megger MFT1552

[stevo09]

Hi guys. Wonder if someone could help me out. Ive just started my electrical training and need advice.
Ive been using a Di Log multi function tester that needs 3 leads for some tests.
Ive Just started to use the megger MFT1552 and its shot my head lol. What i need to know is when using this tester, how do i take Ze readings, also PFC.. with the Di Log while testing Ze i have to remove the earth connection. And test between earth, line and neutral. Guess i dont need to do this with the megger???
Also for PFC i need to connect to the earth, line and neutral.. Am i right in saying the PFC with the megger is taken at the incoming side of the isolator (isolator switched off) between the Line and neutral.??

Cheers Lads

 

[electricAl]

Woh there. Me thinks your thinking on this one is a wee bit off.

To take a Ze the equipotential bonding HAS to be disconnected (to remove parallel paths which will skew your readings)) which can be easiest achieved thru dropping the earth conductor. With the 1552 you`ll need just the 2 probes - as you will for your 2 pfc`s - just swap from L & N, to L & E to get PSCC & PEFC respectively

 

[stevo09]

Is what you said about the di log ze testing the same as what i just said??? remove the earth and test between earth line and neutral?
With a 2 lead test (megger) i test between line and neutral?? on the incoming side of the isolator (isolator off so no parallel paths)??


thought this was a tec question not a tool one????
How come it was moved??

 

[electricAl]

I`ve found de fred!

Steve, with the Megger you test for Ze at incoming side of main switch (as you said) but between Line & Earth only - Neutral doesn`t come into it m8.
You remove the earth conductor irrespective of isolator - this doesn`t come into it, parallel paths will influence your Ze if the earth is still where i hope it is (under our feet) If you think about it hard enough you`ll realise what i`m saying. & assuming you are testing single phase (& i do hope you are as your asking these questions) if you look at the isolator you`ll see it has no bearing on the earthing (2 poles)

As for the PFC, this is not one but TWO tests - pscc between lives (Line & Neutral on single phase) AND pefc between Line & Earth. You need to take both, the greater being your PFC - the maximum possible fault current at the origin.

Any more questions please shoot.

 

[stevo09]

That makes more sence! Cheers for that mate. You explained that better then my tutor lol

 

[electricAl]

Anytime my friend
Just take those steps forward slow & methodical and build from there...

 

[Megger TSG]

Hello

For future reference

To conduct a Zs test on a non- RCD protected circuit the procedure with the MFT1552 is the same as the Ze test....Phase and Earth with red and green test leads .. instrument set to Hi loop

For a Zs reading on RCD / RCBO protected circuits a 3 wire NO trip test has to be conducted.
The green lead is connected between the cpc and LO/L2 terminal.....black lead connected between the neutral and the NO TRIP terminal......red lead between phase and L1 terminal. The NO TRIP setting should be selected on the tester. If a power circuit is being tested then it is recommended the mains test lead is utilised for the Zs test instead of the 3 wire test lead set.

It should be noted the black lead should not be connected with the green lead to earth for a NO Trip test. A (trp) error will result.
Ensure a firm contact with the test leads on the circuit is maintained during the test otherwise a (trp) error will result if a momentary contact is made with the test leads.
Simply trp is an abbreviation for trip...... the tester assumes the supply has tripped.

Regards

Megger Technical Support Group

 

[Walmo09]

Hi Guys,

I have just bought a 1552 and have a question regarding pfc testing, I have an RCD between the meter and CU, so I am measuring PFC on the "No trip" setting. Does anyone know if this is measuring PSSC and PEFC, and just displaying the highest reading?

The instructions only detail this one test for PFC in the "no trip" mode.

Many Thanks.

 

[electricAl]

Simply put, you`ll be measuring the max possible (Prospective) current that can flow between...

a) the Live conductors (Line to neutral on single phase) giving you your Prospective Short Circuit Current

OR

b) Line conductor to Earth which gives you the Prospective Earth Fault Current

as supplied by the tx in either case. Measure both, record the greater (i suspect you knew that bit)

The PSCC will be greater in the majority of cases - with TN-C-S systems they should be quite similiar.

If in doubt in future, the names ^^^ of each type of PFC give a big clue as to what is being measured, & between which conductors


p.s. unless you have good reason, you should measure PFC as close as poss to point of origin, which in your case would be incoming side of front end RCD. Then you can use `Hi` rather than less accurate `No-Trip`

Hope that clears it up for you

 

[Walmo09]

Thanks for that mate. What I really mean to ask is whether, in the "no trip" mode, the 1552 automatically tests for both PSCC and PEFC, without aduusting the three leads. The instruction book doesn't mention conducting both tests whilst in this mode, or adjusting the leads, but in the Hi mode it's the nomal two lead tests.

 

[Megger TSG]

Hi

The MFT1552 cannot automatically perform both PSCC and PFC tests

The neutral connection in the 3 wire no trip mode is used purely for conducting the no trip test

In short, the PFC reading is made with 2 wires (phase & earth) with the tester set to Hi PFC.
The PSCC test requires the same lead combination, same setting on the tester, but with the green lead connected to the neutral.

Regards

Megger Technical Support