Earth Size etc?

Currently reading:
Earth Size etc?

Discuss Earth Size etc? in the Commercial Electrical Advice area at ElectriciansForums.net

P

Piratepete

Hi Guys
I don't normally do 3 phase so just need to confirm this.

Local church has a 100 Amp TNCS 3 phase supply. All electric heating spread across phases.

I have to put a supply to a new extension also with electric heating, water heaters, hand driers etc. I'm proposing running the heating off one phase and the rest off another.

I'm proposing a 63 Amp 3ph Switch fuse at the meter end supplying 2 CUs in the extension via a 22metre long surface mounted 4 core 10mm SWA XPLE cable using one core as earth (I prefer this to using SWA as earth)

Is this OK? In particular cable and earth size.?

Thanks
Pete
 
Tony said:
How are you going to run 3Φ+N and an earth in a 4C cable? Use the 4 cores for the 3Φ+N and the armours as earth.
Click to expand...

Is there is any extraneous services/metalwork etc, in this new extension?? If so, he won't be able to use a 4 core SWA on it's own, it'll either have to be a 5 core, or the 4 core with a separate bonding conductor!! lol!!
 
Piratepete said:
Hi Guys
I don't normally do 3 phase so just need to confirm this.

Local church has a 100 Amp TNCS 3 phase supply. All electric heating spread across phases.

I have to put a supply to a new extension also with electric heating, water heaters, hand driers etc. I'm proposing running the heating off one phase and the rest off another.

I'm proposing a 63 Amp 3ph Switch fuse at the meter end supplying 2 CUs in the extension via a 22metre long surface mounted 4 core 10mm SWA XPLE cable using one core as earth (I prefer this to using SWA as earth)

Is this OK? In particular cable and earth size.?

Thanks
Pete
Click to expand...

How are your loads at the origin going to be balanced? I would recommend you run in a three phase sub main to a three phase dist board and do the thing properly.
 
well if its say tn-c-s if he has more than 10mm armour can he not just add to this for bonding??? why not?

isit because is being used as main earthing conductor

- - - Updated - - -

<< its hard being experienced confident spark..
 
i=p/u said:
well if its say tn-c-s if he has more than 10mm armour can he not just add to this for bonding??? why not?

isit because is being used as main earthing conductor

- - - Updated - - -

<< its hard being experienced confident spark..
Click to expand...

No you can't, SWA and copper conductors have different resitivity K factors, so you can't just add together and hope for the best!! It doesn't work like that!! lol!!
 
i=p/u said:
but surely of 16mm swa the armour i think = 30mm copper ... so is fine and danty...
Click to expand...

Copper is something like 8 times that of SWA, so think in terms of around a 70mm SWA being required for a 10mm copper equivalent!! lol!! Off the top of my head that, but it gives you an idea of WHY!! lol!!
 
Engineer54 said:
Is there is any extraneous services/metalwork etc, in this new extension?? If so, he won't be able to use a 4 core SWA on it's own, it'll either have to be a 5 core, or the 4 core with a separate bonding conductor!! lol!!
Click to expand...

Why cant he use the core for the earthing conductor as a combined earthing and bonding conductor. If it is 10mm2 surely that is big enough. If the supply neutral at the head is 35 or less than the 10mm is big enough for the bonds!
 
images
 
Sintra said:
How are your loads at the origin going to be balanced? I would recommend you run in a three phase sub main to a three phase dist board and do the thing properly.
Click to expand...

Hi Guys
Thanks for all your interest. First, cost is a factor on this job (isn't it always!) Client thought he could just have a 1ph supply and a domestic CU. lol. Requirements have changed today (again)!
Yep, you're right! You've clarified my muddled thinking! Best is a 3ph board, 4 core SWA using the armour as earth. I can just about balance demand across all phases. Max 35 amps/ph so may even drop to 6sqmm ( with 40 Amp fuses in the switchfuse) after checking volt drop calc. Whether 10sqmm or 6sqmm I think I'm correct in saying that the Cu equivalent csa of the armour on both sizes is 13.5 sqmm and 11.5 sqmm respectively so no seperate earth required.
Re bonding - none required at the mo. - no extraneous services/steel (water only in plastic).
I assume that if bonding is required, I have to take a seperate 10sqmm conductor all the way back to main earth terminal in the meter cupboard?

Cheers
Pete
 
Based on what you have said in your last post, I personally would opt for 10mm sq cable. The type of loads you have specified you are supplying seem quite juicy to me. Another thing to consider is future add ons? I know this is an extension but for the sake of 22m of 10mm you give the client better options in the future. Who knows they might turn around and say, the heating is insufficient lets slap a couple more in?
 
re bonding it needs to go back to the main earth terminal as the csa of the armour your running would be insufficiently sized.
 
So you can use the armour OF SWA IN DIS CIRCUIT AS bonding conductor if it is sized correctly, is there a table for this or can i see where this is and work it out for myself.. Maybe with help from yourself with my buts and whats, y
 
I have my own table, cant remeber where i got it from but it shows you the cross sectional areas of swa required as an earthing conductor along with what size is suitable and what isnt.
 
i=p/u said:
So you can use the armour OF SWA IN DIS CIRCUIT AS bonding conductor if it is sized correctly, is there a table for this or can i see where this is and work it out for myself.. Maybe with help from yourself with my buts and whats, y
Click to expand...

I'm getting confused here. If I was main bonding services in the extension I would be running a separate earth conductor from the MET............end of. Is it because the supply is to a DB and not a load that he is allowed to use the armour as a bonding conductor??
 
I'm relieved it was a DB. But like we both said, separate Earth for main bonding.............I wouldn't do it any differently regardless of what I've seen.
 
yeah i agree. but you cant legislate for the way other people do things sometimes, especially when they dont do it the way you would do it and your trying to find a fault. :)
 
So for my 16mm 5c swa as im not using swa as cpc i could use it as bonding conductor as it would be equivelent to 31mm copper

meaning i could run bonding to this board instead of back to met at service fuse?

Could i use armour as cpc and bonding conductor in this case
 
New posts

Reply to Earth Size etc? in the Commercial Electrical Advice area at ElectriciansForums.net

Similar Threads

R
  • Question
5 amp earth leakage?
Replies
6
Views
528
pc1966
P
N
  • Question
Incoming size cable ??
Replies
10
Views
689
bennie
B
P
Earthing on wooden shed
Replies
7
Views
425
MDJ
MDJ
timhoward
  • Question
Halogen Lamp heating system, diversity?
Replies
27
Views
1K
brianmoooore
B
A
  • Question
Cable sizing earthing conductor
Replies
3
Views
470
An Buachaillín Bán
A
Tiling Forum

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

YOUR Unread Posts

UK Tiling Forum
This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
    • Tiling Advice
    Back
    Top
    AdBlock Detected

    We get it, advertisements are annoying!

    Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

    I've Disabled AdBlock