I don't think most street lights are grounded unless they connect to the ground wire on the wooden pole. But my GE 201SA has a screw hole marked ground near the slipfitter, but there was no screw or wire attached to it. So I just wired it up to a two wire lamp cord for testing and it seemed to be fine without a ground.

Although, I'm sure consumer type area lights would have a ground wire per code, I don't think street lights have to be.

From many pictures on the gallery of open Cobraheads and other streetlight fixtures. From what I can see they have a ground but it's not visible.

HID don't need grounding for their functionality, so they will work pretty well without any ground connection at all.
The problem is, they are mostly designed as Class I devices, so only with working insulation. That means a posibility of faults involving breakdown of this insulation is not eliminated by the design. So to keep it safe the fixture has to be grounded, if any conductive part is accessible (according to the Code).
If it is high on an insulating pole, it is considered as "not accessible for not qualified", so the grounding is not needed. But if it is e.g. mounted on a metal pole, that pole has to be grounded. Same if it is sold or installed for a home use, the grounding should be connected (using a 3-prong cord,...)

All of my newer cobraheads have a tapped hole marked GND for the ground screw or lug. My older ones don't but I install a ground lug/screw when I wire them up. I ground all my lights for safely since they're wired up to a cord and plug. In a actual installation the lineman may sometimes omit the ground connection in the actual luminaire and ground the luminaire using the pole or the arm.

Any metalwork on a fixture should be earthed/grounded, unless it's defined as double-insulated, see here.

In my area, most HID street lights and area light rentals are not grounded except on metal poles. There are some older Westinghouse Vanguard ones that have the neutral run through the grounding screw, effectively grounding it on the neutral.

New LED street lights do have a ground wire as you can see a black, a white and a green conductor come out of the arm. Usually, the white and the green are connected together on the pole neutral wire.

My Cooper Vanguard is grounded in the same fashion as any indoor light fixture (not through the neutral).

I see, I will try to get a grounded cord for my GE NEMA and if I get other street lights to ground them. It's easier and cheaper to get a 2 wire lamp cord, the GE ones from Walmart because the only 3 wire cords are the HDX appliance cords at Home Depot, and they cost a lot more.

If I installed a light on a pole, I would ground it. But yeah, most of the NEMA heads I've looked at on wooden poles just have the white and black wire connected and I don't see a ground connected to the copper pole ground. Which as you say, it's considered not accessible because nobody can reach it unless it's a lineman with insulating gloves.

Some double isolated luminaires do have Earth connection. It is not required to connect it according to standards

But here comes a consideration : Some of the lanterns have metal body, with the second isolation provided by a Plastic gear tray and double isolated internal wiring. For the code they are double isolated, and the Earth is optional. However, there are numerous failure modes in which the double isolation would still fail from a single fault :

 - Wire got loose from a terminal and rests on the metal

 - Water filling up inside the luminaire

 - Capacitor melted or exploded and it's foils rest on the metal

 - Ballast overheated and melted through the gear tray, as well as melting it's primary isolation (as result of a short across the lamp, such as a SON-E with stuck starter)

The automatic cutout (that breaks the circuit when the luminaire gear cover is opened) does not help there, as the luminaire body will be live before it is opened and the cutout is disconnected. In the case of the loose wire or water ingress, it is possible that the wire that broke or got submerged is the Phase before the cutout, in which case it does not help at all



Some double isolated lanterns do have double isolation and an Earth connection is provided for no good reason, sometimes in a way that makes no sense. For example, there are all-plastic E27 (non HID) bulkheads, in which the Earth terminal connects just to a square of Aluminum reflector above the lamp, of all things (the lamp socket is not mounted to it and no wires go through it or so)

It makes little sense to connect the Earth there..

From outside this square of Aluminum is not accessible

From inside, when you replace a lamp you are likely to touch it. So, if you replace a lamp and it breaks in your hands and the power is on, this square increases your odds to get a pikachu (especially considering that this bulkhead is mostly used with CFLs and LEDs, where you are likely to touch only one pole of the supply), while if the reflector would not be Earthed, you would not get any significant shock at all (since most likely you don't have other connection to Earth)



Neutral is not Earth and cannot be used as Earth. If there is a bad connection in it upstream, the "Earthing to the Neutral" will result in the enclosure becoming live, through the luminaire (or other appliance) load - without any additional faults present other than the bad connection itself

Since bad connections do happen (and atleast as often as isolation faults, if not much more frequently), using Neutral as Earth provides additional risk, instead of providing protection

Main Neutrals of the grid are sometimes actually designed for use as Earth. They are called PENs (PE and N) and there are special requirements for their layout, connection, points where they are connected to Earth (using rods etc), and conductor cross section). But connecting to them must be done accordingly : For example, you cannot splice one wire to the PEN and then use it as PE and as N (by jumpering it at the luminaire terminal), there are requirements how to split PE and N properly to avoid the connection reliability issue



Over here, modern code requires that luminaires are either double isolated or Earthed. In most old setups (80s or before), lanterns on metal poles are Earthed properly, while lanterns on wood poles are not Earthed, most lanterns at the time were not double isolated

Here, many installations use Protective Multiple Earthing, or PME.

Many standards allowed for fixed installations the PE to be joined into a common conductor with N, the wire called then "PEN", the system "TN-C".
It was "invented" in Germany in the 30's, here it was still the preferred method even for home installationss till 90's, but then it was obsoleted.
Even today it is common in power distributions, but it is limited to conductor cross sections above rather high limit (if I remember well the limit is 16mm^2 conductor minimum, so nothing for home uses).
Normally the street wiring/cables are TN-C (with way above 16mm^2 of course), at the meter connection the PEN is then split so the system converted to TN-S (PE is separate from working conductors).


Of course, the TN-C could be split at any place to TN-S, but once it is TN-S, it can never be joined back to TN-C.

I think they ground through the neutral.

Of course, the TN-C could be split at any place to TN-S, but once it is TN-S, it can never be joined back to TN-C.

TN-C-S or PME is the most common arrangement for new residential installations here in the UK.

TN-C-S or PME is the most common arrangement for new residential installations here in the UK.

There is no "TN-C-S". It is either "TN-C" (here usually upstream the meter) or "TN-S" (downstream the meter).

Beside to the two, here quite often is still a "TT", so with L1/L2/L3/N power wires and PE connected via a fault sensing coil of the voltage fault detector/breaker (breaks the working conductors if it senses >36V at PE line vs the grounding electrode) to a local grounding electrode. It was a way how to get a reasonable safety without really a low impedance grounding electrode (back in the 50..80's); the drawback is, the PE should never be connected by any means to that grounding electrode, what meant the grounding can not use water pipes as an electrode, because that would short out the sensing coil...
The N is then grounded tat the substation.
Newer installations use RCD instead of the voltage fault detector and rely on the current mismatch

There is no "TN-C-S". It is either "TN-C" (here usually upstream the meter) or "TN-S" (downstream the meter).

All I can say is I refer you to the article I mentioned earlier, see here where that is how PME is described (see just above the diagram at the top of the page).