Earthing conundrum

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The coumn root is often insulated due to coatings, these days a polymer based coating, it used to be bitumen or similar.

If you look at the latest version of the IET “Guide to electricl street furniture” in para 2.5.2, that it is perfectly acceptable for a DNO TN-C-S supply to feed a single column, or feeder pillar.

If the feeder pillar then has distribution from it, this must be TN-S, but, additional means of earthing are not needed , over and above a means at at the feeder pillar with a recommendation only to add another means of earthing at the ultimate or penultimate column in the radial circuit.
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no you cnat use that mate jeeeez😤 this is why people like you should be shot
Really!

Perhaps you had better tell the IET, JPEL64 & the IEC, I have a few direct email addresses and mobile numbers of some of the senior staff at the IET, and quite a few of the members of JPEL64 & the feeder panels.

 
Hi guys , I've been away for a few weeks , now back to this bloody job ( looks like I've started a bit of an argument ! Any how I've managed to find an alternative TN S supply for these lights , bit of a longer cable run . I've wired the posts in 3core 6mm swa , this is the biggest cable size I can physically fit in the posts . Gona use armouring  and core for c. P .c and combined I think it works out to about 9mm crossection . Will be protecting with 6 amp r c b o . As mentioned on previous post , I'm classing lamppost as exposed conducive part so green and yellow is c. P .c in my opinion . What do you guys think 

 
Never knew that , think my main concern is definition of exposed or extraneous , part 2 regs seems pretty clear that lamppost is exposed as its part of electrical equipment , although I can see that I could obviously introduce an earth potential . I spoke with a guy from IET and he argread that it's exposed , if I had to bond like gas water pipe I can't see how I could physically do it , any thoughts

 
Hi mate , sorry to bother you , I'm sure you've better things to do on a saterday , I've had a look at the IET guide , but just to clarify the guide seams to relate to DNO street furniture , my lamppost are from a private supply 

 
Nope it applies to all street furniture, as little if any of it belongs to the DNO, more likely the local council.

This is where the feeder pillar concept comes in.

DNO supply to a feeder pillar.

Private supply owned and operated by the street lighting company, whether that be the council, or it may have been contracted out by the local authority to a private company.

The supplies leaving a feeder pillar are private, not DNO.

 
Cheers mate I do appreciate your time / advice, so just to recap im running a circuit 6mm swa  3core buried in ground 600mm deep in a ducts to 5no lamppost will led lamps total load 50watts. Supplied from customers consumer units with TN/s earthing arrangement.

With 6amp rcbo . Lamppost are metal class 1 , can you see anything wrong with this ?  

 
Think about one thing at a time.

Why 6mm?

Why 3 core?

Why ducted?

Why 600mm deep?

How is the circuit configured?

How long is the run to the 1st post, to the 2nd, to the 3rd, 4th, 5th?

What is the loading at each post?

Are there any upstream RCD's from your proposed RCBO?

What is your means of isolation for the whole circuit?

What is your means of termination/connection at each lamp post?

Are the lamp posts extraneous-conductive-parts as well as exposed conductive parts?

 
Hi mate, here goes,

600 deep as I think this is the common rule (I know it's not in the regs)

Ducting ( in case of additions / or rewiring) 

Load is 12w per lamp

Distance 50metres run

Post evenly space

3core ( because this is a rewiring job, initial wiring failed as armour corroded, in cut out , ie lost earth continuity ) 

6mm as biggest  cable I can physically fit in post , all cable calculating done, voltage drop ect , obviously 6mm smashed it low load , shortish run

No rcd up stream 

Rcbo ( additional protection) 

Was planning to terminate in ip rated box in bottom of post ( as opposed to cut out ) to avoid them rusting again, termination very close to ground

Could isolate via double pole switch ( as I understand it this ok with regs)

Exposed/extraneous ? Good question, from definitions would say exposed, how good a contact they have with earth ? Some are actually on a stone plinth, and rest on ground , 

 
Depth must be adequate such that the cable cannot be damaged.

You should bury the duct in accordance with NJUG standards and use the correct ducting for LV Lighting.

Do the lamps require fusing down at the column?

Without a cutout how will you implement local isolation at each column?

If the SWA corroded away, it was not terminated correctly.

Remember that even if you use a core for earthing, the SWA must still be connected reliably to earth tight through the run to the earthing system of the supply, ergo at the supply end.

You need to test to check if they are extraneous-conductive-parts.

 
Cheers pal, to be totally honest I wish id never got involved with this bloody job!! Can't see why I would need to fuse down at each post if using 6amp breaker, in section 715 if I understand it correctly , it only mentions isolation for each circuit 714.537.2.1.1.

Regarding exposed/ extraneous I've done a bit of searching , general opinion seems to be exposed ( voltinium do an article on this) if my thinking is correct even if tested an was extraneous as soon as I put the class one head on it turns into exposed again ? By the way im not trying to be at all argumentative. These posts are old , can't get rid of them because listed building.  They do need repainting , even though of using dielectric paint , and kind of making them class 2

 
You need to consider what the lamp oem requires for fusing.  That might need protection at the columns.

You need to be sure that there is no requirements for individual isolation of the columns for maintenance before you commit to a single point & don’t allow yourself any options for changing this.

 If you paint them with non-conductive paint, then it becomes site applied insulation, with the additional requirements for that.

 
A sparkys life is never easy ! Im definitely not getting paid enough for this , thanks again for time and help , will do some research to points you've raised  , cheers

 
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