    14844785937_f6d04d69a1_b.jpg

    it is safe to call in the milkmaid (just as well; as it is hassle cleaning up spilled milk and cow manure from the carpet).

    This is what is in the meter cupboard

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    a close up of the earth – it is taken from the metal shield of the service cable which is connected to solid copper earth rods and everything metal in the nearby substation (and is bonded to the neutral point of the 400V side of the trafo).

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    I am not sure if my house gets the brown (former red) phase or the red is just the marker of which tail is the live. This is known as a TN-S (separate) earthing system.

    in other installations the electricity distributor provides a cable where there are 1 or 3 phases and a combined neutral/earth which is split at the incomer into neutral and earth connections and should be bonded in this way only once at that point.

    This is called a TN-C-S (combined then separate) or (in the UK) PME (Protective Multiple Earthing). It is widely used in the USA and some European countries but has the disadvantage that all the interference from cheap PSUs that appears across the mains is often radiated across a larger building by the earth wire; this getting worse the further away it is from the incomer or if the neutral and earth are inadvertantly misconnected at any point (which regularly happens). Also stray electricity from unbalanced 3 phase loads gets on the earth.

    One site at work has this and it is a cause of all sorts of hassles as the servers and comms rack are at the far end of the building 😥

    After looking at the wiring I realised the ring final (socket) circuit starts at the socket below this distribution board in the porch (not sure what it was intended for, presumably plugging in hoovers or 1970s style lamp standards as this house was built in 1970; although the phone often was in the porch, very few people had telecoms equipment that needed a power supply….

    it does however provide a convenient source of “Board Earth” using a 13A plug with a single pin (so there is no chance 230V ends up being connected)..

    14844590009_152d972119_c.jpg

    I’m not sure if its that quiet but the idea is this earth is brought back into the studio, then connected to everything metal that doesn’t already have an earth connection as well as the accus for the LSD01/02/03 system and some telecom kit.

    14844718358_2c0fe2f8bd_b.jpg

    The blue wires below are not 230V mains; they are the midpoints of the +12V and -24V DC supplies from accus (in the nuclear free metal case)

    15028270101_cbb328af4f_c.jpg

    Provided you use correctly wired balanced audio cable and audio transformers for unbalanced connections you do not get a loop from the frame earth (as it is kept away from signal earth) but create a mesh of randomly shaped metal objects all connected to earth. The idea of this is to catch any stray electromagnetic fields at all frequencies and route them back to earth; instead of into audio equipment or radio receivers where it becomes noise.. (since doing this I’ve noticed I can even use this earth for the HF radio, previously it just swamped the incoming signals…)

    #1278144
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    sinner69
    Participant

    We got a earth grounding last year(as we have started to rewire the whole house, its about time, the old system is from the -40s) a proper one two meter metal straight in to the ground

    #1278143
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    General Lighting
    Moderator

    @!sinner69! 562852 wrote:

    We got a earth grounding last year(as we have started to rewire the whole house, its about time, the old system is from the -40s) a proper one two meter metal straight in to the ground

    .

    I think the TN-C-S system was thought up around then so the Electricity Board could use less copper cable or that cable with aluminium added (as they thought nuclear power would produce endless cheap electricity; which reduces the cost of making aluminium)

    DK and SG (being small countries with a lot of communal buildings full of clever folk with loads of AV equipment) as well as the high tech areas of DE are way ahead of the UK now with regard to both safety and EMC interference avoidance. (British Telecom and the BBC used to separate the “quiet earth” from the mains earth; they must have kept quiet too when people got shocked or electrocuted). This practice is banned throughout the EU (although the quality of protective earth varies in Southern Europe, a few clubbers are sparked each year due to this).

    It is permissible for the Electricity Distributor to put the earth spike in and bond it to their MET (Main Earthing Terminal) which can clean up a TN-C-S supply to some extent (it is still not as clean as a TN-S); but illegal (potentially dangerous and can make the problems worse) for anyone else to put the spike in.

    I ended up having to read 30 pages of German to investigate what could be going on at my work (most likely phase imbalance from the laundry machines and dishwasher, added to electric pump WCs in the residents rooms downstairs!)

    for some reason the best info about 230V earthing systems is in German (and Estonian; but other than picking out a few words form a sea shanty that is a bit too difficult for me)

    http://de.wikipedia.org/wiki/TN-System

    Singapore has many 20 floor tower blocks full of extended Asian families with all sorts of gadgets – everything from Nan’s bedroom TV set and Ipad , the teenagers laptops a wifi-linked cat and dog feeder with weighing scales; all with the usual €5 China PSU. They also switched to digital TV this year, so more set top boxes etc…

    I expect a fair few discussions between harrassed building managers and the electric company led to this…

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