Zs, Ze how the tester works?

[westward10]

Understand the principles of circuit protection and don't lose too much sleep over the operation of an earth fault loop impedance tester, I commend you for wanting to know but it is clouding over what you NEED to know. Trust me it doesn't matter how it works.

 

[mickfred]

My mistake it just you use all the right terms so i thought you may be a spark yourself

 

[Ian1981]

but how can it record the volt drop when your not at the other end of the cable to measure the volt drop!!! does it magically go around the live and back through the earth?

In simple terms, the impedance of the phase-to-earth loop is measured by connecting a resistor (typically 10 Ohms) from the phase to the protective conductor as A fault current, usually something over 20 A, circulates in the fault loop, and the impedance of the loop is calculated within the instrument by dividing supply voltage by the value of this current. The resistance of the added resistor must be subtracted from this calculated value before the result is displayed. An alternative method is to measure the supply voltage both before and whilst the loop current is flowing. The difference is the volt drop in the loop due to the current, and loop impedance is calculated from voltage difference divided by current.

 

[assegayer]

My mistake it just you use all the right terms so i thought you may be a spark yourself

I am almost a 'spark' mate am2 in june and done!

 

[assegayer]

In simple terms, the impedance of the phase-to-earth loop is measured by connecting a resistor (typically 10 Ohms) from the phase to the protective conductor as A fault current, usually something over 20 A, circulates in the fault loop, and the impedance of the loop is calculated within the instrument by dividing supply voltage by the value of this current. The resistance of the added resistor must be subtracted from this calculated value before the result is displayed. An alternative method is to measure the supply voltage both before and whilst the loop current is flowing. The difference is the volt drop in the loop due to the current, and loop impedance is calculated from voltage difference divided by current.

THANK YOU!! now that has made a switch flick in my head, just a one more thing if you can how does Zs effect the tripping time of a MCB or RCD?

 

[Wilko]

but this is the concept i am struggling with you cannot measure the resistance of one piece of wire unless you have long leads either end or unless of course you cross connect and measure at end point?! thats why i am wondering how the meter does it for Ze

Ahh - the missing piece for you may be - the line and the protective conductors ARE linked by the supplying transformer secondary winding. That is the circuit you are measuring. Does that help?

 

[assegayer]

Ahh - the missing piece for you may be - the line and the protective conductors ARE linked by the supplying transformer secondary winding. That is the circuit you are measuring. Does that help?

THANKS! believe me that was a missing piece mate now it really is coming together its just sometimes at college they dont clarify things like this and it keeps you wondering. Just thinking of it now that piece of information you just said clarifys alot of other things. Thanks alot

 

[mickfred]

Look in your post you have asked why a efli tester would trip a rcd , that each circuit is cross connectied for R1+R2 test and that you seen a video of some one pluging a tester in and if you add ze on to that value . That's why i thought you where either a diyer who has read this forum and picked up some of the terms or was a spark taking the Mick but if your doing you AM2 soon best of luck

 

[assegayer]

Look in your post you have asked why a efli tester would trip a rcd , that each circuit is cross connectied for R1+R2 test and that you seen a video of some one pluging a tester in and if you add ze on to that value . That's why i thought you where either a diyer who has read this forum and picked up some of the terms or was a spark taking the Mick but if your doing you AM2 soon best of luck

No problem mate thanks for the info anyway. I think there may be a misunderstanding i was asking why Zs has anything to do with how fast a RCD trips in fault conditions

 

[Wilko]

THANKS! believe me that was a missing piece mate now it really is coming together its just sometimes at college they dont clarify things like this and it keeps you wondering. Just thinking of it now that piece of information you just said clarifys alot of other things. Thanks alot

No worries, I've had plenty of wtf moments myself

 

[mickfred]

just a one more thing if you can how does Zs effect the tripping time of a MCB or RCD?

Not buying it

 

[assegayer]

Not buying it

Mate i am not selling anything honestly. I am asking this question seriosuly whats so hard to get? i have been told so many times you need low zs readings to achieve the correct disconnection times but i have never been told why and how Zs effects the disconnection times. I dont know if i come across as a wind up but honestly not/

 

[Ian1981]

THANK YOU!! now that has made a switch flick in my head, just a one more thing if you can how does Zs effect the tripping time of a MCB or RCD?

Take a 32 amp type b mcb max zs is 1.37 ohms.
Tripping time between 0.1-5 seconds is 5x the rated current of the mcb so 5x 32amp type b is 160 amps.
230v x cmin 0.95= 218.5 volts.
218.5 volts / 160amps gives you 1.37 ohms.
Basically whatever mcb type b device you have multiply it by 5 so 6amp mcb x6 = 30 amps.
218.5/30 amp = 7.28 ohms max zs.
Type c mcbs are multiplied by 10x rated current
Type D by 20x rated current.
aslong as your zs values are within their max values you will have compliance by ADS including any equipotential bonding conductors required

 

[mickfred]

Look i don't want to be a div and if your just having one of them days fair enough

 

[Ian1981]

Take a 32 amp type b mcb max zs is 1.37 ohms.
Tripping time between 0.1-5 seconds is 5x the rated current of the mcb so 5x 32amp type b is 160 amps.
230v x cmin 0.95= 218.5 volts.
218.5 volts / 160amps gives you 1.37 ohms.
Basically whatever mcb type b device you have multiply it by 5 so 6amp mcb x6 = 30 amps.
218.5/30 amp = 7.28 ohms max zs.
Type c mcbs are multiplied by 10x rated current
Type D by 20x rated current.
aslong as your zs values are within their max values you will have compliance by ADS including any equipotential bonding conductors required

A max zs value for a 30mA rcd used for fault protection will be 1667 ohms as 50volts touch voltage /0.03 amps = 1667 ohms.

 

[assegayer]

Take a 32 amp type b mcb max zs is 1.37 ohms.
Tripping time between 0.1-5 seconds is 5x the rated current of the mcb so 5x 32amp type b is 160 amps.
230v x cmin 0.95= 218.5 volts.
218.5 volts / 160amps gives you 1.37 ohms.
Basically whatever mcb type b device you have multiply it by 5 so 6amp mcb x6 = 30 amps.
218.5/30 amp = 7.28 ohms max zs.
Type c mcbs are multiplied by 10x rated current
Type D by 20x rated current.
aslong as your zs values are within their max values you will have compliance by ADS including any equipotential bonding conductors required

I see, I think the problem i was having was i was thinking of Zs as some sort of special test when its actually just the line and cpc conductors resitstance combined with the external earth, you mentioned ADS? what is that?

 

[Ian1981]

I see, I think the problem i was having was i was thinking of Zs as some sort of special test when its actually just the line and cpc conductors resitstance combined with the external earth, you mentioned ADS? what is that?

ADS is automatic disconnection of supply.
It's the mcb tripping under fault conditions

 

[assegayer]

A max zs value for a 30mA rcd used for fault protection will be 1667 ohms as 50volts touch voltage /0.03 amps = 1667 ohms.

also why 50volts touch in particular?

 

[Ian1981]

also why 50volts touch in particular?

Its the maximum touch voltage allowed
An example would be if you try to carry out an rcd test on a circuit if the meter detects a voltage above 50v line and earth it will abort the test

 

[mickfred]

9

Mate i am not selling anything honestly. I am asking this question seriosuly whats so hard to get? i have been told so many times you need low zs readings to achieve the correct disconnection times but i have never been told why and how Zs effects the disconnection times. I dont know if i come across as a wind up but honestly not/

firstly MCB and rcd do different jobs ,so if you asking about tripping RCDs when doing efli tests that cool or if you asking why we have maximum zs for tripping times that fine too , it just your overloading your self with questions and adding them together so it doesn't make sense when your responding , if we got off on the wrong foot sorry ,i always said i wouldnt do the "get a electrian in , that under part P etc response s so it my bad