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DISTRIBUTOR CANNOT BE TRUSTED...

Former Community Member
Former Community Member
Hi folks!


This is my first forum post and hopefully and interesting topic. I am looking for some advice on where to start!

Background:
  1. 4th floor apartment tear-out in the city of Baku, Azerbaijan in a very old Soviet-era building block with unknown amounts of modifications.

  • 4 wire system (3-phase and neutral) entering and distributed throughout the building (no armoured cable / no separate earth).

  • No enforced local regulations as the general wiring in the city is a free-for-all (I am told it should be to PUE 6 standard). I could share many examples but this is not the aim of this post!

  • No building plans available from the council / no wiring / single-line diagrams available for the building or from the distributor.

  • No option available for a reliable survey - Partly being that most of the local electricians think that an earth core is a waste of money!

  • Basically the local distributor cannot be relied upon as can be seen by the photo example of the electrical panel closest to the apartment from the local government electrical company...

  • I am an electrical engineer wanting to get my hands dirty with my own project compliant to the BS 7671 wiring regs. I will design the domestic electrical installation and will have it verified by an (UK) electrician / expat before proceeding and sourcing materials.

Aim:


  1. Brand new domestic apartment electrical installation to BS 7671 18th Edition in which is in my control (full rewire, new consumer unit etc.). BS exceed the local regulations.

  • Keep politics / what-should-be for the incoming panel out of the discussion, it is what it is and there is not much I can do except wait decades for regulations and enforcements to catch up!

  • Provide the safest solution to protect my family without running away from the building / country.

Closest Panel to my Apartment:

  • Ok lets cut to the chase - this may just be the worst panel that you have ever seen however I cannot modify it as it is owned by the local government electrical company. It gets no points for compliance to any regulation (maybe 1 for being metal only!). I unfortunately has to live with this monstrosity until the building is knocked down in the future (and this is one of the newer / better panels in the building believe it or not…1 of 3 panels up to the apartment).

34853545ae5c04645e1bb134ec9267e3-img_1749.pdf


Queries:

  1. Can I assume that the incoming supply is a TN-C-S (and I know this is the distributors responsibility…) i.e. connect the MET and neutral together before the consumer panel? I know we should never assume so what is the best way to test? I am trying to source a Megger. My concern is that this could bypass some protection elsewhere in the building although it appears to have only overcurrent protection (fuses).

  • Should I have a dedicated earth run from the incoming of the building (from the neutral bar) up to the apartment consumer unit instead? My concern is that there my be a potential difference between the neutral and the earth at the apartment which could require 2P RCBOs throughout. Yes there should not be a potential difference however there is a lot of twisted wiring (junction boxes are a luxury…) and poor looking connections as well as all the apartment neutrals connected together in the block.

  • A third option would be to have an earth pit installed in the car park and run the dedicated earth to the MET in the apartment although 2P RCBOs may still be required.



Any assistance is greatly appreciated including verification / testing methods before I dive into the design of the consumer unit. Thank you in advance,


Chris
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  • Former Community Member
    0 Former Community Member
    RESPONSES:


    mapj1:

    I assume the unmetered GY from phase 1 is a sub-main to another similar board.



    Simon Barker:
    Somebody seems to have tapped in an extra un-metered live, in green-and-yellow, from the incoming breaker, and fed it out the bottom of the panel alongside two earth wires.  Is this a sneaky way to hide abstraction?

    So the unmetered GY from L1 is a 63 A supply... to the door bell! And has also been tapped into another panel which is where the trail goes cold. Let’s just say I am very cautious to press the plastic door bell button now and not touch the surrounding metal!   1.jpeg

     
    mapj1:
    An example of the better earth problem - not quite in the UK, but almost, as Lyle works in Ireland, and it certainly is could happen here. 

    Very interesting case! As long as a L-E fault at my end is disconnected within the required time period as per the regulations then I do not see an issue with my new earth electrode potentially being better (lower resistance) than the one in the substation. It sounds as if this is not unusual for customer TT installations.

     
    mapj1:
    An all pole breaking RCD at the incomer is a good start, good, along with some sort of external earth connection- which at the FOB may be associated with comms antennas /equipment. Either a direct N-E bond or via a capacitor after the RCD will trip the RCD if the neutral voltage is too far off earth or if the LN are reversed - which you have to assume can happen at any time as other things may be severed and reconnected outside.  Then under-voltage and over-voltage trips will guard against the worst errors such as being fed 2 phases instead of one phase and a neutral, though if possible small electronics equipment is designed to work OK from less than 100V to over 400V so that we do not really care to much. Note that there are situations where driving an earth electrode is not desirable,  the most extreme example would be suspected buried ordnance, but in a more domestic setting,  to buried strike water and gas pipes could be almost  as disappointing. 

    Also very interesting - I will add it to my homework! The earth electrode will be tricky however a job for the local workmen so I do not cause chaos!

     
    AJJewsbury:
    So generally any new CU installed in the UK in the last 5 years or so will be steel cased.

    Thanks Andy, I was leaning towards metal anyway and is what I’m used to!

     
    mapj1:
    In an installation with such an iffy earthing culture and random taped joints, I suspect the metal vs plastic argument may swing the other way - you cannot get a shock off a plastic box  !!


    Hmm… I am now unsure whether plastic piping / plastic consumer unit or bonding all extraneous metal pipe work & exposed metal surfaces is the way to go… food for thought!

     
    AJJewsbury:
    I'm confused. There appear to be 3 outgoing C32 MCBs and three meters. However the top left meter seem to be connected directly to one of the apartments without going through a C32 (dark blue wire) - could it be that the highlighted single pole C32 MCB is actually in the N?

    Correct - 3 outgoing C32 MCBs and three meters. The dark blue wire you mention is the outgoing neutral from the top left meter (Also see the relevant page from the meter manual with the order of the terminals here). The light blue cable from terminal 2 (second from the left) is the outgoing live. This goes to the right of the panel and up to the left side MCB. It is difficult to see because of the blue trunking which I have only ever seen used on intrinsically safe cabling systems. Also I’ve had a voltmeter in the panel so the MCBs are in fact connected to the live wires.

     
    mapj1:
    Well it is not that clear which cores are lives and neutral/earth in the supply or the loop supply, or indeed which is which incoming and which is daisy chained, so the safest thing is probably to use a meter to identify the 3 phases (400V between each pair) and the neutral/earth (230V to each of the lines you think are phases.) Zooming in on  the bottom of the box is just confusing, and we cannot see if wires are crossed over in the channels where they are hidden from view.

    There is certainly scope for polarity reversal,  or being fed 2 phases instead of one phase and a neutral, and it would be hard to spot.

    Andy / Mike - Hopefully this clears things up now (confusing I know - cannot trust the cable colours).   2.jpeg

    Another point is that the national voltage is not quite to IEC 60038 and is not expected to migrate as the country is not in the EU. I realised this when installing 660 V switchgear instead of 690 V (non-domestic installation).

     
    broadgage:
    Install a consumer unit with true double pole  RCBOs for each circuit.

    The RCD section gives good protection against electric shock.

    The MCB section give protection against overcurrent in EITHER pole of the supply.


    I would instal three wire circuits to grounding type socket outlets. I would earth the installation to the water pipes, this IS NOT best practice and is prohibited in the UK, but under the local conditions is in my view the least bad option.

    Even if the earth via the water pipes becomes ineffective, SOME protection is still given by class one appliances and plumbing being at the same voltage. The "earthing" has in effect become "bonding" under such conditions and still gives some protection against shock.

    Thanks broadgage. Agreed - I had decided on 2P outgoing RCBOs to isolate any dodgy neutrals in the event of a fault plus for peace of mind with a baby in the flat. My understanding is that, if the circuit is off, any external backfeed via a N-E fault within the flat on the same circuit through the RCD would also trip it. I also plan to install a 300 mA time delayed S type 2P RCD on the incoming side, purely as a backup and for good practice (especially if my new earth electrode is better (lower resistance) than the distributors! - thanks Mike for the example).


    Sockets - Agreed 3-wire grounding type. I am still leaning towards UK type to avoid polarity reversal. I am now sure that I need a new earth electrode down in the carpark which the metal pipework could also be bonded too. Ok so another tally for bonded metalwork instead of plastic...

     
    broadgage:
    I can not recomend earthing to the suppliers neutral, too much risk of an upstream open neutral in view of the questionable standards observed.

    Agreed, the TN-C-S route is dead. TN-S is not available from the distributor (no separate earth conductor). So my only option is TT.



Reply
  • Former Community Member
    0 Former Community Member
    RESPONSES:


    mapj1:

    I assume the unmetered GY from phase 1 is a sub-main to another similar board.



    Simon Barker:
    Somebody seems to have tapped in an extra un-metered live, in green-and-yellow, from the incoming breaker, and fed it out the bottom of the panel alongside two earth wires.  Is this a sneaky way to hide abstraction?

    So the unmetered GY from L1 is a 63 A supply... to the door bell! And has also been tapped into another panel which is where the trail goes cold. Let’s just say I am very cautious to press the plastic door bell button now and not touch the surrounding metal!   1.jpeg

     
    mapj1:
    An example of the better earth problem - not quite in the UK, but almost, as Lyle works in Ireland, and it certainly is could happen here. 

    Very interesting case! As long as a L-E fault at my end is disconnected within the required time period as per the regulations then I do not see an issue with my new earth electrode potentially being better (lower resistance) than the one in the substation. It sounds as if this is not unusual for customer TT installations.

     
    mapj1:
    An all pole breaking RCD at the incomer is a good start, good, along with some sort of external earth connection- which at the FOB may be associated with comms antennas /equipment. Either a direct N-E bond or via a capacitor after the RCD will trip the RCD if the neutral voltage is too far off earth or if the LN are reversed - which you have to assume can happen at any time as other things may be severed and reconnected outside.  Then under-voltage and over-voltage trips will guard against the worst errors such as being fed 2 phases instead of one phase and a neutral, though if possible small electronics equipment is designed to work OK from less than 100V to over 400V so that we do not really care to much. Note that there are situations where driving an earth electrode is not desirable,  the most extreme example would be suspected buried ordnance, but in a more domestic setting,  to buried strike water and gas pipes could be almost  as disappointing. 

    Also very interesting - I will add it to my homework! The earth electrode will be tricky however a job for the local workmen so I do not cause chaos!

     
    AJJewsbury:
    So generally any new CU installed in the UK in the last 5 years or so will be steel cased.

    Thanks Andy, I was leaning towards metal anyway and is what I’m used to!

     
    mapj1:
    In an installation with such an iffy earthing culture and random taped joints, I suspect the metal vs plastic argument may swing the other way - you cannot get a shock off a plastic box  !!


    Hmm… I am now unsure whether plastic piping / plastic consumer unit or bonding all extraneous metal pipe work & exposed metal surfaces is the way to go… food for thought!

     
    AJJewsbury:
    I'm confused. There appear to be 3 outgoing C32 MCBs and three meters. However the top left meter seem to be connected directly to one of the apartments without going through a C32 (dark blue wire) - could it be that the highlighted single pole C32 MCB is actually in the N?

    Correct - 3 outgoing C32 MCBs and three meters. The dark blue wire you mention is the outgoing neutral from the top left meter (Also see the relevant page from the meter manual with the order of the terminals here). The light blue cable from terminal 2 (second from the left) is the outgoing live. This goes to the right of the panel and up to the left side MCB. It is difficult to see because of the blue trunking which I have only ever seen used on intrinsically safe cabling systems. Also I’ve had a voltmeter in the panel so the MCBs are in fact connected to the live wires.

     
    mapj1:
    Well it is not that clear which cores are lives and neutral/earth in the supply or the loop supply, or indeed which is which incoming and which is daisy chained, so the safest thing is probably to use a meter to identify the 3 phases (400V between each pair) and the neutral/earth (230V to each of the lines you think are phases.) Zooming in on  the bottom of the box is just confusing, and we cannot see if wires are crossed over in the channels where they are hidden from view.

    There is certainly scope for polarity reversal,  or being fed 2 phases instead of one phase and a neutral, and it would be hard to spot.

    Andy / Mike - Hopefully this clears things up now (confusing I know - cannot trust the cable colours).   2.jpeg

    Another point is that the national voltage is not quite to IEC 60038 and is not expected to migrate as the country is not in the EU. I realised this when installing 660 V switchgear instead of 690 V (non-domestic installation).

     
    broadgage:
    Install a consumer unit with true double pole  RCBOs for each circuit.

    The RCD section gives good protection against electric shock.

    The MCB section give protection against overcurrent in EITHER pole of the supply.


    I would instal three wire circuits to grounding type socket outlets. I would earth the installation to the water pipes, this IS NOT best practice and is prohibited in the UK, but under the local conditions is in my view the least bad option.

    Even if the earth via the water pipes becomes ineffective, SOME protection is still given by class one appliances and plumbing being at the same voltage. The "earthing" has in effect become "bonding" under such conditions and still gives some protection against shock.

    Thanks broadgage. Agreed - I had decided on 2P outgoing RCBOs to isolate any dodgy neutrals in the event of a fault plus for peace of mind with a baby in the flat. My understanding is that, if the circuit is off, any external backfeed via a N-E fault within the flat on the same circuit through the RCD would also trip it. I also plan to install a 300 mA time delayed S type 2P RCD on the incoming side, purely as a backup and for good practice (especially if my new earth electrode is better (lower resistance) than the distributors! - thanks Mike for the example).


    Sockets - Agreed 3-wire grounding type. I am still leaning towards UK type to avoid polarity reversal. I am now sure that I need a new earth electrode down in the carpark which the metal pipework could also be bonded too. Ok so another tally for bonded metalwork instead of plastic...

     
    broadgage:
    I can not recomend earthing to the suppliers neutral, too much risk of an upstream open neutral in view of the questionable standards observed.

    Agreed, the TN-C-S route is dead. TN-S is not available from the distributor (no separate earth conductor). So my only option is TT.



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