Separating fluorescent and incandescent loads

[jbelectrical]

The electrical engineer that reviews jobs before they go out prefers that we keep fluorescent and incandescent loads on separate circuits. I've heard varying opinions, but it appears that the reason for doing this is to prevent the incandescent lights from flickering. Is there any truth to this?

Thanks,

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[CJFlatters]

Where abouts are you and what is your application ?

Most fluorescent luminaires these days are specified as high frequency (typically 25kHz), they do not have flicker / stroboscopic problems.

Do you really mean incandescant ??? - if you do, they are terribly inefficient and rather outmoded light sources.

Why not use high pressure sodium, MBI (metal halide) or induction lamps if you are looking at highbay, lowbay or area/flood lighting applications.

The presence of third harmonics on fluorescent is something you need to take account of and may be the reason why your colleague has separated the fluorescent luminaires from other circuits.

You also need to check and carefully select the type / rating of the circuit protective device you are using.

_______________________________________
Regards -

Colin J Flatters
Consulting Engineer & Project Manager

 

[jbelectrical]

We're located in the U.S. - Florida, to be exact. Most of our jobs are located here, as well.

In this scenario, I have a floor plan of an office building. At the meeting room, I have several 2' x 4' wraparound lights with electronic ballasts and 2-32w T8 lamps/each along with several incandescent downlights. These are going on separate circuits. Both will be on single-pole, 20 amp breakers.

I was told that this used to be a problem with magnetic ballasts, but no longer holds true with electronic ballasts.

 

[jbartos]

Suggestion: It is sufficient to keep incandescent and fluorescent luminaires controlled by different switches. However, a different circuit implies a different switch automatically. The incandescent lamp cold filament has lower resistance than the hot one, when lamp is lit. This means that there will be an inrush current that may potentially cause the branch circuit voltage drop to less than 90% of the nominal voltage. This impacts some fluorescent ballasts that are supposed to operate within 90% to 110% of the nominal voltage. When the voltage is below the bottom limit, the fluorescent lamp may or may not properly start.

 

[CJFlatters]

Thanks jbartos, cant say I've hareally heard of many problems of this nature in the UK but always worth keeping in mind.

I guess the converse is also true, since electronic high frequency controlgear does produce a transient on energisation, a voltage dip will follow which would flicker the dichroics as the output is a function of voltage^2, ie 90% voltage = 81% light output.

MCB manufacturers in UK / Europe produce tables for MCB's indicating the number / rating of HF luminaires which may be fed from a given rating / type of MCB without the likliehood of nuisance tripping.

Not quite sure what the system used in US, but UK use IEC 60947-2 curces A thro D, typically we may use a 16A type C for such an application.

TTFN

_______________________________________
Regards -

Colin J Flatters
Consulting Engineer & Project Manager

 

[davidbeach]

I usually keep fluorescent and incandescent separated simply because incandescent doesn't work very well at 277V. ;-)