Oh you can all scoff , theres a lot to be said for poking with a stick , banging on the top or Meggering sensitive electronics @ 500V . ( Visualise a Tongue in cheek Emogi here)
Earthing conundrum
- Thread starter Danny k
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Funny I was visualising the Megger going across your tongue and your cheek, now that would have been funny granted a bit nippy, but then I reread.
Sharpend
"It Just Is"
It’s about time you upgraded your zx81 deke, perhaps try the Zx Spectrum, Vic20, Commodore 64, or the almighty Acorn?
( Visualize Emogi pulling his tongue out )
Sharpend
"It Just Is"
Sharpend
"It Just Is"
Dunno the difference TBH I lifted it off your link but its not moving .
Hi thanks for all replies , on closer inspection I've discovered one of the supply's for a number of lights is actually a P M E , as I understand it that takes me back to table 54.8 . The nutral supply cable to this building is 150 mm so that means 35 mm Earth cable ???
thats how I read it anyway , obviously this is not practical or cost effective , so I'm now thinking of going the TT route , any thoughts advise greatly appreciated
thats how I read it anyway , obviously this is not practical or cost effective , so I'm now thinking of going the TT route , any thoughts advise greatly appreciated
phil d
Well-known member
35mm! I'd be looking at that again if I were you, a normal street lighting column, as found alongside any road just has a short length of cable feeding it that is usually jointed into the cable feeding the houses along the road, round here I think they use split concentric, there's usually an earth strap from the isolator to the door and that I believe is a lump of 10mm G/Y. The fact that you are bolting the columns to a concrete pad rather than burying them will still have some effect on the loop values, it should lower them. Any brick/stone/concrete material is conductive to a greater or lesser extent, look at a house, now the metal back boxes are fixed to the brick walls, which always have some moisture in them, the back boxes are connected to the circuit earth either by a fly lead or by the screw fixing the accessory to the box. If you measure the value of loop at the CU with the main earth in place and also the bonds to gas and water, but with any other earths disconnected from the earth bar, you will get a reading, now, if you reinstate the other earths and measure again, you will find the reading drops, because of the parallel path through the brickwork. This is why you cannot simply put a clamp meter around the earth cables when you are trying to locate earth leakage on a circuit.
If you have a number of columns connected together this will lower your loop value quite a bit, nowadays when the DNO joint a street cable they leave a short pigtail of bare copper coming out of the joint, it's only about 300 mm long and probably not more than 6mm cross section, but if you get a few of these in a street it's enough to lower the loop value quite substantially once they are buried in the ground. it's the same with your columns, they are bolted to a concrete pad which will in reality never be completely dry so there you go, when you factor in everything your 35mm earth isn't necessary, neither are your rods.
Thanks for replying , to be honest I think I've got myself into bit of a kerfuffle over this , but if you look in regs special location ( outside lighting ) think 714 , it does seam to be what the regs say , I'm meating with a bloke from York city council on Tuesday apparently he's there top man for street lighting so will be interesting to get his opinion ( I will report back )
when I got my spade out discovered that there is a metals sleave in the ground witch goes about a meter down , how I wish I could ditch these bloody old post for some nice new double insulated bollards !!!!
when I got my spade out discovered that there is a metals sleave in the ground witch goes about a meter down , how I wish I could ditch these bloody old post for some nice new double insulated bollards !!!!
To show what Phil meant about the joint pigtail.
This is starting to do my head in now 
But as I understand it goes like this
if there is a break in the PEN conductor of a tncs supply the cpc and all exposed and extraneous conductive parts , could rise to mains potential . As their is no imbalance R C D will Not operate , and as the lamppost are in contact with general mass of earth it may have to carry the diverted neutral current , hence the need to bond as you would a gas pipe or water pipe , revert to table 54.8 150mm neutral 35mm Earth . I'm seeing guy from council tomorrow HELP !!!
But as I understand it goes like this if there is a break in the PEN conductor of a tncs supply the cpc and all exposed and extraneous conductive parts , could rise to mains potential . As their is no imbalance R C D will Not operate , and as the lamppost are in contact with general mass of earth it may have to carry the diverted neutral current , hence the need to bond as you would a gas pipe or water pipe , revert to table 54.8 150mm neutral 35mm Earth . I'm seeing guy from council tomorrow HELP !!!
pretty much, but youre worrying about it too much imo
@Danny k, you are efinitely over thinking this.
Both Andy & myself have worked on pubic street lighting and it is run off TN-C-S supplies.
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.
You can download the IET guide free from their website after filling in a form.
Both Andy & myself have worked on pubic street lighting and it is run off TN-C-S supplies.
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.
You can download the IET guide free from their website after filling in a form.
So just to translate, if your feeder pillar is distributing to multipe points, it must be a TN-S supply not TN-C-S?
'add another means of earthing at the ultimate or penultimate column in the radial circuit.' - drive an earth rod in?
Outgoing to the columns must be TN-S it is part of the consumer installation where it is not allowed under ESQCR to share an N & E conductor.
The supply to the feeder pillar can be TN-C-S or TNS.
A rod might be acceptable for use as a means of earthing, it might not, it’s not always possible to sink a rod.
You are also aiming for a max. of 20 Ohms remember.
The supply to the feeder pillar can be TN-C-S or TNS.
A rod might be acceptable for use as a means of earthing, it might not, it’s not always possible to sink a rod.
You are also aiming for a max. of 20 Ohms remember.
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?
you cant make TNCS into TNS. the outgoing cable would have a seperate N&E regardless of earthing type
It's just a description of the supplies to the columns, they have to be TN-S, taking the feeder pillar as the source of supply.
Because they are public street lighting, imho experience people seem to forget that it is only the DNO that can use CNE/PEN, the street lighting has to be a separated N & E supply.
ie it has to be L, N & E from the supply pillar?
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