Table 54.7 (p130 17th)

[tom79]

Hi there,

I might be having a silly moment but, can someone please help me understand table 54.7

I understand what it is showing I think, it is telling me what is the minimum earth size I can use on something being earthed (protective conductor not bonding)

But, I cant work out this table, assuming the line/earth conductor are of the same material...

What is the C.S.A of a protective conductor selected from table 54.7 where the line conductor has a csa of...

1) 6mm2

2) 25mm2

3) 50mm2

and how do you work it out?

headbang

 

[tom79]

Oh hang on...

does it mean this?

(reading table from top to bottom...)

If.. line conductor is less than 16mm2, then use the same size? so.. 16mm line, I use a 16mm earth?

if.. greater than 16 but less than 35mm, use a 16mm earth

if greater han 35mm, use S/2 so.. for example, 40mm line I would use a 20mm earth? is there such a thing?!

 

[tom79]

so...

1) 6mm line - use 6mm earth

2) 25mm line - use 16mm earth

3) 50mm line - use 25mm earth

Hmm hows that look?

 

[Apache]

Admin - Tom's talking to himself agan..........

(sure someone's said earth not less than half CSA of line.......)

 

[spinlondon]

I think you've got it, but remember that this only applies to separate CPCs.

If you are going to use the conductor for bonding as well, other factors will apply.

There's also whether it is buried and mechanically protected to take into consideration.

 

[tom79]

Admin - Tom's talking to himself agan..........(sure someone's said earth not less than half CSA of line.......)

Yer i am talking to myself again! :coat so I assume I got the answers wrong?

 

[Apache]

Yer i am talking to myself again! so I assume I got the answers wrong?

I wouldn't say that. Sometimes talking to myself is the only way I get any sensible conversation........

 

[tom79]

the only problem is the voices in my head have not passed 2381 either so talking to them is useless! ROTFWL

 

[spinlondon]

Admin - Tom's talking to himself agan..........(sure someone's said earth not less than half CSA of line.......)

Don't really think that is relevant, as all the Earths are greater than half the CSA of the Phase conductor anyway.

The table shows that with a phase conductor up to and including 16mm

 

[spinlondon]

Yer i am talking to myself again! :coat so I assume I got the answers wrong?

No you haven't got it wrong.

 

[tom79]

Ah good stuff, cheers mate