Exothermic welding: Cable to cable connections

Just a few pictures today … on exothermic welding joint of earthing copper cables.

Picture 1: Cable-and-mould set-up for a cable-to-cable exothermic joint

(Click on the picture to enlarge it.)

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RELATED ARTICLES:
Electrical Grounding Electrode Pictures | Electrical grounding  | Substation main earth bar pictures  | Switchboard earthing pictures | Lightning Earth Rods Installation | Temporary Electrical Earthing Pictures | A simple electrical installation |  Electrical installation pictures

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The above picture shows the set up for a cable to cable connection.
For the uninitiated, I have labeled the components in Picture 01 and show them again in Picture 02 below.

Picture 02: Exothermic welding process set-up labeled

(Click on the picture to enlarge it.)

I will not write much today and I have serious doubt that I will be able to write long posts again in the near future.

The best I can do is to show you some pictures. When I have more time I will write longer.

Note that the part that I labeled “explosive powder” is not really explosive powder. Well, It IS explosive, but it is not an EXPLOSIVE.

It is actually some powdered mixture of copper oxide and aluminium. When ignited, the mixture produces a very high temperature reaction that molten the copper and aluminium components which then flow into whatever cavities between the conductors to be joined, as well as form a thick layer of alloy envelope around them.

This you can see in Picture 07 below.

Picture 03: Just a closer view of the mould.

(Click on the picture to enlarge it.)

Picture 04: A shot during the combustion

(Click on the picture to enlarge it.)

Picture 05: A cable-to-cable joint still red-hot

(Click on the picture to enlarge it.)

For the curious, the earthing cable conductors in the pictures are 95 mm.sq stranded copper cables.
This installation was part of an earth mat type earthing system. High voltage substations for voltages 33kV and above usually have some sort of “step voltage” protection and the earth mat or earth grid is part of the “step voltage protection system”.

For beginners who have no idea at all of what all this means, have no worry. I will send a post or two on “earth mat” and “step voltage“ soon.

Picture 06: A completed cable-to-cable joint

(Click on the picture to enlarge it.)

Picture 07: A closer view of the finished exothermin joint.

(Click on the picture to enlarge it.)

Okay, folks. See you in the next post.

Jimmy Lee Wan Seng
(Information Trader)

Copyright http://electricalinstallationwiringpicture.blogspot.com Exothermic welding: Cable to cable connections

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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RELATED ARTICLES: Exothermic welding: Cable to cable connections | Substation main earth bar pictures | Electrical Grounding Electrode Pictures  | Switchboard earthing pictures | Lightning roof conductor installation | Lightning Earth Rods Installation | Temporary Electrical Earthing Pictures | Electrical installation pictures
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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.

Copyright http://electricalinstallationwiringpicture.blogspot.com Electrical grounding

Lightning Earth Rods Installation

The installation of a lightning earth rod is similar to an electrical grounding electrode. In fact, both are exactly the same thing. There is one small difference though. A lightning earthing need only achieve 10 ohms of maximum resistance, while an electrical grounding may need less than 1 ohms. That is ten times lower resistance, which may mean ten times the number of electrodes that need to be installed.

Diagram 1 – The overall diagram of a lightning protection system



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RELATED ARTICLES:
Exothermic welding: Cable to cable connections | Electrical grounding  | Substation main earth bar pictures | Electrical Grounding Electrode Pictures  | Switchboard earthing pictures | Lightning roof conductor installation  | Temporary Electrical Earthing Pictures | Electrical installation pictures

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Diagram 2 – A closer view showing the grounding rod chamber and the lightning test point on the wall of the building



Diagram 3 – Cross section diagram of the earthing rod installation



Picture 4 – An existing ground rod chamber



If you have read the other post, Electrical grounding electrode pictures, you will see that this chamber looks the same as the electrical grounding electrode. They are the same materials and construction.

Only the required maximum resistance values are different.

Picture 5 – A grounding rod installation in progress. The earthing chamber is not installed yet



This lightning rod has been connected as a temporary measure. Later a proper and more permanent connection would be done with the chamber installed to protect the electrode connection.

Picture 6 – The earth chamber for the earth rod in Picture 5



This chamber is bigger than the chamber in Picture 4. The sizes of grounding rod chambers vary between 10 in x 10 in to 13 in by 13 in. As far as I know there is no real technical reason for the difference other than that bigger chambers would give more room for the servicing and maintenance work during the life of the installation.

Why should you care about lightning rods?

This is my first post on the subject of lightning protection in this blog. Therefore, I am trying to make it light so that beginners have no trouble digesting the materials.

Another reason for making it easily digestible to casual readers is because every year many people die of lightning strikes whether indirectly or by direct strikes.

I know of a few cases already in my area where a few people died inside their house when the lightning hit the houses.

The worst of these types of incidents that I know was about 4 years ago where all members of a family of four died from a single strike to their house at night.

The point I am trying to make here is that the issue of lightning protection relevant to everyone, not just the lightning specialist or the electrical engineers.

Everyone should be concerned about the dangers of lightning just like the dangers or road accidents.

What Is Lightning?

The lightning strikes come from the clouds that have been charged with static electricity to a very high voltage (i.e. electrical pressure).

These clouds get charged due to the movements and frictions among themselves up in the sky. The electric currents do not flow from the clouds until the air separating them breaks down, that is when it can no longer handle the high voltage difference between a cloud and the earth surface, or between the clouds themselves.


How Is It Created?

When the air breaks down, electric current flows through the air from the cloud to earth and currents in the magnitude of tens of thousands of amperes for each strike are daily occurrences in some parts of the world.

In fact a strike can carry over 200,000 amperes of electric current.

Just consider an electrical overload or a short-circuit in our house wiring. These electrical faults would usually result in the current of only a few hundred amperes. Yet, they can already start fires and cause a lot of damage to properties.

Compare this to the 200, 000 amperes that can be carried by each of the lightning strikes, then we can imagine what kind of damage a lightning strike can do.

Even multiple human casualties are common results from a single lightning strike to an occupied house.

Is your Home Safe From Lightning Strikes?

The question now: Is your home, office or shop building adequately protected against these highly possible attacks from the sky?

Buildings of significant sizes usually have a proper lightning protection system installed. This sort of buildings normally has a knowledgeable management to look after their maintenance.

However, for houses or very small buildings, they may not have the people knowledgeable enough to ensure that adequate protection has been installed and maintained in a satisfactory condition.

How Lightning Protection Works

The conventional design of a lightning protection system is actually an electrical cage. The electrical cage is constructed of electrical conductors or cables interconnected in a network over the roof and the sides of a building.

A few vertical air finials approximately one foot high are normally visible above the roof, and these are connected to and become part of the roof conductor network.

When a lightning bolt strikes, it usually (even though not all the time) strikes these roof electrical conductors. The electrical current will be routed to the ground through a number of down conductors installed uniformly around the perimeter walls of the building or the house at approximately 20 meter spacing.

Once the electrical charge is routed into the ground, the charge must be dissipated into the mass of earth quickly enough.

If not, a high voltage will be developed at ground level and this can damage equipment cause injuries or even death to the building occupants.

The quick dissipation of the electrical charge into the earth mass is accomplished by the installation of steel rods of approximately half-inch in diameter to the depth of a few feet into the ground.

On the ground surface, the top of this steel rods are usually enclosed inside a small square concrete inspection chambers called the earth chambers.

The lightning earthing rods

Seen from the perspective of a building structure, a lightning protection system generally consists of three sections: the aerial conductor network, the down conductors, and the earthing part or what is usually called the lightning rods.

By design, the function of the aerial conductor network is to present at the highest point of the structure an area that will attract lightning strikes away from other parts of the building.

The electrical current carried by the strikes will then be routed down through the down conductors to the lightning rods at the ground level or the lowest level in multiple basement structures.

The purpose of lightning rods

The purpose of the lightning rods is to help dissipate the discharge of the electrical energy carried by up to 200 kilo-ampere of electrical current into the earth mass as quickly as possible.

This is very critical to the performance of the whole system, because a lower rate of energy dissipation will expose a higher risk of injuries or fatalities to human lives (or livestock) due to the presence of a higher voltage gradient on the ground.

Besides, with a slower rate of dissipation there is a higher risk of damage to properties due to flashovers from the lightning down conductors to any ungrounded metal parts nearby.

It is also essential that the down conductors be routed along the most direct path to the ground. Therefore the location of the rods should be beneath the building or as near as possible to the building structure.

Location of the grounding rods

Quite often designers locate the rods at some distance away from the building. This is unnecessary and it may in fact increase the risk of electrocution due to the presence of the voltage gradient across a wider area of the ground.

The Materials

The lightning rods are usually steel reinforced copper rods approximately half an inch in diameter, and driven deep into the ground. In an area free of rocks, they can easily be driven 18 feet or more into the ground.

The Installation Methods

This method of lightning rod installation can give a good reading because the rod surface easily makes an effective contact to the earth mass. Deep driving like this also gives good reading because as the rod is driven into the lower level of soil, it comes into the water level that is not affected by seasonal conditions.

Other Installation Methods

Other methods are also used instead of the deep driven steel rods to provide the best possible contact with the earth mass. The choice depends on the prevailing ground conditions: the soils resistivity and the soil moisture content.

Urban Areas

In urban areas, a few earth rods are usually installed first and looped below ground using copper conductors. Their combined resistance with all rods in parallel is measured and it must not exceed 10 ohms as required by the international standard.

If the combined resistance is above 10 ohms, more rods are driven and connected until the 10-ohm requirement is met.

Isolated Areas

However, in locations away from recent developments, the soil conditions may not be known without actual measurements. Therefore, the soil resistivity tests must be carried out to determine the earthing method most suitable and the extent of the work required.

At times when the soil is sitting on rocky subsoil below ground, a hole may have to be drilled deep down. A depth 100 m or more is not uncommon in more serious cases.

In these situations, a long copper rod is inserted deep into the hole to get the 10-ohm requirement.

In more extreme cases, even this is not enough and soil conditioning agents like Bentonite or conductive cement need to be used.

These compounds are prepared as a slurry or mix, and poured down the vertically drilled hole, creating a lower resistance between the embedded copper earth electrode and the surrounding soil.

The cases that require this method of lightning rods installation may not be very common. However, it does happen.

An example may be a district gas pressure reduction stations, or other similar type of plants.

Combine all the grounds

Finally, it should be remembered that a combined earth with other services can much reduce the overall cost of the grounding for these separate systems.

This is also necessary to prevent side flashovers from the lightning conductors.

In the end it may well be that the lightning rod network is the shared earthing system for all services.

Check out the following posts for more pictures on grounding rods and other issues:

Electrical installation pictures;
Temporary electrical earthing pictures.


Copyright http://electricalinstallationwiringpicture.blogspot.com Lightning Earth Rods Installation

Electrical Grounding Electrode Pictures

The following pictures show examples of grounding electrodes and earthing chambers for electrical earthing systems.

Picture 1 – Earthing chambers

=== RELATED ARTICLES:  Exothermic welding: Cable to cable connections | Electrical grounding  | Substation main earth bar pictures  | Switchboard earthing pictures | Lightning roof conductor installation | Lightning Earth Rods Installation | Temporary Electrical Earthing Pictures | A simple electrical installation | Electrical socket extension unit  | 1- Phase ELCB connection pictures  | Bare fluorescent light pictures  | Recessed down lights installation  | Bollard light pictures  | Light switch installation pictures  | Home wiring pictures  | Electric Meters  | Most Basic Principles of House Wiring | MATV antenna bracket pictures | Electrical installation pictures |   Temporary electrical installation pictures |  Temporary lighting installation pictures

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Grounding electrodes are driven several feet into the ground soil using a hammer or powered rod driver tools.

The connection is made at the top of each electrode to the earthing conductor coming from the electrical equipment to be grounded, or the down conductor of the lightning protection system.

This connection must be protected and it should be available for inspection and servicing in the future. It is therefore enclosed inside a chamber that is provided with a removable cover so that the grounding connection is easily accessible.

Picture 1 above is an example of the earthing chambers. This one is one of the smaller-sized types, approximately 8 inch by 8 inch of internal clearance inside the square chamber. Some designs are bigger.

Picture 2 below shows the same grounding chamber with the cover removed. Notice the strong metal pull eye provided to help removal of the cover. The earth chamber is installed in the ground and over time the gaps between the cover and the chamber are eventually filled with dirt, sand and soils. This makes the opening of the cover very difficult sometimes.

Picture 2 – The earthing chamber with the cover removed



What you can see inside the chamber in Picture 2 is the earthing copper tape that has been bonded to the grounding electrode. Picture 3 shows the bonding this better.

Picture 3 – Another view of the grounding chamber



Picture 4 – Closer view of the grounding rod



I have attached a diagram (see Diagram 5 below) that gives an overall picture of the installation of the electrical grounding electrode.

Diagram 5 – Grounding electrode and earth chamber



From the diagram you can see how the earthing copper tape is installed below ground and enter the grounding chamber from below. Then the end of the copper tape is connected to the top of the electrode using a clamp.

However the copper tape connection to the earth rod in the above pictures does not use a clamp. That is why you cannot see any sign of a clamp in the picture.

The earthing connection in this case uses thermo-weld bonding. That is the reason you can see the copper see to connect to the vertical rod at ninety-degree angle. The thermo-weld joint can be done much easier in this formation.

Whether the choice is to use the compression clamp or the thermo-weld bonding is a matter of choice depending on the number of factors.

Properly done, the thermo-weld joint is virtually maintenance free. You would not even need the inspection chamber, even though it is better to have one because you may need to make more connections to the grounding rod in the future.

The joint made by the compression clamp, on the other hand, need to be inspected regularly at certain intervals to make sure there is no interference to the joints. The earthing resistance test also need to be tested every one or two year to ensure it is within the acceptable level.

A total earthing resistance that is too high will present a serious shock hazard to users of the electricity within the premise concerned.

The pictures below show joints of earthing conductors to grounding rods.

Picture 6 – Copper tape to earthing electrode connection



Some readers may ask where the earthing chamber in this picture is.

Actually the installation here has not yet been completed. I have allowed the contractor to proceed with the earthing installation so they can energize the power supply early.

The earthing chamber would be installed later after the roadwork is ready for the installation of the earthing chambers. This particular earth chamber was actually installed near the road curb of the internal road. Try to avoid this if you can.

Picture 7 below shows a broader view of the electrode



As you can see, the connection and part of the electrode seems too high above the ground. Actually that would be the real finished level of the internal road which was still under construction. That was the reason the earthing chamber was not installed yet.

Picture 8 – Earthing copper cable connection to earth rod



Picture 8 above shows another earthing connection inside the earth chamber using the compression type brass clamp.

Observe that the top end of the electrode in this picture does not have the screw thread that is clearly visible in the electrode of Picture 6.

That is because the real top end of the earth rod in Picture was much higher but it was cut to match the expected final ground level.

Copyright http://electricalinstallationwiringpicture.blogspot.com Electrical Grounding Electrode Pictures