cable run- meter squared?

[w crane]

Help brain has turned to mush.
A simple ring circuit 2.5 twin and earth.
can supply upto an area of 100meter squared, stated in IEE Regs. Right. (O yes please negate any correction factors that might normally apply).

And if i remember that is: 100 meters squared = 100meters x 100meters
simply giving 10,000square meters (not getting muddled with meters square)
This in its simplistic form can be represented by a square with all four sides equal to 100 meters.
the sum of the parimeter of this square would be 4x100meters.
would this parimeter (400 meters) not be equal to the length of cable run allowed to meet this figure of 100meters squared. if not then why please help before all i lose the will to live.

 

[telectrix]

nope. it's 100 square meters, that 10m x 10m. floor area.

 

[w crane]

ah yes thank you. After reading your reply telectrix it got me thinking so did bit of elementry research. Meter squared & Square meters = same thing, one writen and one pronounced.
Great but that leaves me with same idea but different figures.ie 100 "square meters" would have a perimeter of 10 + 10 +10+10 = 40 meters . Hence the length of cable run would ,for 100 square meters, would be equal to 40 meters. can you please show me the errors of my ways pleeeeese

 

[bugsy]

oh dear what was Howard saying

 

[Colin Integrale]

Imagine a 100m x 100m front room. Crumbs.

 

[ezzzekiel]

pretty much works out as a downstairs and upstairs ring on a standard domestic sized property coincidentally

 

[telectrix]

going by that ( 10+10+10+10 ) are all the sockets mounted above the ceiling. or are you going to allow for drops?

 

[w crane]

just curious Telectrix to know where ive gone wrong. No trick question, ideal circuit, only impeadance is that of the cable run its self. the drops if any in this imaginary circuit would have to be part of the calculated 40 meters. yes? as the drop is part of that 100 square meter, which presumably is curtailed by the resistance of the cable run.. or for simplicity ignor drop just one massive ground floor room.
Idea! could the calculated 40 meters be 40m of feed to load and then another 40m return(neutral),of the twin and earth cable run?
this would give 40 + 40= 80 Meters. which would be closer to the accepted, rule of thumb, 100Meter run for an area of 100 square meters.
Cheers to all for help up to now.
dont like knowing things parrot fashion, i like to understand reasoning behind it, easier to remember then.

 

[telectrix]

try calculating R1+R2 for 100m of 2.5/1.5, then add say a value of Ze. ( 0.35 for TNCS, 0.8 for TNS ) see if that result exceeds your max. permitted Zs for, say, a 32A type B MCB. even if you get an acceptable answer, then assume a load of, say, 26A, and calculate volt drop. that will answer the question.

 

[Deleted member 26818]

I think your main problem is sticking to for instance a square, which has the 2nd shortest perimiter for the given area. The shortest being a circle.
Consider the length of the perimiter for a rectangle that is 100m by 1m. Such a rectangle would have the same area as a square 10m by 10m, but the length of the perimiter would be 202m, as opposed to 40m. In an extreme case, the same area would be found, if the rectangle was 10km by 1cm.
The 100m² rule, is a rule of thumb. Conductor lenghts and VD etc. should always be verified, even when installing a standard circuit.

 

[Chr!s]

Just calculate the maximum length of circuit with all factors taken into account, approximate the length of the circuit required for the installation, if its not long enough and say volt drop is to high select a larger cable.

 

[w crane]

thank electrix . but being a difficult sod i didnt want to involve any thing that could be a varriable ie 0.35, 0.8, 200 TT, just needed to understand the relation between IEE 100square meters and rule of thumb 100meter cable run . On your train of thinking your 1000000% right thanks.

 

[w crane]

Spot on thats the "Glitch"
That what i coulnt see . Dooooopey me! Your right right right right right right right right right right right right right right right right right right! i can now sleep at night again thank you . Its the perimeter thingymajig.
yes! thats why electrix asked about the drops.

There are always two sides to a question, but the answer is always, answer squared or squared answer, if you prefer.
thank you all.

 

[Deleted member 26818]

Two sides to a question, but four to a square.

 

[telectrix]

and 2 to a circle......... inside and outside