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420 Watt Hedge Trimmer.

Zoomup
The owner of the 420 Watt hedge trimmer decided to redesign the 0.75mm2 two core flex by cutting through it. This caused a dead short. His house is supplied by a TN-C-S supply. It has a consumer unit in the house with a B16 M.C.B. dedicated to supply his garage. The house consumer unit is a split load type with 30mA R.C.D.s. The hedge trimmer had a 13 amp plug fuse fitted. It was supplied via an extension lead fused at 5 Amps.


In the garage, where the hedge trimmer was plugged in,  there is a two way garage unit with a B16 M.C.B. for the sockets and a 30 mA R.C.D.


When the hedge trimmer flex was cut through which protective device(s) tripped off or ruptured?


Z.




  • 0
    Probably the house B16 MCB
  • 0
    As you are asking the question I will take a punt on the least likely to go: the supplier fuse.


    Well someone has to ?
  • 0

    kfh:

    As you are asking the question I will take a punt on the least likely to go: the supplier fuse.


    Well someone has to ?




     A very brave assertion there. Very brave indeed.


    Z.

  • 0
    I'd guess either or (more likely) both the B16 plus the 5A fuse. One or more of the RCDs might have tripped as well if conditions were damp or the fault current saturated the RCD's cores.


    Unless it was a very long extension lead, then perhaps the 5A alone.


       - Andy.
  • 0
    The whole lot? Is this the lead up to the weekend quiz Zoom?
  • 0
    First thought, neither of the RCDs 'cos there is no mention of a fault to earth - our careless gardener hasn't picked up the live end of the severed cable.


    We have to make a few assumptions about the length of the various components of the circuit and then do some calculations ? before referring to the trip curves, but my guess is the 5 A fuse alone.
  • 0
    Getting warmer. But not warm enough.


    Z.
  • 0
    A unrelated RCD could have tripped due to the fault current causing a larger than normal voltage drop along the N tail and thus causing N-E leakage current along an existing N-E fault somewhere to increase above the 30mA threshold.
  • 0
    I'm going to say one or other or   Both 16 amp trips and the 5 amp plug fuse
  • 0

    Kelly Marie:

    I'm going to say one or other or   Both 16 amp trips and the 5 amp plug fuse 




    Is that your final answer Kelly Marie?


    O.K.


    I will accept your CORRECT answer. Well done.


    Yes, both the house M.C.B. and the garage M.C.B. (both B16 types) tripped off, AND the 5 Amp fuse in the extension lead blew as well.


    No other devices tripped off, no R.C.D.s tripped off, and the 13 Amp fuse in the hedge trimmer plug did not blow.


    P.S. The hedge trimmer flex was renewed.


    Z.

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