Help with discharge lights

[66jonny]

Hi all..... here goes!

Appendix 1 of OSG states the demand of a discharge/fluorescent circuit is taken as the rated lamp watts multiplied by 1.8. I was taught this and thought that I =(P x 1.8)/230 would indicate the amount of lights you could put on say 10A MCB protected circuit,

eg. 15No fluorescent switch start lights (each 4x18w)

I = (15 x 72w x 1.8)/230

I=8.5A

Therefore possible to install 15No lights on 10A MCB type C protected circuit

(assuming cable size, length of run, volt drop etc are ok.)

I'm now starting to think that maybe I'm missing something, Im just starting out and want to do things correctly. A new job requires 16No Thorn Chalice 190v discharge recessed lights (each with a 70w HIT-CE lamp) for a reception area. The ballasts are Mag Tridonic Ombis 70w, connected load 82.2w lambda 0.99.

My calculations using I =(P x 1.8)/230

I = (16 x 70 x 1.8)/230

I = 8.76A

therefore possible to put 16 on 10A typeC MCB

However, as Ive been doubting myself, though I'd check with Thorn Tech help line....big mistake - blood out of a stone comes to mind! Eventually got starting current of 0.58A which seemed good and related to my calculations I = (70x1.8)230 =0.55A x16 =8.8A.

I ask for clarification on number of lights eventually was told max of 7No on 10A typeC, 12No with PF correction capacitor fitted. He got this from a tridonic chart but couldnt give me any other details.

so 7x 0.58A = 4A

So can someone with a better grasp of this tell me what Im doing wrong, I thought the 1.8 multiplier accounted for losses/harmonics etc??? Is it the difference between starting current/steady state, or the 190v, Im lost??

Sorry bit long winded but Im completely confused, so any help appreciated

Thanks Jon

 

[Northern Electric]

I've had a bit of a look over the spec of these fittings on the website. I couldn't find any tech spec on the website, but looking at the specs you posted I can tell you the Lambda is the total power factor per fitting, 0.99 power factor is as good as you are going to get. The 1.8 correction factor for discharge lights is allowing for a much higher power factor, ie, switch start fittings. In theory you should be able to wire 16 fittings on the circuit, however, I would not wire that many onto 1 circuit, I would split the circuit in half and wire 8 per circuit. You could still power via 1 10A mcb, but it gives you the advantage of being able to split the circuit at a later date. Personally, if there are enough spare ways, I would split them over 2x 6A mcbs.