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Posted By Topic: Street light earth an neutral linked.

slaw54
Aug 26 2018 14:06

Was dismantling some damaged led street lights to salvage the led power supplies. The lights have a seperate electronic lightning protection module that I assume takes the HV to ground however these lights were were supplied by 2 core cable so the neutral had been divided(literally twisted into two conductors) and taken to the earth terminal as well. Can see the thinking with the network neutral earthed at multiple points but a broken neutral making contact with a phase would liven the frame of the fitting ? any thoughts ?
   

DougP
Aug 26 2018 15:24

I\'m not an expert on \"works\".
But a broken active could also liven the frame.
Neutral is \"earth\". So what they have done will be correct for their procedures.

Test before you touch.

Does anyone test for live on a metal meter box before you open it?
   

pluto
Aug 26 2018 17:22

In Works (distribution lines used Lines company lines)and this includes street lighting, have for many years when wired used an TN-C system of supply in which the neutral and earth is the same conductor and is often called a PEN conductor.

In street lighting fittings the neutral connection should be connected to the metalwork of the fitting first and then looped to the neutral connection. The use of this system does need some periodic inspection to verify the correct polarity of the connections.

Unfortunely since deregulation o9f the supply industry, the periodic inspections are not being done, and a number of lines companies have tried to change the use of TN-C by other systems of supply and usually in an unsafe method of supply and no periodic inspections.

The recent roll out of LED street lighting means that many of these new fittings are not being correctly installed and in some cases may be electrically unsafe, in particular, when a metal street poles is being used.

Metal street light poles (in Works) usually have a plastic coated base which means the metal pole can NOT be used as an earth electrode. The plastic coating is to give somne corrosion protection. When the LED light fitting is being installed it is earthed to the pole thinking that it is connected to the mass of earth via the pole base. If a active earth fault develops in the LED fitting, the pole could be made alive.

Energy Safety are aware of this potential problem and the steps to remove this potential electrical hazard are current under consideration.

BTW when Street light fittings supplied by an MEN electrical installation should be wired as for a TN-C-S (so called MEN in AS/NZS 3000)system of supply.

   

zl2aj
Aug 27 2018 08:27

Hi Pluto. Why is the streetlight column \"Works\"?

The streetlight column is not owned by the electricity distributor. Usually it is owned by the council or roading authority (NZTA). To help clarify this most distribution companies have, by agreement with their councils and as set out in their network connection agreements, defined the point of supply (ref Act Section 2 (3d) so that the streetlight is classed as an installation. As such it is given the same treatment as any other installation. The description given in the OP does not sound like a compliant EN link (removable for testing).

We know that streetlights (appliances) can be connected directrly to works, (energy safety did clarify this recently) and this is usually the method applied to streetlights fixed to network poles. But for columns with a greater risk of touch voltage, most networks prefer to consider them as installations. This is to increase the level of safety (arguably) and to delineate them from their PSMS obligations.

Interestingly an installation does not necessarily require a point of supply for it to be an installation. Streetlights can happily exist in this territory as well. (Section 2 Electrical Installation a ii). In this scenario we need to then assess the bits from b that would exclude it being an installation. i - the appliance (streetlight head is not an installation). ii - generator (not applicable here). iii - distribution and transmission lines. Council owned streetlight assets do not meet the definition of a distribution line (ref electricity distributor - must provide a line function to another person(s) - not to itself).

So even without an agreed POS - streetlight columns are not works. Thus they must be installations. AS/NZS 3000 applies.
   

AlecK
Aug 27 2018 09:26

Historically most street lighting was done as \"works\".
Even today, a lot is still owned by networks, who contract to provide the street-lighting service wanted by Councils.
But correct that street-lighting can also be \"equipment connected to works\", and increasingly as \"installation\". For both these there is always a Point of Supply. The provision in definition of \" electrical installation\" (in Act) for installations without PoS really only covers standalone installations not connected to any network.

So not true to say that streetlight columns \"must be installations\". They can be installed as installations, but they can also be installed as \"equipment connected to works\" similar to streetlights on distribution poles. In both cases there are conductors between poles that are not \'distrubution\' conductors (though for pole-top generally only an active as the distribution N is used directly).

If they are done as installations, they either must comply fully with \"3000\" (including such provisions as main switch and main earthing system - which can\'t include the column as electrode); or under Part 1 (which requires both Certified Design and inspection.

When old streetlight system are upgraded, there\'s a risk of getting it wrong due to not understanding how the original system achieved safety (assuming it ever did). And it simply does not work for existing systems, installed as \"works\", to suddenly be declared to be \"installations\" for administrative convenience.


Anyone asked to install or work on streetlighting should check carefully to establish clearly not only which system the design for the work is done to; but also (if applicable) under which system the existing system was installed.

   

DougP
Aug 27 2018 10:11

I\'m just wondering how the metal poles are \"earthed\"?

There\'s two brand new ones near my house.

There isn\'t any visible connection to the neutral that I can see. And there doesn\'t seem to be any other earth conductor into the ground.

I can only assume that they are only earthed through contact with the ground.

I can\'t see how contact with the ground only, would provide a low enough impedance to operate the circuit protection on the 200kVA supply, or achieve a low enough level of touch voltage.

Are they just relying on a low step potential around the pole in the case of a fault?


   

gregmcc
Aug 27 2018 14:06

I spent some time a few months back inspecting a overhead to under ground conversion of a street, this included a whole lot of new street lights, these were installed as an installation for each light, they had a POS from a nearby pillar box, each pole before it was put up had an earth stake put in the ground, and the pole put over it, each pole had it\'s own E&N bars, and MEN link, so as far as the earthing goes, there was no reliance on the pole it self to asct as the main earth, it was simply bonded to the earth bar like and other exposed metal work
   

pluto
Aug 27 2018 16:06

Even though some street lights may have been converted to other supply arrangements, there will be significant number of street light installation originally installed to the system of supply using TN-C when the neutral and earth conductor is the same comductor. So my previous report is still a major safety issue.
   

DougP
Aug 27 2018 16:32

Or is the grey/green coating on the lower part of the pole supposed to insulate against contact?
I haven\'t looked closely to be honest..
   

pluto
Aug 27 2018 16:43




Metal street light poles usually have a plastic coated base which means the metal pole can NOT be used as an earth electrode. The plastic coating is to give some corrosion protection against from the soil around the pole base.

   

DougP
Aug 28 2018 09:35

Hey Pluto.
I just went past the network yard where they have the new poles.. the bottom 1m or so doesn\'t have the coating on it. It\'s just galvanized the same as the rest of the pole.
   

AlecK
Aug 28 2018 14:30

a pole base is not an accepted form of electrode, so if installed as \"installation\" using pole as electrode would be a Part 1 solution.

would be classed as accessible conductive parts requiring earthing, also conductive structural parts in contact with ground so requiring bonding.


   

CraigW
Sep 08 2018 16:43

IF installed as an installation, and every pole had a main switch, men link, earth rod then every one of them requires a ROI yes?
   

Sarmajor
Sep 09 2018 19:06

Yes. Issued a few while working for Top Energy.