fluorescent lighting

[RMS]

Hi all,

when calculating the design current for a circuit with a large amount of fluorescent lighting do you have to take into account for inrush currents on starting and does this apply when calculating voltdrop?

thanks for any replies

 

[ricicle]

A multiplication factor of 1.8 should be used when calculating fluorescent loads.A type C mcb should handle any inrush current

Ricicle

 

[ricicle]

Sorry yes it should be used when calculating volt drop also

R

 

[RMS]

Thanks for the reply, can this be found in the regs?

I'm not worried about the OPD as the lights will be split up onto separate circuits of 6. The lights have 4 lamps each rated at 35w.

I just want to be able to calculate voltdrop and shock protection of the circuits.

 

[Spark123]

Afiak it isn't in the regs, it is a rule of thumb but can be over-ruled with more specific information from the manufacturer. Are the lights high frequency? Are they all going on the same phase? A lot of standard flouros on the same phase all flickering at the same instance is not nice. Calculate volt drop the same way as normal using the x1.8 factor, shock protection as normal though you need to know your OPD to be able to do this.

 

[Taylortwocities]

Its not in the regs but the 1.8 multiplier is a part of the pages dealing with diversity in the On Site Guide

TTC

 

[RMS]

thanks for the replies,

Spark 123, don't know if the lights are high frequency yet as this is an optional extra with the manufacturer's and they have not been ordered yet.

They are all fed off the same phase/distribution bard via a sub main. Its a hall in a school. Do you think this set up is a concern?

Do you mean i will need the rating of the OPD to compare my shock protection calculations with them as stated for that type in the regs?

 

[RMS]

Thanks TTC,

ive found it in the on-site guide.

 

[ricicle]

It would be better from a loading point of view if you could balance the lighting over 3 phases, possibly using a contactor depending on the switching requirements.But a group of fluorescents on the same phase normally can only cause a problem when they are over rotating machinery as they can make the machinery appear stationery due to the stroboscopic effect.
Your choice of OPD will determine what the maximum EFLI is to allow for the required disconnection time (5 seconds - fixed equipment)

 

[Adam_151]

balance the lighting over 3 phases, possibly using a contactor depending on the switching requirements.

But if you happen to loose the phase that the contractor coil is on...

Surely better to just have some extra switches and loose the contactor I'd have thought

 

[RMS]

The designer has specified a single phase distribution board to be installed and fluorescent luminaires. I can understand the problem with the balancing of loads over three phases but would all the lights on one phase in a school hall be a real problem?

The longest circuit i have for the lighting is 52m. The design current is 3.6A * 1.8 = 6.48A

volt drop = 29 * 6.48 * 52 / 1000 = 9.77v which exceeds 9.2v (using 1.5mm² t+e)

Is my working correct? Will i have to upgrade the size of the cable to satisfy voltdrop?

 

[ricicle]

As I said it depends on the required switching arrangement.I prefer the multiple switches also but the hall would also be backed up with emergency lighting ?

 

[ricicle]

If that is what the designer has chosen then so be it.If you cannot shorten the cable route in anyway or re-arrange loading then if your calculations are correct(havn't got my regs book to hand) you will have to upsize the cable

Ricicle

 

[Spark123]

Probably won't matter too much about all being on the same phase given the application. If you find they strobe too much it is possible to add a capacitor in series to alternate lamps to counter effect this.
Regarding the volt drop the load isn't all at one end of the circuit. Volt drop can be calculated by each leg of the circuit i.e. the first leg of the lighting circuit (from DB-first fitting via switch) will have design current of all the loads it is supplying, the second leg all loads less one fitting, 3rd less another fitting etc etc etc. Don't forget to add the volt drop of the supply to the sub main too!! Depending on the Ze and the protective device the efli may be the restricting factor.
Also please remember to select switches suitable for inductive loading or one twice the rating for a resistive.

 

[ricicle]

Spot on 123

Ricicle