Some MFTs have PSC/PFC test combined, I wonder why others have it as a separate test

[mak]

For example kt63 calculates pfc/psc with Zs but it has no option to go for an L-N test. The calculation is also the same V/Zs or V/Ze. The kt63 plus on the other hand has this option.

 

[westward10]

Just test across L and N, put both the earth and neutral probes to neutral.

 

[davesparks]

For example kt63 calculates pfc/psc with Zs but it has no option to go for an L-N test.

All loop testers can do a L-N loop test, you connect one lead to L and the other to N and press the test button.

 

[mak]

All loop testers can do a L-N loop test, you connect one lead to L and the other to N and press the test button.

That's nice I was just wondering why is there an option L-PE or L-N if you can stay in L-PE mode to test L-N

 

[westward10]

A needless gimmick both tests are exactly the same.

 

[SparkyChick]

A needless gimmick both tests are exactly the same.

This is exactly what I thought until the area engineer asked me why the hell I was using L-PE on 2 lead mode to get the PSCC and L-N loop impedance during my last NAPIT inspection.

My answer was 'why not? they are the same test, they just use different leads'... but there is some difference... the results I got were different, not wildly different, but different enough to make me think about all the times I've not used L-N for getting PSCC.

I have no idea what the differences might be, but there is some difference in how/what exactly they test and the results they yield.

 

[westward10]

This is exactly what I thought until the area engineer asked me why the hell I was using L-PE on 2 lead mode to get the PSCC and L-N loop impedance during my last NAPIT inspection.

My answer was 'why not? they are the same test, they just use different leads'... but there is some difference... the results I got were different, not wildly different, but different enough to make me think about all the times I've not used L-N for getting PSCC.

I have no idea what the differences might be, but there is some difference in how/what exactly they test and the results they yield.

You can use the same leads and method it makes no difference. You should have scuffed their shins.

 

[timhoward]

I have no idea what the differences might be, but there is some difference in how/what exactly they test and the results they yield.

I’m certainly not trying to teach you of all people to suck eggs, but what comes to mind is that on one well known tester L-PE is low current by default but L-N only ever does high current as it will never trip a RCD. Any chance with all the excitement of tea and biscuits with Napit that you weren’t on 2-hi?

(Another reason that I prefer simpler testers where the actual test is selected on the dial not by submenu options! )

 

[SparkyChick]

I’m certainly not trying to teach you of all people to suck eggs, but what comes to mind is that on one well known tester L-PE is low current by default but L-N only ever does high current as it will never trip a RCD. Any chance with all the excitement of tea and biscuits with Napit that you weren’t on 2-hi?

(Another reason that I prefer simpler testers where the actual test is selected on the dial not by submenu options! )

I'm open to learning at any time

And you are quite right, my MFT is a 1731 so it starts on the 3-Lo when I select loop impedance for L-PE and 2-Hi for L-N, so I have to select 2-Hi manually, but rarely do I connect all three leads, I'm usually dobbing around with just line and earth connected.

I can't explain it, I have to do a double take and make sure it wasn't just a one off, and it wasn't. I got different results and I have absolutely no idea why.

 

[timhoward]

I can't explain it, I have to do a double take and make sure it wasn't just a one off, and it wasn't. I got different results and I have absolutely no idea why

You have certainly piqued my interest. I have a 1731 that I rarely use. I illogically grab the 1553 almost every time as the screen is easier to read, it ‘just works’, the batteries last forever and it never confuses me. I’ve also found the low current loop tests are more accurate than its successor manages.
I’m going to try my 1731 later and see if it does the same as yours.

 

[pc1966]

In "no trip" mode my DL9118 does high current L-N and low current L-E on the one test, afterwards you can press the top 'function' key and it toggles between the Zs/PFC and the Zsupply/PSCC results.

In high current mode it only measures the one you select, which is odd.

My suspicion is it makes some use of the PSCC data to help with the no-trip test, but there is nothing said about any of that in the instruction book, etc. For example, with the 3 wire connection while you measure the L-N drop you could also measure the N-E rise to get some idea of R1 and Rn separately (at least as far back as the N-E link point in the distribution system), and it might help when you do the L-E test to get some idea of R2 by knowing R1 from the first test, etc. But that is speculation!

 

[HappyHippyDad]

All loop testers can do a L-N loop test, you connect one lead to L and the other to N and press the test button.

Could you explain in clearer, more simple terms please Dave.

 

[westward10]

Could you explain in clearer, more simple terms please Dave.

Do you use three leads or two leads?

 

[HappyHippyDad]

Do you use three leads or two leads?

Right, I was joking, as Dave had explained it extremely clearly.
Now I feel silly as I 'think' you've taken it seriously.

 

[timhoward]

I can't explain it, I have to do a double take and make sure it wasn't just a one off, and it wasn't. I got different results and I have absolutely no idea why.

What scale of difference do you see?
For me the readings are generally slightly higher on the L-N setting, using the same lead and simply moving the plug. We are talking 0.05 ohm variation at most.
The readings on both settings are however slightly inconsistent in their own right; 10 tests in a row with suitable pause between each one also yields variation within a 0.05 ohm window.
The N socket on mine has had considerably less use and I also wondered if it might simply have more tarnished contacts!