In rush current

[Wilson12]

Hi with florescent lights and motors is there a in rush current you have to multiply by the ib to get in

 

[Darkwood]

I think your key term you're looking for is inductive loads, filament lamps are resistive where as flourescents are inductive so its wrong to broadly catagorise them with the term 'lights', motors and transformers are also inductive loads and the inductive nature of these loads needs to be included in any calculations when designing a circuit.

 

[Wilson12]

Ahh I see cheers and is there a standard calculation to work out inductive loads?

 

[Darkwood]

For lighting your usually taught to apply a 1.8 factor when working out the design current, in small installations this will be sufficient to allow for cable sizing and the correct switch ratings and overcurrent protective device.
On large commercial and industrial installs others factors like the inrush characteristics of a motor or high wattage light need to be taken into account, poor design on big installs often end up with nuisance tripping when switching banks of lighting on or a DOL motor etc.

For now though don't worry about the latter, just concentrate on what you are taught.

 

[Wilson12]

I know leds have quicker inrush current but will you also have to apply the 1.8 start up factor for.these

 

[malcolmsanford]

I have always designed HF Flouries with a C type breaker................

Though you don't get what is commonly an inrush, you could though if you have quite a few as in a office, get tripping problems with a normal B type MCB

 

[Darkwood]

Its an inductive load, the LED driver has the inductive trait here so yes it requires the factor to be applied, also because you normally stack these loads onto 1 switch you need to be cautious you dont have too many switching together or you can get nuisance tripping when switching multiple fittings on.

If a lamp hasn't got a coiled filament acting as a resistive component then its probably inductive, if in doubt just apply the factor and at least your calc's are good for design.

 

[Simonslimline]

If i remember correctly, the 1.8 factor need not be applied when dealing with high frequency fittings.

Not 100% sure though if i am honest.

 

[Darkwood]

If your tutors are expressing this to be the case then the market must have pulled itself together and a EU standardized model for compliance adapted, it was the case though not long ago where electronic ballasts and drivers varied widely in quality and although they could allow for a reduction in the applied factor there was no guarantee your fitting didn't have cheap chinese drivers or electronic ballasts in which were poor quality and gave a wide range of required factor needed from one fitting to the next - I may look into this myself to see if we have any definate guidance to go by.

 

[Simonslimline]

If your tutors are expressing this to be the case then the market must have pulled itself together and a EU standardized model for compliance adapted, it was the case though not long ago where electronic ballasts and drivers varied widely in quality and although they could allow for a reduction in the applied factor there was no guarantee your fitting didn't have cheap chinese drivers or electronic ballasts in which were poor quality and gave a wide range of required factor needed from one fitting to the next - I may look into this myself to see if we have any definate guidance to go by.

The 1.8 aires on the side of caution i was taught. You may not need to apply 1.8 if you speak to the manufactures regarding there products spec. I imagine each manufacturer varies though.

 

[malcolmsanford]

I agree Simon that you should design as per the manufacturers guide. I guess though trying to re-train someone like me is a bit of a pain.

I still to this day would never load a circuit with control gear more than 50% of the In of the protection device. Old hat I guess