EARTHING- FIRST STEP IN SAFETY

An presentation shows the written text EARTHING with a symbol of Earthing. — Earthing symbol (extreme right)

There are two types of powers; AC & DC. Both the powers have benefits at their respective places. Most of the cases; in general, AC power is used for Electrical Motors, Transmission & distribution system While DC power is used at low level voltage; in electronics.

ACor DC ; Whatever the power, Normally works inside the enclosed metallic chamber, Near the chamber; a risk of Electric shock is always there.

AC power is comparatively more dangerous because :

DC because AC power is used at high voltage level than DC ; comparatively.
AC power has capability of induction which get induced in nearby metallic element.
AC power’s maximum magnitude is higher than its rated RMS value. Which means rated voltage of AC power is lowered than its peak voltage value.

Electrical power is sign of progress & development if used in an appropriate way. But Above from all, Safety is the top most priority which can not be ignored. A single phase domestic voltage 230VAC; is lethal if Electrocution of more than 30mAmps get happened.

That’s why there should be complete provision that no potential get induced on metallic chamber even when a potential carrying conductor get directly fall on the chamber. That thing is possible with one of the simple & basic method which is known as EARTHING !

EARTHING

“EARTHING is a type of safety node; a sink node which is potentially stays at 0 Volts !”

This Earth, Where we are residing is the biggest sink which can consume infinite current.

“The arrangement; in which Conductor get buried in Earth with additives which makes the soil resistivity lower & further; Buried conductor is connected to the metallic body of Electrical appliance through a conductor is known as EARTHING. “

Transmission Tower | Image shows Earthing wire connected at the Top of steel tower

EARTHING SYMBOL

” Three horizontal lines with equal gap in between & A single vertical line on above on the horizontal lines represents the sign of Earthing ! “

How does the Earthing works ?

Earthing works on two major phenomenon’s; ‘Potential difference‘ & ‘Minimum Impedance‘ .

For a flow of Electrical Current, A potential difference is must in between the two nodes. In a same way, Earth work as a one of the node Which contains zero potential. While for a potential difference against the Earthing; Another node is required with having some potential level.
Current always follows the path with Minimum Impedance.

In Earthing, The metallic Electrical chamber get connected to Earthing Which result metallic chamber remains at zero potential at any circumstances; even there is no chance for Induction potential !

In worst circumstances, When a potential carrying conductor directly falls on the panel, A short circuit will happen & infinite current will flow towards the earthing which results backup circuit breaker trips.

When potential get induced on unintended part of the panel than there are possibly many chances that current may flow in any direction. But when earthing is working, Then it definitely flows towards the earthing because current follows the path with minimum Impedance.

” A GIF below shows How a circuit breaker trips when potential get induced on the metallic surface of motor which is connected with earthing.

When potential get available on Motor’s surface, A short circuit current flows towards the earthing which results circuit breaker get trips at the back end.“

GIF Shows How a circuit breaker perform when potential get available on earth connected motor's surface — GIF Shows How a circuit breaker perform when potential get available on earth connected motor’s surface

EARTHING USAGE

Apart from safety, Earthing is used in multiple ways. Earthing usages are discussed one by one, next.

SAETY OF HUMANS & MACHINERY

As discussed above, In an Electrical chamber which is having a metallic body, Chances of potential generation is always there either due to induction or insulation failure. For the safety of humans; Earthing should be connected to metallic chamber so that panel’s surface always remains at zero potential.

Even for the safety of machinery itself; Earthing is very much important because potential generation at unintended part leads to the damage of the whole system.

USE WITH NEUTRAL

Single phase loads runs through phase & neutral. In which phase represents potential which is a type of current source While neutral act as a return path back towards the power source. neutral get generated from the mid point of STAR connections. Ideally; mid point of Star connection represents 0 Volts.

In practical, neutral position is all depend upon the load balancing on Star connections. If neutral contains some potential than STAR Winding is not perfectly balanced. Potential at neutral side may create unbalanced voltage fluctuation. For neutral stability & Harmonics elimination; neutral is connected with an Earthing.

TO ELIMINATE THE NOISE & INTERFERENCE FROM COMMUNICATION SYSTEM

Communication circuit contains a signal at very minor voltage level. A little noise or interference can create the distortion in the circuit which can lead to malfunctioning of the system.

To eliminate the noises; Communication cables are specially designed with protective shield to prevent the interference. These protective shields are further connected with an Earthing.

Shielded Earth attached cables used for communication of VFDs

SAFETY FROM LIGHTNING & SURGES

On this Earth, Chances of unpredictable strike of lightning is always there. That lightning strike can create a high spike surge on the system which can damage the whole system. From the prevention of lightning strike buildings structures are Earthing connected.

” A Gif shows how a Earthing connected house get protected from direct lightning strike. Lightning current get diverted towards the Earthing.“

Gif shows How A House remains safe in direct lightning strike

“Due to switching, Charging & discharging of loads; High Voltage spikes get generated. That high magnitude voltage spikes appears for a small interval of time for micro seconds; are known as Surge .”

This surge can go beyond multiple time to the working voltage level. In worst cases, These surges can damage the whole system. That’s why protection from the surges is very important. From surge protection; Arresters are been employed which are also known as surge suppressors or surge protection devices(SPD).

Surge arrester is a type of element which diverts the path of high voltage spikes, Either through blocking or Either through shorting it. Surge arrester actually do these things with the help of Earthing. As explained through a GIF below :

A phase neutral supply connected load parallelly connected with surge arrester. When surge appear across the line, Surge get diverted towards the Earthing.

TESTING OF EARTHING

Earthing is checked through 3 methods :

Earthing Resistance
Voltage between neutral & earthing
Earth ground clamp

1. Earth resistance

In this method, Soil resistance around the soil is been measured. Metallic electrodes been buried on Earth at fixed distances. A known current is been applied at Earth electrode & one of the outer test electrode. A voltage is been measure in between earthing electrode & inner test electrode.

Through Voltage & ampere values, soil resistance is been calculated(R=V/I).

This method of earthing testing is known as “fall of potential method“.

A GIF below shows the working procedure of fall of potential method.

” In this 2 stakes are buried in the ground at equal distance most probably around 20meters in same single direction. When a Test button is pressed, A known current flows through the Terminal E & P2 While a potential is measured in between E & P1 & finally resistance value is been calculated through voltage & current. “

GIF shows the working Fall of potential method

2. Voltage between neutral & earthing

In this method, With the help of multimeter or volt-meter, An AC voltage is been measured in between neutral & Earthing.

Earthing is a type of zero node. The working Earthing node should always stay at 0 V.

Neutral is a type of return path towards the source. Ideally neutral also stays at 0 Volts. But in real circumstances, Neutral can attain some potential residue of AC voltage specially when neutral wire/cable length is long.

Voltage between working Earthing & Neutral should always be less than 2 Volts. “

3. Earthing ground clamp

Earthing is a type of sink which provides a path for the flow of infinite current. For proper functioning of Earthing; Earthing path should be clean Which means Earth should provide a path with minimum resistance. That’s why earthing quality is been verified through its resistance value.

Clamp type Earthing tester are special devices made for earthing measurement. In this method, A known voltage is been generated by this meter around the testing Earthing. While a current is measured through the clamp of the device.

With the help of voltage & current, Resistance value is been measured.

After some time due to natural forces like moisture, dust & air; The Earth’s quality degrades That’s why Earthing’s resistance should be recorded at regular intervals.

Ideally, 0 ohm is the earth’s resistance but in actual; resistance value varies. According to Institute of Electrical & Electronics Engineers (IEEE)- The resistance value should be lower than 5 ohm.

There are both analog & Digital earth testers are available to verify the Earthing resistance. Next, We will discuss one of the method which is known as ‘Fall of potential method’.

Earthing Resistance Standard

There is no fixed standard for Earthing resistance. But as we know, Lower the resistance better the earthing will be.

As per IEC 62305 Protection against lightning , 10 Ohms are the highest value required for lightning protection systems

As per 80-2013 – IEEE Guide for Safety in AC Substation Grounding , 0.5 to 1 ohm is the value required in substations .

SUMMARY

Earthing is a type of safety which represents Zero potential !
A working earthing can consume infinite current.
In earthing, Conductor get buried in Earth with additives which makes the soil resistivity lower. Further; Buried conductor is connected to the metallic body of electrical appliance through a conductor.
Three horizontal lines with equal gap in between & A single vertical line on above on the horizontal lines represents the sign of Earthing.
Earthing works on two major phenomenon’s; ‘Potential difference‘ & ‘Minimum impedance‘.
Earthing is; used as a safety for humans & machines, used in voltage balancing with neutral, Used to eliminate the noise from communication system, Used for the safety from surges & lightning.
Earthing is been evaluated with numerical value known as resistance; Which is having the units ohm.
Ideally, Earthing contains zero potential with zero resistance While in practical condition; Earthing is having some resistance value.
According to Institute of Electrical & Electronics Engineers (IEEE)- The resistance value should be lower than 5 ohm.

Tagged Basics of Electricals

EARTHING- FIRST STEP IN SAFETY