shower on 6mm for future

[i=p/u]

i was asked to pull in a shower cable and leave in wall for future as customer has been roked into other work, so makes sense now as they have the room.

9.5kw shower on 6mm is fine according to osg upto 43m on ref method c. i only have an 8m run and is in rafters with kingspan but kingspan wont be touching it. it has 150mm rafter with only 100mm kingspan..
so at least a 50mm gap around cable
i said its dead on for 8.5kw shower but i do think 9,5 will be fine aswell.


thoughts

 

[telectrix]

mmm tadpole wellington. makes a change from beef.

 

[i=p/u]

still cant get me adibiatic right for this shower.. its a tn-c-s so say max of 0.35 ohms and its 10m max so say 0.45 as calculated zs = 511A

511 x 511 = 261121 x 5 = 1305605 / 115 =11353 and the square root off 11353 = 106 which is wrong.

 

[Risteard]

Why do you think your protective device will take 5 seconds to operate?

 

[derek preece]

Are you assuming a 5 sec disconnection time for a 60898?

 

[i=p/u]

well its over 32A

 

[JUD]

still cant get me adibiatic right for this shower.. its a tn-c-s so say max of 0.35 ohms and its 10m max so say 0.45 as calculated zs = 511A

511 x 511 = 261121 x 5 = 1305605 / 115 =11353 and the square root off 11353 = 106 which is wrong.

511 x 511 = 261121
261121 x 0.1 = 26112.1
√26112.1 = 161.6
161.6 ÷ 115 = 1.41mm²

 

[JUD]

well its over 32A

The disconnection time is taken from the time/current graphs at the back of the regs.

511A would cause the 40 breaker to go in 0.1seconds

 

[i=p/u]

if i use .4 it still comes out @ 30mm.. its probably the computer calculator

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ok jude, this why i used 200 as this is the limit on 40A breaker

 

[derek preece]

well its over 32A

perhaps you should look at the trip time graphs in the regs book

 

[i=p/u]

it comes out @ 6mm cpc where 6mm t&e only has 2.5 cpc

 

[JUD]

if i use .4 it still comes out @ 30mm.. its probably the computer calculator

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ok jude, this why i used 200 as this is the limit on 40A breaker

You're thinking about it all wrong. The current that will flow in fault conditions is determined by the Zs of the circuit. It has nothing to do with the Ia of the breaker, this is the minimum value that will cause the breaker to operate in the required time.

 

[JUD]

it comes out @ 6mm cpc where 6mm t&e only has 2.5 cpc

Did you notice my post #21

 

[i=p/u]

i can see it now jude , i was square rooting everything but now know have to square root then divide by k value.. ty for being patient .... ps mostly domestic so just follow green book so id know 43m is maximum on a 2.5mm cpc

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i did notice jude , that's when i went i am a engineer ))

 

[JUD]

i can see it now jude , i was square rooting everything but now know have to square root then divide by k value.. ty for being patient .... ps mostly domestic so just follow green book so id know 43m is maximum on a 2.5mm cpc

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i did notice jude , that's when i went i am a engineer ))

The maximum lengths in the book are more often than not limited by voltage drop and not cpc size or Zs.

I'm a bit confused actually as in the red On-site Guide the max length was 40m which is more or less what I get...

L = (MaxVD x 1000) ÷ (Ib x mV/A/m)
L = (11.5 x 1000) ÷ (40 x 7.3) = 39.38m

Now in the green On-site Guide that value has increased to 43m for some reason