TP & N Continuity & Polarity

[Shpark]

Just practicing for my AM2.

When testing a 3P and N socket, as I understand, R1 to R2 is CPC to any live (L1, L2, L3) to prove continuity, but how do you prove polarity?

 

[pc1966]

Fundamentally N-E voltage close to zero = correct "polarity" as then all OCPD are in the line conductors.

However, if you are testing without reference to E then you could verify the voltages are nominally 400V for all 3 L-L options, and nominally 230V L-N for all 3 options.

 

[Shpark]

Fundamentally N-E voltage close to zero = correct "polarity" as then all OCPD are in the line conductors.

However, if you are testing without reference to E then you could verify the voltages are nominally 400V for all 3 L-L options, and nominally 230V L-N for all 3 options.

Nice one, cheers

 

[Aaron b]

I don't know what they expect in the AM2 exam as I am just following the Experienced worker route myself. In practice however I would also check phase rotation while doing this, if you are using a modern voltage probe there's often a "clockwise" or "right" indicator, it should light between L1 > L2 and L2>L3. It's required under 643.9 so it might be worth making a note of it in case they ask.

 

[loz2754]

I don't know what they expect in the AM2 exam as I am just following the Experienced worker route myself. In practice however I would also check phase rotation while doing this, if you are using a modern voltage probe there's often a "clockwise" or "right" indicator, it should light between L1 > L2 and L2>L3. It's required under 643.9 so it might be worth making a note of it in case they ask.

643.9 relates to phase sequence, not phase rotation. GN 3 suggests this may be confirmed by testing in a similar way to testing R1+R2, or by visually confirming the correct colours are in the correct terminals at each point in the circuit.

Polarity testing is a dead test, particularly for initial verification purposes, before the circuit is energised.

 

[R-fur]

"clockwise" or "right" indicator,

Be carefull, rotation is relative, traditionaly in Britain correct rotation was anti-clockwise, it is only fairly recently that phase rotation meters go clockwise for correct.

 

[Aaron b]

I might be wrong but my understanding that phase sequence and rotation is the same thing. I don't have a copy of the latest GN3 so perhaps it's changed since amd 3.

I agree that the distribution may have it differently from what you expect, In an industrial or commercial setting, it's common to see the phase sequence corrected/changed at a socket or a contractor.

If it's a circuit with a 3phase socket and a DOL as I expect it to be in the AM2 I would assume it was a relevant point and thus 643.9 would apply but I suppose it says maintained not correct...

 

[loz2754]

I think my main point is that phase rotation testing involves live testing, whereas phase sequence testing only involves confirmation of polarity by dead testing and or visual inspection.

So, when installing a new 3 phase socket for example, a phase sequence test must be performed for initial verification, before energising the circuit. Therefore dead testing only. Whereas, an existing 3 phase socket has already been energised, so a phase rotation live test can done.