MCB Trips after 4 hours ?

[onesongrg]

Hi bit of advise needed please:
I installed 3 security lights with pirs onto an existing lighting circuit, swoped the 6amp mcb for a 10amp, there is only 7 lights on the circuit max demand 630 watts it is only using 320 watts so at its max it is only using 9 amps.
It all works fine for a few hours and then the 10 amp mcb type 2 trips, swoped the mcb still getting the same fault.
The consumer unit is in water proof box on the side of the house its bone dry inside no damp.
This fault only started after the lights were fitted.
I can only think i will have to intall the security lights on its on circuit?

Any help would be greatfull!!!!

 

[ZenStalinist]

Your mathematics are somewhat curious.

 

[securespark]

6 amp breaker at 230V will supply 1380W continuously.

10 amp breaker at 230V will supply 2300W continuously.

630W at 230V = 2.74A

320W at 230V = 1.39A

So yourloadings are nowhere near. Try disconnecting your recent wiring to see if the mcb still trips. If not, you will have to go over what you have done to see where you have gone wrong.

 

[onesongrg]

Sorry

The maths are not correct, i was including the the 3 x 500 watts security lights in the figure, but did't put it in so the it looks wrong the total load at its max is 2130 watts which adds up to 9.2 amps.

A 10 amp mcb should not trip as far as i am aware?

 

[securespark]

Have you included surges in your design?

I mean, in theory, a 5A breaker should supply 2 x 500W floods, but I came across an installation where it was tripping left right and centre. The result of my investigation was that when the lights came on, the current surged above the mcb rating for a short period of time, then dropped down.

You could temporarily (i mean temporarily - only for testing puposes, mind!) try a C type breaker or a 16A breaker to see if this solves your problem.

If it does, you need to wire your 1500 watts of security lighting onto a dedicated circuit or ringmain.

Floodlights are not really designed for ordinary lighting circuits, anyway.

 

[onesongrg]

Thanks for the reply m8
It crossed my mind about trying a 16 amp mcb the installation is a TT only 5 brackers on cu to rewire the circuit was not easy and i will have to change the cu.
But you are probably correct about surges, i will try a clamp meter across the circuit see what it pulls

Thanks