length of cable runs

[i=p/u]

is this correct for lighting circuit of 1.5mm line and 1mm cpc
ze+R1+R2=zs

b6 mcb ze R1+R2
6.18ohms - 0.8ohms =5.38ohms


cable per meter = 0.03020ohms so 5.38ohms/0.03020=178.1M

does this mean my lighting circuit can be this length 178M and still be within zs value... cheeers if makes sense

 

[telectrix]

i=p/u, not checked your calc. yet, but pleeeeease distinguish between r1,R1, etc. 2 different measurements!!!!!!!!!

also Ze and Zs mixed up mate. being picky i know, but you got to get it right terminology.

 

[Chr!s]

is this correct for lighting circuit of 1.5mm line and 1mm cpc
ze+R1+R2=zs

Correct

b6 mcb ze R1+R2
6.18ohms - 0.8ohms =5.38ohms

Dont apply a factor to the Max zs value, i presume you are using a tns .8

does this mean my lighting circuit can be this length 178M and still be within zs value... cheeers if makes sense

I think you will find volt drop your overriding factor

 

[i=p/u]

yes just tn-s as example, what factor am i applying, didnt even know i was.

 

[telectrix]

where does 6.18 ohms come from?

 

[i=p/u]

appendix 2 table 2d osg maximum measured efli for circuit breakers

 

[IQ Electrical]

where does 6.18 ohms come from?

The 80% ROT value is 6.13 Ohms

 

[i=p/u]

so am i correct

 

[IQ Electrical]

so am i correct

In theory yes, but as Chr!s mentioned, voltage drop will limit the theoretical maximum length of run due to the 3% limit on lighting circuits.

 

[i=p/u]

so when you designing a lighting circuit , how do you approach it? ive seen page 45 in the osg would give you 90 meters would this include switch drops aswell???

 

[Guest123]

Circuit length would be limited by the circuit VD in this instance

As a rough guide assuming a load of 5A and a Ct factor of 1 gives a maximum length of 47.5M to comply with the 3% (6.9V) permitted VD.

 

[i=p/u]

thanks len, would this include the switch drops aswell???

 

[i=p/u]

it says in osg pg 44 5amp on 1.5mm/1mm would go 71m , and i think vd is included

 

[andyb]

i=p/u, not checked your calc. yet, but pleeeeease distinguish between r1,R1, etc. 2 different measurements!!!!!!!!!

also Ze and Zs mixed up mate. being picky i know, but you got to get it right terminology.

In this instance i=p/u is correct,

Ze+R1+R2=Zs

 

[Guest123]

As I said, rough guide.

I used a Ct value of 1 just as an example, which errs on the side of safety when in actual fact Ct will be less than one due to the CCC of 1.5mm T+E and the fact you would be limiting it to a max of 5A when it is capable of carrying more.

Also it is impossible to say what the ambient temperature of the area surrounding the cable will be........is it in an attic, under insulation etc etc, the OSG bases it's values on ideal situations but does make you aware in the notes associated to the particular table.