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Immersion heater split

Discussion in 'Electrics UK' started by jtonline, 4 May 2016.

  1. jtonline

    jtonline

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    My immersion heater stopped working recently. I measured 240V across the ends of the element so I knew the time switch and thermostat were OK. The immersion heater (a 14" Gold Dot) had been in the combi cylinder for at least 11 years. I got a plumber to remove it and found it had split along its length, so I got a new one fitted.

    I have a Wylex 604/N consumer unit and the fuses have been replaced by plug-in Wylex MCB's during its life. The immersion heater is on its own 16A MCB within the consumer unit.

    I am a bit surprised that the immersion heater could fail in such a way and yet not trip anything. Is this because I don't have RCD protection and is it an indication that I should get an electrician in to inspect / upgrade the electrics?

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  3. stillp

    stillp

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    Yes.
     
  4. ericmark

    ericmark

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    In real terms assuming every thing earthed as it should be the immersion heater caused no danger, it would be simple to swap the fused connection unit (FCU) for a RCD FCU and then it would trip with that fault.

    In the main the RCD is a good thing. We started fitting 100 mA RCD's to houses using earth rods (TT supply) many years ago and they worked well, however 100 mA is considered too high to protect personal, it is considered in the UK that 30 mA should be used. However with 30 mA they trip easier and many people have problems with tripping for no good reason. The larger the system is the more likely it is to trip for no good reason so instead of one 100 mA trip we use at least 2 x 30 mA trips and with the RCBO where the RCD is combined with the MCB we can have 12 RCD's to protect the home.

    The main problem is the fridge/freezer although auto resetting RCD's are made these are not allowed in the domestic installation so if the one feeding the fridge/freezer trips then you can lose your food. My fridge/freezer and freezer show the temperature they got to at the point where the supply was returned until door is opened so one is away if it got too warm. As to independent supply to fridge/freezer it is possible but not sure it helps. When my lights go off, or computer fails I look for an RCD that has tripped, but I don't really notice if there are no little blue lights of the fridge/freezer.

    Also even with a 30 mA RCD this does not limit the current to 30 mA it only limits the time to 40 mS it does very little to help with direct contact. Any item going faulty like you immersion heater it will disconnect before any one has a chance to get a shock be it washing machine or dish washer it will trip first, however so would the 100 mA version in most cases.

    So using RCD FCU or sockets for venerable equipment like the lawn mower can work out better. One would hope you don't change the bulb in the bathroom standing in a full bath. Or drill walls without testing first and looking at socket and light switch positions. However I had a son take up Ham radio at 14 years old and also building his own PC, so for me I decided to fit two 30 mA RCD's one for each consumer unit back in 1990's and I have got use to resetting every so often.

    As to if it saved him or me well hard to tell, I have had a shock enough to send me to the floor and take some time to recover when sawing a channel for water supply to fridge I did survive and the 30 mA trip did trip but not sure if it would have been any different had there not been a trip. Fact my legs gave way and I fell to floor auto disconnected me. And the shock was one of the worst I have had even with RCD protection. Point is I likely had far more than 30 mA it was only the duration which was limited to 40 mS so they only really protect when the earth leak is not through the human body but through something else like a water leak. So it trips out before the human touches anything. Likely a 100 mA would do the same job.
     
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