Earthing conundrum

[Danny k]

Hi, I'm new to the forum so bear with , 

I'm doing project with involves re wiring some lamp posts In a public park ,  the lamp posts are metal class 1 ( exposed conductive part ) supplied from tn-s. Earthing system . No probs I thought did cable calculation happy days . Then when on my 18th course I asked the tutor about this and they recommend I ditch the tn-s and rod it !! The explanation was that dno will no longer say if a supply has 

a true separate earth . Seems counter productive to me to ditch a perfectly good earth for a rod and ze of up to 200ohms and relying on an Rcd , I've seen many rcd s fail . Any thoughts advise would be greatly appreciated 

should I rod the posts as well (belt and braces) ?? 

 

[Andy™]

you can use TNCS for street lighting, so cant see any issue with TNS....

probably down tot he fact your tutor hasnt worked on streetlighting at any point so doesnt know how its done, although youd expect them to be aware of the requirements in BS7671 if they are teaching it...

 

[binky]

big metal pole stuck into ground, how big an earth rod do you want  :^O   You will need to bond the pole/ access hatch, so you will basically get TN-s with an earth rod regardless.

Section 714 External lighting (might have moved section) applies to street lighting, no RCDs required 

 

[Andy™]

big metal pole stuck into ground, how big an earth rod do you want  :^O   You will need to bond the pole/ access hatch, so you will basically get TN-s with an earth rod regardless.

Section 714 External lighting (might have moved section) applies to street lighting, no RCDs required 

the big metal pole thats usually painted / covered with something to protect it, isnt always as good of an earth rod as youd expect

 

[Danny k]

Thanks for replying guys , the posts are actually bolted to concreat slabs so not in contact with the ground , have checked out section 714 and I only makes reference to P M E supply reg 714.411.203 and refers to table 54.8 for earth size 

but bizzarly reg 544.1.1 says table 54.8 doesn't apply to highway supplies and street furniture 

so that's as clear as mud !! Gonna rcd it anyway 

 

[Andy™]

its clear enough. if its TNCS 714.411.203 requires bonding conductor size of 6mm  for a neutral upto 10mm, otherwise use table 54.8

544.1.1 states that where section 714 applies, then you follow that, which then refers you back to 54.8 in certain conditions, instead of all conditions which would be required by 544.1.1. basically, it allows a smaller bonding conductor or 6mm rather than the usual 10, in certain circumstances

but back to the TNS not being allowed etc... unlike other locations (722, 709 etc) which specifically state restrictions on earthing types (usually TNCS), 714 makes no reference to not allowing TNS or TNCS or TT, therefore all are acceptable and can be used

as for RCDs being required, in some cases under 714 it will be required, 714.411.3.3. normal columns it doesnt apply to

back to ADS and your disconnection times. if you have a TN system, then its unlikely your Zs will be too high to use the MCB / fuse. you probably will require one for TT though

so, feel free to fit an RCD if you want even if its not required, but there is no need to ditch your TNS earth and TT it

 

[Danny k]

Thanks Andy , I appreciate your time , as I mentioned previously I'm classing the posts as a exposed conductive part so in my opinion the green and yellow is a c.p.c . Would you argree ? Would you put a couple of rods in for good measure , can't see what harm this would do 

thanks again kind regards 

 

[Andy™]

i wouldnt be using rods. not required and more hassle.

common on street lighting for a bit of 10mm from the column to the earth terminal on the cutout, regardless of a private feed or a DNO feed

 

[Danny k]

Thanks again much appreciated 

 

[Sidney]

6.2.14 in this link should help: http://www.dcode.org.uk/assets/uploads/ENA_EREC_G12_Issue_4_Amendment_1__2015_.pdf

 

[Evans Electric]

Good advice from the guys above  ...forget the rods Danny ..you're  becoming obsessed  with them   .   ( I'd put a winking face emogi thing  here  but they are now getting right up my nose  ,  the proper Forum ones have been relegated to the bottom , the top ones are rubbish  and when I open them  , they freeze my PC  )   

By the way  , If the posts were in the street / public highway  I'd be scared stiff of hammering an earth rod down  ...into what ?  ...gas main ..water main ...High tension cable   .       (Now here I might have put a shocked smiley face  but I don't want my PC frozen again )  

 

[Sidney]

By the way  , If the posts were in the street / public highway  I'd be scared stiff of hammering an earth rod down  ...into what ?  ...gas main ..water main ...High tension cable   .       (Now here I might have put a shocked smiley face  but I don't want my PC frozen again )  

BT now insist we use conductive concrete rather than rods for this very reason. Plus we get cracking readings.

 

[Evans Electric]

Now theres something I  never heard of ..conductive concrete ,  blimey ! 

 

[SPECIAL LOCATION]

 I'd put a winking face emogi thing  here  but they are now getting right up my nose  ,  the proper Forum ones have been relegated to the bottom , the top ones are rubbish  and when I open them  , they freeze my PC....   

Now here I might have put a shocked smiley face  but I don't want my PC frozen again   

What!?   cant Do emoji's...…      

Brian will be running amock, causing mayhem if you are not popping in regularly to check up on him....

He was already lining up drinks at the bar when I just opened to door to have a look....   :C  

Sounds like your PC or tinternet  is getting as responsive as Steptoe's old horse, since he hasn't been down the paddock feeding it!.  eadHorse:

have you tried the bang it with a hammer trick?       :Computerproblem:

It really is all very worrying indeed!   :shakehead  

:coat

 

[Evans Electric]

Are you saying its just my emojis  that have gone wrong ?       Ever since those rubbish ones appeared  , if I select them on the task bar  they freeze my PC  for about 3 minutes .   Brian will have to fend for himself .    

I'll try it again , if it freezes  thats it ...I've finished with the damn things .  :C :innocent utthekettleon    Well that worked  ...I'm still not gonna use these horrible things 

 

[SPECIAL LOCATION]

Are you saying its just my emojis  that have gone wrong ?       Ever since those rubbish ones appeared  , if I select them on the task bar  they freeze my PC  for about 3 minutes .   Brian will have to fend for himself .    

I'll try it again , if it freezes  thats it ...I've finished with the damn things .  :C :innocent utthekettleon    Well that worked  ...I'm still not gonna use these horrible things 

You shouldn't be getting any slow/delay/freezing problems AFAIK??

:C

 

[Evans Electric]

Try them again ..... :C    well its working but takes 40 seconds for Brian to put in an appearance .   Usually it doesn't load .   I'll keep trying it .  Or as Forum IT consultant  might try poking a stick into the PC  and rattle it about .....that works sometimes .  

 

[SPECIAL LOCATION]

Spray copious amounts of WD40 on it....

That fixes EVERYTHING!!!!

:lol: ROTFWL msl1:

 

[Sharpend]

Or as Forum IT consultant  might try poking a stick into the PC  and rattle it about .....that works sometimes .  

Oh that’s why the forum was down for a prolonged 60 mins was it. You were poking around with your stick looking for unsuspecting emojis!!  ROTFWL

 

[Doc Hudson]

Oh that’s why the forum was down for a prolonged 60 mins was it. You were poking around with your stick looking for unsuspecting emojis!!  ROTFWL

If it wasn't that, it may have been when Deke diverted all of the forum server processing power, to try and get his phone photographs back form the cloud. 

Doc H.