2396 design project teaser

[Guest125]

What about computer socket circuits?

How do you mean?

 

[Leesparkykent]

How do you mean?

Just wondering if you still use radials for circuits designed for lots of IT equipment? Or a ring or run another cpc back when using a radial

 

[Engineer54]

Less work. Easier. Less testing. we only do ring mains when wiring in T&E.

Then more fool you, i hope your clients appreciate the extra costs and the possible restrictions using 4mm cable when additional branch wired sockets are required in the future. You design circuits that best suits the installation, both Radial and Rings circuits should be considered and not just based on what is easier for the installer!!

 

[Guest125]

Just wondering if you still use radials for circuits designed for lots of IT equipment? Or a ring or run another cpc back when using a radial

Have not really come across it. We don't do banks of computer sockets.

 

[Guest125]

Then more fool you, i hope your clients appreciate the extra costs and the possible restrictions using 4mm cable when additional branch wired sockets are required in the future. You design circuits that best suits the installation, both Radial and Rings circuits should be considered and not just based on what is easier for the installer!!

I am not sure I follow.

Why would it cost extra to wire in 4mm? Why would there be branching issues?

Again you are making assumptions that you know better than me about the installations that we do.

 

[GEOFF S]

Hi all, I am slowly working through my design to gain this qual, and have come up against a little teaser when starting my ring main design calcs. I have (at the moment) split the ring mains into 5 or 6 seperate ones, and they range in length from about 90M to 130M total length (including drops and return leg). The problem I have is when I do my grouping factors. I was going to run all circuits in a suspended trunking around the building and then take them in conduit down to their positions. Now, as soon as I put 20 (will be more at the origin) circuits in the grouping factor table, I instantly get a 0.38 multiplier, which takes the cable size over 4mm2 and stops me having a ring main. I know I can maybe change to tray and run the cables in a single layer, to increase the multiplier, but in reality with the amount of circuits involved it would take about a 3M tray! Almost all installs I do at work contain many more than 20 circuits, in a single trunking, and unless very long are usually designed at 2.5mm2. I am just wondering if I am missing anything here, or if anyone has any thoughts. Any help or ideas would be greatly appreciated. Thanks.

okay, you have two ways to address this problem.

Firstly, look at what diversity you have applied to the ring circuits, often on comercial a factor of 0.2-0.4 is used.

Try and stick to 5 circuits per group.

So lets say we work to a 2/3 split, and our diveristy factor is 0.2, after diversity IB = 0.2 x 32 = 6.4 Amps. Now two thirds split leave us with IB = 4.28 amps down one of the legs.

So, bottom of tabe 4C1, IB=< 0.3 x IZ

We have 5 Circuits Enclosed trunking. Cg = 0.6. Now we will use IB(no simultaneous overload), 4.28/0.6 = 7.133 amps

So 4mm Trunking = 32 Amps. So IZ = 32 x 0.6 = 19.2,Group rating = 19.2 X 0.3 = 5.76 amps IB = 4.28, so IB=< 0.3 x IZ has been met.

So we can omits this cable from the grouping and in effect all of the 5.

The second method ill post when i get chance, its no to disimilar, rings are not heavily loaded.

Your the designer after all, and your maximum demand is set by all your circuit including any diversity.

Cheers

 

[E.E.I]

A couple of guys I studied with on the course used xple cable when the cTA was looking on the large size, I believe it has a higher current carrying capacity. I didn't like this idea! Like others have mentioned the 30% full load rule will help. Or use two compartment trunking, 1 for power and 1 for lighting, as long as you have specified that the installer is to separate the two there shouldn't be a problem, should halve your grouping factor.

 

[ImpededLoop]

A couple of guys I studied with on the course used xple cable when the cTA was looking on the large size, I believe it has a higher current carrying capacity. I didn't like this idea!

One side effect to watch is the volt drop. Although XLPE can be used to 90 degC the resistance per metre increases with temperature so sometimes there's no gain over 70 degC PVC.