Real novice question

Discussion in 'General Electronics Chat' started by Shanes_world_05, Nov 16, 2013.

  1. Shanes_world_05

    Thread Starter New Member

    Nov 15, 2013
    1
    0
    Hi guys,

    I am a mechanical engineer so my electrical knowledge is very poor so apologies straight of the bat.

    I have been tasked to make up some components for an electrical device for a client. Its a long story but basically they want to be able to attach to a live circuit (NZ - 240 Volts 50 HZ) and via this device power other devices from typical household TPS cable. 1.0mm^2, 1.5mm^2 and 2.5mm^2 three core cable are the specified cables.

    Problem is that we can't shut off the mains power, the sheath can't be peeled back so that means you don't know which conductor is facing you on the left or the right.

    So my questions are:
    What happens if the main circuit (being hacked into) supplies active/phase/line current into an attached electronic device's neutral line?
    Are there any electronic or electrical devices/components that can be incorporated to guard against this like an RCD guards against current overload or seepage?

    Ihave comlpeted most of my requirements for this project and it is supposed to be handed off to a proper electrical engineer to fix this up but I don't know when this will be (could be years) so wanted to give the project a head start on that. Also just curious (and its been my baby for 9 months).

    Any help appreciated. Again apologies for such a weird bunch of questions

    Cheers

    Shane
     
  2. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
    315
    Need some clarification of terms.
    Much different in US.

    In US terms I'm thinking you want to tap into live romex.
    Romex or type nm is nonmetalic sheathed cable.
    Is that what TPS is? thermoplastic insulated cable?

    2 conductors and a ground?

    2 conductors carrying the load one of which (neutral) is grounded?

    If those assumptions are correct, most devices, from an operational point of view, don't care if polarity is reversed or which conductor is grounded.

    Devices are only approved for a certain polarity however. I'm not addressing safety issues.

    If you are tapping into all three then your device can sense polarity and route the output correctly.

    Be interesting to see what this is and how it could ever be approved.

    ps.
    midnight post, I may still be asleep!
     
  3. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    If you are tapping into the circuit, why can you simply measure the voltage on the two main conductors relative to the earth ground as part of this process?
     
  4. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
    315
    I'm thinking it's going to be a self piercing type tap.
    Once its attached the polarity is set.
     
  5. inwo

    Well-Known Member

    Nov 7, 2013
    2,435
    315
    Where did you go?

    Woke up with an idea.

    I just connected a load to a lamp cord on the bench.

    My fluke "volt alert 1ac-a" non-contact,will check for hot side of cord.
     
  6. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,808
    1,105
    So how do you propose actually attaching your device to the line, neutral and earth conductors?
    I hope your client isn't planning to bypass his electricity meter :D.
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,777
    4,805
    But what is preventing you from doing a "pretap" in which you pierce the jacket with thin probes in order to determine the polarities and then install the tap? I can imagine having a little jig that does both steps in such a way that the actual taps go into the same holes that the probes made.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,565
    2,379
    You can either obtain needle probes for your meter or make up an insulated probe from a stout pin or sewing needle with heatshrink or other insulation, you only need one, as the other probe would go to earth ground, I don't think the meter current will be enough trip the RCD or GFI.
    If this is for a insulation pierce contact device, I am surprised it is allowed, especially in a 240v system.
    Max.
     
    Last edited: Nov 18, 2013
  9. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,808
    1,105
    Have you determined that the existing cable won't be overloaded if your client taps into it to power household appliances? Those will draw considerable current.
    I'm dubious that an insulation-piercing tap could provide a reliable high current connection.
    The tap method will have to comply with any applicable Regulations.
     
Loading...