Discuss Earth Cable To Sub Distribution Board. in the Commercial Electrical Advice area at ElectriciansForums.net

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G

gerard

Hi All,

I recently installed a new dist. board with 95mm sq 4 core swa cable. I used 35mm sq earthing cable even though I should have used roughly half the size of the live conductor. I used this because I had it, and was hoping it will be ok. I now fear that the cross section of the cpc. Is it possible to install an earthing point close to the new board to prevent me from installing a new earth cable?

Confused?!?
 
can you calculate for the armour and add that to the 35mm, see if it satisfies the adiabatic?
 
I could only terminate the swa on one end with a compression swa gland, access to the other side made it impossible so I just used a brass bushing. So, although it's a good idea, I can't use the armour. Any thoughts on another earthing point?
 
The armour needs earthing correctly but if you run a seperate earth that meets the csa needs of the sub mains then you only need to earth the swa at the supply end, but it still must be earthed regardless of the additional earth cable.
 
Hi All,

I recently installed a new dist. board with 95mm sq 4 core swa cable. I used 35mm sq earthing cable even though I should have used roughly half the size of the live conductor. I used this because I had it, and was hoping it will be ok. I now fear that the cross section of the cpc. Is it possible to install an earthing point close to the new board to prevent me from installing a new earth cable?

Confused?!?

I could only terminate the swa on one end with a compression swa gland, access to the other side made it impossible so I just used a brass bushing. So, although it's a good idea, I can't use the armour. Any thoughts on another earthing point?


I’m sorry Gerard. But all the above would be totally unacceptable to me!
 
Hi All,

I recently installed a new dist. board with 95mm sq 4 core swa cable. I used 35mm sq earthing cable even though I should have used roughly half the size of the live conductor. I used this because I had it, and was hoping it will be ok. I now fear that the cross section of the cpc. Is it possible to install an earthing point close to the new board to prevent me from installing a new earth cable?

Confused?!?

Had you terminated this 4 core 95mm SWA correctly, you would not have needed any separate CPC. The armouring would have been more than sufficient for your needs....
 
I do hope it's a cw gland.

By brass bushing I'm hoping its not just got the swa shoved through the hole in the panel.



edit:

I've seen it before so it wouldn't supprise me.
 
You can get liquid tight swa gland which is like a stuffing gland on the back of the swa gland to seal upto the sheath cw are not waterproof as many assume with their outdoor use.
Ive a feeling though this isnt the gland hes refering to.
 
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You can get liquid tight swa gland which is like a stuffing gland on the back of the swa gland to seal upto the sheath cw are not waterproof as many assume with their outdoor use.
Ive a feeling though this isnt the gland hes refering to.

Yes it's stated for outdoor use with cw glands, never seen a problem with properly fitted ones, even with a jet wash used to clean the plant down. The mistake most people make is over tightening the compression seal.

I have seen the ip65 swa glands, but I don't use them very often.
 
The swa is passed into the panel at one through a 50mm brass bush. I considered this OK under the circumstances as:
1. I would never have been able to fit a cw gland
2. the cable has no chance of moving as it is under ground, well supported, will never move and completely protected from people and elements.
My only concern is the size of the CPC, it is 35mm sq and the rule of thumb is half the size of live conductor. I do think the cpc is sufficient but I would be happier if it was say 50mm sq. So, my original question was - can an earth rod be installed near a new db to compensate for the undersized cpc?
 
In my opinion, there's not many places a gland can't be used. Even if you have to use the cone types with a jubilee clip like the ones found on some street lighting cut-outs. Not my favourite by a long shot, but would be better than not bothering at all.

As for the CPC, why can't the adiabatic be used? A 1 min calc, and you will be left in no doubt.
 
I sorry to side step your question here but the cable has to be glanded correctly regardless of how you found it, if you do any work on the sub-mains you take on the responsibility for the safety and condition of the existing supply to the submains, it may be buried but you cant predict issues like, subsidence, chemicals in the ground, inherent fault with the cable and any or other issues could create a fault down to the armour and if you havent correctly terminated it it could make the armour live without operating a protective device.

If you are in a situation as you say and truely can't gland it then i would suggest you cut a ring section of outer sheath away and fit a DNO style cable sheath earthing clamp (not a bonding clip!), then i would seal it with plenty wraps of amalgaming tape, this cable armouring must be earth at the supply regardless of the limited risks you perceive. Also because it has no rigid fixing to the dist' board you need to ensure the cable is fully supported and cannot be physically moved this way no movement will stop the termination from working loose.

In answer to your question the 35mm as you have realised is under sized and i would say no rodding the local ground, IMHO this isnt a solution and you will find it hard to prove compliance although others may suggest otherwise for which im open to discussion, rodding is really for TT where its your only option regarding earthing and a few other situations where you cannot export the earth but when your installation has a full earth provided system and you are not exporting it then you should be using the earthing provided.


I know you have probably looked over this time and time again but is it really impossible to fit a gland as this seems hard to believe or is it just really arkward and inconvenient.

I also drag up the correct glanding issue because if you can manage it then all your worries are solved regarding compliance.
 
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most definitely impossible to fit a gland, cable is 100% secure and in no fear of damage or movement. ok, so an additional earthing point is out of the question then!! in reality the current drawn by the board will never be large enough to render the cpc dangerous, but I would be happier with next size up cpc
 
most definitely impossible to fit a gland, cable is 100% secure and in no fear of damage or movement. ok, so an additional earthing point is out of the question then!! in reality the current drawn by the board will never be large enough to render the cpc dangerous, but I would be happier with next size up cpc

I've fitted glands in seemingly impossible places before and with much larger cables. That's not my main concern.

If this is a new install, why did you not just work out the size of the cpc you need using the adiabatic equation? I'm sorry but something about this job seems like you've just thrown it in using a 'rule of thumb' and hoped it's ok.
 

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