Ask a Tradesman
Why does my cicuit breaker keep tripping?
I have two socket outlets on a circuit and its protected by n 16amp circuit breaker. the cable size is 2,5sq mm and the length about 12meters to the first socket and the a further 8 meters to the next. I have 2 heaters connected to it , each about 2,5 kW. My problem is that the breaker keeps tripping after about 15 - 20 minutes of it working. does that mean i have to make the cable size bigger ? I also have a reading of 223V at the breaker and 213V at the furthest socket, does the volt drop make a difference?
Volt drop makes a huge differnce! A 2500watt load at 230volts = 10amps, at 213volts it rises to 11.73 amps, if you have two 2500w heaters then the curent will be 23.4amps!
This is dangerously close to the maximum current rating of 2.5mm cable, so you are in danger of the conductors exceeding their maximum operating temperature of 70 degrees and the insulation breaking down. Once the insulation starts to degrade then its a serious fire risk.
As a BSEN60898 type B miniature circuit breaker will have a fusing factor of around 1.25 (16amps x 1.25 = 20amps) it will operate (i.e. trip) at around 20amps. As in theory your drawing around 23 amps, I'd say your lucky its been doing its job as you could easily have had a fire.
To solve the problem you can either run a second 2.5mm cable from the second socket that only has one cable at it, all the way back to the fuseboard. This will then create a ring circuit and you can then upgrade to a 32amp MCB.
Or alternatively rewire the radial circuit as it is using 4mm twin and earth cable.
Remember that all electrical work comes under part P of the building regulations, so you will need to get part P consent from your local authority to carry out the work if your doing it yourself.
Answered 30th Jan 2013