HELP Steet Light Design(Cable Size,Pole Out of Reach,Earth Pit) 2

[T83]

Hello & Merry Christmas to you all!!!

For the first time ever I am working on a street light design and I have some questions and I will be extremely grateful to those that will help,I am gonna briefly explain about the project and I am going to attach a sketch for it so that you can further visualize.


The place is an industrial plant that has its own private roads,the plant with its outdoor boundaries has a triangular shape as you can see from the image and their substation is in the middle of the longest side of the triangle.

First things first calculating the cable size,I am coming out from the substation with four single phase 2 core cables and go with two of them in one direction and the other two in the opposite direction I want to connect the upcoming pole with one cable then the next pole with the other cable and so on...The used lamp is a 250W High Sodium Pressure,I checked around the actual power demanded seem to be 274W and I should expect the current to be 3A if there is no pf correction and 1.4A if there is pf correction,each cable will be connected to 6 poles and will cover a distance of 265m,I want my cables to be buried underground is a 2x10mm2 cable good ?? Assuming 1.4A per pole & considering voltage drop & everything.

Second of all,if you look at the sketch there are two poles which are kind of out of the way (highlighted in the red square),does that mean that one cable will make that distance twice,meaning going towards that pole going through the electrical cut-out & going back,I can't connect to the other following pole directly because there are already buildings next to them we cannot cut the distance,or should I use a Tee-joint(if that's what it is called or smth) and have a cable simply for this extension & what size should it be & in this case does it require its own earth pit???(assuming 80-100 meter distance)Plus can somebody please explain to me "Electrical cut-out" to make sure I understood it correctly it is basically at each pole so I can distribute from the incoming cable to the pole before it continues its path???

Third of all,I read that I can earth the poles from the armoring of the cable and that at the end of the circuit I should have an earth pit,can somebody give me the details of such a connection.Also,if you look at the sketch the last pole of one of the circuits will be far from the area of where I can put an earth pit(highlighted with a read square),so is it still feasible & logical to connect the last pole to that earth pit??or should I consider something else,it may not appear like that on the sketch but the other circuit & earth pit are actually far from the last pole!!!Plus how is the earth pit connected to the circuit?with an earth conductor from the rod in the pit to the armoring of the cable ?

This is it,I know it was long & I am sorry for that!
Thank you for your time !!!

 

[7anoter4]

1) I suppose the frequency is 50 Hz and the voltage 230 V rated [nominal].
2) I suppose the 2 cables running in one direction will supply each 5 lamps-one of them the first 5 close to Substation and the second the further 5 poles.
3) Usually the distance between two poles is about 100 ft [30 m].So the first cable length will be 150 m and the second 300 m [roughly].
4) I think the underground cables get out from Substation through duct-manholes system.
5) The main cable is T connected with lighting pole wires without any interruption.
6) The soil thermal resistance is usual [90-100 K*cm/w] and the soil temperature is 20 Co.
If the cable is PVC insulated copper conductor 2*10 mm^2 the maximum caring capacity will be 90 A [buried directly in the soil]
The same cable in common power duct [as seems to be the second cable for a half of its length] the maximum permitted-supposing the duct bank will be of 9* 6 inch PVC duct and 30% filled with other power cables- caring capacity is not less than 15 A.
So in any case 5*1.4=7 A will be well supported.
7) The voltage drop:
Let's say that all the required current [7A] is concentrated at the end of the longer cable [300 m] and the cable resistance at 70 Co[maximum permitted for PVC] is 2.19 ohms/km then 0.66 ohms per 300m and the reactance will be 0.045 ohms/km [0.0135 ohms/300m] .The impedance is per one conductor then for 2 will be double. Z=1.34 ohm and the voltage drop will be 1.34*7=9.38 .That means 4% from 230V and it is still admissible.
8) A grounding wire -may be bare copper of 16 sqr.mm-buried along the poles line and connected to the grounding electrode from grounding pits and with all lighting pole grounding screws[with no interruption] will be indicated.
The lighting pole foundation will be designed to use as foundation grounding also [Ufer grounding] and connected to the grounding screw.

 

[T83]

Thanks a lot 7anoter4 as usual,you basically replied to everything,I would like to ask you one thing,what do you think regarding the grounding of lighting poles with the armoring of the cable?

 

[7anoter4]

I think the cable is jacketed over the armoring so is not in direct contact with the ground. A buried conduit may be used as grounding electrode but not the armoring due to high resistance and lack of contact with the ground.