Testing Question

[Andy™]

i still think a transformer between 2 lines to give 230v, or the star point as you said, may work

any volunteers to test it?

 

[Sidewinder]

The way I understand the fluke is it sort of charges a cap to bleed enough current for the Zs test while still keeping the RCD balanced via the N, 

So, it NEEDS the N probe on the N to keep the RCD balanced.

I don't think it's possible to test without it. 

To much detail Steps!

I could not think of anything on the day, so I just copped out and used another tester to get me out of a hole.

It's just something that I had only come across once before, and I could not remember what I had done then, it was about 6-7 years ago now.

I did the test with the LTW.

Left this one with NIC AE after today's assessment too...

i still think a transformer between 2 lines to give 230v, or the star point as you said, may work

any volunteers to test it?

No star point final load was delta wired.

Tx could work, & I have one in the van for a control system, but it may be a 110V secondary, but it is 2ph 400V primary.

I'll look on Friday I am hoping to be in the workshop sorting several motor, control & mechanical jobs out then.

 

[kme]

I`m assuming the 4 pole RCD is actually located WITHIN the DB you can`t open?

If its an external RCD & enclosure - then you open it to reveal the Neutral ( if there`s one there!!!!!)

As for the Fluke - it won`t do what you`re asking it to - it has to have a N connection for non-trip mate.

Besides - surely, if the RCD was there, you needed to verify its correct operation, within the required parameters.

The only other option, which might well cook the Fluke, is using another phase conductor for the N - but I`m not convinced that would work, either.

I think you`re stuffed -  without 3 biggish, equally sized resistors, to create a star - or another meter

 

[pewter]

When i first bought my Megger MFT 1730 a couple years ago,  it did a 2 wire low current loop test & high current 2 wire test.

The low current test was ment to not trip RCDS, though it did used to make Wylex and something else trip. I contacted Megger and they sent me an email with this,

'We have found that there are a few breakers on the market that act
differently and can occasionally trip whilst testing when using the
MFT1730. I would suggest reversing your test leads, so your green lead
is connected to line and the red lead is connected to earth. This should
then perform the loop test and give you a reading.'

So reversing the L & E did work and stopped RCD's tripping.

The software got updated on the tester and it now test a lo current non trip test with 3 wires, which does work better.

 

[Sidewinder]

I`m assuming the 4 pole RCD is actually located WITHIN the DB you can`t open?

If its an external RCD & enclosure - then you open it to reveal the Neutral ( if there`s one there!!!!!)

As for the Fluke - it won`t do what you`re asking it to - it has to have a N connection for non-trip mate.

Besides - surely, if the RCD was there, you needed to verify its correct operation, within the required parameters.

The only other option, which might well cook the Fluke, is using another phase conductor for the N - but I`m not convinced that would work, either.

I think you`re stuffed -  without 3 biggish, equally sized resistors, to create a star - or another meter

The RCD is the "main switch" in the board that I can't open.

I thought I could not do the test with the Fluke, but, was not sure, hence the post.

I'm not interested in the RCD, nothing to do with me, not part of the scope of works, all I'm interested in is a Zs @ the point I'm working at.

I didn't even, have, to do that, as I was not doing any works under BS7671 that required test & inspect, and recording of results anyway.

Not sure if using 2 phases & the earth would cook the Fluke, I know it's ok with the three leads one on each phase to do phase rotation, as I have done it.

Also according to pg 25 of the meter manual, it is fine doing line-line loop impedance with the red & blue leads in their respective connections.

Again though not really interested in te line-line loop.

As I said, I could not think of any way to do it, so fell back on the LTW, which was fine.

 

[Phoenix]

Firts thought on reading the strt o he thread was you need an LTW series meter, and then I realised you had alread worked that one out

The fluke multifuctions require a neutral to do the non tripping test and there is no way to cheat this, they use the D-lok system invented by robin, and as far as I know it passes a DC current N->Cpc applied gradually in order to saturate the coil of the RCD and prevent it from operating while the loop test is carried out.

All you could do in the situation described is to borrow a neutral from another circuit which must be protected by the same RCD, creating an artificial star point will not work.

All other testers including the ltw425 test at 15ma repeatedly and average the results in order to try and get a reasonabe approximation

 

[steptoe]

I think my tester will do a 2wire loop test, but only at 15mA and only reads down to 1ohm, fine for anything under a B32, not much use for anything else really,

I normally calculate tbh.

 

[Sidewinder]

I could not calculate as I could not do an R1+R2!

 

[steptoe]

I could not calculate as I could not do an R1+R2!

I thought as much,

and, as much as I love the meter I have, that is its big, massive, humungous flaw, 

but, I suppose you pay your money and take the middle ground compromise somewhere along the line whatever you buy