Testing 3 phase (r1+r2)

[The apprentice]

Hi there thanks for helping if you do, but was wondering on testing r1+r2 on a 3 phase distribution board could I link out L1,L2,L3 to earth and there for take all my reading that way ?

 

[ipf]

No. Individual test each L with E. Highest recording..... (should be the same).
It's the earth you are testing though, one test is generally enough.

 

[The apprentice]

No. Individual test each L with E. Highest recording..... (should be the same).

Sure they made us link out the board to earth at college on testing week

 

[ipf]

They are linked at the board but you are testing each individually with your meter at the furthest point.
Edit. I get your point now. I thought you meant linking L1-3 at both ends.

 

[timhoward]

Sure they made us link out the board to earth at college on testing week

You might be thinking of one method of doing IR tests. GN3 is your friend if you have it.

 

[The apprentice]

They are linked at the board but you are testing each individually with your meter at the furthest point.

Yeah I know what you are saying mate but iam sure they made us link l1 l2 l3 to earth and there for take a reading at every individual point

 

[ipf]

Yeah I know what you are saying mate but iam sure they made us link l1 l2 l3 to earth and there for take a reading at every individual point

That's ok, link at the circuit source then test individually at the circuit end.
R1 (L1) + R2 (E)
R1 (L2) + R2 (E)
R1 (L3) + R2 (E) for example.

 

[timhoward]

I agree it's ok, but to my thinking it's not totally ideal.
As stated above, you are proving continuity of CPC so doing one test is technically sufficient for that.

But this is a good opportunity to check there are no high resistance loose connections in the phase conductors, and prove that phase sequence stays consistent throughout a circuit.
For that reason I join one at a time, and test the other end.
It's not wrong to earth them all and test individually, but phase swaps en-route would be missed, and results could be confused if e.g. you find L2 to CPC has high resistance at the circuit end, but the loose connection is actually on L3 as L2 and L3 are transposed in an upstream isolator.
I'm splitting hairs a bit, but hopefully you get my point.

All that said, while in college it's simpler to do what they want!

 

[The apprentice]

That's ok, link at the circuit source then test individually at the circuit end.
R1 (L1) + R2 (E)
R1 (L2) + R2 (E)
R1 (L3) + R2 (E) for example.

Yeah so that’s ok to link l1 l2 l3 all to earth and there for take reading at all 3 phase that’s maybe where iam getting mixed up then we must have put Kim’s to earth for like I.e socket circuits

 

[ipf]

You may be getting confused because there is only one reading required for R1+R2, even for 3 a phase circuit.... even though they are all linked at circuit source, which means you can test continuity of all three phases.