3 phase motor circuit in 2391

[bluesky1]

hi guys, i am a new spark looking forward to 2391 soon, i never touched 3 phase really, but have to face it in 2391 practical assessment,

first post here. i am asking how to test the continuity of a 3 phase socket test? just like in the 2391 practical exam, i am bit puzzled about the 3 phase circuit, i was told i need to have 2 steps:

1: continuity between cu and isolator/starter, 2: continuity between isolator and socket,

i know i then should add up 2 together, but the most puzzling thing is how to measure R1+R2? shall i unscrew the isolator/starter? then how do i measure R1+R2?

 

[Spark123]

How I'd do it - link the CPC to one of the phases at the CU then measure the phase to CPC at the motor whilst the isolator is on and physically holding in the contactor.

 

[bluesky1]

hi spark123, thanks a lot for your reply, do you mean i can jump the isolator/starter, measure directly between the cu and 3 phase socket?

 

[riveralt]

Using low resistance ohmmeter – null leads or take reading of Line/CPC and deduct from results.

At the distribution board make link between the Line of the circuit being tested and CPC.

For three-phase circuits ensure that each Line and CPC is measured separately. So for a three phase motor connected between L1 and CPC at distribution and measure between L1 and CPC at motor. Then do the same for L2 and L3. Record each measure as the R1 + R2 on the measurement sheet.

Remember that for circuits that have isolator switches to motors etc take the R1 + R2 reading to the isolator then conduct separate R1 and R2 readings from the isolator to the motor. Then add the R1+R2 to the R1 and R2 values to give the overall R1+R2 for that circuit. You should record the three results.

 

[bluesky1]

Using low resistance ohmmeter – null leads or take reading of Line/CPC and deduct from results.

At the distribution board make link between the Line of the circuit being tested and CPC.

For three-phase circuits ensure that each Line and CPC is measured separately. So for a three phase motor connected between L1 and CPC at distribution and measure between L1 and CPC at motor. Then do the same for L2 and L3. Record each measure as the R1 + R2 on the measurement sheet.

Remember that for circuits that have isolator switches to motors etc take the R1 + R2 reading to the isolator then conduct separate R1 and R2 readings from the isolator to the motor. Then add the R1+R2 to the R1 and R2 values to give the overall R1+R2 for that circuit. You should record the three results.

hi riveralt, thanks a lot for your tips, it makes it much more clear now, can i also ask:

1: on the test results, shall i write 3 lines for the 3 phase circuit seperately, like 3 circuits?
2: shall i unscrew the cover of isolator/starter and the 3 phase socket to measure R1+R2? i must confess that i never open 3 phase appliance covers

cheers

 

[Spark123]

You can write it over 3 lines of the EIC yes.
You'll have to remove the cover from the contactor whichever way you do it.

 

[riveralt]

Remember that from the isolator to the motor you are taking the readings of R1 and R2 separately - add them together and then add them to the initial R1+R2 values.

On some 2391 courses the test rig cable distance between the isolator and the motor is very short and they are happy for you to simply show how you measure from the db to isolator and then record an additional notional 0.1ohm reading for the rest.

I think this is because the test board might be wrecked if everyone was dismantling the isolator and plug to get the R1 and R2 reading.

You will need to check with the exam centre.

 

[Adam_151]

You can write it over 3 lines of the EIC yes.

I would just note it down as xL1-L3 for circuit number and phase (where x is, the number of the TP fuseway), so your shedule might read:

1L1
1L2
1L3
2L1-3
3L1
3L2
3L3

etc

 

[bluesky1]

You can write it over 3 lines of the EIC yes.

I would just note it down as xL1-L3 for circuit number and phase (where x is, the number of the TP fuseway), so your shedule might read:

1L1
1L2
1L3
2L1-3
3L1
3L2
3L3

etc

thanks guys for your reply, adam, what is TP fuseway? do you mean i need to write down 7 circuits/lines?

 

[ColJack]

a three phase board will have so many "three phase ways" with "red/yellow/blue", "brown/black/grey", or "L1/L2/L3" markings

depending on how it's marked up ( which will depend on the installing sparky ) then either the top left or bottom left will be 1L1/1L2/1L3, proceeding up or down the left side then returning to the right end of the right side..

 

[bluesky1]

thanks a lot guys