UK Earth loop fault impedance help

Jamiehasadog · Oct 11, 2021

Hello I’m a student learning about industrial wiring and circuits and we’re about to start learning about how to do loop impedance calculations. I have made a drawing of a three phase installation and was wondering if anyone could give me information on how I get the Ze Zs and R1 + R2. How would I do this with a three wire loop impedance meter and also how would I do it without one. Any help is appreciated, just trying to get my head round it first before we start the lessons. Photo is attached.

telectrix · Oct 11, 2021

Ze at the live side of the main isolator with earth disconnected, so isolator OFF. now you have a go at how to get R1+R2 and we cannthen see if you have ther right approach.

Jamiehasadog · Oct 11, 2021

telectrix said:
Ze at the live side of the main isolator with earth disconnected, so isolator OFF. now you have a go at how to get R1+R2 and we cannthen see if you have ther right approach.

0.5ohm with earth disconnected and testing the earth back to the supply with the loop impedance meter. How do I get R1 and r2 and can you get it without a meter. Thanks

telectrix · Oct 11, 2021

R1 is the phase conductor. R2 is the cpc. add them and get R1+R2, or short 1 end and measure in 1 hit. you need a meter set on continuity (low ohms). measure each phase-E. all 3 should be the same reading.

Jamiehasadog · Oct 11, 2021

Thanks for that so r1 and r2 is the same as Ze with a loop impedance meter or is R1 and R2 the part after the panel to the motor ? Thanks again it’s much appreciated

telectrix · Oct 11, 2021

r1 and r2 (lower case) denotes end-end for a ring. important that you distinguish. you measure from isolator to control panel then from panel to motor and add them together.

Jamiehasadog · Oct 11, 2021

telectrix said:
r1 and r2 (lower case) denotes end-end for a ring. important that you distinguish. you measure from isolator to control panel then from panel to motor and add them together.

What’s the difference from doing it with a loop impedance Meter then from a meter reading ohms ? Thanks

telectrix · Oct 11, 2021

,multimtercon ohmscand MFT on ohms should give same readings for R1 and R2 etc.. a multimeter can't measure Zs which is a live test.

Jamiehasadog · Oct 12, 2021

telectrix said:
,multimtercon ohmscand MFT on ohms should give same readings for R1 and R2 etc.. a multimeter can't measure Zs which is a live test.

I think I understand now. I’ve attached my notes. I then add my r1 R2 reading to my Ze reading to get my zs? Does this all look correct ? Thanks

telectrix · Oct 12, 2021

Jamiehasadog said:
I think I understand now. I’ve attached my notes. I then add my r1 R2 reading to my Ze reading to get my zs? Does this all look correct ? Thanks

yes but please get into the habit or R1 as opposed to r1. etc. 2 entirely different measurements. in an exam you'd be marked down otherwise.