What are these wires that are connecting powerlines?

[Vitina]

I would like to add that this is called a grounded Y system.
The neutral carries any imbalance current.
The size of the conductors and direct connections to lighting indicates low voltage (240 volts to ground, 400 volts 3 phase) system. Ground conductor is separate from neutral because
1. Unbalanced currents will develop a voltage on neutral (this is usually small, about 0-10 volts but can have a relatively large current associated with it).
2. The ground dissipates accumulated static charge and protects wires under it from lightning.
That is 5 wires, 4 insulated (phase 1,2,3, and neutral), (and the separate ground over the top).
Oh, and the neutral is grounded but usually only at the transformer end so as not to carry power current.

 

[Baluncore]

Ground conductor is separate from neutral because
1. Unbalanced currents will develop a voltage on neutral (this is usually small, about 0-10 volts but can have a relatively large current associated with it).
2. The ground dissipates accumulated static charge and protects wires under it from lightning.
That is 5 wires, 4 insulated (phase 1,2,3, and neutral), (and the separate ground over the top).
Oh, and the neutral is grounded but usually only at the transformer end so as not to carry power current.

I would dispute some of that. Australia uses the MEN system, so the centre of the 'Y' is neutral and is earthed at the transformer. Then there is an Earth stake connected to the neutral at every pole servicing a customer.

Single phase customers have different current demands so they generate unbalanced phase currents, those currents return through the neutral where they cancel to some extent.

The 4 wire 3PH 400 VAC street level distribution does not usually have a protective Earth wire above to catch the lightning. In built up areas there will usually be a street light on every second pole. I believe the fifth wire seen on the pole is not an earth, but is a control wire for the street lighting.

 

[Nathi ORea]

For a single phase outlet for a customer in Australia and NZ, yes.

The Multiple Earthed Neutral, MEN, is so called because it is connected to Earth stakes at many poles in the street. Inside your distribution box the MEN goes to a “neutral bar”, N. That neutral bar is connected to the 'N' terminal on the top right of every outlet throughout the premises.

Each distribution box also has an Earth stake that connects to the “protective Earth bar”, PE in the distribution box. That PE is connected to the 'E' terminal at the bottom of every outlet throughout the premises.

There is only one place on the premises where there is a deliberate connection between PE and N, and that is a single link between the PE and N bars in the distribution box. PE and N are never intentionally connected inside equipment that will be plugged into an outlet.

The active phase has a service fuse outside the premises before it reaches the meter in the distribution box. (That service fuse can be removed to disconnect the power if you don't pay your bill). After passing through the meter the active goes to a master switch, and then to the “active bar”, A. Active is supplied through over-current breakers to the different parts of the premises, where it becomes the active, A, top left terminal of an outlet. That is the one that bites. It is not unknown for the A and N to be accidentally reversed on an outlet, but that should not kill you. It is also possible for PE and N to be reversed, but that should be detected as residual current through the single link between the N and PE bars.

That is how the three bars, PE, N, and A, in the distribution box are connected through breakers to outlets by three conductor cables. Only the MEN on the poles in the street are connected directly to an outlet without interruption.

During normal operation, the current in A will be equal and opposite to the current in N, and very little PE leakage current should flow. A residual current device, RCD, checks that the A and N currents are equal and opposite.
https://en.wikipedia.org/wiki/Residual-current_device
That can be used to disconnect the circuit if a ground fault occurs.

Thanks for that. I think that makes sense to me.

It is not unknown for the A and N to be accidentally reversed on an outlet,

Yikes!

 

[Baluncore]

Yikes!

The system is fail-safe since the Active and Neutral inside appliances are both assumed to be live, and so are never deliberately exposed, or connected to Earth. The RCD operates on both A and N, while fuses and over-current breakers operate on the Active, before the wires can get crossed.

When the same domestic equipment is plugged into a 230 VAC outlet in the USA, where there is split phase, both the A and N wires are expected to be live. That is quite normal.

 

[awaygood]

In order to work on high-voltage equipment, that equipment must be (1) de-energised, (2) isolated from any live circuits, (3) earthed (grounded) on both sides of the equipment to be worked on, (4) protected by some form of barrier with notices indicating danger of high voltage, and (5) a 'permit to work' issued on the technicians, giving exact details of what is to be done. What you see in this photograph is the protective earthing conductors attached to the de-energised and isolated conductors on one side of the equipment.