Calculating Design and Estimated for mixed Lighting Circuit

[benstoneham]

How would you approach the following (I'm interested both from a theory and practical point of view as I'm studying for 2382 and working out an actual design spec prior to LAB submission right now):

Lighting circuit with mixture of

6 x GU10 w. 11WCF
3 x GX10 HID (Britespot 35w Metal Halide).

Ususally I understand (irrespective of the lamp holder and ignoring diversity for now (see last questions below)) a minimum of 100W per lamp should be assumed i.e. 9 x 100w = 900w / 230 = 3.91A.

What happens when you mix in HID though?

I think I am right in saying that (assuming power factor is not <0.85), the guideline is to assume a 1.8 correction for transient load i.e. on the 35w/ 100v HIDs above this would be (3 x (35w*1.8))/100 = 1.89A.

However, when you think about it, the 100w guideline assumes 230v i.e. 0.43A per lamp. At 100v (which is what the balasts run at), the same calculation produces 0.63A - a 43% difference.

I've searched everything I can think of, but can't see a guide on this.

I suppose a second related question is whether the Design Current for a lighting circuit can take account of the type of lamp holder in use (for example, while a GU10 can take anything upto a 100W GU10, a GX10 can only take a 35W Sylvania HID. If this was the case then the Design calc could use the actual I guess.

Also, if this is a single radial supplying all of these lights in the same room, am I right in saying that it is not appropriate to apply 66% diversity guideline as it is likely they will be used simultaneously.

Apologies for the long post, hopefully someone will have experience on this.

 

[ban-all-sheds]

However, when you think about it, the 100w guideline assumes 230v i.e. 0.43A per lamp. At 100v (which is what the balasts run at), the same calculation produces 0.63A - a 43% difference.

100W is 100W is 100W.

If the lamps were ELV, you'd have a figure of 5.25A for the lamp, but it would still only be 0.27A for the circuit.

I've searched everything I can think of, but can't see a guide on this.

Try this...

I suppose a second related question is whether the Design Current for a lighting circuit can take account of the type of lamp holder in use (for example, while a GU10 can take anything upto a 100W GU10, a GX10 can only take a 35W Sylvania HID. If this was the case then the Design calc could use the actual I guess.

Isn't the whole point of the 100W rule that anyone could come along and change the luminaire or fit a different lamp? I know it's hopelessly outdated though, as it harks back to the time when all there was were 40/60/100W GLS...

Also, if this is a single radial supplying all of these lights in the same room, am I right in saying that it is not appropriate to apply 66% diversity guideline as it is likely they will be used simultaneously.

In any diversity calculation the designer must be guided by his knowledge and expertise. If you judge that they'll all be on then you can't use diversity....

 

[nozspark]

The 100W rule only applies to lamp holders which take standard GLS lamps. Any fitting with a fixed wattage (such as flourescent tubes) can be counted as it's rated wattage.

You design a circuit for what you put in, not to what it might be altered to.

 

[ban-all-sheds]

The 100W rule only applies to lamp holders which take standard GLS lamps. Any fitting with a fixed wattage (such as flourescent tubes) can be counted as it's rated wattage.

That makes a lot more sense.

 

[benstoneham]

OK, that makes sense... always seems obvious when someone points it out.. I'll re-read wikipedia as pennance! thanks for the help.