The MFT1500/2 instruction

[dean7828]

hi chaps, wonder if you could help clarify something for me, i have downloaded instructions just to clarify that my tester will do a 2 lead loop test on high range, im using a megger MFT1502/2, however the instructions i downloaded are The MFT1500/2, i also found a document that said this....'The MFT1500/2 is available in 2 options, the standard MFT1501/2 and MFT1502/2' so i assume they are talking about the same tester.

im only asking as im getting some high zs reading on a PIR im doing and don't usealy use this tester, according to the instructions for example you can do a external earth loop test using two leads, i have always used 3, thanks in advance sorry if this post is a bit confusing.

 

[telectrix]

i have the 1552, which is a later version. no trip loop test uses 3 leads. the high current test generally uses 2 leads.

 

[La Poste]

i have the 1552, which is a later version. no trip loop test uses 3 leads. the high current test generally uses 2 leads.

100% Agreed.

 

[oldtimer]

I have 1553 (bluetooth version that I dont even use) and yep for circuit Zs I use the 3 lead system or the 13amp plug top lead for no trip or high depending on the installation but for Ze or PFC I use the high 2 lead when testing this.
Also please note do not get confused with the new megger 1700 series that says it can do a Zs test with 2 wires because as it said yes it can do it ie "at a switch with live and earth so it saves you time getting the ladders out and testing at the light" (Megger salesman comment not mine) but you have also touched on the big debate here the registration companies bang it in to you you have to test the Zs at the light with the lamp out and the switch on thus testing the whole circuit the only problem is that they may just change their minds because as I have said who is wagging the tail here

 

[dean7828]

hi, thanks for your reply, after going through the instructions it defiantly states that you can tes high loop with just two leads? hope im not doing this wrong

 

[telectrix]

that's right. you only need 3 leads for no trip.

 

[WayneL]

Also please note do not get confused with the new megger 1700 series that says it can do a Zs test with 2 wires because as it said yes it can do it ie "at a switch with live and earth so it saves you time getting the ladders out and testing at the light" (Megger salesman comment not mine) but you have also touched on the big debate here the registration companies bang it in to you you have to test the Zs at the light with the lamp out and the switch on thus testing the whole circuit the only problem is that they may just change their minds because as I have said who is wagging the tail here

Whoever told you this has no idea what they are talking about.

Zs, by definition, is a 'Loop' test - you can test it anywhere on the circuit.......although you would have to link out 'Line' and 'CPC' at the furtherest point and the load should be removed..........does stop you balancing on top of a set of steps with your meter though.


You can even test Zs at the board..........saves using the no-trip.:yesnod:

 

[ringer]

Not sure where you are getting this idea from, Wayne. Even if you link out L and E at the light, by testing at the DB you are creating a loop from supply line -> mft probe -> through the mft -> mftprobe -> supply earth, all of this via cables in the circuit being tested only up to the point at which you connect the tester. This will then ignore the cables further upstream from the tester, whether linked or not. Unless of course there are parallel paths to earth upstream that give less impedance than the supply earth.

 

[WayneL]

Hi Ringer,

It's not done like that, mate.

Anyone reading this please ensure that you are confident in your testing (and competent), and that you understand what you are doing before attempting this test.

Safe isolate.

Link out 'Line' and 'CPC' at furtherest point on circuit.

'Open' RCD that is feeding circuit under test.(OFF)

'Close' MCB of circuit under test (ON) - all other MCBs open (OFF)

'Close' Main Switch (ON).

Test Zs of circuit by placing one probe on incomming side of 'RCD' and one probe on outgoing side of 'RCD'.

RCD bypassed so not going to trip - and your're not testing up a set of ladders.

 

[ringer]

Bypassing the RCD using your MFT - interesting method, and I can see now how that would work. Thanks for the clear explanation mate.

Sent from my HTC Sensation using Tapatalk

 

[oldtimer]

Whoever told you this has no idea what they are talking about.

Zs, by definition, is a 'Loop' test - you can test it anywhere on the circuit.......although you would have to link out 'Line' and 'CPC' at the furtherest point and the load should be removed..........does stop you balancing on top of a set of steps with your meter though.


You can even test Zs at the board..........saves using the no-trip.:yesnod:

WayneL yep the furtherest point to me is the light point but as I said the Megger salesman key point was time saving asyou could test it at the light switch so you did not have to open up the light fitting now you say you can test it anywhere on the circuit so ok you have 3 twin sockets connected to a 16 circuit breaker the first socket is just below the board so I could test it their and test sy 10% of the circuit or I could go to the 3rd socket and get a reading of the full circuit and if I did the 1st socket only and then 3 months later I get a call saying there was no earth at sockets 2 and 3 then who do you think they would point a finger at also the scenario with the testing at the switch yep you can do it but what happens if the light fitting has no earth and jow public get electrocuted when changing a lamp ? so in theory yes you can test anywhere in reality and in my opinion it is good practice to test the whole circuit.

Also I have found a light point with no earth and trced the problem to the cable not being connected back at the junction box

 

[ringer]

Linking L-E at the furthest point on the circuit, and doing dead test R1+R2 before doing live test Zs will confirm continuity of cpc.
Socket circuits and light circuits are two different circumstances - the advantage of taking measurement for lights at the CU is you are not balancing atop a ladder. Sockets can generally be reached whilst both feet are firmly on the floor

 

[Kiers1970]

when I got my 1553, I used to forget to switch the earth/neutral leads/probes round...... Was fuming that it wouldnt work properly.

 

[WayneL]

WayneL yep the furtherest point to me is the light point but as I said the Megger salesman key point was time saving asyou could test it at the light switch so you did not have to open up the light fitting now you say you can test it anywhere on the circuit so ok you have 3 twin sockets connected to a 16 circuit breaker the first socket is just below the board so I could test it their and test sy 10% of the circuit or I could go to the 3rd socket and get a reading of the full circuit and if I did the 1st socket only and then 3 months later I get a call saying there was no earth at sockets 2 and 3 then who do you think they would point a finger at also the scenario with the testing at the switch yep you can do it but what happens if the light fitting has no earth and jow public get electrocuted when changing a lamp ? so in theory yes you can test anywhere in reality and in my opinion it is good practice to test the whole circuit.

Also I have found a light point with no earth and trced the problem to the cable not being connected back at the junction box

Hi mate,

As Ringer pointed out - I was talking mainly about radials - you should normally take Zs readings at every socket and record the highest, so it wouldn't apply.

With a radial, if you link Line and CPC at the furtherest point on circuit then you can literally break into that circuit at any point (even the switch) and measure your Zs.

I know what your saying about measuring Zs at the switch - you're talking about measuring between 'Line' and 'backbox' (CPC).......my method measures either side of the switch with the switch 'open'.

This debate about the furtherest point on the circuit crops up often (with R1 + R2 and Zs) - and there isn't much in it.

If you think of the lighting circuit including the switch drop:

If you measure Zs at the light, you will include the two conductors that go to and from the switch - but not the CPC that drops to the switch.

If you measure Zs at the switch, you will include the 'Live feed' and the CPC that go to the switch - but not the 'switched live'.

So, each method misses a conductor out of the measurement - both of equal length to each other.

So, assuming 1.5mm T&E - Which method will give the highest Zs reading?........and should therfore be recorded.