AM2

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Matthew terry

Morning all, Matthew here

Have my pre AM2 this week and then the real deal starts Monday! So I signed up to look at any previous posts about the AM2 ( Pobably a few on here id imagine)
 
Welcome aboard Matthew, site:electriciansforums.co.uk AM2 - Google Search - https://www.google.co.uk/search?q=site%3Aelectriciansforums.co.uk+AM2&oq=site%3Aelectriciansforums.co.uk+AM2&aqs=chrome..69i57j69i58.6973j0j7&sourceid=chrome&ie=UTF-8 - Some searches from Google. Change that to "AM2 Assessment" to find assessment related threads and posts. You can add the year to the search too if you want just the more recent threads and posts. :)

If you have any specific questions, post in the main electrical forum and I'm sure some of the lads will be able to help a bit.
 
Welcome to the forum.
A fair number of posts on here about AM2, have a look at similar posts, just below these this thread, but do watch the dates.
 
Best tip I can give you for the AM2: Write everything on the back of your schedule of test results. R1+R2 at each point, Zs at each point, RCD values x1 and x5, FPC / FSC, 3 phase double PSC value, the more the better.

Ring Circuits:

Use the formulas to calculate expected R1+R2, Ring Continuity for the neutral / earth and Zs

Expected R1+R2: r1+rn /4
Expected Zs = Ze + (r1+r2)
Expected Ring continuity for Neutral: r1 = r2
Expected Ring continuity for Earth: r2 = r1 * 1.67 NOTE: Assuming you are wiring your Ring circuit in 2.5mm If not take the line and divide it by the earth. Example: 2.5/1.5 = 1.67

Cross link your ring final circuit and test each socket for the same reading or a reading within 0.05 Ohms.
Anything higher than this is typically a spur from another socket but not always.
Sometimes it's worth plugging your tester in and out a few times to clear the muck off the brass in the sockets.

Mark the outgoing and incoming ring cables in the distribution board for ease of testing later on.


Testing:

DONT FORGET TO NULL YOUR TEST LEADS AS IT LEADS TO FALSE VALUES

DO THE TESTS IN THE CORRECT ORDER:
RING CONTINUITY, CPC, IR, Zs, RCD, Polarity, RCD Test Button

IR test should be done at double the working voltage. 500V up to 500V with the exception of SELV / PELV (250V)

Make sure nothing is plugged in and any neon indicators / lamps are removed from the circuit. Switch all light switches to ensure all the cables are IR tested. A lot of people forget to do this with 2-way lighting circuits. Personally, I like to test at 230V first to make sure I get a good reading before pumping 500V down the circuit and blowing up someone's appliance.


Ensure the RCD Tester is set to the correct mA for the RCD /RCBO, 30mA usually (Could be different for you)

Safe Isolation

10 TESTS FOR 3 PHASE

L1 - E
L2 - E
L3 - E

L1 - N
L2 - N
L3 - N

L1-L2
L2-L3
L1-L3

N-E

3 FOR SINGLE PHASE

L-N
L-E
N-E

Make sure you select the GS38 compliant tester and proving unit and follow the safe isolation procedure step by step.


I could keep going but I would be here all night, maybe I will get around to making A tips and tricks guide some time ;)


Honestly a lot of the things I am telling you, you will be told on your pre AM2 but you need to ensure you do them on the day of your exam.

Good Luck!
 
Thanks all much appreciated! Two days of pre am2 complete, alot to take in regardless of containment taken out, everything has to be wired as they spec and tested how they want it! Like a global IR test with the ring disconnected (earths still connected neutral and live blocked separate) then tested againt the the outgoing side of the main switch ( L-N L-E N-E of the ring, then L- L1 L-L2 L-L3 N-L1 N-L2 N-L3) thats new to me! And i cant remember if we had to disconnect the lighting feed or just switch it off via the mcb during the global IR! Also a lot of formulas thats need to be wrote down on scrap notes otherwise you will fail. Eg motor overload convert Kw into W then divide by 3 ÷ 230 x 1.1. Load of nonsense but there we are. To say my head hurts would be puttint it lightly!
 
You lost me on the motor. You set the OL to the nameplate FLC. Simples.
 
I must be missing a trick here Matt.

The reason why you take the nameplate figure to set your overload is because the kW rating is the shaft output not the electrical load.

You need to use powerfactor and efficiency in the equation don't you?

A 3 phase motor is around 6 amps IIRC, a single phase will be more.

So the 4.78A makes no sense to me.

Did the tutor not explain why?
 
I must be missing a trick here Matt.

The reason why you take the nameplate figure to set your overload is because the kW rating is the shaft output not the electrical load.

You need to use powerfactor and efficiency in the equation don't you?

A 3 phase motor is around 6 amps IIRC, a single phase will be more.

So the 4.78A makes no sense to me.

Did the tutor not explain why?


Nope, no explanation just a sum which was ÷3 ÷230 x1.1... they dont really explain stuff he just said ' make sure you note the equation down on the paper provided' if they explained everything the 2 days wouldn't be enough in dont think!
 
Hi Matthew - can I ask where you did your prep, and any thoughts? Thanks
 
Hello, the formula I was given for setting a motor overload is as follows:

(Motor current / 1.73) + 30%

So take the Motor rating; in Your case its 3kW


using I = P / V
I = 3000W / 400V = 7.5A

Now you divide the motor current by 1.73 (Square root of 3) to get the current per phase.

7.5A / 1.73 = 4.34A

Take 30% of the above and add it to the existing value for max operating current to be achieved without the overload tripping.

4.34A * 1.3 =5.64A

You would set your overload to 5.64A





The way the formula you have been given is as follows:

The Value of motor is 3Kw, Convert this into watts.

3kW = 3000W

Now divide the value by 3 as there are 3 phases giving you 1kW per phase

3000W / 3 =1000W

Divide the 1000W by the voltage to give you the current per phase

1000W /230V = 4.35A

Now Multiply the current given by 10% to allow for max operating current to be achieved without the overload tripping.

4.35A x 1.1 = 4.79A



The difference between the 2 is: My formula applies A 30% Addition, Yours applies a 10% Addition.


Hope that Helps you understand it a little better.
 
Hello, the formula I was given for setting a motor overload is as follows:

(Motor current / 1.73) + 30%

So take the Motor rating; in Your case its 3kW


using I = P / V
I = 3000W / 400V = 7.5A

Now you divide the motor current by 1.73 (Square root of 3) to get the current per phase.

7.5A / 1.73 = 4.34A

Take 30% of the above and add it to the existing value for max operating current to be achieved without the overload tripping.

4.34A * 1.3 =5.64A

You would set your overload to 5.64A





The way the formula you have been given is as follows:

The Value of motor is 3Kw, Convert this into watts.

3kW = 3000W

Now divide the value by 3 as there are 3 phases giving you 1kW per phase

3000W / 3 =1000W

Divide the 1000W by the voltage to give you the current per phase

1000W /230V = 4.35A

Now Multiply the current given by 10% to allow for max operating current to be achieved without the overload tripping.

4.35A x 1.1 = 4.79A



The difference between the 2 is: My formula applies A 30% Addition, Yours applies a 10% Addition.


Hope that Helps you understand it a little better.

So if my motor is 4.5kw

I have 4500 ÷ 3 ( for each phase) = 1500

1500 ÷ 230 ( should this not be 400 if its three phase) = 6.52

6.52 x 1.1 ( for 10% overload ) = 7.15a?

Im getting confused as why is it ÷230 if its a three phase motor? Or is it becsuse each phase is 230?

Thanks for your help though.
 

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