Zs, Ze how the tester works?

[assegayer]

I understand how to test Ze and Zs and that Zs is the total impedance from the suppliers tranny to the final accessory in a circuit your testing. Also that Ze is the suppliers earth resistance.

However i have a few questions

1.) how does the test meter actually work to measure Ze by connecting the meter to the main earth (obviously main earth disconnected from MET) and to the phase conductor? does it link it out or send a current or what?

2.) Why and how does Zs effect a devices tripping time? like what is the theory behind it. I know Low Zs means that fault current will be higher thus tripping the device but how does it trip the device and what device MCB ? RCD? how does fault current going down earth trip a MCB?

3.) Would you be able to just do a test from the main isolator in the disboard and record that measurement for all the Zs readings (adding Ze reading off course) on different circuits or does it have to be done individually for each circuit to get the furthest point in the circuit?

4.)Does the meter measure prospective fault current by just using ohms law and dividing mains voltage by resistance of the cable but what i dont understand is how does the meter find the resistance of the cable does it pull a load on it and then calculate or what?


Thank you for your time

 

[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

 

[assegayer]

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

makes sense mate thanks

 

[assegayer]

9
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

I know mate i wasnt very clear we were just discussing the topic in college for our test and inspect exams so had a lot of clearing up that needed doing. I was asking why we have maximum Zs for tripping times and how an MCB or RCD would trip any quicker with lower Zs.

 

[assegayer]

I really apreicate all you guys times honestly it makes much more sense now

 

[Ian1981]

makes sense mate thanks

Another example for touch voltage would be take a bathroom with just a lighting circuit 6 amp type b mcb not rcd protected but supplementary equipotential bonding has been carried out.
If you wanted to test the affectivness of the bonding then a continuity test between exposed pipework and the cicrcuits cpc would need to be within 1.67 ohms before the max 50v touch voltage is exceeded as the formula would be 50v/ 30amps (to trip a 6amp type b mcb ) = 1.67 ohms.

 

[Pete999]

Another example for touch voltage would be take a bathroom with just a lighting circuit 6 amp type b mcb not rcd protected but supplementary equipotential bonding has been carried out.
If you wanted to test the affectivness of the bonding then a continuity test between exposed pipework and the cicrcuits cpc would need to be within 1.67 ohms before the max 50v touch voltage is exceeded as the formula would be 50v/ 30amps (to trip a 6amp type b mcb ) = 1.67 ohms.

Another example for touch voltage would be take a bathroom with just a lighting circuit 6 amp type b mcb not rcd protected but supplementary equipotential bonding has been carried out.
If you wanted to test the affectivness of the bonding then a continuity test between exposed pipework and the cicrcuits cpc would need to be within 1.67 ohms before the max 50v touch voltage is exceeded as the formula would be 50v/ 30amps (to trip a 6amp type b mcb ) = 1.67 ohms.

Ian, sorry I'm confused, where did the 30A come from in your calculation? I may have missed something, hence my question