Saturday, April 3, 2010

Feeder pillar single line diagram

Today I will show the readers a simple schematic diagram of a compound lighting feeder pillar. It is for those who need to know a few basics of a compound lighting system in order to carry out other tasks such as architectural landscape design and costing works, etc.

There are also a few pictures of feeder pillars so the single line diagram will make some sense. If you need to allocate some space for the feeder pillar plinth, then I have already uploaded a few diagrams towards the end of this post. They should give you enough information to solve the technical problems.

Diagram 1 – Single line diagram of a small feeder pillar for compound lighting




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A feeder pillar single line diagram is similar a house electrical panel schematic diagram with the addition of an automatic time switching circuit added.

In the single line diagram, the time switching circuit is the circuit portion towards the top left corner of the dotted rectangle box. The sub-schematic is shaded into lighter grey.

Diagram 2 – Timer switch circuit



There are three items I wish to highlight to readers at the time switching circuit: the time switch, the contact coil and the “SWITCH BY PASS”.

The TIME SWITCH

First, the time switch. This is drawn with a symbol of a circle with the “TS” letters inside it.

A time switch is a component that is common to all street lighting and compound lighting. Its purpose is to eliminate the need for human actions to turn “ON” and “OFF” the lighting at the intended operation hours.

For example, the external carpark of a shopping complex may need to be lighted up at 7 every evening and be turned off at 3 A.M.

So this ON and OFF times can be set at the time switch inside the feeder pillar.

A human operator may miss the exact time one day, which can leads to complains by customers, but a machine would not forget. They may break down, but a properly cared machine can be much more reliable than human most of the time.

In large installations, even indoor lights are sometimes installed with similar automatic timers. It is not just for good service, but also to reduce operating costs as the setting of the timer can be authorized to only selected individuals of the organization.

One hour of delayed switching off the lights every night can mean significant additional dollars monthly on electricity bills in large installations.

The SWITCH BY PASS, or MANUAL BYPASS SWITCH

Another important component here is the normally open switch that is labeled SWITCH BY PASS in the single line diagram.

In many drawings, it is called MANUAL BYPASS SWITCH, which I think is more appropriate and more accurate. But one of my draughting lady tends to prefer SWITCH BY PASS label so much that I need to let her have her own way.

The manual bypass switch is used for maintenance or trouble-shooting works. It simply bypass the time switch to ON or OFF the external lighting or street lighting.

For genuine beginners, observe that the bypass switch is connected in parallel with the contacts of the timer relay (Diagram 2 above). With this configuration, either contact in a closed position would energize the contact coil and turn on the external lights.

Often the switch is also the key-operated type so that the ability to bypass the timer can be restricted to only authorized individuals.

The contact coil

This is the third component in the time-switch circuit.

The load currents to the lighting cables are usually higher than the current that the timer contacts can handle. Therefore, another coil with heavy current contacts need to be provided to switch the heavy currents.

That is the purpose of the coil with a symbol of the circle with the “C” in it.

Observe the dotted line connecting the coil to the three contacts at the lighting load circuit.

That is all I wish to say on the timer switch circuit today. For electrical-based readers, the above explanations are never necessary. However, for no-electrical readers, these details on the schematic diagram would probably confuse many of them

Now let’s go through a few more components inside the feeder pillar cubicle that may confuse the readers from understanding the simple single line diagram.

The cubicle lighting

Towards the right edge of the dotted rectangle, there is a fuse labelled “20A SPN S/F”. You may not see this extra component inside a normal distribution board.

It is used to supply a fluorescent light inside the feeder pillar. As you know, the feeder pillars are installed outside. Any problem to the compound lighting would probably be noticed at night, when the lights are supposed to function.

Because of that, maintenance, trouble-shooting or repair works need to be done in the dark outside. The lighting from the compound lights would not be enough for work inside the feeder pillar. Additional light lighting is needed and that is what the fluorescent light fitting is for.

The socket outlet is also provided for the same purpose (i.e. to operate the tools for the maintenance work).

These are the accessories for the street light feeder pillar or compound lighting feeder pillar.

The timer switch circuit is actually a control circuit.

Other that that, the circuit schematic is almost similar to a simple house schematic.

The main schematic

Now let me give a short brief on the main schematic, the power circuit of the system.

As explained above, the dotted line rectangle represents the physical area of the feeder pillar cubicle.

Components and symbols located inside the dotted rectangle means they are located inside the metal cubicle. That is how to interpret an electrical diagram of this type.

The electric supply is taken from the Consumer Main Switchboard as shown at the lower part of the diagram.

A short introductory brief on armored electric cables

One length of underground armored cable is used. Underground means the cable is installed inside the ground about 3 ft below the surface.

Armored cable cost much more because of the steel wire armor protecting the cable from physical damage. The letters SWA in the cable tag “XLPE/SWA/PVC” is an acronym for “steel wire armor”.

“XLPE” at the front means the insulation of the cable conductor. When we say a cable, the terminology is actually not precise enough.

In this case, inside the incoming supply cable there is actually 4 inner cores each with an electrical insulation. Therefore, each of the four insulated inner cores (the inner core is usually made of either copper or aluminium) is a complete electrical cable by itself.

The four of them are bunched together to make it easier to run and it can reduce the cost. We can actually use 4 independent cables instead of one cable with 4 inner insulated cores.

The XLPE label mentioned above indicates the type of insulation of each of the inner cores.

When these cores are bunched together in a bunch like these, an outer insulation is again extruded or layered over the whole bunch, making it look like a single cable. It is actually 4 cables that are bunch together.

The outer insulation is called outer sheath.

If this cable is to be installed underground, it is always better and always considered necessary to provide something strong over the cable in case an excavation work accidentally hits it.

That is why the steel wire armor wrapped around the cable spirally all along the cable length. The armor protects the cable physically.

Then in order to protect the armor against corrosion and other degradation, another layer of insulation is applied over the steel wire armor. Most of the time, it is of PVC (poly vinyl chloride) materials.

That is the label “PVC” on the right of the cable tag.

I did not finish the XLPE part, did I?

What is XLPE?

The XLPE is just like the PVC, but is more expensive and of better quality. That is why it is used only at the inner core of the cable. The PVC material can be used instead of the XLPE, and it will work just fine.

But with XLPE, the inner cores can usually carry higher current for the same inner core size.

I know many readers already now this, but I always wanted to put it down somewhere so I can just give a link whenever an issue requires a further explanation on this cable topic.

What is 1 – 25 SQ. MM. / 4C?

“4C” – I just explained above, the 4 inner cores. If there are 5 or 3 cores inside, then it would have been 5C or 3C accordingly.

“25 SQ. MM.” – I mentioned about the size of each inner core, the copper or aluminium material underneath the XLPE insulation. This is the size. It is always in the form of net or real cross-section area. This means if an inner core is constructed of several smaller cylindrical copper wires, then the total cross-section area of those individual wires is taken and used to indicate the size in square millimeters.

I am following the British or European Standards here.

“1 – “ … well this mean one length of the 4-core cable is used here. We can use 2 lengths which will give us 8 cores of same sizes. They are installation conditions that may force us to do that, which is a more advanced topic. In that case, it would have been written like this:

“ 2 – 25 SQ. MM. /4C XLPE/SWA/PVC”.

That is all about the incoming cable.

The feeder pillar isolation switch

“60A TPN MCCB” – this is the isolation switch. The type of switch used is MCCB (moulded case circuit breaker).

So this switch is also a circuit breaker. It can automatically switch OFF when there a fault inside the feeder pillar cubicle or the cables going to the light poles.

You can actually use a switch and a fuse instead of the MCCB. That is the protection used to supply the cubicle fluorescent light explained above.

The outgoing circuit protection

Going downstream of the power flow path, you can see the outgoing circuit breakers (i.e. 20A SPN MCB) that are used to protect the cables going out to the light poles.

Six MCB’s are installed here.

Three are spares however. No cable is connected to the spare MCB’s even though there is a red line drawn to each one of them. This is the practice when drawing these types of electrical diagrams.

Each of the three MCB’s that are electrically loaded (they have electrical loads i.e. the lights connected to their outgoing cables) has 6 compound light fixtures connected to it.

Each of the fixtures is 70 watt. So we have 6 x 70 = 420 watt connected to a 20A circuit breaker. That is how to read the diagram.

The type of the compound light fitting is HPSV (high pressure sodium vapor).
(UPDATE: A low-pressure sodium type of street light or compound lighting would give you the yellowish light like those seen on the highway. Not a nice color but this type is very energy efficient.
But the high-pressure sodium vapour (HPSV) type that is used here has a good "color rendering". This is the terminology lighting people use to say that the colors produced by a lighting fixture allow human to distinguish different colors easily and correctly.
The low-pressure sodium lamp as mentioned earlier is very energy efficient. However, the yellowish color that it produces have a very poor "color rendering". Have you ever seen the color of your own skin under one of these lights at night? )

The number of lights connected to each outgoing circuit is quite standard for compound lighting. Most installations only connect 6 lights to a circuit regardless of the MCB rating or the rating of the light fixture which usually varies between 70 watt to 250 watt..

So you can actually know how many outgoing circuits you need once you know or estimate how many lights would be installed inside the building compound.

Now let us look at a few of the feeder pillar pictures

Picture 3 – Feeder pillar for compound lighting


This is for a compound lighting system at a public building. Notice the concrete plinth that it is sitting on.

Here there is also an additional power socket installed but it is located outside the cubicle. Therefore, it has to be of a weatherproof type.

Picture 4 – Outdoor power socket



When you install electrical equipment outside of a protected room, under the rain and hot sun, it need to be of a weatherproof type.

Electric voltage inside an electrical equipment and appliance is very dangerous. It can easily kill people.

Every knows that. But when it is installed at a location where there is a possibility of water seepage into the enclosure, then the equipment become extremely dangerous.

That is why when we say weatherproof, the design, manufacture and installation must comply to a certain criteria and quality standard.

The category of degree of waterproofing is graded by what is called IP rating.

Picture 5 – Weatherproof socket IP rating



The 13A power socket here is rated as IP 66. The letter IP stands for Ingress Protection. I think that was how it came to be.

The first number after IP is the grade of protection against ingress is dust and solid objects into the enclosure.

The second number shows the class of protection against harmful ingress of water. The number 6 in this case means that the outdoor socket unit has been designed and manufactured to withstand against water jets to the unit from any angle.

This is important because being installed at a landscape area there are possibilities of strong water jets when the caretaker is watering the landscape garden.

A cleaning work of the compound area after parties and functions may also expose the unit to water jets.

IP Rating of the feeder pillar metal enclosure

I have spoken of the need to waterproof the outdoor socket outlet. The feeder pillar metal cubicle is even more important to be waterproofed.

I did not take the photo shot at the manufacturer label of the feeder pillar. However, I think the IP rating of the above feeder pillar would not be less than IP 56.

This means that the protection against the ingress of water is of the same grade as the 13A socket.

However, the protection against the ingress of dust and solid objects is probably at grade 5, which is one step lower than that for the socket.

At grade 6, the enclosure would not permit any ingress of dust at all. But at 5, some very small dust particles may still be able to enter the feeder pillar enclosure without any harmful effect to the operation and quality of the components and installation inside the cubicle.

The photographs above was taken of an existing feeder pillar for a compound lighting. The other 2 more below are from a new installation that is still in progress.

Picture 6 – New feeder pillar installation in progress



You can see that the underground cables to and from this feeder pillar are not yet terminated.

This unit seem to be much bigger than then existing one shown above. However, that does not necessarily mean it carries more electrical load or anything.

It only means the cubicle design provides more space inside for the access to the components and parts. Usually a bigger unit cost more even if the schematic design used to manufacture them is the exactly the same one.

Picture 7 – Cable entry to the feeder pillar



For readers who are looking for some details on the construction of the feeder pillar, bellow is an example. These 4 diagrams provides you enough measurements to locate the unit precisely at a tight space in a building compound.

With the single line diagram in Diagram 1 above, you can even get a pretty accurate estimated cost from the manufacture and supplier if you allow them to use their standard parts and components.

Diagram 8 – Feeder pillar front view



Diagram 9 – Interior component layout



Diagram 10 – Side dimensions



Diagram 11 – A section showing how the components are to be arranged and routed


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7 comments:

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