Time switch keeps blowing fuse out.

Discussion in 'Electricians' Talk' started by MM82, Nov 27, 2021.

  1. MM82

    MM82 New Member


    we've recently installed a timeguard NTT03 timeswitch to a water heater that was always on,
    but the fuse keeps blowing after maybe an hour or so and I'm not sure why,
    do this connections look about correct to you?
    timeswitch.jpg 15775471430488401796345771421623.jpg
    thanks in advance!
    Last edited: Nov 27, 2021
  2. seneca

    seneca Screwfix Select

    What size fuse are you using and what's the rating of the water heater?
  3. terrymac

    terrymac Screwfix Select

    Are these immersion heater elements ,within an unvented cylinder by any chance ?
    I suspect you had two seperate switches ,one for each element ,only allowing one to be used ,but not both simultaneously. You have now connected both elements to come on at the same time ,which would cause a 13 amp fuse to blow.
  4. The Happy Builder

    The Happy Builder Screwfix Select

    As @terrymac says, I assume you have a hot water cylinder with two immersion heaters.

    If that’s the set up it’s quite possible that the bottom heater doesn’t need a time clock because it is supplied from an off-peak electric supply and the top immersion was intended to be left turned off unless you ran out of hot water and wanted a daytime boost.

    So it’s probably the wrong timer and you have messed up the wiring.

    If it has two immersion heaters with one supplied by an E7 Off peak supply take the time clock out and reconnect the bottom immersion with a 20 amp switch, then reconnect the top immersion using an immersion countdown timer https://www.toolstation.com/2-hour-electronic-boost-timer/p66796

    If you have two immersion heaters, but not an E7 supply, leave the bottom heater connected to the timer and install a countdown timer to the top.

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