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ADS

Former Community Member
Former Community Member
How exactly does ADS work?
  • Former Community Member
    0 Former Community Member
    Unless of course ADS doesn't work indoors!


    Rcd's only work, in my experience, when the human body is in good contact with earth, either an earthed conductor or wet grass!



    Are you claiming then that the use of EEBADS as set out in the 16th Edition does not cause disconnection of supply within 0.4 seconds when a fault of negligible impedance occurs?


  • 0
    I think you have missed a point Coby. The only way an RCD can trip is to provide an alternative path for current to the line and neutral conductors. So in your example, you would need yourself firmly Earthed by an alternative path, so that the live current did not return via the neutral. Contacting both live conductors (or either with no other path) does not trip an RCD. However, if you contact one conductor and some Earthed item the RCD will trip at about 20mA current which you may not even feel at all. Touching live and neutral at once can still be rather nasty if you are well insulated from Earth.
  • Former Community Member
    0 Former Community Member
    Lisa Miles:

    This topic does have a strong sense of 'deja vu' about it and i believe was discussed in GREAT LENGTH in our previous forum before the webmaster stepped in ...


    Can I please remind everyone to be respectful of each other, be mindful of the language in their contributions and if you spot anything that does not align with our T&Cs or etiquette guidelines please report the content to the admins by using the three dot menu in the posts themselves. 


    Yes it was Lisa and the thread was closed down when these gentlemen ran out of things to say!


  • Former Community Member
    0 Former Community Member
    davezawadi (David Stone):

    I think you have missed a point Coby. The only way an RCD can trip is to provide an alternative path for current to the line and neutral conductors. So in your example, you would need yourself firmly Earthed by an alternative path, so that the live current did not return via the neutral. Contacting both live conductors (or either with no other path) does not trip an RCD. However, if you contact one conductor and some Earthed item the RCD will trip at about 20mA current which you may not even feel at all. Touching live and neutral at once can still be rather nasty if you are well insulated from Earth.


    So you do understand that RCD's do not work indoors and therefore ADS is a myth!


  • 0
    Maybe it's time to quote Wolfgang Pauli: "That is not only not right; it is not even wrong"
  • 0
    Coby:

    So you do understand that RCD's do not work indoors and therefore ADS is a myth!

    They certainly work in the event of a L-E fault, but if you are thinking of protection against direct contact, it may be the case that in some premises the resistance of the floors is sufficient to prevent any shock at all. I wouldn't like to rely upon it. ?
  • 0
    To your two points,

    1) Significant shock current (more than a fraction of a mA ) only flows when you grab both  L and N.  Grab just L and a small displacement current flows from your capacitance to free space, but even a fairly corpulant body , that will be hundreds of pF, so nary a tingle, at 50Hz enough to light a neon screwdriver or operate a no-touch voltage sensor, but not enough to do you damage or to trip an RCD. Only once there are two metallic (or perhaps ionic liquid) contacts does a possibly dangerous current flow.

    You might get there with capacitance  only if you are lying on the thin ground sheet, spread eagled, but it would be a push.

    So for the L-N shock both currents start together (or within c/d of each other, where c is the speed of light and d is the path length difference - for any RCD or MCB, that is the same "instant").

    point 2)

    All ADS mechanisms work for faults of negligible impedance -  the humble  13A fuse will do the task of disconnection  the face of any fault loop resistance  lower than a few ohms.

    You may need some  EEB to provide part of that path, or maybe the CPC (the green wire in the mains lead usually) is enough, depending where exactly that fault is.

    The clever part is ADS for faults of non-negligible impedance, such the few k ohms of the human body, and to still detect that sort of impedance L-E  when tens of amps are flowing L-N. - enter the RCD.
  • 0
    Simon Barker:

    Maybe it's time to quote Wolfgang Pauli: "That is not only not right; it is not even wrong"

     


    He almost certainly did not say quite that but he was famous for not holding back with the criticism of substandard works.

    however ..
    https://www.math.columbia.edu/~woit/wordpress/?p=271


  • 0
    So you do understand that RCD's do not work indoors and therefore ADS is a myth!

    Not really - indoors we still have earthed metalwork on class I equipment indoors, more earthed metalwork (both exposed- and extraneous-) likely within reach of that, so plenty of scope for a shock to Earth potential even indoors.

      - Andy.
  • 0
    Coby:
    davezawadi (David Stone):

    I think you have missed a point Coby. The only way an RCD can trip is to provide an alternative path for current to the line and neutral conductors. So in your example, you would need yourself firmly Earthed by an alternative path, so that the live current did not return via the neutral. Contacting both live conductors (or either with no other path) does not trip an RCD. However, if you contact one conductor and some Earthed item the RCD will trip at about 20mA current which you may not even feel at all. Touching live and neutral at once can still be rather nasty if you are well insulated from Earth.


    So you do understand that RCD's do not work indoors and therefore ADS is a myth!




    What makes you think that RCDs don't work indoors?


    Many years ago, I was living in a student flat.  Someone in a bathroom on the floor above let water spill onto the floor, and it got into the lighting circuit of the flat I was in.  The RCD tripped.


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