Posting a message to the forum will remove the above advertisement
  1. angel While you're here, woud you mind checking out our Electrician's Insurance section to see if we could save you a few quid? - Specifically our Van Insurance Deals and Public Liability Insurance Deals. Thanks for supporting the forum! angel

Discuss Immersion tank, element fault, hot lives, heating 13A fuse in the DIY Electrical Forum area at ElectrciansForums.co.uk.

Please make sure you checkout our forum sponsors, many do discounts for members and, they keep the forum free to use.
  1. Delectrician
    Offline

    Delectrician EF Member

    Location:
    Edinburgh
    Hi,

    I have a fault somewhere on my immersion heater circuit, the 13A fused spur switch is getting hot & there is visible insulation damage to the live conductors only, the fuse in the spur is where the heats being generated, I disconnected everything & tested the resistance of the element alone, its a 2.8KW rod & I recorded a value if 18.5 Ohms, Fairly normal for an element that size, I thought!

    The circuit is governed by a 16A MCB, through a 80A RCD unit, on a duel RCD fully loaded board, I tested the functionality of the RCDs & both are operating as normal, I am suspicious the fault is the element, but with no faults to Neutral or Earth, I'm a little perplexed! The property was EICR tested only 1 year ago by an NIC EIC registered company, so all the continuity values, IR readings & loop impedance have been recently checked.

    Any help would be brilliant, I don't want to pay for the element to be replaced & find out It wasn't a fault with it!

    Thanks in advance!
     
  2. Matthewd29
    Offline

    Matthewd29 Regular EF Member

    Location:
    Belfast
    What size of cable is it? Maybe it would be better with a 20a Double pole water heater switch rather than a 13a fuse spur as at 2.8kw your not far off 13a so it will heat up if on for long periods of time
     
    • Agree Agree x 4
    • Like Like x 1
    • Optimistic Optimistic x 1
  3. snowhead
    Online

    snowhead Trusted Advisor

    Location:
    Mildlands
    The fault is the Fused Spur, bad contact between fuse and carrier.
    The fuse holder won't take 13amp continuously for the length of time the heater is on.
    20amp DP. is the answer as above.
     
    • Like Like x 3
    • Agree Agree x 3
  4. Wilko
    Offline

    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    No problem with that immersion element resistance.
     
    • Agree Agree x 1
  5. Delectrician
    Offline

    Delectrician EF Member

    Location:
    Edinburgh

    Its 2.5mm cable, if the element was pulling above 13A for a long time then Id expect the fuse to blow, but It is instead just creating loads of heat & not blowing, the last switch had melted the plastic fuse holder to the fuse but never popped, I replaced the whole switch today and after 10 minutes on the new fuse was very hot, so I isolated & left to come her for advice, by my calculation there should still be an Amp headroom, with the 13A Slow blow, its a very short run of cable.
     
  6. Delectrician
    Offline

    Delectrician EF Member

    Location:
    Edinburgh
    This is the 3rd one in a row with the same fault then, as EICR company changed it out for the same reasoning (ie it was a faulty switch), then it began to heat again, so I changed it out after testing the elements & RCD function & began to pull heat to that fuse again, Can it be possible that 3 switches in a row have the same problem, or is it more likely that the element is drawing above its rated amount, even if so, why is the fuse not just blowing? Why is it getting so hot that its melting plastic but not breaking continuity?
     
  7. 123
    Online

    123 Electrician's Arms

    Your answer is in posts #2 and #3. Change it out for a 20A DP Switch.
     
    • Like Like x 2
  8. SparkyChick
    Offline

    SparkyChick Making a banana smoothy for my fave gorilla Electrician's Arms

    Location:
    South Wales
    Business Name:
    SparkyChick
    Fuses blow by getting hot. Run a fuse close to it's rating (which you are doing) for extended periods of time and it will get hot, but sit there quite happily.

    And, running it close to it's rating assumes a voltage of 240v. More than that and you'll be running on the raggedy edge.

    You've already received the best advice... lose the switched fused connection unit and replace it with a 20A double pole switch.
     
    • Agree Agree x 4
  9. buzzlightyear
    Online

    buzzlightyear Electrician's Arms

    Location:
    star command
    you bang on the monie there. drawing to much current on that e/heater
     
  10. Delectrician
    Offline

    Delectrician EF Member

    Location:
    Edinburgh

    Thanks

    This makes sense!
     
    • Like Like x 1
  11. GeorgeCooke
    Offline

    GeorgeCooke Active EF Member

    Location:
    UK
    You don't need a fused spur so replace it with a double pole switch as you have already been told twice.
     
    • Like Like x 1
  12. Murdoch
    Offline

    Murdoch Electrician's Arms

    Location:
    Woking
    problem these days are the carp switches and when the voltage drops, the amps increase .... so a 3KW [email protected] 250 v pulls 12a
    @ 240v pulls 12.5a
    @230v pulls 13a
    @220v pulls 13.6a
    @212v pulls 14.5a (lowest voltage I've seen recently)

    then allow for poor connections in the switch / fuse
     
    • Disagree Disagree x 1
  13. 123
    Online

    123 Electrician's Arms

    You sure about that? The resistance of the immersion element coil is constant, so as the voltage drops, so should the current.
     
    • Agree Agree x 3
  14. Marvo
    Offline

    Marvo Gender Confused Staff Member

    Location:
    South Africa
    I'm going to disagree, if it's a linear load of fixed resistance the current decreases as the voltage decreases. A 3kW element is only 3kW at it's rated voltage. At a lower voltage it has a lower kilowatt output. I would however agree with the statement about poor manufacturing quality.
     
    • Agree Agree x 4
  15. telectrix
    Offline

    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    agree with marvo and 123. lowering the voltage will reduce the current and hence also reduce the wattage.

    i = V/R, so for a 18 ohm element...

    250V,.... I = 250/18 = 13.888888888A

    230V .... I = 230/18 = 12. 77777777777A
     
    • Agree Agree x 3
    • Like Like x 1
  16. static zap
    Offline

    static zap Regular EF Member

    Location:
    west midlands
    I agree with the first bit .
    The Quality of current parts -is soon shown up by this circuit !
    ( possibly running in a warm enviroment )
    If spare element is rated at 230V and being given 240V ..may be running a higher current than in past .
    (Its not a switched mode PSU --YET)
     
    Last edited: Nov 22, 2017
  17. Wilko
    Offline

    Wilko Electrician's Arms

    Location:
    Berkshire
    Business Name:
    Wilko Electrics
    A couple of thoughts :
    - maybe all 3 are carp brands? But from what I've seen I'm inclined that none of them are any good for 13A continuous nowadays.
    - a 13A fuse definitely won't melt at 13A but will be warming up for it :)

    IMG_0416.jpg
     
    • Like Like x 1
  18. marconi
    Offline

    marconi Regular EF Member

    [QUOTE
    The circuit is governed by a 16A MCB, through a 80A RCD unit, on a duel RCD fully loaded board, I tested the functionality of the RCDs & both are operating as normal, I am suspicious the fault is the element, but with no faults to Neutral or Earth, I'm a little perplexed! The property was EICR tested only 1 year ago by an NIC EIC registered company, so all the continuity values, IR readings & loop impedance have been recently checked.]


    A few observations and remarks:

    1. The EICR was a year ago. Had the IR of the element, L-E, N-E been measured before the last FCU was replaced?

    2. The IR measurement must be done when the thermostat contacts are closed - A year ago it may have been that the contacts were open during the measurement. Only sure fire test is to test IR by connecting to the element's terminals.

    3. It's time to AMPCLAMP one of the conductors supplying the IH to establish how much current is actually flowing. Measure the voltage too across the element.

    4. Is the thermostat actually opening when the required HW temperature is reached?

    5. Is the element cycling on and off - this can happen if the element/thermostat is at the bottom of the tank and it is covered in limescale and detritus or if you have a hot water leak somewhere. The resistance of the element will increase slightly as it heats up to its operating temperature but during this warming up period a higher current than the running current will flow causing more Ohmic heating of the fuse.

    6. The thermostat needs to be a modern one which includes a safety cut out as well as the normal bimetallic contacts. Is the thermostat the correct length for the element and the element the correct length for the tank?

    7. Is your water being heated to a temperature above 60C? Is it steaming/scalding hot when you draw hot water. If so, the element is on longer than usual and heat loss from the tank will be higher too requiring more heating from the element.

    8. Is the tank lagged and lagged with the latest low heat loss thermal insulation?

    The rated power dissipation of a BS1363 fuse is 1W at 13A. Modern plastic FCUs unlike the older ones tend to have higher thermal resistance to heat flow between the fuse and the surrounding air which means they can often run hotter, especially if the ambient is high too as is the case near an IH. And they are white - black is better.
     
    • Like Like x 1
    • Informative Informative x 1
    Last edited: Nov 23, 2017
  19. ruston
    Offline

    ruston Trusted Advisor

    Location:
    Northumberland
    @marconi@marconi . 4. Is the thermostat actually opening when the required HW temperature is reached?

    I had this just recently on an old immersion heater . The thermostat was burnt to a crisp inside , although it was still functioning to a degree it was enough to melt the insulation from the the stat to the element.
    The water was heating but not to the selected temperature.
     
Loading...
Similar Threads - Immersion tank element Forum Date
Immersion tank with two immersion? Electrical Forum Oct 6, 2017
Solar PV Immersion diverter Solar PV Forum Oct 15, 2017

Share This Page

Electricians Directory Post a Domestic Job Post a Commercial Job