MFT1720 & loop testing

[krishcanag]

Hi there

I don't work as a full-time electrical, but I have 16th edition and also I am electrical graduate so I understand theory but I have just got my hands on the megger 1720.

I want to do Ze and Zs or R1+R2 and therefore via equation work out Zs.

When I look at the tester it has: Z, Max Z, Zref, R1+R2

I think Zref is Ze measured on the discounted incoming earth and incoming phase

R1+R2 is taken from socket outlet and again from lighting circuit

What is Z taken between phase and earth supposed to indicate
What is Zmax taken between Netural and phase supported to indicate?

If anyone could answer these questions it would be much appricated.

thansk

krish

 

[trypod]

Hi
have you got Meggers Application note 31?

There are issues with loop testing with the MFT 1700 series

 

[krishcanag]

Hi
have you got Meggers Application note 31?


No I do not, where can I get from?


There are issues with loop testing with the MFT 1700 series

What are the issues, I am suprised such a good make would have issues? What makes you say this?

krish

 

[IQ Electrical]

Hi
have you got Meggers Application note 31?

There are issues with loop testing with the MFT 1700 series

I knew of the continuity null problem but what is the loop testing issue and where is the application note?

 

[trypod]

Application note 31 on megger web site

RCBO tripping on no trip

low loop readings

 

[trypod]

good point

fast RCD tests

 

[i=p/u]

so would you send this back if you were getting one??????????????

 

[trypod]

no
you talk to the technical team at Megger if you have any issues

they try to sort out any problems and have sent out loan equipment if the problem can not be solved quickly

 

[krishcanag]

Application note 31 on megger web site

RCBO tripping on no trip

low loop readings

Hi

How would you know the loop reading was incorrect for sure?

krish

 

[i=p/u]

test it on a known circuit or compare with other tester, i would think..

 

[skel23]

HI, I've recently started using a new mft1720 and found that it trips rcbo's on loop test no matter which settings you have it on.
I called the megger technical line and was told there is an issue with this tester and some rcbo's. Particularly wylex and Crabtree. Apparently it's something to do with the way they are manufactured. The solution was to reverse the line and earth leads on the tester. Red into green and green into red. Sure enough this solved the problem and I got the loop reading without it tripping. Apparently they are in progress of coming up with a more permanent solution.
Hope this helps.

 

[krishcanag]

Thanks for the response, but my orginal question was:::

What is Z taken between phase and earth supposed to indicate
What is Zmax taken between Netural and phase supported to indicate?

 

[oldtimer]

Just to highlight Megger announced that this unit could do a lighting Zs reading via 2 wires at a switch so happy days !!!! Eh well no because the registration companies have been banging it into everybody that you have to test the full circuit ie lamp out and testing at the light because this tests the switchwire and earth through the switch and megger are selling the 1700 promoting this function so it saves time climbing up to the light but other people ie me see it as cutting corners only problem is has I have banged on about just whose wagging the tail here because no doubt in 6 months time you will get told yep it ok to test at the switch and we will have to wait until someone gets electricuted via a light fitting just after a PIR from a company who is using a 1700 mmmmmmmm

 

[krishcanag]

wish someone would answer my question

 

[tonycoysh]

I use the 1720. If you read the instructions on the disc included it will explain the different settings. L-PE is obviously for testing Live to Earth and L-L L-N will test between phases or between Live and Neutral. Then you select your settings on the knob on the right. Z is the only setting I use to be honest. Z will give you a Z e/s reading (depending on what part of an installation you are testing) Zmax is useful for doing Zs readings as it stores all of the readings for you to review and find the highest (like the auto RCD test.) Zref stores your Ze result and then when switched to R1+R2 the tester is supposed to deduced the Ze result stored on Zmax from your Zs result obtained on the R1+R2 setting to give you a R1+R2 value. This is how I understand it anyway. I'll happily stand corrected.

I agree 'oldtimer' on the Zs from a light switch.