Am2 exam live testing part need some help please!

RyanF · Feb 16, 2018

Hi everyone,

My resit on my AM2 live testing is monday coming and I need some help/ gudiance on anyone who has sat theres to help me.

Confim polarity by measuring the voltage between each phase to N and each phase to earth, then phase to phase to ensure I am getting 230/400V etc.

So then, Ze test disconnect main earth and test each phase ( 3phases) to earth . Highest value record on test sheet as Ze. Then reinstate the main earth. Make sure test equipment is set to 2 test lead LOW or NO TRIP.

Zs test at db, same as ze but, the main earth is connected. Again test each phase to earth. Record highest value on the test sheet. Again, test meter on 2 test lead Low or No trip.

Then, PFC testing, set the test equipment to 2 test lead high I think it is... then measure PEFC so each phase to earth so L1- E, L2- E and L3-E. Mental note of this value.

Then same test again but PSCC so measuring each phase to neutral. So, L1-N , L2- N, L3-N. Mental note of this value.

The test equipment I am using cant measure phase to phase so. Simply take highest value and double it normally PSCC value.

Record this on test sheet as IpF.

Then cover back on db. Then the board can be fully energised/ lock off taken off. Then carry out RCD tripping times on the ring at the FURTHEST point. Record tripping times on test sheet and functional testing of the test button. Then, functional testing of all other circuits to confirm that they are working as they should be etc.

Then phase rotation ensure I am getting correct phases at the commando outlet point and the motor circuit.

Does that all sound right? If not let me know please as my resit is Monday morning!

Cheers!

sevuk · Feb 16, 2018

You should confirm three phase polarity at the origin with your rotation meter as well as your commando socket.

On three phase the highest fault current will be phase to phase, so to get this you would have the prospective short circuit current (phase to neutral) x 2 as a rough guide. This would be done with the Earth connected as you want the worst case scenario.

RCDs can even be tested in the DB if there is a limitation, makes sense to test them at the furthest point though if you can.

RyanF · Feb 16, 2018

So do you measure PFC on high setting on the test meter but, would this trip the rcd in the main board? As this exam is carried out in a workshop environment?

Also do you just test live polarity on the incoming tail side of the 3 phase DB?

sevuk · Feb 16, 2018

RyanF said:
So do you measure PFC on high setting on the test meter but, would this trip the rcd in the main board? As this exam is carried out in a workshop environment?

Also do you just test live polarity on the incoming tail side of the 3 phase DB?

If you have a three phase RCD protecting the workshop boards you wouldn't be able to do a high current test after it, but if it you have the facility to test before it this is not a problem. Have they given you any guidance notes to your practical assessment?

Three phase polarity should be tested throughout the installation.

RyanF · Feb 16, 2018

sevuk said:
If you have a three phase RCD protecting the workshop boards you wouldn't be able to do a high current test after it, but if it you have the facility to test before it this is not a problem. Have they given you any guidance notes to your practical assessment?

Three phase polarity should be tested throughout the installation.

I believe the workshop for the am2 exam has a 3 phase RCD protecting the workshop. So you would test everything on 2 lead low? Both pfc and ze/zs testing?

There is only two outlets which have 3 phase and thats a commando outlet and a motor outlet point. Rest are single phase outlets i.e ring final, lights, smoke alarm etc

sevuk · Feb 16, 2018

RyanF said:
I believe the workshop for the am2 exam has a 3 phase RCD protecting the workshop. So you would test everything on 2 lead low? Both pfc and ze/zs testing?

There is only two outlets which have 3 phase and thats a commando outlet and a motor outlet point. Rest are single phase outlets i.e ring final, lights, smoke alarm etc

'

For exam purposes it might be beneficial to point out why you are using the calculation of the PFC x2 with the low current 3 wire test and normally you would be doing it at origin before the RCD.

I haven't heard of any testers that do a 2 wire low current test.

Just make sure you do your safe isolation to the letter and don't energise anything with the cover off or not put back together, and you should be ok.

RyanF · Feb 16, 2018

So doing a ze and zs test you can use a 2 lead low test? So it doesnt trip the rcd obviously. Then a 3 lead no trip test to measure pscc and pefc? That right or wrong?

The x2 rule of thumb method is because the fault current that could be generated could occur between two phases. As some test instruments wont let you measure between phases due to the high current.

Ive already passed all the safe isolation, i just simply need to do a few live tests.

sevuk · Feb 16, 2018

RyanF said:
So doing a ze and zs test you can use a 2 lead low test? So it doesnt trip the rcd obviously. Then a 3 lead no trip test to measure pscc and pefc? That right or wrong?

There is no 2 lead low test as far as I'm aware, my megger only does 2 Hi and 3 Low. If you can't do it a 2 wire high test , you'll have to use the 3 lead low test.

RyanF said:
The x2 rule of thumb method is because the fault current that could be generated could occur between two phases. As some test instruments wont let you measure between phases due to the high current.

Mostly correct, most instruments won't let you measure the PFC between Line and Line due to the voltage.

RyanF said:
Ive already passed all the safe isolation, i just simply need to do a few live tests.

Good job, and good luck, I'm sure other guys will add to this post later.

RyanF · Feb 16, 2018

In the exam we have a megger mft1740 I believe so could you let me know what setting to set it to for the tests ive described?

sevuk · Feb 16, 2018

Left dial - L-PE Right dial - Z - it will come up as 3 Lo - if you select Z max i'll just keep the highest loop reading at the top rather than the PFC. All these settings are green

on the left you can select V in black, if you want to do a rotation test (not on MFT 1710) use Red probe L1 Green L2 and blue L3. any incorrect line sequence will display L1 L3 L2, correct will display L1 L2 L3.

search Chris Kitcher on YouTube. He uses a Megger in his videos though not always an MFT, also you'll find it good reference for what you're doing.

RyanF · Feb 16, 2018

Ah right Ive watched his videos hes good to watch.

So since the workshop has a rcd would that mean I would do all tests on a low setting/ 3 lead test? As in pfc, ze and zs?

polo1 · Feb 16, 2018

Newer Meggers do have a low current, two lead test facility -

[ElectriciansForums.net] Am2 exam live testing part need some help please!

RyanF · Feb 16, 2018

So Im i right it thinking that since the board has a 3 phase Rcd I would have to carry out Ze, Zs, PfC test on a 3 lead low test or not? Im honestly baffled like. Some people say 3 lead, some say 2 lead.

But when I done 2 lead Hi test on Ze it tripped the rcd in the workshop. So, if I do it in 2 lead LOW ze zs test etc this wont trip the rcd?

polo1 · Feb 16, 2018

Ryan, you can test using two or three leads on low test, just making sure that you have selected the correct setting on your tester.
Using low test prevents the RCD from tripping, but readings tend to be a bit higher than when you test using the higher test current.

RyanF · Feb 16, 2018

But surely if your testing line to earth of the Ze test wont this still trip the rcd due to the imbalance? So surely you would do a 3 lead test?

As in for pfc what setting would you go on and you can do a 2 lead low test on that as well? But, again wont this trip the rcd?

Some people say do it as a 3 lead test to not trip the rcd and some say do it as a two lead test which wont trip the rcd.

I just need someone to clarify the tests and the setting on the megger tester please!

Am2 exam live testing part need some help please!

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