Maximum cable length

[ted26]

Does anyone know the maximum cable length that can be used for a ring circuit using 2.5 t+e with a 32amp breaker?

 

[ukpablo]

page 362 of brg

100m squared as a rule of thumb.

 

[ted26]

I thought that was floor area 100m squared!

I was concerned with atual cable length of total ring circuit

 

[telectrix]

ithink its about 50m end to end but that's just a guesstimate.

 

[malcolmsanford]

the OSG has a table in there giving maxium cable lengths for cable size but as I haven't got mine with me can tell you which one, sure if one of the other lads are following this thread they can give you the table reference

 

[Hawk81]

Table 8a in the OSG gives you the maximum length. Which is as someone has already said is 100m2

 

[vitoboy]

page 44 table 7.1
it depends if you got a fuse or mcb what type of mcb or rcbo ect ect..
also you need to get past your max zs and thats the real limit..

 

[J@mes]

if the area covered is 100m2 then does that mean that the cable can be 40 meters long end to end (ie going around a square room that is 10x10m meaning it would cover 40m end to end?

subject to all other criteria being met

 

[vitoboy]

100m squared is not a cable length!
its an area to be served.
you could still have a zs thats to high even within that..
and then it wont comply..
honest.

 

[vitoboy]

in a 10X10 meter square what about the drops or rises.....if the rooms got a 5 meter celing hight and your drop is from there then how big would your ring main be...
its all about cable resistance and what protection you have and the temperature and the insulation around the cable.....
if i were you id look into some cable calcs....they are a wonder to behold..

 

[ted26]

I atually searched and found a reference earlier which said something like 98m for 2.5 and 178m for 4.0

this i think must be the maximum for each and could be lower depending on other influences

 

[telectrix]

what about the drops/rises to sockets. as vito says, have to meet Zs less than 1.2 for a 32A type MCB, so knowing Ze and the resistance of R1 and R2 per 100m each, you can work it out

 

[ted26]

in a 10X10 meter square what about the drops or rises.....if the rooms got a 5 meter celing hight and your drop is from there then how big would your ring main be...
its all about cable resistance and what protection you have and the temperature and the insulation around the cable.....
if i were you id look into some cable calcs....they are a wonder to behold..

You are right but have forgot more than i now know!! been working easy for 10 years and need to refresh my electrical installation theory.

anyway thanks for any help from all

 

[vitoboy]

and table 8a...is for minimum live size in mm for final circuits...

where are lenny and the big boys on this...

 

[pushrod]

type b circuit breaker, tn earth,installation method a, c, 100 or 102 length = 106 metres.