Lights tripping

Dantheman · Feb 1, 2012

The problem is all the lights in the house are on a 6 amp type B MCB (new wylex) the approximate load is 2.5kw – 3kw and every time a bulb goes the breaker trips out. It’s not on the RCD side as the CU only has one RCD which the sockets up and down are on.
Please can you give me any advice on how to solve the problem do I just split the load of the light to up and down on two separate breakers?

Many thanks

Darkwood · Feb 1, 2012

Where do you get 2.5kw - 3kw from as this would equate to 10 - 13amps, are you allowing for diversity when calculating lighting load???

Its common for incandescent lamps (filament type) to trip standard mcb's when they blow its just something to put up with or change to CFL low energy type they done suffer this side effect.

Edd · Feb 1, 2012

3kw at 230 volts givs you 13 amps!!!! the mcb will be slowly heating up if you had all the lights on, when a lamp blows it causes a momentry fault that most MCBs can handle as their not run at such capacity, in your case your running over capacity and the slightest upset, like a lamp blowing is causing the tripping. only real solution is to spread the load across circuits.

Edit to add what darkwood just put,, CFL lamps will help here

Dantheman · Feb 1, 2012

2.5kw - 3kw is the assumed load with no diversity each lamp 50w x 57 lamp outlets

Darkwood · Feb 1, 2012

Edd said:
3kw at 230 volts givs you 13 amps!!!! the mcb will be slowly heating up if you had all the lights on, when a lamp blows it causes a momentry fault that most MCBs can handle as their not run at such capacity, in your case your running over capacity and the slightest upset, like a lamp blowing is causing the tripping. only real solution is to spread the load across circuits.

I suspect OP hasnt calculated lighting load correctly and as ive just mentioned and may i correct you in your assumptions that the mcb is more readily tripping due to mcb been up to capacity, when a incandescent lamp blows the filament is vapourised leaving an ionised trail in the gas which is a more or less a short circuit hence you see a bright flash as the lamp pops - this is an electrical arc flowing through the ionised gas with no resistance, normally the gap between the filament stalks would require several thousand volts to cause a spark to jump across but the white hot failing filament has already created a path so allowing 230v to jump this gap at the expense of the mcb seeing the short circuit, whether the mcb had no load or was fully loaded it would still react to this as a short circuit and trip.

Darkwood · Feb 1, 2012

Dantheman said:
2.5kw - 3kw is the assumed load with no diversity each lamp 50w x 57 lamp outlets

Is this a large house and/or a new install or has the board only been changed recently, and are you a family who likes to have all the lights on in the house???