earth fault loop impedance

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carl riddehough

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hello every1 im new and just about to come out my time.

im struggling with earth fault loop impedance, this may sound realy stupid but i can do all the testing and understand most of the results i should be obtaining etc but im acyually struggling with what earth fault loop impedance is and what im actualy doing the test for, is it just the resistance of the circuit?? detailed answers if poss as its doing my head in as not knowing or throughly understanding things drives me madX(X( X(

 
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rainydays

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Hi carl riddehough, Ze is a measurement of the impedance(resistance) external to the installation and includes: the supply transformer winding, the supply phase conductor and the earth return path of the supply.

Zs includes all of the above as well as the impedance (resistance) of your final circuit

 
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no1electrician

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Hi carl riddehough, Ze is a measurement of the impedance(resistance) external to the installation and includes: the supply transformer winding, the supply phase conductor and the earth return path of the supply.Zs includes all of the above as well as the impedance (resistance) of your final circuit
ive not looked at the links suggested but zs =ze+r1 +r2 at the furthest point on the circuit ,not the final circuit (r1&n)

simply its a verification that the resistance of the phase to earth doesnt exceed the limit for safe operation of the device (mcb etc )theres more it this is a simplification

 

septiclecky

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hello every1 im new and just about to come out my time.im struggling with earth fault loop impedance, this may sound realy stupid but i can do all the testing and understand most of the results i should be obtaining etc but im acyually struggling with what earth fault loop impedance is and what im actualy doing the test for, is it just the resistance of the circuit?? detailed answers if poss as its doing my head in as not knowing or throughly understanding things drives me madX(X( X(
Impedence and resistance are 2 totally different things even though they both use the ohms sign.

Resistance as it states is a pure resistance but impedence is is made up of both resistance and either inductance or capacitance reactance.

 
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hello every1 im new and just about to come out my time.im struggling with earth fault loop impedance, this may sound realy stupid but i can do all the testing and understand most of the results i should be obtaining etc but im acyually struggling with what earth fault loop impedance is and what im actualy doing the test for, is it just the resistance of the circuit?? detailed answers if poss as its doing my head in as not knowing or throughly understanding things drives me madX(X( X(
Hello Carl...

welcome to the forum..

As KME say's do have a read of the existing threads & posts he has highlighted! ;)

It is in essence the resistance from the supply right up through your live wires to the furthest point on a particular circuit.....

Then back down the earth path from the furthest point on your circuit back to the supply transformer.

We can measure the final circuit part of this circuit strapping R2 & R2 together at the CU, then measuring the resistance at the furthest point. Because the circuit is dead and we are measuring it with a DC powered meter, the value is a resistance.

Because the bit from the supply transformer to our CU, is still live, (unless you can get your awfully nice supply company to turn it all off and strap L&E at the transformer!!! :^O :^ O) we measure it utilising the AC supply voltage, the AC supply will introduce capacitive & inductive components into the circuit. Thus it is an impedance we are reading. This is the external Ze part of the path.

The total path, Zs, is the Ze+R1+R2.

Zs could also be read at the furthest point, when the circuit is live.

The Max Zs values are given in the tables in chapter 41 of regs,

to verify MCB's / Fuses will operate quick enough in the event o a Live-Earth fault.

I think most other bits are covered in those posts KME noted!

:DGuiness Drink

 

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