Z Line & Z loop

[eskimo39]

I did some sub contracting today for a local company who had a lot of testing to do at a factory. I was helping an oldish chap who was using an old Metrel Easytest.

When doing a Ze test he set the unit to Z Line and took the reading (0.11 ohms) however I asked him to do it on Z loop and got a reading of 48.4 ohms.

He didn't know what the Z Loop function did and had always used the Z line for testing. Can anyone shed some light on this feature.

Coinsidently I went and got my Fluke 1652B from the van and did the same test on the mains using the Loop Z (No Trip) feature and the setting for L-PE which gave the result as 48.7ohms, I then pressed the F1 button and changed the setting to L-N which gave 0.11 ohms.

Does anyone know of a guide on which settings to use for each test on the Fluke 1652b? I did my T&I with a megger I owned and the fluke is new to me. Also when would you have to choose between 'No Trip' and 'Hi Current' on the meter

Are these tests, functions correct>

Ze - Loop ZI (No Trip)
Zs - ????????
R1 + R2 - Continuity R LO
Insulation Resistance - Insulation R ISO
RCD - T RCD Time on AUTO

Cheers and sorry for the ignorance

 

[roukel01]

Its basically as it sounds, Z line meausures the impedance between the two line conductors (Live and neutral on single phase, or Live and Live on 3 Phase) and the tester will give you the Prospective Short Circuit Current value also, Z Loop measures the impedance between line and earth, where the tester will also display Prospective Eart Fault Current. A measurement of 48 ohms, in this case indicates it should be a TT system hence the big difference between the two readings.

If it were a TN-C-S the Z line and Z loop readings should be very similar (Because Neutral and earth are the same conductor from the cutout back to the suppliers transformer) however, TN-S systems, the two readings could vary slightly because of the seperate earthing conductor.

Remember, doing the Z loop test you are measuring the resistance down the earth conductor, back to the suppliers transformer, up the windings and back down the live conductor, to the supply cutout and back to your tester.
Z Line is exactly the same but you're measureing down the neutral conductor, up the winding and back down the live. (Or two live conductors on a 3 phase supply)

Hope this makes sence.

 

[Mark_Burgess]

The Loop (no Trip) is for testing Zs without tripping RCD's
The Hi Current setting is for Ze testing.

 

[Johnny-G]

I've got a pdf of the 1652b user manual that I got with mine a couple of weeks ago, you can have a copy if you'd like one mate?

 

[Grant Naylor]

I've just bought a Metrel 3125B and you are right. I'm no expert though as not even qualified yet! However, I have read the manual

Zloop I assumed would be to measure the Ze at the origin of the supply and also it calculates PFC.
Zrcd can measure Zs from a socket or accessory terminal without tripping an RCD.

Zline only uses live conductors (the terminal readings confirm it) so it's PSC. Oh I assume it also can calculate R1 + RN?

I guess you need to take both readings and use the worst case? I'm still trying to understand what leads go where on the consumer unit though.