new ring main in attick

[outrageous]

hi to all, my first posting after viewing the forum for a month. please can you check ive got this right. putting a ring main in attick, the design current i have in mind is 3000 watt/13A ive picked a 16A B type MCB, the cable is 2.5mm it will be fed through conduit in plaster which derates it to 18.5A. Also a correction of o.94 [35 deg. c] because its hot up there, putting the rate of the cable at 17.39A. so i times this by 1.45 to get max short term loading for cable, which is 25.21A. The 16A MCB i have trips at 1.45A above its face value so that will be 23.2A which is below max short term load of cable. Have i got it right, if so B.A.S pat yourself on the back its your link i learnt this from.

 

[breezer]

first question

if you have been reading the forums, how can it be a ring with one cable?

 

[outrageous]

hi breezer, the cable will leave the cu going to attick sockets then back to cu, 1 cable

 

[breezer]

hi breezer, the cable will leave the cu going to attick sockets then back to cu, 1 cable

lets see.

1+1 = 2

1...........................+............................1............... =.................2

oneplusoneequalstwo

1+1=2

1+1=2

1+1 =2

no, its no good, i have tried several times and ways i still get the same answer

to stumble at this stage does not sound good

 

[outrageous]

i must of missunderstood a section i read about cable grouping that said 1 circuit is classed as 1 cable. so 1+1 is 2.. ok but have i got the right undersranding of the rest

 

[breezer]

i must of missunderstood a section i read about cable grouping that said 1 circuit is classed as 1 cable. so 1+1 is 2.. ok but have i got the right undersranding of the rest

i do not wish to appear to being alkward, i really am trying to help

is this the first forum you have been on? its just that you not seem to read very well / type too fast?

my reply actually said

if you have been reading the forums, how can it be a ring with one cable?

 

[outrageous]

there will be only 1 cable with sockets on it then it goes back to cu. does this sound right . i dont type fast

 

[PowerTool]

there will be only 1 cable with sockets on it then it goes back to cu. does this sound right . i dont type fast

Yes - a ring has a cable going out from the CU,to a socket,then to the next one,and the next etc. then back to the CU.

The main advantage of a ring is it can carry current in both directions,giving a higher carrying capacity for the size of cable

If you are only planning on a couple of sockets,and low power useage,why not do a radial and save 50% of the cable..

 

[breezer]

there will be only 1 cable with sockets on it then it goes back to cu. does this sound right . i dont type fast

that makes two cables then doesn't it, but you said it was one, fas i said falling down at this stage is not good, but i also agree with powertool. i woulld also wonder what you are going to be using in the loft that draws that much. lots of "garden lighting"?

 

[outrageous]

is it a lot of power to be supplied to a loft

 

[breezer]

yes, we know that, but why?

 

[outrageous]

thanks powertool i thought it was 1 cable that left cu then to sockets then back to cu

+++++++++++++++++++++++++++

i thought of a 16A MCB so theres plenty of power up there. there are 2 rooms

+++++++++++++++++++++++++++

how do you know that im going to use garden lighting up in the loft breezer,

____________________________
moderator

outrageous, may i ask that you read the forum rules, which are here in particular 10a

thank you

 

[Steve]

thanks powertool i thought it was 1 cable that left cu then to sockets then back to cu

Yes, your definition of a ring final is correct, but i think Breezer was merely taking the p*ss and being quite pedantic with regard to your description of it.

i thought of a 16A MCB so theres plenty of power up there. there are 2 rooms

fine, as long as your not having any heating appliances up there. A 16A radial can be fed in 2.5mm² cable, it doesn't need to be a ring.

 

[Spark123]

so i times this by 1.45 to get max short term loading for cable, which is 25.21A. The 16A MCB i have trips at 1.45A above its face value so that will be 23.2A which is below max short term load of cable. Have i got it right,

No, you do not need to apply a fusing correction factor to a cable if you are using a cartridge fuse, mcb or bs88 fuse.
The only time you really need to use a fusing correction factor is when using a bs3036 rewirable fuse, a rewirable fuse has a fusing factor of 2, hence a correction factor of *0.725 needs to be applied to the rating of the cable.

 

[outrageous]

so what benefits would i be gaining in wiring as a ring as apposed to a radial as suggested, i will not be using any electrical heating up there but who knows what would be used if im not in.