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Can you overload a lighting circuit

MrJack96
My question is if you’ve got a lighting circuit and you ad addition loads to the circuit will this always trip the breaker if you add too much load on a circuit? 


thanks for your help guys
  • 0
    That is very unlikely to do anything Andy, unless your 2 13A loads were 24/7.
  • 0
    This is correct up to a point...........If you loaded a 40A lighting circuit up to 60 amps, on a 6mm circuit - it would last for - about an hour I believe - perhaps more -  before tripping - repeated loading to 60Amps on a cable not rated for this would stress it out and lead to eventual failure of the cabling...... Id guess.



    That cannot be right.


    The given cable ratings must allow for the current likely for any compliant OPD and cable combination.
  • 0
    Unfortunately, one should never underestimate the natural stupidity of a client. If it can be overloaded then it will. Such an example would be the use of BS1363 13A sockets to feed table lamps and standard lamps which are then likely to be used by the clients or cleaners to run their vacuum cleaners.


    Even head teachers will declare their observancy when told not to use the 13A socket connected into the lighting circuit for anything else than the table lamp positioned in a small alcove on a stairwell. Then to find when next on site a vacuum cleaner plugged in to the very socket then to be told that "as an electrical novice I see a socket and use it because it fits and is the nerest to the stairs".

    I changed it for a BS546 5A socket..
  • 0
    Yes, I have had to rectify overloaded lighting circuits.


    Andy B
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    Why are domestic 'lighting' circuits normally 16A cable (1mm² T&E) yet have a 6A MCB?


    Not to mention the fashion now for using 1.5mm² 20A T&E.
  • 0
    geoffsd:

    Why are domestic 'lighting' circuits normally 16A cable (1mm² T&E) yet have a 6A MCB?


    Not to mention the fashion now for using 1.5mm² 20A T&E.


    Worst case might be a fully loaded lighting circuit protected by a 6A MCB and supplied using 1.0mm^2 cable will often be covered entirely with thermal insulation.

    Most likely situation might be a loaded circuit to 2/3rd protective device rating.

    The chances of any overloading in a domestic environment is minimal. Although you might have start-up current problems with 20 or 30 LED lamps firing up together, or LED lamps blowing to a short as opposed to an open circuit.


  • 0
    Because there’s lot of insulation in buildings and 1.5 mm is or mechanically sound, which is why you cannot wire emergency lighting in 1.0 mm.


    In most homes the lighting circuits are the the only circuits buried in insulation in the loft.


    Andy B.
  • 0
    Yes, but that is hardly a reason as it applies to all circuits.
  • 0
    I always say putting a 13a socket on a lighting circuit is bad practice. I can't really understand why it is permitted.
  • 0
    We seem to have moved from the OP.

    Realistically a circuit wired in 1.0mm with 6A CPD cannot be overloaded in a domestic install. If I add a 13A socket, it still cannot be overloaded. Moving on, if I have a larger CPD say 16A, and a 1.5mm cable I can overload (not the right term really) the cable if the installation method (insulation) is unfavourable. If I have a large cable feeding football floodlighting, then I probably cannot add sufficient extra load to make much difference unless it is a 125A BS4343. I suspect this question is a "homework" one to make the students think of scenarios, it certainly has done that!

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