Lighting Circuit.. Surely This Isn’t Right?

[Tag]

Evey lighting point should be calculated as a min 100w bulb regardless of whats actually installed

 

[ian.settle1]

Would someone please come up with the answer

Why this posting is nearly 12 months old

 

[Tag]

...what was the question?

From the first post I'm counting 24 lighting points. 24*100w = 2400w / 230 = 10.43A. I'd say 1mm t+e is border line if ref method is 101 but the volt drop is very high. Best use 1.5mm t+e on a 16A breaker in my opinion.

 

[Sintra]

...what was the question?

From the first post I'm counting 24 lighting points. 24*100w = 2400w / 230 = 10.43A. I'd say 1mm t+e is border line if ref method is 101 but the volt drop is very high. Best use 1.5mm t+e on a 16A breaker in my opinion.

If you are using ref method 101 as stated you can not use a 16A breaker as your 1.5mm T&E is rated at 13A.

Table 4D5 BS 7671 2008

 

[Tag]

ah your right, I think I ment 100...

 

[Stuart King]

Its the same question as a year ago but there was no answer
50w at 230v i=p/v i=50/230 i=0.28 amps
50w at 12v i=50/12 i=4.2 amps
Is this correct?

 

[Tag]

50w at 12v i=50/12 i=4.16

 

[Stuart King]

Always round up.
Is the 12v sum correct?

 

[Tag]

I was told to never round up... I think that WAS how it was done but I was recently told different

 

[Stuart King]

Anyway,is the 12v sum correct?

 

[Tag]

yes it is

 

[Doomed]

yes (for the secondary side of the transformer)

Now calculate the primary current

 

[Modernelectric]

yes it is correct.

 

[Stuart King]

The primary side is fine, just can't get my head around the secondary

 

[sparks1234]

You are forgetting that you are working it out at 12 volts, if you transpose it to 240 volts (for ease of calculation then divide your 4.2 amps by 20 which comes to 0.21 amp, so 5 LV lights to 1 ampish, so why not put 20 or so lights on a circuit, calcs work out alright.

 

[Stroppy]

Don't forget to add in the power factor load of the transformers

On a serious note, all these quotations of loads on the 1.0 don't mention that the cable should be de-rated as, being a lighting cable, it will undoubtedly be going through loft insulation, bunched with other cables, and goodness knows what else on its route, knocking the CCC down considerably. I know 'official' cable calcs often give ridiculously pessimistic results, like demanding a 10mm cable for a lighting circuit because of all the factors, but in this case 1.0 really doesn't seem enough.

It would be be interesting to do a proper calc with the given load, and all the insulation, grouping, and other factors, and real length and see what it comes up with.

 

[i=p/u]

and did any one mention diversity..... ive pushed circuits to limits .... forget future proofing...... will keep us in work and are quotes will be slightly cheaper

 

[Engineer54]

You can probably count the amount of times ALL of a circuits lights are on, within a domestic setting on one hand over the lifetime of the installation!! As far as i'm aware, 100W incandescent lamps are no longer available, and 60W lamps are soon to follow.

I'm not saying that the circuit as described by the OP is a particularly good one, but most are over assessing the actual demand load that this circuit will ever see!! Diversity is a wonderful thing, to those that know how to use it!!! lol!!

 

[jumpin jax]

This is 2009, time warp

 

[Engineer54]

Just Noticed that!!! lol!! All Stroppy's fault digging up an ancient post!!... :56: