Hi, Im doing some work on my 2400 Design and verification course (or whatever its called now) and i have drawn my circuits onto my building plan, but having worked out the outside lights they are way over for VD, i increased the cable size to 2.5mm from 1.5mm this helped, but not enough. As i've already drawn it, separating into 2 separate circuits will make the drawing look ruff, so i was thinking of turning it into a ring circuit instead. What do i need to change in my calc for the fact it is a ring?? i know that my cable length will increase but that alone makes it worse, what else do i need to do?? Circuit 8 - Outside Lights Length of circuit - 65.5mts There is 11 light fittings, each with 1x 150w lamp per fitting. 150w ÷ 230v = 0.65A per fitting 0.65A x 11 (fittings) = 7.15A (Ib) After 90% Diversity is applied... 7.15A ÷ 100 = 0.0715 0.0715 x 90 = 6.435A (Ib) (In) needs to be equal to or greater than (Ib), so (In) = 10A Using table 4D4A from BS7671... 1.5mm Armoured cable using reference method D6 has a capacity of 22A Volt Drop, This is (mV/A/m) x Ib x Length of circuit ÷ 1000, so from table 4D4B... 1.5mm = 29 (mV/A/M) 29 x 6.435 x 65.5 ÷ 1000 = 12.22V As this is a lighting circuit, it must be under 3% or 6.9V to be satisfactory. This fails. Any thoughts???

I have another question.... Although this is a colleague of mine who is also doing this course. He wants to use trunking, he has a lighting circuit that he can put on a 6A MCB, but when doing the correction factors calculation, the only one that has any relevance to him is the grouping factor. So he would do In / Cg Looking in the regs, his Cg is 0.03 as he has 30 circuits in this trunking. 6 / 0.03 = 200A 10 / 0.03 =333A Is this correct? Is his only option to use a separate run of trunking and split up the circuits? Grouping factors in the regs only go up to 20 circuits. But extrapolating to a horrendous 30 circuits would only give you a grouping factor of about 0.3 not 0.03 which would require you to use a cable having CCC of 20A so you would be looking at 2.5mm2 and some large trunking. It's also worth keeping in mind that circuits carrying less than 30% of their grouped current-carrying-capacity can be ignored when calculating the rating factor for the rest of the group. (Note 9 under table 6C in the red OSG)

I have another question.... Although this is a colleague of mine who is also doing this course. He wants to use trunking, he has a lighting circuit that he can put on a 6A MCB, but when doing the correction factors calculation, the only one that has any relevance to him is the grouping factor. So he would do In / Cg Looking in the regs, his Cg is 0.03 as he has 30 circuits in this trunking. 6 / 0.03 = 200A 10 / 0.03 =333A Is this correct? Is his only option to use a separate run of trunking and split up the circuits? Grouping factors in the regs only go up to 20 circuits. But extrapolating to a horrendous 30 circuits would only give you a grouping factor of about 0.3 not 0.03 which would require you to use a cable having CCC of 20A so you would be looking at 2.5mm2 and some large trunking.

Navigation

Welcome Forum Electrical Tools Electrical Forum UK USA Australia Canada
Electric UFH Advice Lighting & LED CCTV & Security (Public) Electrician Courses Access-Only Training
How to Access Training Central Heating Advice DIY Electrical Advice Talk Electrician
Site Supporters Forum
Pro's Only

Electricians Arms Electrician Talk How to Access The Arms Domestic Electrician Industrial Electricians Wiring, Theories, Regulations Engineering Chat Periodic Testing Problems Electricians Downloads Commercial Electricians Security (Access-Only) Access Private Area Business Related Advice Certification Schemes Electrical & PAT Testing
Thread or Forum Controls
Tags

If the forum is NOT loading any colour PLEASE CLICK HERE.

Cable calcs?

Thread starter Sparky83
Start date May 6, 2012
Tags

cable calcs electricians' talk

Sparky83

May 6, 2012

Sort by date Sort by votes

JUD

May 7, 2012

Upvote 0 Downvote

i=p/u

-

Arms

May 7, 2012

Upvote 0 Downvote

Facebook X Bluesky LinkedIn Pinterest WhatsApp Email Link

OFFICIAL SPONSORS

These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc