Loop testers

[Chris Whitehead]

what does a loop tester do?



Is a cheapo ebay job adequate or do you have pay fluke prices?


:6:

 

[telectrix]

a loop tester, or to be correct, an earth fault loop impedance meter , measures earth fault loop impedance. Zs, Ze etc. there are a few avo megger ones 2nd hand on ebay that will do the job as well as any other. be wary of the china/hong kong units, though.

look for a megger LT7. lovely bit of kit, and has no trip test facility.

 

[tony mc]

Just curious and dont mean to offend!

What do you want one for if you don't know what it does.

 

[Chris Whitehead]

Just inquisitive because I've never used one, was wondering why you'd need one. We can't all know everything, otherwise forums would be pointless.Still not sure what they do :19:

 

[tony mc]

This might help!

View attachment TN-C-S Fault path.doc

View attachment TT Fault path.doc

 

[Chris Whitehead]

excellent, thanks.

This is why I love forums

 

[GLENNSPARK]

you done any live testing then Chris?

 

[Chris Whitehead]

nope - live testing is banned in our place!!! I can live with that.

I'm now thinking a loop tester is just a megger, I used to use them a lot (and not for electrocuting each other either), just not for over ten year so am very rusty.

 

[GLENNSPARK]

whats a "megger?"....if you mean an insulation resistance tester...then that aint a megger.....it aint a loop tester either.....take a look at section 9, 10, and 11 in the on site guide for test instruments and how to use them.....testing etc.....may be good to look in guidance note 3 as well Chris...

 

[Des 56]

As you may know,Meggar was a term that encompassed anything and everything to do with insulation resistance testing

You owned a meggar,tested with a meggar and the circuit tested was meggered and if you wanted to borrow one,it was easier to say than insulation resistance tester

 

[mogga]

"Megger" is used for electrical test equipment in the same way "hoover" can acctualy be a dyson Goblin or even sharp

 

[GLENNSPARK]

i know...i was being sarcy...lol...

 

[Chris Whitehead]

thanks for the help guys.

Fortunately for me we have a proper sparky on site so I always refer to him, however when he's not there people think that just because I'm the calibration engineer they can ask me to solve their problems. I have to tread very carefully.

 

[GLENNSPARK]

theres a serious note here though as well.....a lot of the candidates undertaking the C&G 2391 are refering to an insulation resistance tester as a "megger"....and its costing em marks....likewise a low resistance ohmmeter isnt a "continuity tester"....their losing marks for incorrect terminology....

 

[Knobhead]

For an earth loop test in an industrial situation you’re going to need something very sensitive. Forget about doing it live unless you’re suicidal. From a 1000KVA 11/.44KV transformer you will have say two off 500mm² copper singles per phase and a single 500mm² for the neutral. From the incoming neutral I would run two 95mm² singles to the earth bar. If you fancy testing the prospective earth fault current at that point, you’re on your own, I’ll be legging it off up the road. All tests would be done “dead” using a Ductor. The earth nests would be checked by gradient testing. Remember the earth nest would be linked to the structure of the plant.
You will be looking for figures in the Micro Ohm range for all conductors, fault currents of say 50KA+.
I’ve only ever seen a local transformer fault in a training film by GEC (I think) it wasn’t pretty to see. I did see the aftermath of a local failure, a hole blown in ¼“ checker plate!
Obviously as you got out on the plant the prospective fault levels dropped, but the earth return path resistance didn’t due to the thousands of parallel paths. The first plants I worked on were all hot riveted together, no chance of a high resistance return path. It’s the reason for M&Q statutory testing we used a 70mm² wander lead and the Ductor to measure the return path.

Sorry I went in to “Rambling Sid Rumpole” mode