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M

mathias

Hello,
We are upgrading the light circuits in an industrial area. The excising lights are old fluorescent lights.
For the new ones it has been suggested to use a light with the following properties:
T8 fluorescent light 230 V,2x36W., High frequency ballast electronic starter, given inrush peak 30 A for 500 us,

The supply is a 3 phase 400 V TN(3 phases and N). Protected by a MCB C6 (4 phases) There is quite long cable so the minimum short circuit current at the end is quite low(around 65 A). Totality there are 21 lamps, each off them connect between one phase and N. Distributed evenly between the phases so the load current is about 2,2 A.

I have some elements that I am unsure about and would be most grateful to get some input.

*To verify that MCB can withstand the inrush current I have used the peak withstand curve from the manufacturer and the given inrush from the lamp datasheet. Have anyone experience that calculations according to thees curves fit with reality or do you have to account for some extra margin?

*What would happen in the N phase during inrush? I have assumed that the inrush would be time shifted(correct?) but would this cause any problems in N leader. I can add that I don't have much margin before the MCB would trip.

* As I have read due to voltage drop during start-up(caused by inrush) the electronic gear can go in to protect mode and block. How do you do any calculations on this are there any rule of thumb? The stationary voltage drop is off course very low(may be 1 % due the low current).

* Harmonic currents in the n leader. This is a known problem in fluorescent light systems. Is there any thumb rule about how much current to be expected?
 
Me neither, out of interest wher are you from? oh and welcome:welcome:
 
Start up current for fluorescents is I believe 1.8 times the normal operating current.
You may have to use a 'C' type MCB rather than a 'B' type.
Depending upon how. Any fittings are being installed, you may need to use one or more 3 phase contractors fed from a normal light switch/s.
Never found harmonics to be a problem with light fittings.
 

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