The best way is to design it properly in the first place.it is best to run on leg 1 4mm cable to the cluster of high current drawing sockets and then 2.5mm for the rest.
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Discuss Unbalanced final ring in the UK Electrical Forum area at ElectriciansForums.net
The best way is to design it properly in the first place.it is best to run on leg 1 4mm cable to the cluster of high current drawing sockets and then 2.5mm for the rest.
What I wrote was quite clear.The best way is to design it properly in the first place.
Unless method 101 for example, where max ccc permitted for 2.5 t&e is 17Amps, it becomes an issue!19.763A. Almost nothing in it.
For clarity, my posts in this thread focus on the original question, regarding the effect cable heating may have on the flow of current through an unbalanced ring. My examples show how the current may be distributed through the circuit under certain unusual loading situations, before and after cable heating, and my last example shows that under the stated specific circumstances, cable heating has almost no effect on that.Unless method 101 for example, where max ccc permitted for 2.5 t&e is 17Amps, it becomes an issue!
I have come across plenty of open rings in domestic settings, but have never once found one where the cables were showing signs of aging, let alone thermal damage, as a result of overload. I'm of the opinion that the sorts of overload that are likely to occur are not great enough to cause actual damage, even when the ring is open, or the load heavily biased to one leg.What has alerted me, to some surprise, is how out of balance a final ring can be, which must be more typical in British homes than we think as heavy current drawing appliances are clustered. This was not a big problem in the 1960/70s. I measured 82% on one leg while Efixx measured 83%. Previously most I measured were 70-30 at most, giving 22.4 amps on one leg - just inside the max for the cable for the majority of installations. Fitting a ring with sockets in round robin (1st socket on leg 1, 2nd socket on leg 2, 3rd socket on leg 1, etc) will solve a balance issue, but this method can be quite impractical and a heavier in use of cable increasing costs.
This points us to that final rings should be all in 4mm, or 4mm on one leg to the clustered heavy current drawing sockets and then 2.5mm for the rest at least, for many reasons. In a normal house/flat I would lean to put as many appliances as possible on a full 4mm ring protected by an AFDD; diversity taken into account of course. A 3kW-ish oven & low current drawing induction hob on a 4mm radial and of course the immersion, if one on premises, on its own 2.5mm radial. Maybe more economical having the immersion on 4mm as final ring and oven/hob will be on 4mm so cable being cheaper all on the same purchased drum. At TLC a 100m drum of 4mm is £147 (£1.47 p/m), with 100m drum of 2.5mm £72 (£0.72 p/m), about twice the price, but £1.03p on a 25m drum. Costs of 4mm could drop in cable costs as only using one final ring in 4mm. Worth thinking about.
Nice comment. Thanks for your input. It is a valued judgment of course. OK a worst case scenario - like the Christmas dinner scenario in cookers. Wife has the washing on in the kitchen. Tumble dryer constantly drawing 13A, washing machine intermittently cuts in drawing 11A, fridge cutting in and out, TV on in the corner. Her three friends pop in, the 3kW full kettle goes taking a time to heat up, and the 1kW toaster. Dishwasher is also switched on.I have come across plenty of open rings in domestic settings, but have never once found one where the cables were showing signs of aging, let alone thermal damage, as a result of overload. I'm of the opinion that the sorts of overload that are likely to occur are not great enough to cause actual damage, even when the ring is open, or the load heavily biased to one leg.
It's good to explore these things, as it gives us a better understanding of the circuits we work on, but I don't think 4mm is generally necessary for wiring rings.
Reply to Unbalanced final ring in the UK Electrical Forum area at ElectriciansForums.net