Conduit to trunking connections

I attach here a few pictures showing the connections between electrical conduits and trunking. Some few weeks ago a reader left a message on one of my blogs asking how to connect a branch conduit to a steel trunking. So these pictures should be self-explanatory enough how to make the connection.

Picture 1 – Electrical and mechanical services above the ceiling of an office building

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The above picture shows some of the services inside the ceiling space of and office building.

Here you can see some conduit and trunking works. For large office floor space, conduit alone is usually not enough to contain the wiring cables from the floor distribution panels to the lighting and power points.

However, it not practical and a sheer waste to use trunking up to a final circuit point, a light point for example.

A lighting point needs only three wires of 1.0 mm.sq. or 1.5 mm.sq. to make a complete wiring. This does not need a trunking. It is also difficult to connect a trunking to a lighting fixture.

Therefore, the wiring to the lighting point needs to be routed into a conduit. The best is flexible conduit.

The following two pictures show how a trunking branched into rigid and flexible conduit.

Picture 2 – Conduit branching into rigid metal conduits

The above shows two branches into rigid steel conduits. One using a circular draw box as an adapter, and the other is connected directly to the metal trunking without any drawbox.

Either one is fine, but if you have a number of circuits to be run into the branch conduit, then using the draw box might me more preferable. It would ease the work of drawing the wire.

If the tap off needs to supply only one lighting point, then you can save one draw box by connecting the trunking to the conduit directly.

Another reason for using the draw box is when the conduit do not connect to the trunking at 90 degree angle to the connected side. In that case, you definitely need the draw box.

In any case, the conduit and trunking works is a skilled tradesman’s work. Often many aspects of the actual installation tasks require some creativity and experience to do it properly at a reasonable cost.

If some tradesman have a long list of better ways to do this connection than the ones that I show in this post, then by all means follow him.

What I show here are those that are usually practiced locally here.

Picture 3 – Another two connections at the same location

One more important aspect of the connection between the electrical trunking and conduit is how exactly to fix the two pieces of electrical container.

It is not visible how it is done from the above three pictures. I also keep forgetting to open up an electrical trunking and take the picture of the connection inside the electrical trunking.

The third piece of the component that makes up the connection is only visible from inside the trunking which I presently do not have any picture.

However, there is one place where it is easier to see that third component. It is at the connection between a rigid electrical conduit and the concealed metal box of a socket out or a wall mounted light switch. The pictures below show this quite clearly.

Picture 4 – Connection between rigid electrical conduit and a concealed metal box

I have labeled the relevant components so you can see clearly what are involved in the connection between the conduit and the concealed box.

The “copper bush” is the component that I wish to show you. It is this same component that is used between conduits and trunking. When the conduit and trunking are made of metal materials, the “bush” is usually of copper material. This provides a good electrical connection between the conduit and the trunking.

On the other hand, if the conduit and trunking are of plastics or PVC materials, which are also quite commonly used in certain types of electrical installations, then the “bush” would be made of plastic or PVC.

The functions of the copper bush are three fold: one is to keep the connection firm and strong. The second is to provide a smooth finished that would not injure the insulation of wiring cables when they are drawn through the joint or connection. Lastly it serves to provide a good electrical continuity between the trunking and the conduit.

The following three more pictures give more view of the copper bush.

Picture 5 – A closer view of the copper bush in Picture 4

Picture 6 – Copper bush at another lighting switch with some wiring being installed

Here I use a picture that has some wiring already drawn in to show you how wiring cable can be damaged if the area around the connection is not smooth enough.

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Cable ladder pictures

Below are a few pictures of one of the most important components of a building’s cable support system: cable ladders.
Picture 1 – Cable ladders at Consumer’s High Voltage Switchgears

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These pictures were taken inside the Consumer HV Room of a new office building.

Picture 1 above shows the cable ladder connecting to the consumer HV switchgear panels.

Observe that there are four switchgear panels there.

On the cable ladders, there are only three HV cables. Is one of the HV switchgear panels kept as a spare?

Nope. Actually the supply authority’s HV Room is just next door to the consumer HV Room. The multi-core 11kV cable feeding supply to the consumer HV switchgears is run inside a cable trench connecting the two HV rooms. So it is not visible here.

To beginners in electrical installation works, observe carefully how the cable ladders are hung from the concrete slab using steel hanger rods. Observe also how close the spacing between adjacent hanger rods.

HV cables are heavy. The weight of the cables is one thing. There are also the bending forces of the cable when they are routed and bent along the cable ladders. At certain positions along the cable routes, the opposing bending forces of the cable ladders add to the weight of the cable itself.

What you can see in Picture 1 above are only very few cables. On many occasions in you career, you will see situations where cable ladders of the size shown in the picture sag. The forces and weight from the power cables can be that strong.

Picture 2 – Close up view of an angle iron support and the hanger rods

Observe how the angle iron support is supported at each end by a hanger rod.

Picture 3 – The cable ladder connecting HV switchgears to a transformer

Here the worker standing behind the transformer enclosure is doing the termination works of the 630 mm.sq. low voltage copper cables.

Recall that here we have four HV switchgear panels. One for the incoming cable from the supply authority switchgears in the room next door. The other three are the feeder cables for the consumers’ transformers.

In many designs, a consumer substation is designed to have separate rooms for HV switchgears and transformers. Here it has been designed to share the same room.

It does not really make much difference whether the rooms for both are shared or separate. The only real difference is the total space taken.

If separate rooms are used, it would take more space. In some installations, the space is expensive. Commercial buildings at prime areas of a big city are a classic example. Private owners count every dollar they spent on every functional space of the building. Many consider space taken by mechanical and electrical plants as a waste. So often design engineers end up with very little space to install their machines and equipment.

Here it is not so bad because it is a government office building.

The cable ladder shown in Picture 3 above provide a cable support for the HV cables from HV switchgear to a 1600 kVA transformer. This transformer serves the chiller plant behind the HV room.

The low voltage cables being terminated by the worker are also run on a cable ladder to go to the chiller plant LV switchboard.

Picture 4 – Cable ladder to 1000kVA transformers

This picture show the cable ladders to the other transformers in this substation.

Here you can see low voltage cables more clearly.

The transformers are 1000 kVA ones. While the 1600kVA transformer is dedicated to serve only the chiller plant (the main plant of the building’s centralized air-conditioning system), all other building electrical and mechanical loads including external loads (street lighting, carpark lighting, etc) are served by these two 11kV/415V transformers.

Observe how the low voltage cables coming out of the transformers are run of separate cable ladders to go to the main distribution switchboards in the LV Room at the other side of the wall.

Wall openings on the wall would later be sealed by an approved fire seal to prevent spreading of fire from one electrical room to the next.

Notice also the automatic fire suppression units (the red-painted round cylindrical objects mounted on the walls) installed at locations around the switchgear room. I will talk on the automatic fire suppression system in another post.
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Electrical grounding

I believe I have uploaded to this blog quite a number of pictures on electrical grounding. However, there is one work of the grounding system that I have always wanted to show the readers especially true beginners (i.e. students and young engineers). That is the process of exothermic welding.

Picture 1 – 25mm x 3mm grounding copper tape permanently bonded to ground using exothermic welding

This ground rod and the inspection chamber are in place. The grounding copper tape has been permanently bonded to the ground rod.

The inspection chamber has been placed tentatively at the approximate finished ground level.

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Picture 2 – A closer view of the exothermic welding.

Personally I would prefer all grounding connections inside inspection chambers to be of the compression type (eg. using brass clamps). That is the purpose of the chamber, so that the maintenance people can inspect the grounding connections and do some work to improve the grounding resistance if and when necessary.

If the grounding resistance has deteriorated over time (i.e. the resistance to earth gets higher), then maybe we need to add one or more grounding electrodes and loop them to the existing grounding network.

The “looping” of the new electrodes to the existing ones would have been done inside this inspection chamber.

If the existing connections inside the chamber use exothermic welding such as that in Picture 2 above, connecting new earthing conductors here can be difficult.

Having said that, it should be acknowledged that under certain circumstances it might be better to have a permanent bonding. Exothermic bonding is a form of permanent bonding and it is maintenance-free.

In fact, with a properly carried out exothermic welding, the inspection chamber may not even be necessary. Some engineers may disagree with that, but that is how I think.

The above connection at the inspection chamber was already completed when I inspected it. Just for the purpose of showing it to readers of this blog, I have asked the electricians to make another joint so I can take some pictures. They are shown below.

Picture 3 – The grounding conductor and electrode before exothermic welding

This electrode was just another electrode not far from the one in Picture 1. There was no particular reason that I chose this one for the demonstration.

Maybe it was just because the top of the electrode was protruding quite a few inches above the expected finished ground level.

I guess I wanted to show that the driven electrode needed to be cut first before the exothermic welding process was carried out.

Picture 4 – A close-up view of the ground rod and copper tape conductor

Picture 5 – Cutting the excess top part of the electrode.

Keep in mind that later the top of the rod and joint between the rod and the copper tape should be inside the inspection chamber.

The concrete inspection chamber itself would have a removable concrete cover.

Therefore the top of the ground rod should be just below the concrete cover when the cover is in place.

The whole of the chamber and the cover should be flushed to the finished ground level, or flushed to the finished road level if it is installed under road.

Picture 6 – Preparing the top of electrode to accept the copper tape.

If you look at Picture 2 again, you can observe that the copper tape is like “standing” or “slicing” the electrode. Some electricians prefer to put the tape flat on top of electrode.

I think it makes no difference either way. It’s just that the opening at the mould (you will see the mould soon) should be cut accordingly. Electricians do not normally make the mould themselves. They order them from electrical shops.

In the above picture, the two workers were making a shallow slit at the top of the electrode. It was cut small enough to just “park” the copper tape into it.

That would give the joint a stronger mechanical strength, they said. I doubt that, but then I didn’t think it would much difference either way.

Picture 7 – A closer view

Picture 8 – The workers trying to park the copper tape onto the ground rod.

Picture 9 – A closer view

Picture 10 – Now the worker places the mould to the joint and encloses it.

The work you see here requires is not difficult, but it requires at least two or three persons. Now the workers place the mould in such a way so that it encloses the joint between the copper tape and the copper-jacketed steel earth rod.

Picture 11 – Now the mould is in place.

Observe how the mould is constructed with a handle that can grip both conductors to be jointed.

Picture 12 – A closer view of the mould enclosing the joint.

By now even a first time viewer should be able to make a conclusion that a different mould would be necessary if two other different types of conductors were to be jointed.

Picture 13 – Tying the mould with a metal wire for extra strength.

Here the workers tried to give the grip of the mould over the joint an extra strength by tying it with a metal wire.

Picture 14 – Filling the mould with an explosive powder mixture.

Now the mould is being filled with a type of explosive powder mixture. Contained in the mixture also is a form of copper material so that during the quick combustion the copper elements melted onto the joint and forms a permanent joint.

It is similar to jointing two different pieces of concrete blocks with liquid concrete. After the liquid concrete has hardened, the two concrete blocks would become one larger block. The difference is that the liquid concrete takes much longer to harden. Whereas here the copper element in the powder mixture melts during the explosive combustion and then hardened. So the process here is very much quicker.

Picture 15 – A closer view of the powder mixture.

Picture 16 – Preparing a gas torch to ignite the powder.

Picture 17 – The gas torch

Picture 18 – BOMB! Take cover!!

I do not remember exactly what I was doing, but I did not have my camera ready when the worker ignited the explosive powder in the mould. So I was not able to catch the bid smoke during the hard combustion.

Actually during the whole process, I was have a visitor to the site who wanted to see the exothermic welding process. So while I was taking pictures for this blog, I was also sort of “entertaining” the visitor, and missed the big smoke.

If you click on the picture to make it larger, you may still be able to “feel” the remaining smoke there. I am so sorry about that. I will try to catch the big smoke some other time.

Picture 19 – The explosive powder has been spent.

Now the mould seems to be empty. After the combustion, the mould had to be left there for a few minutes so it can get cooled enough before anyone can try to pry it open.

Picture 20 – Untying the metal wire around the mould.

Picture 21 – Now the mould has been taken off.

Picture 22 – A closer view of the joint after the mould has been taken off.

I heard someone actually chuckled and said “ Wow! It’s like a cup cake!”.

I don’t think it is in any way resembling a cup cake.

However, after so many years seeing it done, I always have that little excitement inside whenever a new mould and powder mixture is used to make exothermic joint.

Because when the mould is cracked open, the resulting joint piece is like a new artwork.

Picture 23 – Someone knocked off the still hot copper flakes off the joint.

Picture 24 – A beautiful exothermic joint

Do I need to say more?

See you guys around.

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Compound lighting storage yard

I took a few pictures of the storage area for compound lighting parts at a project site recently. With these pictures I think I have explained the whole system of compound lighting in this blog. So this post wraps up the topic of compound lighting. Of course, if I find more pictures that I think readers would be interested in, I will attach a link to this post also.

Picture 1 – 10 meter light poles: the lower piece

This is the lower part of 10-meter lighting poles. The upper pieces are shown in Picture 2 below.

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Picture 2 – 10 meter lighting poles: the upper piece

As you can see, these poles are still tied into bundles. These are how they get packaged and transported in lorries or trucks.

As you may already know, lighting poles are usually made of hot-dipped galvanized steel materials or some form of fiber. In this case, it is hot-dipped galvanized.

These materials are chosen for their resistance to the effects of rough weather and resistance to corrosion.

That is why when they are delivered to a construction site, it is usual to see that they are sort of “dumped” to the ground, and be left there until the time to erect them to the concrete foundation.

Picture 3 – Compound lighting concrete foundation

Observe the four anchor bolts that are visible on top of the concrete foundation. These component can also be found at the storage yard. See Picture 4 below.

Picture 4 – Anchor bolts

Picture 5 – Control gear access door

This is the access door for the light pole control-gears. I am not trying to promote any particular brand here. However, observe the design of the hinch for the control door and also the special shape of the door locking screw.

Picture 6 – Access door hinch

Picture 7 – Access door lock

Picture 8 – Complete assembly of an 8-meter compound lighting pole

Finally, the above picture shows the complete assembly of an 8-meter light pole.

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1600 kVA Transformer Pictures

You can see below a few pictures of a 1600 kVA electrical power transformer being unloaded from a transport truck.


Picture 1 – 1600 kVA, 11kV/415V electrical power transformer being unloaded

I will not be writing much today. I have not been sending posts to this blog for a while because my new project was taking much more of my time than I originally expected. It not yet finished even now.

So I decided to take a little time off just to get refreshed, and maybe send a post or two to this blog.

To regular readers who keep visiting this blog, I thank you for your time.
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RELATED ARTICLES: | Building’s electrical room layouts | Electrical installation pictures  |
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Picture 2 – Also the same transformer, just at a different angle

This 1600 kVA, 11kV/415V transformer was one of three units for this new office building. The other 2 units were both rated 1000 kVA each.

Picture 3 – On-board crane lifting the transformer

Picture 4 – The lifted transformer approaching the electrical substation entrance door

Picture 5 – Powerful machines still need men’s help

Here you can see that even a powerful machine like this crane still cannot do all the work. Human strength and assistance are still needed to finish the job.

The transformer has been delivered when the substation building has been fully completed. If the transformer had come two or three months earlier (it should have actually, but that is a story for another day), there was a bigger opening left at the entrance so that the crane could just slide through a little bit into the substation.

That would have allowed it to be placed directly on the flat surface of the substation floor.

In this case here, the crane could only bring the transformer as far as a few inches before the substation room door. That was really not good because it is a practice to build a substation floor 8 inch to 12 inch above the finished ground level around it.

So if you see closely in the picture, there is a concrete slope right outside of the entrance door.

I cannot recall the precise weight of a cast resin transformer of this rating. My guess is around 8,000 kg to 12,000 kg. That is really a huge weight to be pushing up that slope.

That is why you can see the seriousness of those men.

Picture 6 – Past the entrance slope, and inside the transformer room

Here the workmen have made it past the entrance slope and is now inside the transformer room.

Notice the light green pulling rope tied close to the two transformer wheels. The workmen made use of the concrete cable trench (just outside of the picture on the right) and use it as a hedge to provide the pulling strength when overcoming the resistance at the slope.

Observe also the 11 kV high voltage switchgears behind the moving power transformer. These HV panels were delivered four or five months before the transformer.

At that time, the brick-wall around the substation entrance was left uncompleted so that switchgears and transformers could be landed directly by the mobile cranes onto the flat substation floor.

The HV switchgears were delivered on time, but all three 11/.415kV transformers were delayed by three months. The works on the substation front wall and the installation of the entrance door had to proceed.

Picture 7 – A closer view of the 1600 kVA transformer

It is still wrapped, but I believe the plastic sheet is clear enough that you can still see the connection terminals of the low voltage windings.

The high voltage connection terminals are on the other side of the transformer.

Picture 8 – Delivery of the two 1000kVA transformers

This is the delivery of the other two units of the transformers for the building’s electrical substation.

This time the delivery truck had no on-board crane, so a mobile crane had to be called in. I believe this was a 25-ton crane. So even if the 1000 kVA transformer weighs 12,000 kg, it should be no problem at all for the big machine.

Picture 9 – Again, the 25-ton crane still needed the help of a few Bangladeshi workers

Okay, folks. That’s all I have for today. Hope to see you all again soon.

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