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Breaker keeps tripping when lights are turned off

Postby suprafan » Thu Jan 31, 2008 9:50 am

In a warehouse there are 3 rows of 3 fluorescent lights, each row is switched on and off via a wall switch which has 4 inbuilt switches on it, one for each row and the 4th controls a light outside..

now when 1 of the rows is switched off as normal it takes out the breaker in the consumer unit, only does this when switching OFF that said row the other 2 are fine, if its switched off slowly its ok sometimes, any ideas what may be the problem?
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Postby ericmark » Thu Jan 31, 2008 8:42 pm

I have thought about the problem and nothing I can think of should cause this. However, I will ask a few questions. Is it an earth leakage trip or MCB that trips out? Are there any emergency lights on the row that trips out and if so are there any on the other rows? With a warehouse you may be operating a contactor which could turn something else on like exit lights is there anything like that?

Postby sparx » Thu Jan 31, 2008 8:57 pm

two possibilities come to mind, first the power factor correction capacitor in one of the fittings is duff or disconnected, allowing the choke to cause inductive back EMF on switch off much like the arc across the point on older cars.
Or maybe the switch is the wrong type for fluorescent lights as if correct should be 'snap action' and not allow you to turn off slowly, or could be burnt by arcing, try swopping switch wires between 2 rows and see if prob moves to new switch in which case its the lights, or if same switch still trips then its the switch, regards SPARX
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