Zs, Ze how the tester works?

assegayer · Mar 31, 2017

Ian1981 said:
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 · Mar 31, 2017

mickfred said:
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 · Mar 31, 2017

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

Ian1981 · Apr 1, 2017

assegayer said:
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 · Apr 1, 2017

Ian1981 said:
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

saspm · Apr 1, 2017

I think he possibly means 50v/0.03 for 30 mA

Ian1981 · Apr 1, 2017

Pete999 said:
Ian, sorry I'm confused, where did the 30A come from in your calculation? I may have missed something, hence my question

A 6amp type b mcb will trip instantaneously at around 3-5x rated current.
6amp x 5 is 30amps for type B.
That's where the 50v/ 30 comes in for that particular type of mcb.

Ian1981 · Apr 1, 2017

Ian1981 said:
A 6amp type b mcb will trip instantaneously at around 3-5x rated current.
6amp x 5 is 30amps for type B.
That's where the 50v/ 30 comes in for that particular type of mcb.

As the max zs is 7.28 ohms on a 6amp mcb type b it's 230x cmin 0.95=218.5volts /30amps=7.28 as this is max zs value for the mcb.

Ian1981 · Apr 1, 2017

saspm said:
I think he possibly means 50v/0.03 for 30 mA

No that would be 1667 ohms which I've already explained earlier in the thread

saspm · Apr 1, 2017

Ian1981 said:
No that would be 1667 ohms which I've already explained earlier in the thread

Yeah sorry! Just seen that

Pete999 · Apr 1, 2017

Thanks thought I had missed something

Deleted member 26818 · Apr 1, 2017

There are as Westward said, two parts to an MCB.
The magnetic and the thermal.
The thermal part and fuses work because they get hot.
Fuses get hot and melt.
MCBs have a bi metal strip which heats up and bends until it trips the switch mechanism.
The bi metal strip is made up of two metals which expand at different rates, as the strip heats up it bends towards the side which has the metal with the lowest expansion rate.
This is similar to an indicator relay in a car or motorbike.