3 Phase Install | on ElectriciansForums

Discuss 3 Phase Install in the UK Electrical Forum area at ElectriciansForums.net

Joined
Jan 9, 2021
Messages
4
Reaction score
1
Location
South Wales
Hi All,
Happy new year to you all!

I’m working for an engineering company, been here for a few years.

im currently working towards my NVQ level 3 in electrical maintenance and I’m in the middle of supplying a 100A Distribution board from a newly upgraded main 250A board. When the new board was installed I asked the sub contractors to run a armoured cable from this new board to the 100A board but they only supplied a 4 core 25mm cable.

Obviously this 100A board needs 3 phase, neutral and earth (5 core)

I have read somewhere that the armour of the cable can be used as the earth?

personally that doesn’t sound good practice?

any advice will be much appreciated! Thanks
 
Hi All,
Happy new year to you all!

I’m working for an engineering company, been here for a few years.

im currently working towards my NVQ level 3 in electrical maintenance and I’m in the middle of supplying a 100A Distribution board from a newly upgraded main 250A board. When the new board was installed I asked the sub contractors to run a armoured cable from this new board to the 100A board but they only supplied a 4 core 25mm cable.

Obviously this 100A board needs 3 phase, neutral and earth (5 core)

I have read somewhere that the armour of the cable can be used as the earth?

personally that doesn’t sound good practice?

any advice will be much appreciated! Thanks
Standard practice to use the armour as cpc,but not normally used as a main bonding conductor.
regards,S
 
What would be good practice would be to have the new board and its supply designed properly by a qualified and competent person in accord with EAWR.
Who will be signing the Electrical Installation Certificate as the designer?
Once the install is complete we will have a approved contractor to sign the work off. As I'm working towards my NVQ I need to create job reports. Would like to get everything right before sign off
 
Hi All,
Happy new year to you all!

I’m working for an engineering company, been here for a few years.

im currently working towards my NVQ level 3 in electrical maintenance and I’m in the middle of supplying a 100A Distribution board from a newly upgraded main 250A board. When the new board was installed I asked the sub contractors to run a armoured cable from this new board to the 100A board but they only supplied a 4 core 25mm cable.

Obviously this 100A board needs 3 phase, neutral and earth (5 core)

I have read somewhere that the armour of the cable can be used as the earth?

personally that doesn’t sound good practice?

any advice will be much appreciated! Thanks
The Steele wire may be suitable as a earth for the new install, however if the new supply requires any bonding, due to any metallic items in the building, such as water ,gas A.C or oil pipework, entering the building from the outside,then you will probably find that the armouring won't have the required CSA to act as a main earth AND main bonding conductor, something the designer/contractor that initially did the work should have taken all this into consideration at the outset, a poor design in my book.
 
The Steele wire may be suitable as a earth for the new install, however if the new supply requires any bonding, due to any metallic items in the building, such as water ,gas A.C or oil pipework, entering the building from the outside,then you will probably find that the armouring won't have the required CSA to act as a main earth AND main bonding conductor, something the designer/contractor that initially did the work should have taken all this into consideration at the outset, a poor design in my book.
great, thank you for the advice
 
What did your design calculations show for volt drop, expected PFC, Zs, adiabatic etc?
 
The chances of the armour being inadequate as a cpc is pretty slim providing the cable is correctly terminated and correct circuit protection is provided. You should however prove this. The use of cable armour and steel containment as a cpc seems to have become a no no when in fact for most applications it is perfectly acceptable.
 
As above, in most cases the armour is perfectly adequate from an adiabatic limit point of view, but should be checked anyway as some cases it is not.

However, it might not be enough for TN-S-C bonding, and it might not have a low enough impedance to meet the end of cable Zs for disconnection times.

25mm 4-core has about 70mm of steel, which is about 8.75mm copper equivalent and too low for TN-C-S bonding that demands 10mm. Also the R2 is about 2.3 mOhm/m, compared to the R1 of about 0.8mOhm/m so on a longer run it dominates your Zs term.

If you have run a 25mm copper line in parallel the problems go away, but that ought to be driven by design, not as a seat-of-pants reaction.
 

Reply to 3 Phase Install in the UK Electrical Forum area at ElectriciansForums.net

News and Offers from Sponsors

  • Article
Join us at electronica 2024 in Munich! Since 1964, electronica has been the premier event for technology enthusiasts and industry professionals...
    • Like
Replies
0
Views
376
  • Sticky
  • Article
Good to know thanks, one can never have enough places to source parts from!
Replies
4
Views
944
  • Article
OFFICIAL SPONSORS These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then...
Replies
0
Views
1K

Similar threads

Think all has been covered already, but echo-ing the above if I was getting my DB swapped and had a 3 phase head, I would put a little TPN board...
Replies
5
Views
386
  • Question
I'm assuming the cable will have to be cleated well to hold it in place anyway, as a stuffing gland ain't going to hold it tight like a SWA gland...
Replies
10
Views
710

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

This website was designed, optimised and is hosted by untold.media Operating under the name Untold Media since 2001.
Back
Top