fluorescent lighting

[RMS]

Thanks for the replies,

done some calculations for voltdrop and with the 1.8 multiplier and its bringing the volt drop too high also due to the long cable runs through 2way switching etc.

Tried upgrading the cable to 2.5mm² but its still too close with the voltdrop of the submain cable. Think i will have to split the lights up onto separate mcb's controlling 3 lights each to reduce the load thus reducing voltdrop. Has anyone ever experienced the same problems? I suppose i could contact the manufacturer and get an exact figure for the current on starting.

 

[ricicle]

Have you thought about using the contactor method.That way your feeds go direct to light via contactor and any switching over long runs is only supplying contactor
This assuming you've got your calcs right

Ricicle

 

[RMS]

There are 18 lights in total. 12 in the large hall and 6 in a small class room. If i were to have 6 lights per MCB, then the cable run to the first light in the small class room is 61m.

Each light is rated at 4 * 36w = 144x / 240 = 0.6A * 1.8multiplier = 1.08A

so 6 lights = 6 * 1.08A = 6.48A

VD = 28 * 6.48 * 61 / 1000 = 11.1v and thats only taking into account the first light.

 

[ricicle]

Hasn't the designer worked all this out for you?

Ricicle

 

[RMS]

no, its a project that i am doing for college, its the plans for a job that a friend did a while ago that i have got and i am basing my project on it. The designer only specified the size of the sub main cable which is 25mm² SWA and the location of lighting and power circuits. don't think any calcs will have been done for the job when it was carried out.

 

[Steve]

1728 watts of lighting in a large hall? Doesn't sound a lot, IMO. One school I went to had some kind of recessed square discharge lamps in the hall.

 

[ricicle]

If no calculations were done then your friend couldn't have been certain that his circuits were correct.But as you are doing it theoretically you can experiment a little.I havn't got my regs book here in my lounge but if you are confident your figure for volts drop is right and that is the length of circuit then you will have to find a size of cable that will satisfy volts drop, current carrying capacity for install method and EFLI for the OPD

Ricicle

 

[Spark123]

Can you shorten cable lengths by using singles in conduit?

 

[RMS]

Nice idea, but don't think it will help much.

I think i will split the lights up 3 per circuit and that will limit my design current and length. So there will be 18 lights off 6 MCB's. Does anyone see a problem with this?

The calcs with the allowance for starting currents have shocked me as i can recall allot of jobs i've been on in the past with plenty of fluorescent lights wired in 1.5mm² with some long cable runs.