[Tech1] Static versus Mains

[phider]

A bit more than static. The Mole camera crane, developed by the Motion Picture Research Council in the US, was the mainstay of all TVC, TV Theatre, Riverside and Lime Grove studios drama and LE. Being American it ran off 110 volts DC.In the '60s I was rigging for a drama in Studio E at Lime Grove and plugged the Mole power cable into the very large 110v DC outlet on the wall box. Little did I know that the whole box was live and I took a belt that  cooked me like a lobster  My temperature was about 105 F when I got to the surgery on the ground floor. The Sister on duty said how lucky I was that my heart was on the downbeat or it would have ended both my career and possibly my life. I had a lay down, a cup of tea and Mike Bond sent me home.I could have sued for millions.On a different tack, where have all the cameramen gone from this forum?Is anybody out there other than Bernie?Peter HiderSent from my Galaxy
-------- Original message --------From: Pat Heigham via Tech1 <tech1 at tech-ops.co.uk> Date: 09/02/2023  15:17  (GMT+00:00) To: chris at chriswoolf.co.uk, tech1 at tech-ops.co.uk Subject: Re: [Tech1] Static was Tape machines 
    Chris - thanks to you & Dave. I always
        got in a pickle with Ohm's Law.
    My intial interviews with the BBC were not
        covered with glory:
    
      At
          the Langham, I came across a BBC Engineer, who proved to me
          that I didn’t know Ohm’s
          Law (Yes, I did – but he tied me in knots). Walking out, I
          felt that that was
          g’bye.
      Six
          weeks
          later, I was invited for a selection board. Blow me! Back in
          the Langham. The
          Board consisted of three people – a daddy chairman, a chap
          from the Television
          Service (later identified as John 
          Eden-Eadon, and YES! Esler! who was my bête noir at the
          earlier
          interview – my heart sank.
      I
          was
          asked several questions about the sync pulses transmitted with
          the TV signal,
          and not actually knowing the answer, used my Latin to
          formulate some sort of
          reply that I thought might be intelligent. These were
          partially right!
      Esler
          was
          then asked by the Chairman if he wished to pose questions to
          me.
      Esler:
          “ I
          think that Mr. Heigham and I know where we stand” (G'bye,
          again!)
        
      However,
          I was accepted into the Television Service.
      Pat
        
    
    On 09/02/2023 13:05, Chris Woolf via
      Tech1 wrote:
    
    
      
      On 09/02/2023 12:34, Pat Heigham via Tech1 wrote:
      
      .....
        
        (need Chris Woolf, here) I believe that measured static voltage
        can be very high,
        
        but it's the current that kills you. Never understood why US
        went for 110/115v
        
        - surely the current involved is far more lethal?
        
        
        
      
      Well you can't divorce voltage and current - they are part of the
      same thing. The human body has a resistance in the range of
      300-1000 Ohms (ish). But dry skin can have a resistance of
      anything from 1kOhm to 100kOhms. So the voltage of the shock has
      to overcome these sort of resistances to push the damaging current
      through you.
      
      
      A painful current is >10mA - a lethal one is >100mA
      (particularly if flowing for more than 10s of mS). Ohms Law will
      tell you that you would have to be unlucky to get a lethal current
      pushed through you by 120V. And explains why the EU reckons that
      <50V is considered safe enough to not need most safety
      regulations.
      
      
      Aircraft can charge up to 100-200kV quite easily, but also have
      static dischargers on wing and tail tips (where the charge usually
      accumulates) to get rid of as much as possible. However they do
      need grounding before refuelling. With luck the charge density
      will be low enough that, although very painful, the current flow
      through a person touching an ungrounded aircraft is unlikely to
      get a high current for long enough to be lethal - but it could
      produce a burn.
      
      
      A Taser can deliver 50kV, but should control the current to
      <10mA.
      
      
      Caution is always necessary!
      
      
      Chris Woolf
      
      
      
    
  

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